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Laser and Particle Beams ~2003!, 21, 197–209. Printed in the USA. Copyright © 2003 Cambridge University Press 0263-0346003 $16.00 DOI: 10.10170S0263034603212076 Repetitively pulsed high-current accelerators with transformer charging of forming lines GENNADY A. MESYATS, SERGEI D. KOROVIN, ALEXANDER V. GUNIN, VLADIMIR P. GUBANOV, ALEKSEI S. STEPCHENKO, DMITRY M. GRISHIN, VLADIMIR F. LANDL, and PAVEL I. ALEKSEENKO Institute of High-Current Electronics, Siberian Division, Russian Academy of Sciences, Tomsk, Russia ~Received 1 April 2003; Accepted 16 May 2003! Abstract This article describes the principles of operation and the parameters of the SINUS setups designed at the Institute of High-Current Electronics, Siberian Division, Russian Academy of Science, over the period from 1990 to 2002. A characteristic feature of accelerators of the SINUS type is the use of coaxial forming lines ~in particular, with a spiral central conductor! which are charged by a built-in Tesla transformer to produce the accelerating high-voltage pulses. This ensures a reasonable compactness and long lifetime of the setups. The range of parameters of the SINUS setups is as follows: • Voltage amplitude at the cathode: 200–2000 kV • Electron beam current: 2–20 kA • Equivalent load impedance: 30–180 V • Accelerating pulse duration: 4–130 ns • Pulse repetition rate: up to 400 Hz • Pulse amplitude instability ~RMS!: 0.7–2.5% A number of setups of this type use a three-electrode controllable gas gap switch. This has made possible on-line electronic control ~from pulse to pulse! of the output voltage pulse amplitude. The control band width d 5 DU0Umax was up to 75%. Studies have been performed on the lifetime of explosive-emission cathodes. At current densities of 25–30 A0cm2, a pulse duration of ;20 ns, and a pulse repetition rate of 100 Hz, the metal-dielectric cathode in a planar geometry retained its emissivity within 108 pulses. The SINUS accelerators are traditionally employed for producing high-power microwave radiation in various systems with a coaxial electron beam in a longitudinal magnetic field. For this purpose, magnetic systems with a solenoid powered from the bank of molecular capacitors have been designed. The duration of a quasistationary magnetic field was1satamaximum solenoid power of 365 kW. The possibility has been shown to exist for a self-contained power supply of the accelerator from the bank of molecular capacitors in the batch mode. With an average power consumption of about 120 kW, the setup produces pulses in a batch of duration 2.5 s at a pulse repetition rate of 200 Hz. Keywords: Molecular capacitor; Pulse forming line; Tesla transformer; Trigatron; Vacuum diode 1. PRINCIPLES OF THE DESIGN In each module, time energy compression occurs, result- OF THE SINUS SETUPS ing in an increase in transferred power. The characteristic times of the processes at each step are: seconds— The main idea used as the basis for the operation of the milliseconds—microseconds—nanoseconds. The energy SINUS accelerators is relatively slow energy storage from a conversion takes place on sequential operation of controlla- power supply with its subsequent fast utilization. Figure 1 ble switches. In the primary low-voltage circuit these are shows the block diagram of consecutive energy conversion thyristor switches; in the secondary high-voltage circuit it is in the SINUS setups. a gas gap switch. The energy is transferred from the capac- itive store Tesla Primary to Forming Line through a step-up Address correspondence and reprint requests to: Alexander V. Gunin, High Current Electronics Institute SD RAS, 4AkademicheskyAve., 634055 transformer in the mode of free oscillations. The open mag- Tomsk, Russia. E-mail: [email protected] netic core provides a high coupling coefficient between the 197 Downloaded from https://www.cambridge.org/core. University of Athens, on 29 Sep 2021 at 17:57:03, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0263034603212076 198 G.A. Mesyats et al. cuits. The following relation determines the optimum value of the coupling coefficient k: 2N k 5 k 5 , opt N 2 1 1 Fig. 1. Energy conversion in a SINUS accelerator. here N is an odd number integer. Particularly, for N 51, 3, 5 we have kopt 5 1, 0.6, 0.385. The value ~N 2 1!02 specifies the number of changes in the sign of the charging voltage of transformer circuits. Matching of self-oscillation frequen- the energy store within the time the store is charged. With cies of the transformer circuits allows highly efficient en- d 5 ~12 k! ,, 1, the capacitive energy store can be charged ergy transfer. Forming Line is a long coaxial pulse forming without a change in the sign of the charging voltage. line. The geometrical sizes of the