— AECL—10757 CA9400047

AECL-10757

ATOMIC ENERGY ENERGIE ATOMIQUE OF CANADA LIMITED A> DU CANADA LIMITEE

AN EXTERNALLY HEATED COPPER VAPOUR LASER

UN LASER A VAPEURS DE CUIVRE CHAUFFE EXTERIEUREMENT

P.A ROCHEFORT, F.C. SOPCHYSHYN, E.B. SELKIRK and L.W. GREEN

Chalk River Laboratories Laboraloires de Chaik Rh/er

Chalk River, Ontario KOJ 1JO

August 1993 aout AECL Research

AN EXTERNALLY HEATED COPPER VAPOUR LASER

by

P.A. Rochefort, F.C Sopchyshyn, E.B. Selkirk, and L.W. Green

Physical Chemistry Branch Chalk River Laboratories Chalk River, Ontario, Canada KOJ 1J0

1993 August

AECL-10757 EACL Recherche

UN LASER À VAPEURS DE CUIVRE CHAUFFÉ EXTÉRIEUREMENT

par P.A. Rochefort, F.C. Sopchyshyn, E.B. Selkirk et L.W. Green

RÉSUMÉ

On a conçu, construit et mis en service un Laser puisé à vapeurs de cuivre (LVC) (CVL) aux Laboratoires de Chalk River; sa fréquence nominale de répétition est de 5 kHz. On avait besoin de ce laser pour les essais à l'aide de la Spectroscopie de masse associée à l'ionisation résonnante (RIMS) et pour les projets associés aux études de la Séparation isotopique par laser à vapeurs atomiques (SILVA) (AVLIS). Pour que le laser fonctionne, il faut qu'on mette en place des coupons de cuivre sur la longueur d'un tube en céramique et qu'on les chauffe suffi- samment pour créer une pression de vapeurs appropriée. Le laser à vapeurs de cuivre (CVL) d'EACL comporte un élément chauffant extérieur dont la conception unique permet d'augmenter la température du tube. La forme de l'élément chauffant cylindrique en graphite permet de compenser les pertes importantes aux extrémités du tube du laser par radiation. L'utilisation d'un élément chauffant extérieur empêche l'appareil coûteux de commutation de haute tension de chauffer le tube du laser comme c'est le cas pour la plupart des lasers commerciaux. C'est une caractéristique particulièrement importante étant donné l'usage intermittent qui est typi- que de la recherche expérimentale. En outre, l'élément chauffant permet un meilleur réglage paramétrique du faisceau de sortie lors de l'étude de l'émission d'un faisceau de laser par les vapeurs de cuivre (ou autre). Dans le présent rapport, on donne un aperçu du processus d'émission du faisceau de laser par Z :s vapeurs de cuivre et on décrit en détail tous les trois sous-systèmes principaux du laser, à savoir le corps du laser, l'élé- ment chauffant du tube du laser, la décharge puisée de haute tension, et on signale les mesures paramétriques des sous-systèmes particuliers et du laser dans l'ensemble. On y signale également les techniques opératoires normales à employer pour chauffer, faire fonctionner et arrêter le laser.

Service de Chimie physique Laboratoires de Chalk River Chalk River (Ontario), Canada KOJ 1J0 1993 août AECL-10757 AECL Research

AN EXTERNALLY HEATED COPPER VAPOUR LASER

by

P.A. Rochefort, F.C. Sopchyshyn, E.B. Selkirk, and L.W. Green

ABSTRACT A pulsed Copper Vapour Laser (CVL), with a nominal 6 kHz repetition rate, was designed, built, and commissioned at Chalk River Laboratories. The laser was required for Resonant Ionization Mass Spectroscopy (RIMS) experiments and for projects associated with Atomic Vapour Laser Isotope Separation (AVLIS) studies.

For the laser to operate, copper coupons positioned along the length of a ceramic tube must be heated sufficiently to create an appropriate vapour pressure. The AECL CVL uses an external heater element with a unique design to raise the temperature of the tube. The cylindrical graphite heating element is shaped to compensate for the large radiation end losses of the laser tube.

The use of an external heater saves the expensive high-current-voltage switching device from heating the laser tube, as in most commercial lasers. This feature is especially important given the intermittent usage typical of experimental research. As well, the heater enables better parametric control of the laser output when studying the lasing of copper (or other) vapour.

This report outlines the lasing process in copper vapour, describes in detail all three major laser sub-systems: the laser body, the laser tube neater, the high voltage pulsed discharge, and reports parametric measurements of the individual sub-systems and the laser system as a whole. Also included are normal operating procedures to heat up, run and shut down the laser.

Physical Chemistry Branch Chalk River Laboratories Chalk River, Ontario, Canada KOJ 1 JO 1993 August

AECL-10757 TABLE OF CONTENTS Page 1. INTRODUCTION 1

2. THEORY OF COPPER VAPOUR LASERS 2

3. LASER DESIGN 6 3.1 Laser Body 6 3.2 Heater System Design 11 3.2.1 Power Supply 11 3.2.2 Heater Element Assembly Design 11 3.2.2.1 Heater Element 11 3.2.2.2 High Temperature Insulation 12 3.2.2.3 Heater Element Connectors 12 3.3 High Voltage Discharge System Design 16 3.3.1 Theory of the Resonant Charge Line-type Pulsars 16 3.3.2 High Voltage Pulser System Components , 17

4. LASER PERFORMANCE RESULTS 19 4.1 Methodology of Laser Power Measurement 19 4.1.1 Laser Tube Temperature Measurements 19 4.1.2 Current and Voltage Measurement ,... 19 4.1.3 Laser Power Measurement , 19 4.2 Heater System Performance 20 4.2.1 Temperature Profile 20 4.2.2 Plasma Tube Conditioning and Copper Loading 21 4.2.3 Overheating Effects on the Laser Tube 21 4.3 Discharge System Performance 22 4.3.1 Charging and Hold-Off Cycle 22 4.3.2 High Voltage Discharge 23 4.4 Laser Performance 26 4.4.1 Variance with Plasma Tube Temperature 26 4.4.2 Variance with Plasma Tube Pressure 30 4.5 Laser Operating Procedure 32

5. CONCLUSIONS 35

6. REFERENCES 36

APPENDKA A-l

APPENDIX B B-l LIST OF FIGURES Page

Figure 2.1: A conceptual model of a laser 2

F^-jre 2.2: Photon-atom interaction 3

Figure 2.3: Four level lasing cycle 4

Figure 2.4: CVL energy level transitions 5

Figure 3.1:CVL system 6

Figure 3.2: Laser body schematic 9

Figure 3.3: CVL laser body sitting on the optical table 10

Figure 3.4: Graphite connector tabs press fitted onto the end of the heater element 13

Figure 3.5: Various heater connector tab designs 15

Figure 3.6: Self-tightening bolt assembly on zirconium electrodes 16

Figure 3.7: Pulser discharge circuit 17

Figure 4.1: Temperature distribution along laser tube at various heat currents 20

Figure 4.2: Voltage trace of discharge capacitors charging cycle with 6 nF charge capacitance 22 Figure 4.3: The variation of energy per pulse with prr and temperature using a 10 kV charging voltage 24 Figure 4.4: Variation of the energy per pulse with charging voltage and prr with a laser tube temperature, of 1465°C, 6 nF charging capacitance and 3 nF peaking capacitance 24

Figure 4.5: Variation of the maximum energy per pulse with peaking capacitance 25

Figure 4.6: Trace of a current and voltage pulse with 8 kV charging voltage 26

Figure 4.7: Energy per pulse versus tube temperature at various prr with 10 kV charge voltage 27 Figure 4.8: The variation total laser energy per pulse with charging voitage and laser tube temperature at 6 kHz. 28 Figure 4.9: The ratio of the 578 to 511 nm energy per pulse versus tube temperature at 6 kHz prr and 12 kV charging voltage 28

Figure 4.10: Energy per pulse versus prr at various neon pressures with 10 kV charging voltage 29 Page

Figure 4.11: Energy per pulse versus prr at various neon pressures with 12 kV charging voltage 29 Figure 4.12: Energy per pulse versus changing voltage with various neon pressures at 2 kHz prr 30 Figure 4.13: Energy per pulse versus charging voltage with various neon pressures at 6 kHz prr 31 Figure 4.14: Energy per puise versus charging voltage with various neon pressures at 8 kHz prr 31

Figure 4.16: Typical intensity trace of 511 nm line at 6 kHz prr 33

Figure 4.17: Typical intensity trace of 578 nm line at 6 kHz prr 33

Figure 4.18: Typical intensity trace of the combined 511 and 578 nm lines at 6 kHz prr 34 1. INTRODUCTION

An in-house design for a Copper Vapour Laser (CVL) was constructed in support of the Atomic Vapour Laser Isotope Separation (AVLIS) and Resonance Ionization Mass Spectroscopy (RIMS) research projects.

CVLs are high efficiency (-1%), high repetition rate (1 to 10 kHz) pulsed lasers. CVLs lase at two visible wavelengths: the green 510.6 (511) nm line and the yellow 578.2 (578) run line; the light output pulses are about 50 ns long. The lasing medium is vapourized copper, typically contained in a ceramic tube heated to about 1450°C, and excited by a high voltage pulsed electrical discharge. Because the iasing media is gaseous, the laser can be relatively easily scaled up for high power.

CVLs are used in a number of applications [1,2,3,4] that take advantage of the unique properties of the lasers, such as high speed photography[5] and large scale visual displays. Most importantly, CVLs are used for the optical pumping of tunable liquid dye lasers in Atomic Vapour Laser Isotope Separation (AVLIS) [6,7,8,9], Resonant Ionization Mass Spectroscopy (RIMS) and general scientific work [10].

Tunable liquid organic dye lasers are narrow band tunable visible lasers that can operate,with the large number of available dyes, from the ultra-violet to the near-infrared in ranges of 20 to 50 nm per dye. For both AVLIS and RIMS processes, an atom is selectively photo-ionized by exciting a ground state electron up through a series of energy levels. Multiple pulsed laser beams, the wavelength of each set equal (tuned) to the energy levels' differences, are used as the ionization photon sources. Because of the continuous wavelength tunability and narrow bandwidth, dye lasers are used extensively for both AVLIS and RIMS research.

For a dye laser to operate, the dye must be optically excited (pumped) by either another laser or a flashlamp. Because CVL's have high pulse repetition rates, high conversion efficiencies and a capacity to scale with power, dye lasers pumped by CVLs are proposed for an industrial scale AVLIS process. The high repetition rates combined widi high power are suitable for large scale production. Other pump sources, such as a frequency double NdrYAG1 or UV excimer laser, cannot operate at such high repetition rates and power levels.

The CVL was built to learn about the material problems associated with operating a system at 1400°C, and the high voltage discharge circuit needed to energize the laser continuously. Ultimately, it would be used as a research tool for understanding the lasing mechanism of copper and other metallic vapours. Each of these interconnected goals requires research to increase the laser efficiency and improve the durability of CVLs; this laser is a first step along that path.

1 Nd:YAG refers to the laser media formed by Nd+^ ion impurities in a yttrium aluminum garnet (YAG = Y3AI5O12) matrix. NdrYAG lases at 1.06um. The wavelength can be halved (frequency doubled) to 532 nm using non-linear processes in special crystals. 2. THEORY OF COPPER VAPOUR LASERS

A conceptual model of a laser is that of a positive feedback, saturable light oscillator. The standard laser design is shown in Figure 2.1. The central section, which for the CVL consists of an electric gas discharge, is the saturable amplifying section of the laser. The mirrors at either end of the laser tube form the optical resonator and provide the positive feedback of light for the oscillator. One of the mirrors (RT) is partially transmitting, allowing the light to exit from the laser.

Light Amplifier t Laser Beam Mirror Partially R1=100% Transmitting Mirror Power R <100% Supply 2

Figure 2.1: A conceptual model of a laser

Light in a laser is amplified by stimulated emission. That is, a photon will stimulate an excited atom to emit a photon in the same direction and in phase with the incident one. The energy of the initial photon must equal (or be close to) that of an allowed transition (Figure 2.2 top). In the inverse process, a photon will be absorbed when it interacts with an atom in the lower state of the transition (Figure 2.2 bottom). For light to be amplified, more atoms must be in the upper state than in the lower state. This is termed a population inversion [11].

