Resonance Ionization Laser Ion Sources for On-Line Isotope Separator Facilities

Resonance Ionization Laser Ion Sources for on-line isotope separator facilities

LA3NET school, Salamanca, 2014 VIII International Workshop Laser-2009, Poznan RIB Facilities

stable + decay - decay  decay p decay spontaneous fission

-Nuclear structure far from stability -Understanding the origin of elements -Testing the Standard Model -Applications in materials and life sciences > 3500 of the expected 6000 -Medical Physics nuclei have been observed 9 284 isotopes with T1/2 > 10 year Our “beams” till 1889 ! < 1940 (495) Reactors: n on U

< 1940 1940 (495) (822) First Isotope Separator On-Line (ISOL) experiment Niels Bohr Institute 1951 fast n on U: Kr and Rb isotopes

< 1940 1940 1950 (495) (822) (1244) Selective detection method:  decay

< 1940 1940 1950 1960 (495) (822) (1244) (1515) Light-ion induced spallation Heavy-ion induced fusion

< 1940 1940 1950 1960 1970 (495) (822) (1244) (1515) (2010) Projectile and target fragmentation + In-flight separation

< 1940 1940 1950 1960 1970 1980 (495) (822) (1244) (1515) (2010) (2270) TRIUMF CRC, Louvain-la-Neuve Lanzhou CSR HIARF ISAC I and II (50 kW) ARIEL (500 kW) GSI Fair Dubna DRIBS Beijing HI-13/BRIF ANL CARIBU KoRIA (100 kW) FRIB (400 kW) Legnaro SPES Osaka RIBs Notre Dame TwinSol Catania EXCYPT Delhi HIRA LBNL ORNL HRIBF CERN-(HIE-)ISOLDE RIKEN Texas A&M GANIL 3 kW (8 kW) RIBF (100 kW) Spiral / Spiral 2 CARIF (1 MW) FSU RESOLUT iThemba Calcutta VECC

RIBRAS University of Sao Paulo ISOL-type Facilities In-Flight-type Facilities ISOLDE isotope separator on-line

1-1.4 GeV p

2 mA Ionization

Single charge: •Surface •Plasma Production •RILIS •ECR

Delivers yearly 3200 h of radioactive Mass ion-beams to 30 experiments by separation means of two target stations Post acceleration

Jonson, B., & Richter, A. (2000). More than three decades of ISOLDE physics. Hyperfine Interactions, 129, 1–22. doi:10.1023/A:1012689128103 http://isolde.web.cern.ch/ISOLDE/ 12 9/30/2014 Ionization and extraction ISOL process

target ion source extractor mass separation

• FAST • EFFICIENT • UNIVERSAL kV experiments • SELECTIVE

projectiles target material neutrals ions

Mass separator tuned to A = 205

Isotope 205At of interest At

Mass separated 205Pb, Bi, Po, ion beam: At, Rn, Fr, etc Ion Sources

SURFACE ION SOURCE Arc Discharge ION SOURCE

• Very simple: metal tube (line) from Ta or W • Used for non surface- • Heated up to 2400 °C ionizing elements • Ar or Xe plasma with Ionization efficiency depends on ionization 130 eV electrons potential (and also the plasma potential inside the hot cavity - Saha Equation ) Very efficient, even for high IP elements. Chemically unselective So why is laser ionizaton required?

Isotope production for a 1 GeV proton beam on a lanthanum (La) target

If we want a 132Sn beam:

132Cs

106

132Sn Production rate (a.u.)rate Production • Mass separation – huge 132Cs contamination! • Element selective ion source is essential Z=50 • Note the radioactive inventory: Sn - Reducing isobars reduces transmission of unwanted activity!