line determine its electri- To increase the electric strength of the forming line and cal length and wave impedance. Upon the operation of the also to provide the possibility of employing a thyristor switch gas gap switch, a voltage-dump wave is generated in the line in the primary circuit of the Tesla transformer, the coupling and a nearly rectangular voltage pulse is formed across the coefficient between the circuits in the high-voltage genera- load. The forced circulation of the gas in the discharge gap tors designed was chosen to be close to unity. The geometry and trigatron control of the breakdown makes it possible to of this system is presented in Figure 3. produce accelerating pulses with a high repetition rate and The open ferromagnetic core built in the forming line is with an amplitude stability of no worse than 1–3%. When employed for increasing the coupling coefficient. In this operated in the batch mode, the setup employs an additional case, the coupling coefficient depends only slightly ~com- energy store composed of molecular capacitors. The elec- pared to a closed core! on the properties of the ferromag- tronic system of voltage stabilization in the primary store netic core material, being completely determined by its makes it possible to use up to 50% of the energy stored in the geometrical parameters. In particular, for the case where the molecular bank. This ensures an independent power supply length of the magnetic core is much larger than its external of the accelerator with a power consumption of hundreds of radius, kilowatts within a pulse batch of several seconds duration. 2 8 r2 k 2 ' 1 2 F~b!S D, 3 l 2. TESLA TRANSFORMER M Theoretical consideration of the operation of a Tesla trans- where F~b!5$a@~ b 21!~2b11!# 0b 2 % ln~b!;b5r 0r ;r , former combined with a forming line of the accelerator was 2 1 2 r1 are the radii of the inner and outer conductors of the given by Eltchaninov et al. ~1981, 1983!. The electric circuit forming line; lM is the magnetic core length; and a is a of the generator based on the use of a Tesla transformer is coefficient dependent on the geometry of the secondary coil presented in Figure 2. of the Tesla transformer ~a ; 1!. It follows from this figure that the Tesla transformer is a The achievable value of the coupling coefficient in these system of two inductively coupled circuits operating in the systems is k ; 0.85–0.95. So, this allows a rather high mode of free oscillations. The system allows converting of efficiency of charging of the accelerator forming line during constant or quasiconstant voltage to high-voltage pulsed the first half-wave of the charging voltage. The efficiency of voltage. The maximum efficiency of energy conversion ~from charging without detuning of the self-oscillation frequen- C1 to CFL! in the Tesla transformer is attained at properly specified values of the coupling coefficient between its cir- Fig. 3. Coaxial geometry of the Tesla transformer built in the forming line. 1: outer and inner conductors of the coaxial forming line, 2: external and Fig. 2. Simplified electric circuit of a high-voltage generator based on the central paths of the open ferromagnetic core, 3: primary winding of the use of Tesla transformer. Tesla transformer, 4: secondary winding of the Tesla transformer. Downloaded from https://www.cambridge.org/core. University of Athens, on 29 Sep 2021 at 17:57:03, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0263034603212076 Repetitively pulsed high-current accelerators 199 cies of the Tesla transformer circuit is determined by the cuit, there are actual inductance of the primary circuit LC , expression resistance of elements of the primary circuit R1, and resis- tance of the secondary circuit R2. The circuit is reduced to E p 2 the primary circuit by using the effective transformation 5 2 ' 2 2 2 h 1 ~1 k !, ' 0 ' 0 0 E1 8 coefficient ns N2 N1 !Lsec L1, where N2 N1 is the ratio of the number of turns in the transformer secondary and where E2 is the energy stored in the forming line, and E1 is primary. The values for the quantities present in the equiv- the energy stored in the Tesla transformer primary. Nor- alent circuit satisfy the following relations ~compare Figs. 2 mally, h.0.8, if ~r2 0lFL!,0.25. In the case of detuning and 4!: between the circuits, part of the stored energy remains in the 5 1 1 5 2 primary store and can be used in the next cycles of charging L1 Lm Ls1 LC R2 Rsec ns of the forming line. 5 2 1 2 5 0 2 The time it takes for the forming line to be charged is Lsec ns ~Lm Ls2 ![ns L2 C2 CFL ns determined by the time an electromagnetic wave takes to 5 5 propagate through the windings of the secondary coil of the M ns Lm I2 Isec{ns, Tesla transformer.

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