Most lasers are four level systems (Figure 2.3), which means that the population inversion is created between excited states of the molecule. The atoms can be pumped by a variety of means from the ground state to an intermediate upper state (transition IO>=>I1>). The atoms decay rapidly to the upper lasing level, (I1>=>I2>), and are stimulated to the lower level (I2>=>I3>), where finally they are de-excited to the ground level (I3>=>IO>). To create the population inversion and sustain lasing, the lifetime of state I2> must be longer than I3>. The level I2> state thereby forms an energy deactivation bottleneck, where population can build up reiau.c :o level I3>.

As the number of interacting photons increases in an atomic system, the rate of stimulated emission will approach the absorption rate, so that the populations of the upper and lower states equalize. As the populations equalize, the gain (or absorption) strength of the lasing medium is reduced, and it becomes effectively transparent. This strength reduction is termed intensity saturation, since the output light intensity is proportional to the number of photons [12].

One of the most common ways of exciting vaporized atoms is with an electrical discharge. The electric gas discharge excites the atoms by inelastic scattering of energetic electrons. The probability (cross section) that an energy level will be excited depends to a first approximation on the optical transition probability and the energy of the electrons. For a given dipole transition, the probability cross section has an electron energy threshold equal to the transition energy, with a smooth drop off for higher electron energies. This characteristic is important in explaining the lasing mechanism of copper vapour. -3

@—

Atomic ^_ ^ Energy ^ ^ Excited Atom Level Relaxed Atcx

_ , . „ Excited Atom Helaxec A'om Figure 2.2: Photon-atom interaction (top) stimulated emission; (bottom) resonant absorption

On average, electrons lose a fraction of their energy with each collision with an atom, and regain energy from the imposed electric field until the next collision. After a few collisions, the electron energy distribution equilibrates and can be characterized by a temperature. Assuming a normal statistical distribution, the electron energy can be characterized by a temperature, Te. It can be shown that

[2.1] -4- where e is the electron charge, E is the electric field, 1 is the mean free collision path length, 5 is the average fractional energy loss for each collision and k is the Boltzman constant [13].

Buffer gases are often added to the gas mixture to modify the electron temperature, so that there is a better match between the electron energy and that of the molecule to be excited. Since the mean free path is inversely proportional to the gas pressure, p. Equation 2.1 shows that the electron temperature is proportional to the E/p ratio, a practical parameter when trying to design or scale-up a laser.

Lasing Transition

Pump Transition

Figure 2.3: Four level lasing cycle

CVLs are classified as visible gas discharge lasers. The vapourized copper atoms are the lasing media within a gas matrix, typically neon, with the copper atoms energized by pulse electric discharges. The lasing energy levels of copper are shown in Figure 2.4 [14]. The upper levels for the two lasing transitions are close and there appears to be some interaction between them [15].

During a discharge, a very large population difference is created because of the large difference in excitation rates between the upper lasing levels and the lower levels. The rate difference arises because the transition from the ground state to the lower lasing levels of the two copper lasing transitions (IO>=>I3>) is not allowed and, as explained earlier, has a very low excitation cross- section to electron impact: the I3> levels are often called metastable. As the photon numbers increase in the laser media, the population of the upper decreases and the lower level increases, until they equalize and lasing stops. The metastable levels must de-excite by colliding with the buffer gas or laser tube walls before the copper can be excited again[16,17,18,19,20]. For this reason, CVLs can only operate in pulse mode. This mechanism is referred to as cyclic self- terminating lasing [8].

Several elements have similar self-terminating lasing mechanisms [8]. Because the copper atom nas one of the best energy level configurations for cyclic mechanisms, CVLs are one of the most efficient and have the highest gain of any visible lasers. Because of the very high gain of the -5- copper lasing medium, only a small amount of light needs to be reflected back into the resonator by the output mirror. Typically, the resonator is formed between a 100% reflective flat mirror and an 8% reflective flat quartz-etalon. Flat mirrors are used so that the laser beam completely fills the laser tube.

•IONIZATION

7 -

6 -

5 " •3d94s4p

% 4 3/2 • 3dlO4p(2p)

1 3 511nm 578nm

3/2_ 5/2- 3d94s2(2D)

0 L 1/2. •3dlO4s(2S) -I

Figure 2.4: CVL energy level transitions

With only 50 ns of laser gain time, the light within the resonator only has rime for about 5 to 10 round trips. The number of round trips depends on the length of the resonator. With so few round-trips, the laser beam quality is poor and has limited focussing and beam-projection properties.

However, the CVL's short, powerful laser pulses in the visible are very good for optically pumping liquid uye lasers. A very large population inversion is created within the dye by the short CVL pulse before the dye molecules are deactivated. The dye molecules are deactivated by collisions with solvent molecules. As well, the dye suffers much less degradation with visible pumping than with UV excimer laser pumping [21,22,23]. -6-

3. LASER DESIGN

Most commercial CVLs are self-heated, using the energy from the electrical discharge to heat the laser tube. Therefore, the tube temperature is related to the pulse repetition rate, the discharge energy pulse and the thermal conductivity of the laser tube. One of the most important features of the Chalk River Laboratories (CRL) CVL is that the laser tube is heated externally. Since one of the major goals of constructing this CVL is to study the lasing characteristic of copper vapour, an external heater was needed to decouple the tube temperature from the discharge parameters [24,25,26,27].

Laser Body

Laser Beam

High Voltage Pulse Heater Power Power Supply Supply

Figure 3.1: CVL system

The CRL CVL tube diameter was set to approximately the diameter of high power CVLs, since tube diameter is one of the major parameters that affects the lasing mechanism of copper vapour. The tube length is relatively short, since it affects only output power. The laser system consists of three major sub-systems: the laser body, the heater power supply and the high voltage discharge circuit (Figure 3.1). The following sections describe the various sub-systems and their functions.

3.1 Laser Body

The laser body comprises a ceramic tube sheathed by a graphite heater, contained in a water cooled body (Figure 3.2, Items 3,9 and 13). The laser body sits upon a 4'x 6' x2" thick optical table (Figure 3.3). The copper coupons are placed along the length of the ceramic tube.

The laser plasma tube is made of re-crystallized 99.8 pure aluminum oxide (McDonel Refractory, type 998). The tube is 990 mm long, with an external diameter of 44.5 mm and an internal diameter of 38 mm. The tube diameter is similar to that of the commercial laser presently in the laboratory (Oxford Lasers CVL40). The CVL40 has a 1500 mm long laser tube with an ID of 40 mm, and produces nominally 40 W of power. -7-

The laser body holds the laser tube heater element and the ceramic fibre insulation. The body is 785 mm long, with an ID of 159 mm (6.25 inches), and has a double wall jacket for water cooling (Figure 3.2, Item 14). There are two in-line 25 mm feedthroughs 690 mm apart (Figure 3.2, Items 8 and 6) for the water cooled copper heater electrodes (Figure 3.2, Item 10). As well, there is a 40 mm vacuum feed-through for purging the interior of the laser body cavity (Figure 3.2, Item 4). Two water cooled 235 mm diameter, 18 mm thick end plates cap the end of the laser body. Both ends of the laser tube extend out of the laser body through 48 mm holes in the end plates. At the high voltage end of the laser, the end plate is isolated from the laser body with a 25 mm thick polycarbonate (Lexan) ring (Figure 3.2, Item 5).

Originally, the laser body was to be evacuated to reduce thermal losses from the heater, so that all joins in the body are "O" type ring vacuum seals. Problems encountered with high voltage discharges during commissioning necessitated filling the chamber with dry nitrogen to atmospheric pressure. Very little extra power was needed to compensate for the additional heat loss from convection and conduction due to the nitrogen.

On the ground side of the laser, a 55 mm long bellows is attached to the end plate (Figure 3.2, Item 15). The bellows is needed to accommodate the 8 mm expansion of the ceramic tube as it is heated to operating temperature. A dial indicator is set between the end of the bellows and the laser body to measure the expansion of the tube (Figure 3.2, Item 20). By correlating the tube expansion with the internal temperature, the laser tube temperature can be monitored continuously while it is operating [28].

The discharge electrodes are made from 33 mm OD, 1 mm thick stainless steel tubing, threaded inside the electrode heads (Figure 3.2, Items 2 and 21). The length of the electrodes is such that the end is 25 mm from the start of the tube's high temperature zone.

To avoid contamination from the heater and ceramic insulation, the laser tube is sealed at either end. The seal is made at the end of the discharge electrode head with a high temperature silicone "O" ring [Precision Rubber, compound #11187] sandwiched between the electrode head and the laser tube. The "O" rings' temperature rises to approximately 150 - 200°C at normal operating temperatures, and the seals have functioned without any trouble for over 2000 hours during the research project.

Attached to the electrode head at either end are window assemblies set at Brewster's angle (Figure 3.2, Item 1)[29]. The Brewster windows are made of 100 mm diameter, 12 mm thick fused quartz plates with a X/10 surface finish. The windows are set with their surface normal 35.5 degrees to the laser axis and sealed to the assembly with an "O" ring edge seal, so as to close the optical aperture with the minimum window size diameter.

The gas inlet and oudet ports are located on the barrels of the Brewster window assemblies. The gas is introduced at the high voltage end of the laser through 1/8" copper tubing coiled 50 times around a 65 mm diameter, 250 mm long bakelite form. The coil of tubing forms an inductor and is a low resistance ground path for the slow pulse capacitor charging cycle, but a high resistance path for the discharge pulse (see section 3.3.2).

For normal operation, the neon gas flow is about 0.2 cm^/s and the tube pressure is about 4.7 kPa (35 torr). The gas type, pressure and flow rate is controlled by a gas handling rack located under the optical table. The regulated input pressure for both neon and helium is about 200 kPa, with the gas flow measured by a rotometer (Matheson model 7321 tube 601). The flow is controlled by the inlet needle valve (Edwards Vacuum, model LV5), while the gas pressure is controlled by the -8- outlet needle valve. Gas pressure is measured by a 0 to 13.0 kPa (100 torr) diaphragm gauge (MKS Baratron model 222 AHS-A-100) and 0-200 kPa (1500 torr) mechanical gauge (Helicoid). Both inlet lines have bypass lines, so that the whole system can be evacuated efficiently. Vacuum is provided by a two-stage direct-drive rotary pump (Leybold, model D4A). To I High Voltage Pulser

1 Brewster Window 7 Graphile Heater Electrodes U LaserRody

? Discharge Electrodes 8 Feedlhrough to Heater Electrodes H Laser Borly Waler Cooling jHi:kel a Aluminum Oxide Laser Tube 9 Tapered Graphite Heater 15 Expansion Bellows

4 End Plate (water cooled) 10 Zirconium Oxide High Temperature Fell insulation 16 Vacuum Port

5 High Voltage-I'lnslic Insulator 11 Aluminum Oxide High Temperature Solid Insulator 17 Normally Closed Valve

6 Healer Current Electrodes (water cooledl 12 Aluminum Oxide High Temperature Baling Insulation 18 Nitrogen Gas Purge Inlel

19 Nitrogen Gas Purge Check Valvf? Outlet

Figure 3.2: Laser Body Schematic 20 Dial Indicator ?i Electrode Head FIGURE 3.3: CVL laser body sitting on the optical table. The output coupler mirror is held in a mount on the right, next to the Brewster window. V

-11-

When the laser is operating, the heater chamber has a very slow flow of dry nitrogen introduced on the ground side and expelled through a 21 kPa (3 psi) check valve on the high voltage side. There is also a 40 mm diameter valved vacuum port on the bottom of the laser body connected to the heater chamber. This vacuum port is only used to remove air and water vapour from the chamber after the laser has been opened for maintenance or repair.

The external 1.5 m long laser resonator is formed between a 99% reflecting dielectric coated flat mirror and a fused quartz etalon. Both the mirror and etalon have a 50 mm diameter. The resonator and other optical mounts are held down on the table by means of threaded bolt and hold- down assemblies: the optical table (Newport model CS-46-4) has 1/4-20 threaded holes spaced 1" apart over its upper surface.