Mass separation J. Lettry, V. Fedoseev (CERN) The atomic line spectra is an element’s fingerprint

Absorption lines in solar spectrum

K Emission lines for excited atoms

Photon energy precisely Rb matches the transition energy of an electron in the atom Cs

This energy is unique for each chemical element Tl

In  atomic ‘Fingerprint’ Na

Li Laser ion source – using this fingerprint for selective ionization

A+ + e-

Psat. = Ɛsat. × flaser × Slaser beam

1 1

Ɛ = ћω /2σ Ei sat. i i

RF f = 10 kHz Ø = 3 mm

4 ÷ 11 eV field laser laser

Continuum

Autoionization

radiation

DC electric DC

Blackbody

Collisions

0.6 Rydberg level Step 3

ω3 Ionization Psat ≈ 10 W

1st or 2nd Ionyield

excited level 0.6

Step 2

1100 1100 Å

- ω2

ω1 1st excited

3000 3000 level Psat ≈ 100 mW

= 124 nm photon = 80645 cm photon nm 80645 = 124 =

eV ω 0.6 1 Ground atomic Step 1

Selective Selective excitation level 10 10

ωi(laser) = ωi(atom); Pi(laser) ≥ Pi(saturation) Psat ≈ 10 mW Laser power The Resonance Ionization Laser Ion Source - RILIS Ionization and extraction Stepwise laser ionization scheme target ion source extractor mass separation auto-ionizing state

ionization potential Rydberg state laser beams

kV experiments excited states

Z selective projectiles target material neutrals ions ground State

Laser tuned to Z = 85 At

Isotope of interest 205At Magnet set to A = 205 How can it be applied?

HCRILIS HCLIST

In-cell IGLIS In-jet IGLIS

In-cell PF-IGLIS In-jet PF-IGLIS Laser Ion Sources Worldwide

TRILIS ISTF2 POSTERGISELE ALIS FURIOSTalk IRIS GALS ISAC/TRIUMF HRIB/ORNL JoseGANIL ALTO - Orsay IGISOL/JYFLIain PNPI JINR Henares Moore

LISOL PosterRILIS SPES RISIKOTalk TRIGA-LIS PALIS KISS CRC LLN TomISOLDE/CERN Day INFN KlausIfP/UMz KCh/UMz RIKEN KISS/KEK

Goodacre Wendt

Laser type Operation Source type

Ti:Sa Dye ON-line OFF-line Hot cavity Gas cell planned Projection: Van der Grinten

Limitations of RILIS applications

• Non metals have high I.P • High lying first excited state • Below 210 nm, laser power is low (difficult to generate multiple harmonics) • Absorption in Quartz or other transmissive optics <205 nm Thick target + hot cavity

HCRILIS

• No access to A greater than ~240 (using uranium target) • Short lived isotope beams limited by diffusion and effusion times • No access to the refractory elements (so far!)

IRIS RILIS TRILIS ISTF2 ALIS PNPI ISOLDE/CERN ISAC/TRIUMF HRIB/ORNL ALTO - Orsay # of laser ionized isotopes: ~450 Thin target + gas cell

• Access to A>235 via fusion evaporation reactions Talk tomorrow • Short lived isotopes (~sub ms) are accessible Iain Moore • Chemical independence of release - refractory elements are possible

IGLIS

KISS GALS

KISS/KEK JINR

LISOL FURIOS CRC LLN IGISOL/JYFL >50 Combined ISOL types

HCRILIS

IGLIS

>500 ISOL + projectile fragmentation facilities

HCRILIS

IGLIS

PALIS S3 RIKEN GANIL >500 (+50) PF-IGLIS OFFLINE Talk tomorrow CRIS ABT ABPL RIMS Klaus Wendt

ONLINE HCRILIS IGLIS PF-IGLIS

>600 SUMMARY 1 - Introduction

1. Radioactive ion beam facilities give access to ion beams of exotic isotopes for many applications

2. Many types of facility exist, not all are easily compatible with laser ion sources

3. The laser ion source enables ELEMENT selective ionization, primarily to enable the extraction of ISOBAR free ion beams

This talk concentrates on the technical implementation and outlook for laser ion sources at THICK-TARGET ISOL facilities but many of the considerations and solutions are also relevant for THIN-TARGET GAS-CATCHER Ion sources (See lecture by Iain Moore tomorrow).