3.2 Heater System Design

The laser tube heater comprises two main components: the high current power supply and controls, and the heater element assembly.

3.2.1 Power Supply

The power supply is an electric arc-welding unit (Miller model SRH-666), which can supply up to 40 V at 600 ADC. The unit is used as a direct current source.

The controls are on a separate panel with an on/off switch, coarse and fine heater current control circuits and analog current and voltage meters. There are also three parallel interlock circuits that must be energized for the power supply to operate. The interlocks monitor the laser body, ground side electrode and the high voltage tank (see section 3.3.3) to prevent overheating, the vacuum inside the laser tube, and the flow of cooling water. A seperate electrode head monitor is needed because it is only cooled with forced air, and the body monitor is used as a backup to the water flow monitor. The vacuum monitor shuts off the power if the laser tube fails by overheating, cracking or from other causes.

3.2.2 Heater Element Assembly Design

3.2.2.1 Heater Element

The heater element is machined from a 65 mm OD, 48 mm ID cylinder of graphite (Union Carbide Canada, UGSX grade). UGSX graphite has the highest resistivity of all graphite types (6 to 9 |j.0hm-m).

Graphite is used because it has very good high temperature material properties and is relatively inexpensive. Graphite melts at 3000°C and it has a vapour pressure of 0.1 Pa (1 mtorr) at 2200°C [30]. Graphite has an emissivity of about 0.77, so it transfers heat efficiently to the laser tube. Also, above 700°C, its resistivity increases with temperature, so that the element will not form hot spots. Graphite has good strength under compression and tension that increases with temperature. However, graphite has poor flexural strength, and must be heated in an oxygen-free atmosphere to prevent oxidation.

The 48 mm ID heater forms a close fitting sheath around the central part of the laser tube and is held by its electrode so as not to touch the tube. The tube is heated by radiant energy from the hot element across the 1.5 mm gap. The ends of the heater section suffer proportionally the most heat loss. At the operating temperature of 1400°C, most of the loss is from radiant heat transfer. Radiant heat calculations show that the major loss is within two diameter lengths of the end of heated section. -12-

The heat flux from the heater is increased at either end to compensate for the end loss so that the effective lasing length is maximized. The power of the heater is tailored by varying the thickness of the heater wall (see Figure 3.3). The resistance per unit length is proportional to the cross- sectional area of the heater tube.

The power output of the end section is three times that of the center, while that of the mid-sections is twice that of the center. The central, mid and end sections are 100,100, and 150 mm long, respectively, with a corresponding wall thickness of 13.3, 8.26 and 5.72 mm. The length and ratio of the sections were found by empirical experimentation. The high thermal conductivity of both graphite and aluminum oxide, and the efficient radiant heat transfer, average out any power generation steps, and produce a uniformly heated section with a rapid temperature roll-off at either end. At the ends, where the electrodes are attached, the wall thickness is equal to that of the centre section for strength, which keeps the electrodes cool, and minimizes heat production.

3.2.2.2 High Temperature Insulation

The heater element is insulated using two layers of ceramic insulation. The first layer is a 2.5 mm thick zirconia felt (Zicar Products Inc., type ZYF-1100) that can withstand temperatures up to 1950°C. The felt is cut into strips and wrapped around the heater to form a uniform cylinder. Additional layers of felt are then wrapped around the whole length of the tube until the OD of the cylinder is J.bout 75 mm (Figure 3.2, Item 10).

Initially, the second insulation layer was 38 mm thick alumina batting (Cotronics type 337OUT-1) wrapped several times around the felt layers. The oversized insulated heater assembly was then inserted into the laser body.

At present, solid alumina insulation (Zicar Products Inc., type ALC.) is used, as it is easier to handle and produces less dust than the batting. The solid insulation is made of two cylinders 300 mm long, with IDs of 75 and ODs of 159 mm (6.25"). The cylinders are split lengthwise to facilitate installation (Figure 3.2, Item 11). The heater electrodes and ends of the laser body are insulated with small pieces of batting (Figure 3.2, Item 12).

3.2.2.3 Heater Element Connectors

The heater element connectors are 11 mm thick 25 mm wide graphite rings with protruding tabs (Figures 3.4 and 3.5a), formed from a single piece of graphite. The connectors are pressed (0.05 mm press fit, no taper) onto either end of the heater element. One can be fitted in the shop; however, for alignment purposes, the other has to be fitted with the element in the laser body.

Two water cooled 25 mm diameter feedthroughs complete the circuit between the connector and the the heater cables. The connector tabs fit into a slot at the end of the feedthrough, and the two are held together with a steel bolt and nut. With the relatively small contact surface, the connectors have very little heat loss and the feedthrough stays cool. The feed-throughs are sealed to the laser body with "O" rings.

The present successful connector design evolved from a series of designs that failed because of material problems at high temperatures. The first set of connectors was made of copper and water cooled (Figure 3.5b). The large cooled contact surface area allowed excessive heat loss such that only the very centre part of the heater element was heated appreciably. The electrical connection was through a bolted copper braid. <<«^

-13-

Figure 3.4: Graphite connector tabs press fitted onto the end of the heater element -14-

To lower the heat loss, the second set of connectors was made of carbon steel and not cooled. After a few hours of operation, good contact between the connectors and the heater element was lost, thereby creating a high resistance path. Contact was lost between the connector and the element as the unit heated up, because steel and most metals h~ve larger coefficients of expansion than graphite. With the high power supply as a constant cur.^nt source, so much heat was produced at the electrode-element interface that the electrodes melted.

The third set of connectors was made of zirconium and had zirconium and carbon steel self- tightening bolts to compensate for differences in the coefficients of expansion. The loss of contact problem was eliminated, but the connector became so hot that the copper braid melted, fused with the zirconium metal, and melted the assembly.

The fourth set of connectors were rings of zirconium, with a tab at the top. At the bottom, the ring was split with two opposing tabs (Figures 3.5d and 3.6). Using a self-tightening bolt through the two bottom tabs, the electrodes were fitted to the heater element. This set of connectors operated for over 50 hours of heating. Most of the heating measurements and laser power measurements were made with these connectors in place.

The self-tightening bolts were made up of three parts: a bolt and a nut made of the same material as the connector, and a collar made of a metal with a higher coefficient of expansion. The collar was placed between the bolt head (or nut) and the connector tab, and the assembly was tightened (see Figure 3.6). As the electrode heats up, the collar expands more rapidly than the bolt tightening the electrode around the elements. Knowing the coefficient of expansion of materials, the collar length can be calculated easily. For the fourth set of electrodes, the bolts were made from zirconium and the collar from stainless steel.

The connectors had to be tightened occasionally, because the connector's metal softened, causing the connector to enlarge slightly when it was heated up to temperatures of 700-900°C. After three adjustments, the connectors could no longer be tightened up sufficiently.

The graphite connectors suffer from none of the above problems, because they are made of The same material as the heater element Good contact is maintained throughout temperature cycling because the connectors are press fitted and have the same coefficient of expansion as the heater element They have operated reliably for over 1000 hours and shown no signs of deterioration. - 15-

a) b)

c) d)

Figure 3.5: Various heater connector tab designs. a) present model with connection tab, b) water cooled copper model, c) solid steel model with self-tightening bolts, showing melt damage d) solid zirconium model with self-tightening bolt assembly -16-

Zirconium Electrode

Zirconium Nut Zirconium Bolt Stainless Steel Collar

Figure 3.6: Self-tightening bolt assembly on zirconium electrodes

3.3 High Voltage Discharge System Design

A CVL requires a discharge circuit that produces high voltage, high current pulses with rise times of 50 ns and a width of 100 to 200 ns at a repetition rate of up to 10 kHz. The CVL discharge circuit, as well as most pulse lasers, is based on a radar pulse discharge circuit developed during the Second World War. The circuit is called a resonant charge line-type pulser [311. "Line-type" refers to the energy storage device, being "a lumped-constant transmission line", and "resonant charge" refers to the manner by which the transmission line is energized.

3.3.1 Theory of the Resonant Charge Line-type Pulsers

The basic pulser discharge circuit is shown in Figure 3.7. The storage capacitors, Cs, are resonantly charged through the inductor, Lc, and the hold off diode, Dc- The capacitors are charged to approximately double the high voltage power supply voltage, Vo. The voltage doubling is due to the induced electromagnetic voltage across Lc as the current increases to charge Cs [32]. The voltage is held in the charging capacitors by the charging diode, Dc. The inductor, L5, the gas inlet coil described in section 3.1, completes the charging circuit. This type of charging circuit is very efficient and provides very good transient pulse isolation to the high voltage power supply. Also, Lc isolates the thyratron tube, T, from the power supply during the short time after the stored energy in Cs has been discharged.

The pulsed discharge is formed when the thyratron tube, T, is triggered and effectively shorts the charged storage capacitor, Cs, to ground. The voltage on the opposite side of the capacitor becomes negative relative to ground and a discharge is produced in the laser tube. The peaking capacitors, Cp, stores the pulse energy until the discharge is formed inside the laser tube. Since the reactance of high frequency resistance of the by-pass inductor, L^, in parallel with the laser tube is much greater than the tube, most of the pulse power is dissipated in the gas discharge plasma.

Thyratrons are ceramic (or glass) multi-grid tubes normally filled with hydrogen. When a trigger pulse is applied to the control grid, a small amount of hydrogen is ionized, and the high voltage -17- field inside the tube accelerates the free electrons, ionizing more molecules, thus producing a current avalanche. To avoid current latching (conduction), the tube requires 2 to 8 (is recovery time for the ionized molecules to recombine with the electrons before the high voltage can again be applied across the tube. The size of the charging inductor has to match the recovery time, the charging capacitors and the pulse repetition rate.

Storage Charging Hold-Off Capacitor Inductor Diode

Laser

Figure 3.7: Pulser discharge circuit

A typical CVL type thyratron can hold off 20 kV, and have a current rise time of 2 ns with a peak current of 500 to 1000 A. It can operate from 500 to 1200 hours at 6 kHz.

3.3.2 High Voltage Pulser System Components

The high voltage pulser system has three main components: the high voltage power supply, the thyratron tank, and the laser head/discharge tube. Appendix A shows the circuit drawings and a list of critical components of the high voltage pulser system.

All of the high voltage components are enclosed for safety, and have shut-down interlocks if any of the enclosures are open with the high voltage on. All high voltage cabling is on the floor with protective guards.

The high voltage supply is a 25 kW Hypotronics model 815-1.66a/AEC, which can supply up to 1.66 A at 15 kV. The power supply is overrated for its present use, but it can be used for future, more powerful CVLs.

The thyratron tank is a 385 by 660 by 305 mm deep stainless steel covered box that contains most of the power conditioning components of the circuit: the thyratron, T, the charging inductor, Lc, the hold-off diodes, Dc, the charging capacitors, Cc (Condenser Product Co. model TS6102-30K- J), and the reverse voltage resistance and diode, Rr and Dr. The tank also contains the heater power supply for the thyratron tube and the discharge circuit for de-energizing the unit. For high voltage insulation, the tank is filled with high voltage transformer oil (Voltesso 35). The oil is cooled through an internal water-cooled heat exchanger.

The thyratron triggering unit is an Oxford Lasers triggering circuit (part no. SEP 0006) modified to run off 120 ACV. Trigger pulses of 1.2 kV, with rise times of 65 ns, are produced to trigger the thyratron. An external pulse generator fires the triggering unit with a 10 V pulse. -18-

The power switches for the thyratron heater and the oil circulation pump are on a control panel. A 20 minute delay circuit prevents the high voltage supply from being energized before the thyratron has time to heat up. The control panel also has an emergency shut-off button and interlock indicating lights.

The laser head has three main components: the by-pass charge inductor, Lb, the peaking capacitor, Cp, and the laser discharge tube itself. The capacitors are the same type as the charging capacitors, and both the peaking capacitors and the inductor are fixed vertically. For monitoring, there is also a pulse current transformer (Pearson Electronics, model 110) and a 1000:1 high voltage probe (Tektronix model P6015).

The high voltage pulse is carried from the tank to the laser head by a 1 m high voltage, large diameter co-axial cable. All of the circuit components and laser head components up to the plastic insulation body ring (section 3.1) are within a copper sheathed acrylic shielding box.

The critical component of the pulser circuit is the thyratron (EEV model CX 1735A). The CXI735A type of thyratron is designed for CVLs and other pulsed power systems where there is a large amount of reverse voltage and current with each pulse. With normal thyratrons, the reverse current pits and eventually destroys the cathode: model 1735A has a hollow cathode that tolerates reverse currents. One disadvantage of the hollow anode design is that the recovery time is about twice as long as that of a comparable conventional thyratron (see section 3.3.1). -19-

4. LASER PERFORMANCE RESULTS

There are two major operating units: the heater circuit and the high voltage system. This chapter describes the measurement methodology, the individual operational characteristics of the two systems, and the standard operating procedure for the laser.

4.1 Methodology of Laser Power Measurement

4.1.1 Laser Tube Temperature Measurements

All temperature measurements inside the laser tube were made with an optical pyrometer (Pyrometer Instruments Co., model Micro Optical Pyrometer). Temperature measurements were taken by viewing the internal walls of the laser tube through the laser's Brewster windows. Since it was difficult to gauge measurement locations on the smooth laser tube, coupons of copper approximately 5x5x2 mm were placed as focusing targets at measured distances along the laser tube. Temperature measurements at a given location were repeatable to within ±3°C.

4.1.2 Current and Voltage Measurement

There are two points of interest for measuring voltage and current measurements during a pulse discharge cycle: the laser head and the thyratron. Laser head measurements of current and voltage show the electrical power that is being deposited into the laser. Monitoring the thyratron can avoid damage to the unit.

The voltage is measured at both locations by a 1000:1 high impedance oscilloscope probe (Tektronix model P6015). The thyratron probe is immersed in oil in the high voltage tank. The current at the laser head is measured with a pulse current transformer (Pearson Electronics, model 110,0.100 V/A). The in-line transformer is located on the high voltage lead between the peaking capacitors and the laser head. With this arrangement, only the current going into the laser head is measured, and not the current into the peaking capacitor.

A current monitoring resistor (T&M Research Products model IM-2) is located between the ground return and the cathode of the thyratron. The monitor measures the total current in the system during a pulse discharge. Unfortunately, the thyratron AC ground return had to be routed through the resistor. With this configuration, the current baseline is modulated by a 60 Hz ripple.

During testing, the voltage and current are recorded either by a photograph of oscilloscope trace (Tektronix model 2467B) or with a digital oscilloscope (Gould model 4072). The digital signals are downloaded to a personal computer for storage and processing.

4.1.3 Laser Power Measurement

The laser pulse energies are measured with a modified pyroelectric joulemeter (Molectron model J3-09) and oscilloscope. On the 10 kHz range, the joulemeter has a response of 0.88 V/mJ that is constant throughout the visible range. For power monitoring, a power meter (Photon Control, model 120) with 150 mm aperture is used.

For separate line energy measurements, the total pulse energy is measured, then the 578 ran is separated out from the beam with a dichroic filter and the 511 nm line energy is measured. Taking losses into account, the 578 nm line energy is calculated from the difference of the two measurements. -20-

The laser energy per pulse is dependent on several parameters: pulse repetition frequency, laser tube temperature, gas composition and pressure, and excitation voltage. Most of the laser parameters can be set or controlled; however, when the laser is started, the laser tube temperature increases significantly as the discharge energy is deposited in the laser tube. The temperature rise and new equilibrium point will depend on the pulse repetition rate, the discharge voltage and the gas pressure. Also, during the first 100 to 200 discharge pulses, current loading lowers the output of the high voltage power supply. For the above reasons, during laser power experiments, measurements were taken on the last pulse of a burst of 300. The bursts occurred every two seconds, with variable periods between pulse. Using the tube length as a gauge, the average temperature did not change significantly, + 5°C, during any of the experiments using this methodology.

The burst was generated with a specialized pulse generator (SRS model DG 535), and using the pulse counting gate of a digital oscilloscope (Gould model 4072), only the last joulemeter pulse of the burst was displayed for measurement.

4.2 Heater System Performance

4.2.1 Temperature Profile The temperature profile of the stabilized heated laser tube with respect to heater current is shown in Figure 4.1. Zirconium electrodes were installed at the time of the measurement. The profiles were measured with a copper coupon every 50 mm, with the zirconium heater electrodes.

1500 n

O o I 1000 • •

Heater Current 3 (0 •! 450 A i_ a> O 480 A a. 500 -• E a> — 510 A H -0 550 A

•+• -+• •+- H 200 400 600 800 1000 Tube Position - mm

Figure 4.1: Temperature distribution along laser tube at various heat currents. -21-

The temperature profile stabilizes after 1.5 to 2 hours of heating. Typically, the tube heats up first around the 400 and 700 mm positions, then rises in the center, spreading out toward the electrodes at either end. At position 0 and 1000 mm the tube temperature is between 50-100°C.

The tube heating can be accelerated by turning the pulse discharge on after one hour, or when the copper has melted (see section 4.5).

4.2.2 Plasma Tube Conditioning and Copper Loading

A new aluminium oxide laser tube must be conditioned before being loaded with copper. Trace elements, principally sodium, migrate out of the oxide and vapourize at the elevated operating temperature of the CVL. If a new tube is allowed to cool with a load of copper, the contaminates will mix and condense with copper and take a long time to be eliminated [33].

To condition a new laser tube, a unit should be heated (without any copper) to about 1350°C from 8 to 24 hours, under vacuum (the longer the better). The conditioning can be accelerated by operating the heated laser with a 14 kPa (30 torr) helium flow for a few hours. The discharge appears to drive out the impurities faster than simple thermal heating.

The progress of the conditioning can be monitored by observing the colour of the helium discharge within the hot tube. At the beginning of the conditioning, the discharge will have a yellow tinge from the sodium contaminant. As the conditioning progresses, the discharge colour will change to the more normal white-purple hue of a helium discharge.

After conditioning the laser tube, copper coupons of 2-4 grams should be spaced about 100 mm apart along the laser tube; they should not touch the electrodes. The coupons should not be spaced any closer or the laser output will decrease sharply. The reason for this behaviour is not yet understood.

The copper coupons can come from any quality source; even solid copper wiring is pure enough for the lar For convenience, used copper high vacuum gaskets, surface cleaned, are often utilized to charge or recharge the laser.

When recharging the laser, the accumulated copper on the electrodes and laser tube has to be removed. Vaporized copper migrates from the center of the tube and condenses on the relatively cooled end parts of the laser. Eventually, the deposits block the laser light and power output drops. Residual copper at the center of the laser need not be removed when recharging.

4.2.3 Overheating Effects on the Laser Tube

The laser tube can overheat, usually when the laser is operating continuously, and the heater current is too great (see section 4.5). Overheating softens the aluminium oxide and the tube collapses from the external pressure. The aluminium oxide softening point is between 1400 and 1500°C.

In the early experiments, when the heating chamber was in a vacuum, the ceramic tube wall would thin with time, occasionally to the point of breakthrough. Aluminium oxide has a vapour pressure of 0.13kPa (1 torr) at 2148°C [34], and the wall thinning was attributed to vapour transport A white powdery substance was found at either end of the tube, and assumed to be condensed aluminium oxide vapour. When the heating chamber was filled with nitrogen, the wall thinning phenomena was stopped or reduced to an insignificant level. 4.3 Discharge Svstem Performance

There are two distinct pans to the pulse discharge cycle: the high voltage discharge itself, which lasts about 200 ns, and the capacitor charging and hold-off period. The following two sections describe the high voltage discharge system of the laser and the effect of various components.

4.3.1 Charging and Hold-Off Cycle The voltage and current of the charging cycle depend principally upon the value of the resonant charge inductance and capacitance, LQ and Co Other components have little effect upon the charging cycle. The high voltage power supply can be treated as an infinitely large capacitor in series with the charge capacitor, and the inductance of the by-pass inductor is very small compared to that of the charge inductor. All stray parallel capacitances are in the pF range and are insignificant compared to the 4 to 8 nF of the charge capacitance.

The total charge inductor has an inductance of 250 mH, and comprises three coils in series. One is a large air core coil (47 mH), and the two others are hand-wound small ferrite core coils. All the coils are immersed in the oil tank.

8kV

100 ^ 200 (xs

Figure 4.2: Voltage trace of discharge capacitors charging cycle with 6 nF charge capacitance: a) thyratron discharge, b) thyratron recovery period, c) charging of the capacitors, d) waiting period until next pulse. -23-

Figure 4.2 traces the voltage across the thyratron of a typical charge cycle with 6 nF of charge capacitance. The time required to charge the capacitors is in the order of 60 microseconds, considerably longer than the discharge time. Part a of Figure 4.2 shows the discharge of thyratron, part b shows the hold-off period needed for the thyratron to recover, part c shows the actual charging of the capacitors, and part d shows the waiting period until the next pulse. Even at 1 kHz there is very little voltage drop in the waiting period. The small voltage overshoot at the end of the charging period is probably due to a small amount of circuit "ringing" from the by-pass inductor.

4.3.2 High Voltage Discharge

The ability of the discharge to excite the copper vapour to the upper lasing level depends heavily on the energy of the electrons in the discharge. When the mean energy of the electron energy distribution is equal to the excitation energy of the upper lasing, maximum electrical to lasing power conversion efficiency is achieved. The mean and distribution of the energy depend on the electric field, and the ionization potential and density of the gas atoms (see section 2).

It is difficult to predict the voltage and current of a discharge, because of the non-linear response of the gas and the interrelation of the gas and laser parameters. However, it is known that the discharge must not be longer than about 100 ns, since lasing ceases at about that time, when the population of the upper and lower lasing levels equilibriates. As a consequence, the rise time of the current pulse must be in the order of 10 to 50 ns.

To achieve this, the design of laser components and their layout must have the lowest inductance possible. To minimize circuit inductance, all pulse high voltage leads are kept as short as possible and the ground returns are made wide and flat The thyratron and the capacitors are chosen to have very small inherent inductance.

Once the laser is constructed, only the charging and peaking capacitors can be varied, to optimize the discharge for maximum laser power. Generally, the charging capacitor will control the peak current and the length of discharge, while the peaking capacitor governs the rise time of the voltage pulse and the amount of current ringing.

Until breakdown voltage is achieved, the laser has a very high impedance and effectively is not part of the circuit. When the voltage rises above the breakdown threshold, the discharge is established in a few nanoseconds and the laser tube changes to a very low impedance resistance, changing the dynamics of the circuit

The value of the threshold is dependent on the voltage rise time, the geometry of the discharge path, the gas make-up, pressure, temperature and residual ionization density of the gas. The voltage threshold will increase with discharge path, higher gas pressure and shorter voltage rise time, while higher temperature and residual ionization levels will reduce it [35].

Ion recombination occurs mostly on the walls of the plasma container, so that the residual ionization density depends on the pulse repetition rate, the gas pressure and tube diameter [36,37].

A series of power measurements was done with 4,6 and 8 nF charging capacitors, combined with 0.7,1, 2 and 3 nF peaking capacitors. The measurements were done from 1 to 9 kHz pulse repetition rate (prr) and 6 to 14 kV charging voltage with 4.7 kPa (35 torr.) of neon and the laser tube at 1435°C. The combined energy of the two laser lines was measured. The results are listed in Table B-l of Appendix B. -24-

Laser Tube Temperature -°C • 1390

3 0.

Q> a.

_ a> UJ

0 2 4 6 8 10 Pulse Repetition Rate - kHz

Figure 4.3: The variation of energy per pulse with prr and temperature using a 10 kV charging voltage

1600 T Pulse Repetition Rate • 1 kHz

•° 3 kHz

6 kHz

-0 8 kHz

8 10 12 14 Charging Voltage - kV

Figure 4.4: Variation of the energy per pulse with charging voltage and prr with a laser tube temperature, of 1465°C, 6 nF charging capacitance and 3 nF peaking capacitance -25-

For all combinations of capacitors, the maximum pulse energy reduces with frequency (Figure 4.3), and the associated charging voltages for the maximum energy also decreases (Figure 4.4). As the rate increases, the maximum energy is found with smaller ratios of peaking to charging capacitance.