For non-ion beam production (Laser ion source as an experimental tool): See talk by Klaus Wendt tomorrow. HC-RILIS: laser requirements Ionization and extraction extractor mass separation target ion source auto-ionizing state

ionization potential laser beams Rydberg state

kV experiments excited states

projectiles target material neutrals ions ground State

• EfficientLaser ionization tuned schemes to Z with = a suitable wavelengths transition are needed • Flux/85 Fluence conditions  Short pulse lasers (5-50ns) with ~0.1-10mJ/pulse • Duty cycle consideration: High repetition rate may be neededAt (>10kHz). • Laser line-width for transitions should match the Doppler/pressure broadened transition line-width (~1-2GHz for A > 150 for 2000K) 205At Isotope of interest Attention: RILIS is completely element selective but other ionization mechanisms may still occur

HC-RILIS: laser requirements Diversity of elements tunable lasers ENERGY 10.0 5.0 2.0 1.0 0.5 0.2 0.1 200 300 400 500 600 700 800 900 wavelength nm ~10GHz line width covers HFS Rilisdb: Web 2.0, open to everybody and Doppler broadening www.cern.ch/riliselements UV …VIS… NIR Accuracy: 40 µeV Atom confinement Flux and fluence 34mm TIME geometry 3mm conditions Laser pulse overlap Pulse repetition rate: 10KHz 10-50ns pulse width precise in ~ns range

Saturate resonant 216 nm If hard to saturate apply the following .)

a.u

)

A p

transitions ( t

n 2

u c

n 1

o i

Ion signal ( signal Ion The more power the better Ti Dye 0 UV saturation {216 |795 |532} 0 10 20 30 40 50 POWER power (m W) Power (w) Ensure overlap with atoms Focus at 20m distance -> 0.7µrad angular resolution in RILIS

Consider drifts, SPACE Slide: Sebastion Rothe (CERN)

Only 2 viable tuneable laser options: Dye or Titanium:Sapphire Dye Ti:Sa Active Medium > 10 different dyes =1 Ti:sapphire crystal condition of aggregation liquid (org. solvents) solid-state Tuning range 540 – 850 nm 680 – 980 nm Power < 12 W < 5 W Pulse duration ~8 ns ~50 ns Synchronization optical delay lines q-switch, pump power # of schemes developed 47 37 Maintenance renew dye solutions ~ none 35 10.0 Dye 30 25

5.0 Ti:Sa ) %

( 20 Ti:Sa 2x Dye 2.0 y

c 15 1.0 n

2x Ti:Sa e i

c 10 i

0.5 f f

3x Ti:Sa e 5 0.2 Dye 3x Dye 0 0.1 4x Ti:Sa 550 600 650 700 750 800 850 900 950 200 300 400 500 600 700 800 900 wavelength (nm) wavelength nm Dye and Ti:Sa systems are complementary – ideally use BOTH! Commercial TiSa Lasers

Tuning Range 690 .. 1010 nm Pulse Duration approx. 30 ns Repetiton Rate 1 .. 3 kHz Output Power 2.5 W (at peak wavelength) Beam Size 1 mm (typical) Linewidth < 0.2 cm-1 Diode Pumped Solid-State Lasers

Tunable ns Ti: Sapphire Diode Pumped Solid-State Lasers Commercial TiSa Lasers Tunable ns Ti: Sapphire

Diode Pumped Solid-State Lasers

Tunable ns Ti: Sapphire

Features Applications

Features Applications Commercial TiSa Lasers

Pump laser: Nd:YAG (532 nm), ChangePhotonics of mirror sets in resonator NoRepetition amplifier rate: yet available 10 kHz NoPulse ageing length : 180 ns Power: 60 W Ti:Sa lasers: Line width: 5 GHz Pulse length: 30-50 ns Wavelength tuning range (6 mirror sets): • Fundamental (w) 690 - 940 nm (5 W) • 2nd harmonic (2w) 345 - 470 nm (1 W) Design based on TiSa from LARISSA group, • 3rd harmonic (3w) 230 - 310 nm (120 mW) Mainz University • 4th harmonic (4w) 205 - 235 nm (120 mW) The RILIS (Univ Mainz) Ti:Sa lasers

Ti:Sa lasers: Line width: 5 GHz Pulse length: 30-50 ns

Wavelength tuning range (6 mirror sets): • Fundamental (w) 690 - 940 nm (5 W) 100 mm • 2nd harmonic (2w) 345 - 470 nm (1 W) • 3rd harmonic (3w) 230 - 310 nm (120 mW) • 4th harmonic (4w) 205 - 235 nm (120 mW) 30 SP4440 SP4444 SP0000