Except for the 1 kHz range of prr, the maximum pulse energy is found with 6 nF of charging capacitance. There is a sharp increase in energy as the capacitance is raised from 4 to 6 nF, and a small decrease as the capacitance is further increased to 8 nF. (See Table B-l for maximum energies for each prr.)

In the 5 to 7 kHz prr range with 6 nF charging capacitance, the maximum power increases with peaking capacitance (Figure 4.5). No attempt was made to determine an optimized peaking capacitance, due to space limits on the number of peaking capacity. Clearly, additional improvement could be expected for values > 3 nF.

The standard configuration adopted for the high voltage circuit is 6 nF of charging capacitance and 3 nF of peaking capacitance. Figure 4.6 traces the current and voltage at the laser head with 8 kV charging voltage.

350 -r

300 ••

250 Puls e 200 6 kHz pe r

150 7 kHz ierg y LU 100

50 Pea k

•4- 0 12 3 Peaking Capacitance - nF

Figure 4.5: Variation of the maximum energy per pulse with peaking capacitance -26-

100A

0 100 us

Figure 4.6: Trace of a current and voltage pulse with 8 kV charging voltage

4.4 Laser Performance

Sections 4.4.1 and 4.4.2 describe the output power of the laser with the variation of two important laser parameters: the laser tube temperature and the neon gas pressure. Since it was not practical to take measurements with all combinations of temperature and pressure, measurements were taken with one parameter kept at a representative value while the other was varied through a series of set points. The set of temperature dependence tests was done with 4.0 kPa (30 torr) of neon and the neon pressure tests were done with a tube temperature of 1410°C.

4.4.1 Variance with Plasma Tube Temperature

The output of the laser was highly dependent on the temperature (Figure 4.7). With the present configuration and for repetition rates above 4 kHz, the peak pulse energy output is achieved with a tube temperature of about 1465°C. At lower repetition rates, the optimum temperature rises towards 1500°C and higher (Figure 4.7). These higher temperatures cannot be sustained with the present system, due to the softening of the aluminum oxide laser tube. Interestingly, the temperature range for peak output is quite narrow, approximately 1465 ±10°C for repetition rates of 4 kHz and higher. The peak charging voltage range is proportionally wider, ±1 to 3 kV, depending on conditions at approximately 10 kV (Figure 4.5). -27-

The pulse energy of the 511 and 578 nm lines was measured with increasing tube temperature (see method in section 4.1). The energy ratio versus the charging voltage with increasing tube temperature is shown in Figure 4.9.

The pulse energy ratio between the 578 and 511 nm line increases in general with increasing tube temperature (Figure 4.9). That is, the colour of the beam changes from a green to more yellow beam as the tube heats up. The 511 nm line is more powerful under most normal conditions.

Pulse Repetition Rate - kHz

1375 1400 1425 1450 1475 1500 Temperature - °C

Figure 4.7: Energy per pulse versus tube temperature at various prr with 10 kV charge voltage -28-

• Laser Tube Temperature -°C -• 1390 m 3 -a 1440 O. — 1465 Q. -© 1500 0) c HI

8 10 12 14 Charging Voltage - kV

Figure 4.8: The variation total laser energy per pulse with charging voltage and laser tube temperature at 6 kHz.

1.00 T

0.75 -•

60 i* 01 C W 0.50 •• E c 0.25 ••

0.00 •+• •+• 1350 1375 1400 1425 1450 1475 1500 Temperature - °C

Figure 4.9: The ratio of the 578 to 511 nm energy per pulse versus -29-

Neon Pressure torr (kPa)

0 2 4 6 8 10 Pulse Repetition Rate - kHz

Figure 4.10: Energy per pulse versus prr at various neon pressures with 10 kV charging voltage

Neon Pressure torr (kPa)

2 4 6 8 10 Pulse Repetition Rate ° kHz

Figure 4.11: Energy per pulse versus prr at various neon pressures with 12 kV charging voltage -30-

4.4.2 Variance with Plasma Tube Pressure The pressure of the neon buffer gas, surprisingly, does not affect the output power significantly in the 2 to 7 kHz prr range, with normal charging voltages (Figures 4.10 and 4.11).

At all frequencies with low charging voltages, the energy per pulse decreases as the neon pressure increases. This is attributed to difficulties in gas breakdown, since the breakdown voltage threshold increases with pressure. As the charging voltage increases past the breakdown threshold for each pressure, the energy per pulse becomes more equal (Figures 4. 12,4.13 and 4.14).

At higher pressure, the energy output decreases as the charging voltage is raised past the optimum value, except at high frequencies (6 to 9 kHz), and low neon pressure (16 torr). In this special regime, as the charging voltage is raised past the optimum value, the energy output decreases slightly, but then remains roughly constant with increased voltage (Figures 4.13 and 4.14). The reason for this effect is not known. This phenomena was not investigated further, as this is not a normal condition and there is considerable high voltage stress on the components.

Neon Pressure torr (kPa)

4 6 8 10 1 2 1 4 Charging Voltage - kV

Figure 4.12: Energy per pulse versus changing voltage with various neon pressures at 2 kHz prr -31-

600 -r

Neon Pressure torr (kPa) X 16 (2.1)

39 (5.2)

A 73 (9.7)

• 106 (14.1)

0 2 4 6 8 10 12 14 16 Charging Voltage - kV

Figure 4.13: Energy per pulse versus charging voltage with various neon pressures at 6 kHz prr

350 -r Neon Pressure torr (kPa) 300 -•

0 2 4 6 8 10 12 14 16 Charging Voltage - kV

Figure 4.14: Energy per pulse versus charging voltage with various neon pressures at 8 kHz prr. -32-

4.5 Laser Operating Procedure The typical operating procedure for heating up, op< ating and shutting down the CRL CVL is described below. To start up the laser, the laser tube is first evacuated and then filled with 4.7 kPa (35 torr) of helium. The gas system is set for slow gas flow at about 0.5 cm^/s, the heater chamber nitrogen gas purge line is opened and all the water cooling lines are opened. The heater is then turned on and set to 600 A of current. Because of the resistance change of the heater element as it heats up, the current is re-adjusted after 15 to 20 minutes. Thirty minutes before the high voltage is to be turned on, the helium gas flow is replaced by neon (~0.2 cm^/s). The thyratron heater is also turned on at this time.

After about two hours, the laser tube will be heated sufficiently to operate the laser. Typical settings are 5 kHz prr, 550 A of heater current and high voltage supply to 4.5 kV. The high voltage supply setting corresponds to charging the capacitors to about 8.5 kV. Once the laser is turned on, it takes about half an hour for the laser to achieve thermal equilibrium.

If needed, the laser can be heated up more quickly by turning on the high voltage after an hour of external heating. However, the laser must be supervised carefully, to avoid overheating the laser tube. When the tube length dial indicator (see section 3.1) is at the normal range, the laser heater current should be reduced to the normal operating level.

To shut down the laser system, the high voltage is shut off without ramping down the voltage, the heater current is turned down, and then the power supply is shut off. The gas inlet, outlet and the nitrogen purge are also shut off. All water cooling should be left on for at least two hours, to properly cool the laser body. The thyratron heater and circuit are also shut off at this point, as is the tank pump.

To prevent contamination, the laser tube is then backfilled slowly with 101 kPa (1 atm) of helium. As the tube cools, the gas backfill will contract, so helium should be added one or two hours after, it possible, especially if the shutdown is going to be for more than two days.

The laser can also be left overnight on a warm shut down, to shorten the warm up period the next day. The laser heater current should be set between 200 to 300 A, with a slow flow of helium. The laser tube should be cool enough to make the copper coupons solid. Solid copper is desired, so that there is minimal diffusion of copper vapour to the ends of the laser.

The CRL CVL has operated reliably for several hundred hours, and with very little maintenance. The laser has been used mostly for RIMS experiments in conjunction with the Oxford Lasers CVL40. The CRL CVL 511 nm line has pumped a modified dye laser (Lumonics 350 Hypeidye), and the 578 nm line has been used as the final ionizing photon in the multi-photon process.

When the two lasers are operating at the same time, they must have the same prr, or the CVL40 will 'trip out'. The CRL CVL produces electromagnetic noise at each pulse that triggers a protection circuit in the CVL40.

The combined 511 and 578 nm laser-light pulse is about 55 ns long under normal laser system conditions. The pulse has a rise time of about 10 ns and a fall time of about 30 ns. Figure 4.15 traces the light output of the combined lines at 6 kHz prr and a charging voltage of about 8.5 kV. Figure 4.16 traces the output of the 578 nm line, and 4.17 the output of 578 nm line. The 578 light pulse lags the 511 nm pulse by about 15 ns. The 'spiky' nature of the output of the laser pulse is due to interaction between the optical resonator modes (mode beating). 50 ns 100 ns

Figure 4.16: Typical intensity trace of :> 11 nm line at 6 kHz prr

0 50 ns 100 ns

Figure 4.17 Typical intensity trace of 578 nm line at 6 kHz prr »

-34-

Figure 4.18: Typical intensity trace of the combined 511 and 578 nm lines at 6 kHz prr -35-

5. CONCLUSIONS

The CRL CVL was built to investigate the technology and science of CVLs. In building the laser system, much was learned about the materials and design of high voltage vacuum systems at high temperature. The following are the main conclusions drawn from this project

1. A CVL with an externally heated laser tube system can be built and made to operate reliably under a variety of operating conditions. With its external heating and operating flexibility, the laser is well suited for either research experiments or research of the CVL lasing process. Potentially, the laser system could be used with other metals or elements that need elevated vaporization temperatures for lasing.

2. Using an external laser tube heater, the laser conditioning time and cost are minimized compared to a commercial CVL. Any conditioning needed is done with a relatively inexpensive tube heater. Commercial, discharge heated CVL lasers require substantial conditioning time each time the laser tube is contaminated. This places unwanted service on the thyratron switched, pulse discharge circuits that are used as the heat source. External heating saves both technical and thyratron time. Thyratrons have a typical operating time of 1000 hours and cost -6-7 k$.

3. The CRL CVL laser system is well suited to sporadic and changing use-typical of scientific studies, because of the minimum conditioning time required. For scientific applications, the ease of use outweighs the more involved laser design and construction.

4. A thickness tailored graphite heater element can be used to obtain the flat-topped temperature profile in the laser tube.

5. Pressed fit graphite current connectors for the heater element work very well. The connectors remain in good contact with the element at high currents and all temperatures, without permanent shape changes. Uncooled metal electrodes lose contact with the heater element when elevated to high temperatures, because of permanent stress relief and phase changes in the metal. The loss of good contact, coupled with the large heater current, eventually melts and destroys the metal connectors

6. The limited amount of published information on metal behaviour at high temperatures and currents is a serious impediment to selecting materials for this or another laser system. This necessitated many trial and error experiments to achieve a design capable of sustained operation.

If an AVLIS program is undertaken at CRL, the knowledge gained from this project could be applied to the development of a production type CVL, or the preparation of system specifications for a commercial laser. -36-

6. REFERENCES [1] A. Stance The development of gold and copper vapour lasers for medical application in Australia. In SPIE Vol. 737, New Developments and Application in Gas Lasers, pp. 7-9 (1987).

[2] R.R. Lewis, G.A. Naylor, N. Salked, A.J. Kearsley and C.E. Webb. Improvements in copper vapour laser technology: new applications. In SPIE Vol. 737, New Developments and Application in Gas Lasers, pp. 10-16 (1987).

[3] R.R. Lewis, G.A. Naylor and A.J. Kearsley. Copper vapor lasers reach high power. Laser Focus, 24 (4):92-96 (1988). [4] A.J. Kearsley. Copper vapour lasers. In SPIE Vol. 1225, High Power Gas Lasers, pp. 270- 278 (1990). [5] B.T. Walder. A new generation of copper vapour lasers for high speed photography. In SPIE Vol. 1358, 19th International Congress on High-Speed Photography and Photonics, pp.811-820 (1990).

[6] P. Peuser, G. Herrmann, H. Rimke, P. Sattelberger, N. Trautmann, W. Ruster, F. Ames, J. Bonn, H.-J. Kluge, U. Kronen and E.-W. Otten. Trace detection of plutonium by Three-Step Photoionization with a laser system pumped by a copper vapor laser. Applied Physics B 28:249- 253 (1985).

[7] J.I. Davis and I.B. Rockower. Laser in materials processing. IEEE Journal of Quantum Electronics, OE-18 (2):233-239 (1982).

[8] B.E. Warner. An overview of copper-laser development for isotope separation. In SPIE Vol. 737, New Developments and Application in Gas Lasers, pp. 2-6 (1987).

[9] L. Gilles. Laser et seperation isotopique de l'uranium. Journal de Physique, Colloque £7, supplement au n°12, Tome 48:C7-101-C7-104 (1987).

[10] L.W. Green, M.H.C. Smyth, P.A. Rochefort and G.A. McRae. Polarization and isotope shift effects in uranium isotope ration measurements by resonance ionization mass spectrometry. In, Fifth International Symposium on Resonant Ionization Spectroscopy, Varese, Italy, September 16-21,1990. Institute of Physics Conference Series, no. 114, pp. 243-246 (1991)

[11] O. Svelto. Principles of lasers, pp. 22-35, translated by D.C. Hanna from Principi dei laser, Plennum Press, New York (1976).

[12] Ibid, pp. 127-132.

[13] Ibid, pp. 83-87.

[14] W.T. Walter, N. Solimene, M. Piltch and G. Gould. 6C3-Efficient pulsed gas discharge lasers. IEEE Journal of Quantum Electronics, OE-2 (9):474-479 (1966).

[15] J.J. Kim and N. Sung. Stimulated emission in optically pumped atomic-copper vapor. Optics Letters, 12 (ll):885-887 (1987).

[16] I. Smilanski. Copper hooks - Investigation of the copper-vapor-laser kinetics. Proceedings of the International Conference on Lasers, pp. 327-334 (1979). -37-

[17] D.J. Brown, R. Kiinnemeyer and A.I. Mclntosh. Time-resolved measurements of excited state densities in a copper vapor laser. EEEE Journal of Quantum Electronics, OE-26 (9): 1609- 1619 (1990).

[18] A.A. Isaev, G.G. Petrash and I.V. Ponomarev. Relaxation of metastable atoms during the afterglow in a copper vapor laser. Soviet Journal of Quantum Electronics, 16 (11):1512-1516 (1986).

[19] A. Ya. Litvinenko, V.I. Kravchenko and A.N. Egorov. Measurement of the lifetimes of the lower active levels of a copper vapor laser. Soviet Journal of Quantum Electronics, JJJ (6):778- 781 (1983).

[20] J.L. Miller and T. Kan. Metastable decay rates in a Cu-metal-vapor laser. Journal of Applied Physics, 5jQ (6):3849-3851 (1979).

[21] Z.-G. Huang and K. Namba. High power efficient dye laser pumped by a copper vapor laser. Japanese Journal of Applied Physics, 20 (12):2383-2387 (1981).

[22] R.S. Hargrove and T. Kan. High Power Efficient dye amplifier pumped by copper vapor lasers. IEEE Journal of Quantum Electronics, OE-16 (10): 1108-1113 (1980).

[23] L.V. Masamovskii, A.N. Soldatov and V.B. Sukhanov. Excitation of dye solutions and their mixtures by copper vapor laser radiation. Soviet Journal of Quantum Electronics, 9 (7):900-902 (1979).

[24] M.D. Ainsworth, D.J.W. Brown, D.W. Coutts and J.A. Piper. Investigation of practical high repetition rate copper vapour lasers with external heating. Optical and Quantum Electronics, 23:S539-S548 (1991).

[25] I.H. Hwang, B.H. Cha and S.M. Nam. Externally heated copper vapor laser using a carbon heater. Review of Scientific Instrumentation, 58 (7):1185-1187 (1987).

[26] B. Singh, P.K. Bhadani, J.K. Mittal and R. Bhatnagar. Compact externally heated discharge tube for metal vapor lasers. Review of Scientific Instrumentation, 55 (10):1542-1544 (1984).

[27] S. Gabay, I. Smilanski and Z. Karny. Externally heated copper vapor laser for parametric studies. IEEE Journal of Quantum Electronics, OE-18 (6):996-998 (1982).

[28] I. Smilanski, G. Erez, A. Kerman and L.A. Levin. High-power, high-pressure, discharge- heated copper vapor laser. Optics Communications, 30 (l):70-74 (1979).

[29] F.A. Jenkins and H.E. White. Fundamental of Optics. 3rd ed., pp. 491-495, McGraw-Hill Book Co., New York (1957). [30] H.L. Larson. Graphite elements for high-temperature resistor furnaces, part n. In Industrial Heating (1962-1963), available from Union Carbide Canada, Carbon Product, Welland, Ontario.

[31] G.N. Glasoe and J.B. Lebacqz, ed. Pulse Generators, pp. 8-12, McGraw-Hill Book Co., New York (1948).

[32] Ibid, pp. 356-363.

[33] T.W. Karras, C.B Collins. Contaminants in metal vapor lasers. 3rd international conference on lasers and applications. New Orleans, pp. 168-176 (1980). -38-

[34] O.E. Ryshkewitch and D.W. Richardson. Oxide ceramics, physical chemistry and technology. 2nd ed., p. 125, Academic Press, Florida (1985).

[35] A.J. Palmer. A physical mode on the initiation of atmospheric-pressure glow discharges. Applied Physics Letters, 25 (3): 138-140 (1974).

[36] P. Blau, I. Smilanski and S. Rosenwaks. Simultaneous time-averaged measurements of gas temperature and electron density in a copper-vapor laser using hydrogen emission spectroscopy. Journal of Applied Physics, 72 (3):849-854 (1992).

[37] V.M. Batenin, V.A. Burmakin, P.A. Vokhmin, A.I. Evtyunin, I.I. Klimivskii, M.A. Lesnoi and L.A. Selezneva. Time dependence of the electron density in a copper vapour laser. Soviet Journal of Quantum Electronics, 2 (7):891-893 (1977). A-l

APPENDIX A

Detailed circuit schematics of a pulser system follow, as well as a list of key components.

:Vr:- L4*

- •<• >-:=fsDt-::? -5.-

- e "2:- *£.-

—:—

,-, V A

. I

1 ' i ME V:

—;!-•- : "X,* a—•-- i —T B—r- j t E;~S c. * i * - -

MODJL- TDK - ;i. \ TCPS

£ COKTSCL

NT's; • DE- CTE5. ^•ER .WES i=E q A-2

CCP-ER VAPOUR MODULATOR FILE, CJVflPOURDGN SAVED VIEW: VI^4 A-3

PARTS LIST

ATOMIC ENERGY OF CANADA LIMITED

SPECIFICATION REF. DESCRIPTION DESIGNATION SOURCE QTY.

Cl CAPACITOR MAIN CHARGING

C2 CAPACITOR PEAKING

C4 CAPACITOR .01uf 3KV

C5 CAPACITOR .5uf

CG CAPACITOR .5uf

C7 CAPACITOR 1000pf

Dl DIODE AVALANCHE INTER. RECT. A6F12 (CHARGING DIODE) G AMP I200V PIV

DIODE AVALANCHE D2 (REVERSE CURRENT CLIPPING)

Kl DUMP RELAY ROSS ENGINEERING

COPPER VAPOUR LASER PARTS LIST pnFOoR MODULATOR TYPE DRAWN DATE REV

CHECKED SHEET 1 OF 2

APPROVED DRAWING NO. A -PCH-375

Cf-DWCCEL (85-05-03' USEHNAWE - IUSERNSMES LEVELS -U.EVELSI A-4

PARTS LIST

ATOMIC ENERGY OF CANADA LIMITED

SPECIFICATION REF. DESCRIPTION DESIGNATION SOURCE OTY.

NEELTRAN INC. CHOKE CHARGING 47mH 18KV 5AMPS LI 1106 FEDERAL ROAD BROOKFIELD CONN. 06 804

L2 CHOKE POS. BIAS SUPPLY 14 TURNS OF "18AWG. WIRE ON FERRQXCUBE L3 CHOKE NEC BIAS SUPPLY FX2240 CORE

L4 CHOKE THYRATRDN HEATER 5 TURNS OF *14AWG. WIRE ON FERROXCUBE L5 CHOKE THYRATRON RESERVOIR FX2243 CORE

Rl RESISTOR 100 ohm 10WATT

R2 RESISTOR IK ohm 10WATT

R3 RESISTOR 2.2K ohm 10WATT

R4 RESISTOR 10 ohm 10WATT .01 ohm 20WATT T&M RESEARCH PROD JCTS IN( R5 RESISTOR -CURRENT VIEWING' (MODEL 1M-2) 13^ RHODE ST. N.E. ALBUUUhRliUb NbW M -X. R6 RESISTOR 'DISCHARGE1 20K ohm 100WATT

R7 RESISTOR 'CURRENT LIMITING" 25 ohm 100WATT

R8 RESISTOR .1 ohm 10WATT

THYRATRON EEV CX1735A

PARTS l 1ST FDR COPPER VAPOUR LASER PARTS LIST FOR MODULATOR TYPE DRAWN • ATE REV

CHECKED SHEET 2 OF 2

APPROVED DRAWING NO. A -PCH-375

ZF=OUGJCEL (85-05-03) USERN4ME • JUSERNMO FILENAME - inLEN4ME« LEVELS -ILEVELSI A-5

+?*• -=2 ^.'f- -=* ^,'E- s-~ A-6

PARTS LIST

ATOMIC ENERGY OF CANADA LIMITED

SPECIFICATION REF. DESCRIPTION DESIGNATION SOURCE OTY.

Fl FUSE 2A. SLOWBLOW

1 POTTER & BRUMFIELD Kl RELAY "CONTROL 2PDT KRPA-11AG-120 POTTER & BRUMFIELD K2 RELAY "WATER" 2PDT KRPA-11AG-120 POTTER & BRUMFIELD K3 RELAY "TEMPERATURE" 2PDT KRPA-11AG-120 POTTER & BRUMFIELD K4 RELAY "OVER CURRENT" 2PDT KRPA-11AG-120 POTTER & BRUMFIELD K5 RELAY "OVER VOLTAGE" 2PDT KRPA-11AG-120

LP1 LAMP "POWER ON" RED

LP2 LAMP "WATER FLOW" GREEN

LP3 LAMP "TEMPERATURE" YELLOW

LP4 LAMP "OVER CURRENT" YELLOW

LP5 LAMP "OVER VOLTAGE" YELLOW

API METER Ml CURRENT METER RELAY 0 - 1000 AMPS MODEL »903B OPTICAL METER R LAY

API METER M2 VOLTAGE METER RELAY 0-10 VOLTS DC MODEL *S03B OPTICAL METER R LAY

PflRTq I I«;T imp COPPER VAPOUR LASER TYPE PARTS LIST FOR HFATFR supPLY CONTROL

DRAWN DATE REV

CHECKED SHEET 1 OF 2

APPROVED DRAWING NO. A -PCH-385

CF=DUCLCEL (85-05-03) USERNAJJE - JUSERNAMES FILENAME - SFU.ENAMES LEVELS -ILEVELSI A-7

PARTS LIST

ATOMIC ENERGY OF CANADA LIMITED

SPECIFICATION REF. DESCRIPTION DESIGNATION SOURCE QTY.