) 25 SP1000

% SP1111

( SP1110 y

c 20

c i

f 15

g n

i 10

s a l 5 700 750 800 850 900 950 wavelength (nm) “A complementary laser system for ISOLDE RILIS” S Rothe et al: Journal of Physics: Conference Series 312 (2011) 052020 TiSa Pump lasersDM -532 Series

Nd:YAG /YLF /YVO H(~532igh P nmow),e r Green Nd:YAG Lasers Repetition rate: 10 kHz REQUIREMENTS Pulse length: ~5 - 200 ns (< 50 ns is not ideal) Power: >20 W per laser Power: M2 – depends on pump geometry but for Z-resonator M2>10 is good. DM Nd:YAG Features DM-532 Series Three standLDPard m-XXMQGodels: 60 W, Series100 W a nDPSSd 150 W lasers 532 nm : 10, 25, 50, 150 Watts High Power Green Nd:YAG Lasers

DPhotonicsM Nd:YAG Industries DM-XX series Features Three standard models: 60 W, 100 W and 150 W Owing to its intra-cavity patented technologies, the DM Series Nd:YAG diode pumped laser

at 532 nm (up to 150W from single head and up to 300W from dual head) at kHz repetition rates.

user to change repetition rate from 1 to 30kHz as desired. It is the best choice for high repeti- - tions. The single head DM lasers offer a dual pulse feature and have proprietary driving elec-

Owing to its intra-cavity patented technologies, the DM Series Nd:YAG diode pumped laser at 532 nm (up to 150W from single head and up to 300W from dual head) at kHz repetition rates.

user to change repetition rate from 1 to 30kHz as desired. It is the best choice for high repeti- - tions. The single head DM lasers offer a dual pulse feature and have proprietary driving elec- TiSa Pump lasers

Currently being tested at ISOLDE/CERN HRR Pulsed Dye Lasers Sirah Credo Dye laser Old RILIS dye laser

•Optimized for 10 kHz EdgeWave pump

•Accept both 355 and 532 pumping beams

•Equipped with FCU (up to 2W of “Upgrade of the RILIS at ISOLDE: New lasers and new ion beams” UV) V. Fedosseev et al: Rev. Sci. Instrum. 83, 02A903 (2012) 38 Narrowscan HRR Dye laser LiopStar-HQ Dye laser

http://www.liop-tec.com/19.html Dye Pump lasers – there is only 1 well established option!

Pump laser: Nd:YAG /YLF /YVO (~532 nm) + 355 nm (optional) Repetition rate: 10 kHz Pulse length: ~5 - 20 ns REQUIREMENTS Power: >40 W per laser Power: M2 < 2 Externally triggered with Low Jitter: (<3ns) Good beam pointing stability and low divergence if also used for non-res ionization. beam quality: M² < 2 pulse energy up to 50mJ pulse length down to 1ns peak power up to 10MW pulse rep. rate up to 150 kHz average power up to 400W wavelength 1064, 532, 355, 266nm Independent laser for non resonant ionization • 40W at 10 kHz • 17ns Pulse • Low Jitter • Gaussian beam • Much better transmission efficiency to ion source Blaze laser installed at RILIS in Dec 2012 Laser Laser Power Reference Transport (on table) beam power in efficiency 3 mm aperture Edgewave 43 W 370 mW 33 % Blaze 15 W 350 mW 88% Blaze 40 W 800 mW 76%

A similar efficiency improvement should be expected for the 18 RILIS elements that use non-resonant ionization for the final step! Power dependent thermal lensing in the beam transport optics is to be eliminated Can be used for Dye and Ti:Sa pumping as a back-up laser

B. Marsh et al., Suitability test of a high quality Nd:YVO industrial laser for the ISOLDE RILIS installation. CERN-ATS-Note-2013-007 TECH Multiple harmonic generation – ExtendSecond the RILISharmonic tuning rangegeneration

Most first excited steps require excitation energies above 3 eV (415 nm) – impossible with 532 nm pumping 0

1 Nonlinear

2 /

9 optical crystal

1 1 Nonlinear frequency mixingHarmonicprocesses generation is required! LASER

P 2 /2 P2 0

1 Second harmonic generation (SHG)

/ 9

SHG 0 / UV, blue, green light generation 1 Two conditions need to be fullfilled:

1 2

0 2 2

y 1) Conservation of energy Third harmonic generation (THG) Pp µd P Lh(w(iLth )1 2

2o n eff n

r t

UV, blue light generation c hhh

e 312

p Parameter related to S

THG 3 r Birefringent phase matching e s 3 2 fundamental beam

High harmonic generation (in gases with a

o 0 focusing

high power pulsed lasers) i

i 0

0 1.80 1.80 a

1 2) Conservation of momentum (phase matching condition)

2 Crystal length

/ Soft X rays, ultrashort pulses of 100 Phase matching in BBO

p O r ppFundamentalp power in crystal

1 312 o

DFG a

B B

1 attoseconds!) c

Second harmonic M

B B

1.75 1.75

f f r ppp 0

t wave @ 317 nm 123 h o

o Fundamental Effective nonlinear coefficient

317 nm

e x Differencx e frequency generation (DFG) pk

p wave @ 634 nm e

e nn n 0 S

d 11 2 2 3 3 d 6

Optical axis c

r n

n Light propagating

i i

e Near1.70and mid infrared light 1.70

s o

e a

e along the optical axis

i /

generation t t

o Phase matching c

c n and n (0 ) o

0 o e

a 1

i f

f o Angle 2

a 1.65 1.65 Laser beam e e n (37.8 ) Opt- ical parametric oscillation (OPO) 634 nm e

R 37.8 BBO

o c

k Near and mid infrared light

t M c generation Different materials have different

e 300 400 500 600 300 400 500 600

p S

Wavelength (nm) Wavelength (nm) bandwidths and angular acceptances

a L

/ 12

i n

i BBO - CRYSTAL a

V Optical Axis

r a

M Laser beam PM-angle 37.8 deg 8 Multiple harmonic generation – Practicalities for RILIS use.

Many non-linear materials exist with greatly varying physical and optical properties.

Material requirements Issues to consider Good options • Low absorption at beta-barium-borate required wavelengths BBO • Efficiency (<20 %) • High damage threshold bismuth borate • DispersionWalk-off (GW cm-2) BiBO • Elliptical beam output • High non-linearity lithium triborate • Beam transport LBO coefficient, deff • Care of optics • Phase matching at room temperature

http://www.as-photonics.com/snlo Fundamental beam and 2nd harmonic have orthogonal polarization For 3rd harmonic generation, matching polarization and independent control is needed for each input beam SUMMARY 2 – Laser requirements

1. >1 high repetition rate (10kHz), broadly tunable (~210 – 1000 nm) lasers are needed. 2. Nanosecond Ti:Sa and Dye lasers with 1-10 GHz linewidth are currently the only viable tuneable laser types. 3. Since they are complementary, ideally both should be available 4. Low jitter synchronization is needed 5. For a TiSa system, a high power non resonant ionizing transition requires a dedicated, low M2 Nd:YAG laser. 6. Several high-power, industrial DPSS Nd:YAG or Nd:YVO lasers are suitable for TiSa pumping. 7. Very few (possibly only 2) suitable solid-state dye pump lasers are available. 8. To reach wavelengths below the pump laser wavelength, non-linear frequency multiplication/mixing is required.

HCRILIS RILIS

ISOLDE/CERN

Proton beam from PSB ~10 cm 46 9/30/2014 Optical path from laser lab to target unit

RILIS CABIN The ISOLDE Laboratory

Class A Radiation area Fairly inaccessible due to high radiation levels

Target area

Separator magnets 1.4 GeV protons

Control room

New hall extension Experimental hall Laser optics in separator area

RILIS CABIN

>2 Laser optics Sv/h

Dose rates >20 Sv/h ~ 2.5 m from Target >20 Sv/h Beam transport in separator area

Dust protection of optics needs to established UV induced optics coating should be prevented Assessment of magnet window and fast replacement if necessary  Power meter target  Window extension with port aligner and CF viewport INACCESSIBLE >2 ZONE Sv /h HRS

Broadband optics reference

Quartz plate GPS New GPS prism mount

RILIS TABLE Quartz window Thermal lensing investigation

Thermal imaging camera Dirty prism, Laser ON Clean prism, Laser ON

CONCLUSIONS: Optics cleanliness in separator zone is essential if a high power green beam is used Dust prevention should be installed Monitoring of the thermal lensing effect should be made possible: - Power meter target - Port-aligner adjustable window reflection Thermal lensing investigation

CCD camera, CCD camera, reference beam BEFORE prism reference beam BEFORE prism CLEAN reflective surface

Unclean prism Cleaned prism surface surface

reference beam AFTER prism reference beam AFTER prism

Conclusion: prevention and monitoring of optics cleanliness (prisms, windows, etc) in separator areas is required.

Solutions: ImproveNew dust HRS protection window tube,in optics port alignerenclosures. and prism mount Additional reference beam from window surface. Beam Alignment System “Compact”

User Manual

Manual_Beam-Align_compact_e_vers5.odt version 5 – May 08, 2013 page 1 of 19

Industrial scale operation! >50% of ISOLDE experiments

2012 13 elements 3060 h laser on time 24 runs 344 RILIS operator shifts (24/7)

• RILIS = The most requested ion source at ISOLDE

• RILIS is ultra-selective AND efficient

• To achieve this the RILIS layout and ISOLDE schedule is optimized for fast switching between elements.

RILIS machine protection

Dye Leak or Dye flow interruption  Fire hazard; laser damage risk

Alcohol read Expert User Interface LabVIEW Configuration Program Leak for Machine Protection Interlock System Detector call Thresholds & Overrides Safety Operator Phone / Mail Shutter Dye Flow Sensor

x12 Laser read write Interlock Dye Sensor Data and status Temp. Expert User Interface logged to Network Sensor Variables Variables x10 x6 Dye Inputs Outputs x8 RILIS Machine Protection Interlock System Circulator x8 x5 Door (CompactRIO platform) Motor Interlock Signal High Power Processing Driver x8 Electronics Electronics Spare x8 x8 Switching x8 Relays Spare Analog Inputs Temporary Error Reset / System error Spare Override / Arm MP Sys. / User Alert: Status warning Digital Acknowledge Current State E-Mail & Phone ok Indicator Inputs Error Message „OK“ op override

• ROBUST and INDEPENDENT system • Hardware to control multiple laser interlocks and shutters • Laser dye leak detection / Dye flow detection Preparation for • Sends data to RILIS DAQ / Monitoring system ‘on-call’ • Offline testing round 2 – this week • Installation in January 2014 RILIS operation

In collaboration with EN-STI-ICE (Sergio Batuca and Mark Butcher) On-call operation 4 requirements for On-Call operation: 1) Machine protection / safety

To avoid risk of equipment damage or danger to personnel. This must be a ROBUST system (PC independent). 2) Performance monitoring

Remote monitoring of key parameters with an alert system to request operator intervention. 3) Automation To maintain RILIS performance therefore reducing the frequency of operator interventions. 4) Improved environmental conditions • Better temperature stability. • Rapid fresh air replacement. • Improved air cleanliness and dust protection

Continued work of RILIS technical student Ralf Rossel and CERN Fellow Sebastian Rothe SUMMARY 3 – The ISOLDE RILIS

1. The ISOLDE RILIS is the most frequently used laser ion source of any ISOL facility

2. To exceed the 3000 h of annual operation 2 complementary and compatible laser systems are needed

3. A robust, automated, machine protection system is needed

4. Comprehensive remote monitoring and control of laser parameters is being established.

5. With long optical paths in inaccessible areas, highly reliable reference beam monitoring and beam diagnostics are required.

6. When using high power beams (>40 W), thermal lensing issues must be considered and optic cleanliness becomes critical.

7. The laboratory layout is configured for simultaneous operation and setup to reduce downtime when switching between elements. 800 isotopes (70 elements) tested/produced at SC and PSB Exotic isotopes down to t ~ 10 ms RILIS1/2 isotopes and possible contaminants Intensities up to 1011 ions/s

ISOLDE Nat. & stable 100 ISOBARS

80 Informations on 60

Z Target production Outgasing (stable beam) 40 Operation conditions Yields 20 Release properties (PSB)

0 0 20 40 60 80 100 120 140 160 Neutrons Note: surface ionized molecules are not shown! HD UCx tests-JM15-CERN-15Nov2007 T. Stora How to reduce non-laser ion isobaric contamination?