Rl RESIST0R 'CURRENT ADJ." 15 ohm 150WATT

R2 RESISTOR TINE RCURRENT ADJ." 5 ohm 50WATT

SI SWITCH "POWER ON1

S2 SWITCH 'POWER OFF-

S3 SWITCH 'OVER CURRENT RESET-

S4 SWITCH -OVER VOLTAGE RESET-

PART<; i T<;T pnR COPPER VAPOUR LASER PARTS LIST FOR HpAJFR Rj |pp| y rmrm TYPE

DRAWN DATE REV

CHECKED SHEET 2 OF 2

APPROVED DRAWING NO. A -PCH-365

CF=DWGXEL (B5-05-83J USERNAHE - lUSERNfiWES DATE -SDtTEI A-S

xi - POWER RE_ K2 - WATER Rt •^'ER-QO VACUUM k'3 - "r-P. REL ,',d . PUMP Rt!_A

•Tr *OE:] k'5 - INTERLOCK

•OS- **• H£ftREfiC-C V

^^-ca";osT=:L 6 •• p 3 - V uf h°* ^T3G O 5 BIAS 5UPPL* H1GH VOLTflGE U 6 TRIGGER

M0DULOT0R TANK P^OW T = M=. -' '- - j —

MODULATOR INTERLOCK =MtRG£NC' STOP KS

EMERGENCY STOP

DUMP RELAY AND H.V. ON L 4^-

COPPER VAPOUR LASER CONTROL PILE: CUVflPOUR-ODN SovED VIEW: 1/1=2 A-9

PARTS LIST ATOMIC ENERGY OF CANADA LIMITED

REF. SPECIFICATION DESCRIPTION DESIGNATION SOURCE OTY.

Fl FUSE 10A. SLOWBLOW

1 POTTER & BRUMFIELD Kl RELAY 'POWER 2PDT KRPA-UAG-120 POTTER i BHUMFIELO K2 RELAY "WATER" 2PDT KRPA-UAG-120 POTTER 4 BRUMFIELD K3 RELAY -TEMPERATURE" 2PDT KRPA-11AG-120 1 POTTER & BRUMFIELD K4 RELAY 'PUMP 2PDT KRPA-UAG-120 POTTER & BRUMFIELD K5 RELAY "INTERLOCK" 2PDT KRPA-11AG-120 1 AGASTAT K6 RELAY -TIMER 2PDT SSC 12ANA 0-30MIN.

1 POTTER & BRUMFIELD K7 RELAY -VACUUM 3PDT KRPA-14AG-120

LP1 LAMP -POWER ON1 RED

LP2 LAMP -PUMP1 GREEN

LP3 LAMP "THYRATRON ON"

LP4 LAMP -THYRATRON READY-

LP5

LP6 LAMP 'WATER FLOW-

LP7 LAMP -TEMPERATURE-

LP8 LAMP -INTERLOCK"

LPS LAMP -VACUUM-

p RT COPPER VAPOUR LASER PARTS LIS. FOR LftSER CONTROL TYPE DATE DRAWN REV

CHECKED SHEET 1 OF 2

APPROVED DRAWING NO. A "PCH-373

CF=D»GJ:EL C85-B5-03I U5EBNAW - IUSERNA1CI LEVELS -ILEVELSt A-10

PARTS LIST

ATOMIC ENERGY OF CANADA LIMITED

SPECIFICATION REF. DESCRIPTION DESIGNATION SOURCE OTY.

SI SWITCH "POWER ON1

S2 SWITCH 'POWER OFF-

S3 SWITCH 'OVER CURRENT RESET" S4 SWITCH "OVER VOLTAGE RESET"

PARTS I 1ST FOR COPPER VAPOUR LASER PARTS LIST FOR LflSER CONTROL TYPE

DRAWN DATE REV

CHECKED SHEET 2 OF 2

APPROVED DRAWING NO. A "PCH-373

CF=OWG£EL (85-05-031 USERNAWE - IUSERNAME1 FILENAME - tFILENAMEl LEVELS •ILEVELSI DATE -I34TEI A-11

1 j •:S OC -22 WIRE

—'• <2i- Jrwa^

-C 6 B:»

•"-»- • I »C«£G

R CONTRCL SfWEC Vltlf: VI-3 A-12

PARTS LIST ATOMIC ENERGY OF CANADA LIMITED

SPECIFICATION REF. DESCRIPTION DESIGNATION SOURCE OTY.

Fl FUSE 'PUMP1 1A.

F2 FUSE 'BIAS POS.' .5A.

F3 FUSE 'BIAS NEC .5A.

F4 FUSE "FIL- 5A. SLOWBLOW

F5 FUSE -TRIGGER1.25A.

Kl RELAY 'THYRATRON HEATER"

LP1 LAMP "PUMP POWER1 RED

LP2 LAMP 'HIGH VOLTAGE ON"

LP3 LAMP 'BIAS-

LP4 LAMP 'TRIGGER POWER-

LP5 LAMP 'THYRATRON FILAMENT1

LP6 LAMP 'TRIGGER ON1

LI CHOKE POS. BIAS SUPPLY 14 TURNS OF «18AWG. WIRE ON FERROXCUBE L2 CHOKE NEG. BIAS SUPPLY P2616 CORE

R1.R2 RESISTOR 27 K ohm 2WATT

PARTS LIST FHR COPPER VAPOUR LASER PARTS LIST FOR MDDULAT0R CQNTR0L TYPE

DRAWN DATE REV

CHECKED SHEET 1 OF 2

APPROVED DRAWING NO. A -PCH-374

CF=OWC.CEL (85-05-031 USERN4ME - IUSERNMO FILENAME LEVELS - ILEVELS1 A-13

PARTS LIST ATOMIC ENERGY OF CANADA LIMITED

REF. SPECIFICATION DESCRIPTION DESIGNATION SOURCE OTY.

SI SWITCH -TRIGGER ON1

S2 SWITCH "EMERGENCY STOP-

Tl TRANSFORMER "POS. BIAS- HAMMOND 166G100

T2 TRANSFORMER -NEC BIAS1 HAMMOND 166F120

T3 TRANSFORMER "THYRATRON HEATER' HAMMOND 165V7

1 T4 TRANSFORMER 'THrRATRON RESERVOIR HAMMOND I65U7

HIGH VOLTAGE TRIGGER UNIT OXFORD LASER (MODIFIED FOR 115 fAC INPUT)

paRTq ,.T _nR COPPER VAPOUR LASER TYPE PARTS LIST FOR M0DULATOR CONTROL ORAWN DATE REV

CHECKED SHEET 2 OF 2

APPROVED DRAWING NO. A -PCH-374

CF=DWCXEL (85-85-031 USERNAME - LEVELS -1LCV£LSI A-14

CR1-6 SE

3!CR

CT1-3 CT-3775 W/2 TURNS R1I-13 = F.ft. 25W.375ohm

^wi TO PCH373

FILE: CUVAPOUR.DGN SAVED VIEW: VI=7 TERRY PICARO HIPOTRONICS DC POWER SUPPLY

SECTION 1 L.

HV OUTPUT :RI-6 SEE DETAIL TV 15 KVDC 2A POS-NEG

POLARITY REVERSAL

—g—I CR1-6 = 3PCS IN SER. H1 ' 523MH17ASI VOLTHETER ASSEMBLY RI-S = 1(W.2W(2 IN SER.)

MOVEMENTi 0-50 UADC SCALE: B-3.75/7.5/15KVDC

CURRENT METER ASSEMBLY

MOVEMENT: 0-50 UADC SACLE: 0-400/800/2000MADC

A4 OVERLOAD PCB ASS'Y CS60-11I

•B1 LINE

SECTION2 "] B-l

APPENDIX B B-1 LASER POWER MEASUREMENT FOR COMBINATIONS OF DISCHARGE CAPACITORS

Table B-1 shows the power measurements for various combinations of peaking and charging capacitors. The measurements were done with a tube temperature of 1435°C and a neon pressure of 14.7 kPa (35 torr). The experimental methodology is described in section 4.1. Since the measurements were to assess the influence of the peaking and charging capacitors, the pulse output energy is quoted only in mV. The outlined values are the peak energy per pulse at each prr setting for all combinations of charging and peaking capacitors

TABLE B-l

Charqe Capacitor 4nF Peaking Capacitor 2 nF 1 nF 0.7 nF PRT Volts Energy Error Energy Error Energy Error (KHz) (KV) (mV) (mV) (mV) (mV) (mV) (mV) 1 6 66 3 57 3 17 3 1 8 236 3 226 3 177 3 1 10 373 3 369 3 294 3 1 12 490 5 476 5 410 5 1 14 #N/A #N/A #N/A #N/A #N/A #N/A 1 16 #N/A #N/A #N/A #N/A #N/A #N/A C M 6 41 2 93 3 7 1 8 219 3 270 3 172 3 10 355 3 395 3 190 3 12 441 3 469 5 370 10 14 483 3 400 5 420 5 16 #N/A #N/A #N/A #N/A #N/A #N/A C O 6 22 2 68 3 6 1 8 191 3 231 3 152 5 10 303 3 340 3 256 10 12 368 3 410 5 325 15 14 403 3 434 5 340 10 16 #N/A #N/A #N/A #N/A 360 15 4 6 2 1 33 2 0 #N/A 4 8 154 3 194 4 118 5 4 10 256 3 298 4 205 5 4 12 306 3 346 4 287 10 4 14 319 8 357 5 287 10 4 16 #N/A #N/A 338 5 296 10 i n m 6 0 #N/A 5 1 0 #N/A 8 95 3 158 3 80 3 10 189 3 242 4 175 3 12 208 5 275 3 210 3 14 200 5 270 5 215 5 16 189 5 256 8 220 10 C O D co l 6 0 #N/A 1 0.5 0 #N/A 8 40 3 106 3 45 2 10 117 8 182 5 127 5 12 129 8 185 5 150 5 14 116 10 170 5 160 3 16 93 8 149 5 150 5 B-2

Charge Capacitor 4 nF Peaking Capacitor 2 nF 1 nF 0.7 nF PRT Volts Energy Error Energy Error Energy Error (KHz) (KV) (mV) (mV) (mV) (mV)

Charge Capacitor 6nF Peakinq Capacitor 3 nF 2 rf 1 nF PRT Volts Energy Error Energy Error Energy Error (KHz) (KV) (mV) (mV) (mV) (mV) (mV) (mV) 1 6 200 5 220 5 144 3 1 8 466 5 455 5 357 3 1 10 658 5 632 5 487 5 1 12 805 5 770 5 595 5 1 14 810 10 819 5 651 5 1 16 #N/A #N/A #N/A #N/A #N/A #N/A e o C D 2 271 5 242 5 195 5 2 532 5 494 5 417 5 2 10 693 5 620 5 529 5 2 12 791 5 669 5 598 8 2 14 798 10 680 5 625 8 2 16 #N/A #N/A #N/A #N/A #N/A #N/A i n 3 6 231 249 5 165 3 3 8 457 464 5 368 3 3 10 578 585 5 473 5 3 12 600 10 609 5 504 5 C O 14 564 10 578 5 497 5 16 510 10 #N/A #N/A #N/A #N/A 4 C O 180 210 5 145 C O

4 392 e n 413 10 315 4 10 440 10 455 10 369 5 C M • » D 4 400 10 425 5 362 5 4 336 10 375 5 345 5 4 #N/A #N/A #N/A #N/A #N/A #N/A 5 6 145 5 151 5 104 8 5 8 310 5 308 10 250 8 5 10 335 10 307 10 260 8 5 12 270 10 249 10 228 5 5 14 185 10 205 10 214 5 5 16 #N/A #N/A #N/A #N/A #N/A #N/A 6 6 112 5 110 5 71 3 6 8 228 5 205 5 190 5 C O D 10 187 10 187 5 200 5 12 112 10 135 10 166 8 14 55 10 85 8 133 8 16 #N/A #N/A #N/A #N/A #N/A #N/A 7 6 62 5 78 5 26 C O 7 8 140 10 130 5 122 8 7 10 98 10 105 5 120 8 7 12 30 5 48 5 80 8 7 14 6 3 14 5 50 5 7 16 #N/A #N/A #N/A #N/A #N/A #N/A 8 6 20 3 21 3 2 1 8 8 53 8 73 8 65 5 0 10 28 5 47 5 57 8 12 3 2 10 5 25 8 14 #N/A #N/A #N/A #N/A 7 3 16 #N/A #N/A #N/A #N/A #N/A #N/A 9 6 4 1 4 1 0.5 0.25 9 8 6 2 12 3 5 2 9 10 2 1 4 2 10 3 9 12 #N/A #N/A #N/A #N/A 2 1 9 14 #N/A #N/A #N/A #N/A #N/A #N/A 9 16 #N/A #N/A #N/A #N/A #N/A #N/A Charge Capacitor 8 nF Peaking Capacitor 3 nF 2 nF Prr Volts Energy Error Energy Error (KHz) (KV) (mV) (mV) (mV) (mV) 1 6 245 10 242 10 1 8 553 10 473 10 1 10 714 10 693 10 1 12 805 10 790 10 1 14 861 10 840 10 1 1_6 903 1_0 868 10 2 6 357 10 312 10 2 8 570 10 567 10 2 10 700 10 679 10 2 12 735 10 700 10 2 14 728 10 693 10 2 1_6 71_4 10 693 1 0 3 6 315 10 270 10 3 8 497 10 490 10 3 10 580 10 550 10 3 12 567 10 508 10 3 14 539 10 490 10 3 1_6 51_8 1_0 441 10 4 6 256 10 240 10 4 8 440 10 400 10 4 10 420 10 390 10 4 12 364 10 330 10 4 14 330 10 280 10 4 16 287 10 245 10 5 ? 203 TO 194 TU" 5 8 315 10 280 10 5 10 270 10 230 10 5 12 182 10 158 10 5 14 160 10 138 10 5 1_6 1£7 10 12_7 10 6 6 182 10 173 10 6 8 220 10 217 10 6 10 160 10 163 10 6 12 92 10 102 10 6 14 56 10 84 10 6 1_6 54 10 70 10 7 6 120 10 112 10 7 8 126 10 140 10 7 10 54 5 77 5 7 12 14 5 28 5 7 14 7 5 #N/A #N/A 7 16 #N/A #N/A #N/A #N/A 8 6 20 10 48 5 8 8 40 5 56 5 8 10 6 2 10 5 8 12 #N/A #N/A #N/A #N/A 8 14 #N/A #N/A #N/A #N/A 8 1_6 #N/A #N/A 8N/A #N/A 9 6 3 1 10 5 9 8 3 17 2 9 10 0 #N/A 2 1 9 12 #N/A #N/A #N/A #N/A 9 14 #N/A #N/A #N/A #N/A 9 | 16 | #N/A | #N/A I #N/A | #N/A B-5

R-2 MEASUREMENT OF LASER PULSE ENERGY FOR VARIOUS COMBINATIONS OF LASER TUBE TEMPERATURES

Table B-2 summarizes the pulse energy measurements of the individual 511 and 578 nm lines and their combination at various laser tube temperatures. The measurements were done with 4.0 kPa (30 torr) of neon. The experimental methodology is described in section 4.1.

Temp. CO Prr(kHz) Volts 511 & 578 511 &578 511 Energy 511 AEnergy 578 Energy 578 AEnergy (kV) Energy (uJ) AEnergy (uJ) (uJ) W (MD

Temp. ("C) PIT (kHz) Volts 511 &578 511 &578 511 Energy 511 AEnergy 578 Energy 578 AEnergy (kV) Energy (pJ) AEnergy (fiJ) OLD GU) (HJ) (MJ) 1440 1 6 223 2 206 2 1 6 5 1440 1 8 530 1 437 1 92 2 1440 1 10 713 2 584 2 129 5 1440 1 12 867 5 693 5 174 9 1440 1 14 #N/A #N/A #N/A #N/A #N/A #N/A 1440 2 6 243 2 224 2 19 5 1440 2 8 511 2 396 2 115 5 1440 2 10 660 1 502 1 158 2 1440 2 12 744 1 596 1 149 2 1440 2 14 776 1 612 1 164 2 1440 3 6 188 3 182 3 6 7 1440 3 8 411 2 350 2 62 5 1440 3 10 538 3 449 2 89 6 1440 3 12 581 3 481 2 99 6 1440 3 14 581 3 486 2 95 6 1440 4 6 76 1 76 1 0 2 1440 4 8 315 1 282 1 33 2 1440 4 10 410 3 352 3 58 7 1440 4 12 414 3 361 3 52 7 1440 4 14 388 3 339 3 48 7 1440 5 6 32 1 31 1 0 2 1440 5 8 220 1 209 1 12 2 1440 5 10 292 6 259 6 33 11 1440 5 12 267 6 247 6 20 11 1440 5 14 243 11 239 12 4 23 1440 6 6 1 0 1 0 0 1 1440 6 8 143 1 139 1 4 2 1440 6 10 193 11 171 3 22 15 1440 6 12 138 3 136 6 1 9 1440 6 14 97 8 93 5 3 13 1440 7 6 0 #N/A #N/A #N/A #N/A #N/A 1440 7 8 27 2 26 2 2 5 1440 7 10 52 6 48 7 4 13 1440 7 12 18 6 13 5 5 10 1440 7 14 7 2 5 2 2 5 1440 8 6 0 #N/A #N/A #N/A #N/A #N/A 1440 8 8 13 2 10 2 2 5 1440 8 10 24 3 23 2 1 6 1440 8 12 2 1 5 1 -2 2 1440 8 14 0 #N/A #N/A #N/A #N/A #N/A 1440 9 6 0 #N/A #N/A #N/A #N/A #N/A 1440 9 8 0 #N/A #N/A #N/A #N/A #N/A 1440 9 10 1 0 #N/A #N/A #N/A #N/A 1440 9 12 0 #N/A #N/A #N/A #N/A #N/A 1440 9 14 #N/A #N/A #N/A #N/A #N/A #N/A B-7

Temp. CQ Prr(kHz) Volis 511 & 578 511 & 578 511 Energy 511 AEnergy 578 Energy 578 AEnergy (kV) Energy ()jJ) AEnergy ftj) Oil)

Temp. ("C) Prr(kHz) Volts 511 & 578 511 &578 511 Energy 511 AEnergy 578 Energy 578 AEnergy (kV) Energy (|iJ) AEnergy (pJ) (nJ) (MJ) (MJ) (nJ) 1500 1 6 482 1 367 1 115 2 1500 1 8 1136 11 783 2 353 14 1500 1 10 1659 11 1110 2 550 14 1500 1 12 1989 11 1305 12 683 23 1500 1 14 #N/A #N/A #N/A #N/A #N/A #N/A 1500 2 6 339 2 267 2 72 5 1500 2 8 832 1 608 1 223 2 1500 2 10 1250 11 837 2 413 14 1500 2 12 1511 11 995 6 516 17 1500 2 14 1636 11 1069 12 568 23 1500 3 6 80 2 73 2 6 5 1500 3 8 545 5 389 5 156 9 1500 3 10 808 2 579 2 229 5 1500 3 12 986 2 666 2 321 5 1500 3 14 102 23 723 23 -620 45 1500 4 6 0 #N/A #N/A #N/A #N/A #N/A 1500 4 8 331 2 256 2 74 5 1500 4 10 541 1 404 1 136 2 1500 4 12 600 6 434 2 166 8 1500 4 14 614 1 1 449 6 165 17 1500 5 6 0 #N/A #N/A #N/A #N/A #N/A 1500 5 8 128 1 94 1 34 2 1500 5 10 316 2 242 2 73 5 1500 5 12 375 3 256 3 119 7 1500 5 14 344 11 245 12 100 23 1500 6 6 0 #N/A #N/A #N/A #N/A #N/A 1500 6 8 6 1 1 1 5 2 1500 6 10 91 23 75 5 16 27 1500 6 12 125 23 70 12 55 34 1500 6 14 159 23 122 23 37 45 1500 7 6 0 #N/A 0 #N/A 0 #N/A 1500 7 3 0 #N/A 0 #N/A 0 #N/A 1500 7 10 3 1 2 1 1 2 1500 7 12 9 1 2 1 7 2 1500 7 14 20 6 2 1 18 7 1500 8 6 0 #N/A 0 #N/A 0 #N/A 1500 8 8 0 #N/A 0 #N/A 0 #N/A 1500 8 10 0 #N/A 0 #N/A 0 #N/A 1500 8 12 0 #N/A 0 #N/A 0 #N/A 1500 8 14 0 #N/A 0 #N/A 0 #N/A 1500 9 6 0 #N/A 0 #N/A 0 #N/A 1500 9 8 0 #N/A 0 #N/A C #N/A 1500 g 10 0 #N/A 0 #N/A 0 #N/A 1500 g 12 0 #N/A 0 #N/A 0 #N/A 1500 9 14 0 #N/A 0 #N/A 0 #N/A B-3 MEASUREMENTS OF LASER PULSE ENERGIES FOR VARIOUS COMBINATIONS OF LASER TUBE PRESSURES

Table B-2 summarizes pulse energy measurements of the individual and combined 511 and 578 nm lines at various laser tube neon pressures. The measurements were done at a laser tube temperature of 1410°C. The experimental methodology is described in section 4.1. V i

B-10

Pressure Prr Volts Energy AEnergy Pressure Prr Voits Energy AEnergy (torr) (kHz) (kV) (nJ) (nJ) (torr) (kHz) (kV) (M-J) (nJ) 69.4 1 6 0 0 106.2 1 6 0 0 69.4 1 8 249 6 106.2 1 8 0 0 69.4 1 10 955 1 1 106.2 1 10 418 23 69.4 1 12 1648 57 106.2 1 12 1022 23 71.5 1 14 1818 57 106.2 2 6 0 0 71.5 2 6 0 0 106.2 2 8 342 23 71.5 2 8 636 1 1 106.2 2 10 1106 23 71.5 2 10 1273 57 106.2 2 12 1727 57 71.5 2 12 1636 57 106.2 2 14 1886 57 71.5 2 14 1795 57 106.3 3 6 0 0 72.5 3 6 153 6 106.3 3 8 605 1 1 72.5 3 8 795 1 1 106.3 3 10 1182 57 72.5 3 1 0 1159 57 106.3 3 12 1477 57 72.5 3 12 1364 57 106.3 3 14 1534 57 72.5 3 14 1341 57 106.4 4 6 0 0 72.7 4 6 327 5 106.4 4 8 636 11 72.7 4 8 684 1 1 106.4 4 10 1057 11 72.7 4 10 986 1 1 106.4 4 12 1122 1 1 72.7 4 12 994 1 1 106.4 4 14 1002 11 72.7 4 14 818 1 1 106.3 5 6 16 2 72.5 5 6 239 6 106.3 5 8 602 11 72.5 5 8 633 1 1 106.3 5 10 835 23 72.5 5 10 773 1 1 106.3 5 12 727 1 1 72.5 5 12 636 11 106.3 5 14 500 1 1 72.5 5 14 438 1 1 106.2 6 6 7 2 72.4 6 6 180 6 106.2 6 8 517 1 1 72.4 6 8 530 6 106.2 6 10 557 11 72.4 6 10 530 6 106.2 6 12 405 1 1 72.4 8 12 330 6 106.2 6 14 207 11 72.4 6 14 195 6 106.2 7 6 5 2 73.0 7 6 161 6 106.2 7 8 398 11 73.0 7 8 426 6 106.2 7 10 291 1 1 73.0 7 1 0 305 6 106.2 7 12 145 11 73.0 7 12 164 6 106.2 7 14 66 6 73.0 7 14 102 6 106.3 8 6 7 2 74.2 8 6 143 3 106.3 8 8 273 11 74.2 8 8 315 6 106.3 8 10 113 6 74.2 8 1 0 141 6 106.3 8 12 34 6 74.2 8 12 38 6 106.4 9 6 1 1 74.2 8 14 22 3 106.4 9 8 55 6 73.4 g 6 97 6 106.4 9 10 24 6 73.4 9 8 148 6 106.4 9 12 5 1 73.4 9 10 30 3 106.6 9 14 2 1 73.5 9 12 9 2 tm

CaL No. CC2-10757E No.au cat. CC2-10757E ISBN 0-660-15377-7 ISBN 0-660-15377-7 ISSN 0067-0367 ISSN 0067-0367

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