The key lies in evaluating the differences between laser and surface ions:

Surface Ions Laser ions Point of origin All hot surfaces (inc Anywhere with a laser/atom overlap target/transfer line) Species Predominantly the low Only the chosen element IE elements (alkalis, alkaline earths), molecules Temperature High: Temp directly Low: temp influences atom transport dependence influences SI efficiency and ion survival only (electron emission, plasma potential) Time structure None Pulsed @ laser rep rate, pulse width depends on ion drift time to extractor Influence of cavity High – depends on Low, but requires electron emission material work function (plasma potential) Hot-cavity RILIS

81 81 Proton beam Rb/ Zn ratio (1.4 GeV, 2 μA) 150000 Ionizer Cavity (W or Ta) RILIS lasers

Thick Transfer target line

UCx target Ta or W transfer line Ta or W hot cavity High yield, universal High temperature, fast High temperature, production effusion Robust mechanism Efficient for laser and surface ionization Pre-ionization isobar suppression methods

78 78 81 81 Proton beam Ga/ Ni ratio Rb/ Zn ratio (1.4 GeV, 2 μA) 100000 150000150000 Low work function cavity e.g. GdB6 0.4

RILIS lasers

Neutron convertor

UCx Cooled quartz target transfer line

500xNeutron supression Quartz3 transfer line Low work function cavity 81 10 supression ~ 10x Rb supression convertorof Rb High low temperature, High reduced temperature, Robust (depends on surface ion rate from High slightly reduced fast slower effusion Efficient for laser and surface 7x LOSS of 81Zn other structures) yield, universal Trapping2 x LOSS of alkalis ionization selective production Ideal selective laser ion source? Repeller and trap

Switchable Ion repeller 10 mm electrodes RFQ segments

Electron repeller

Hot cavity Buffer Gas Atoms Laser Beams Ions

End plate

U DC

Accumulate

Laser ions Surface ions Electrons Release

Z 63 K. Blaum et al., NIMB 204 (2003) 331 Implementation of such a device

Challenges:

High voltage-cage -> 20m • High radiation  radiation hard material  Gas extraction • High tension

 electronics in HV-cage  remote control  Amplification of rf at target  Feedthroughs

• Robot  Connectors  Stability  Size limitations Robot Technical Lay-out and Installation of the LIST

• Significant selectivity enhancement by LIST  Complete suppression of surface ions by repeller electrode • Resonant ionization within a RF quadrupole structure  High purity beam of the elements of interest

Suppressed Repeller Electrode LIST surface ions laser ions

Exit Electrode RFQ Structure Extractor 21st of August 2013 | RILIS selectivity improvements | Sven Richter ([email protected]) 65 Post-ionization isobar suppression methods Laser Ion Source Trap (LIST)

78 78 81Rb/81Zn ratio Proton beam Ga/ Ni ratio (1.4 GeV, 2 μA) 100000 150000 2000 300 Ionizer Cavity LIST RFQ Open questions: (W or Ta) High-power target use? RILIS lasers Ion-guide mode at high current? Secondary ionization process? Efficiency loss factor?

Repeller End plate UCx Transfer electrode target line

Repeller electrode: Ionize inside RFQ Note: Suitable for all >104 supression surface ion of Ga and Rb 1/20 LIST efficiency loss contaminants

LIST time structure

Extra factor of ~10 78Ga/78Ni ratio 81Rb/81Zn ratio

300 200 30 U Repeller: 10V 250 U Repeller: 40V U Repeller: 120V 200

150

# Events # 100

0 0.00000 0.00002 0.00004 0.00006 0.00008 0.00010 Time (s) Issues with LIST

• Loss factor due to laser/atom overlap (>20) • Secondary ionization mechanisms Possibly serious issue for • Problem with ion-guide mode at high ion currents higher power targets • Extra complexity and setup time

LIST mode ion guide efficiency decline at high proton intensity. Daniel Fink, PhD work

Currently under further investigation by S.Richter @ Mainz Inc other developments: Mass selective LIST etc Micro beam gating on laser ion bunch

78 78 81 81 Proton beam Ga/ Ni ratio Rb/ Zn ratio (1.4 GeV, 2 μA)

High Ω 20000 3000 Cavity e.g (thin glassy graphite) Open questions: Min-pulse width? Suitable cavity design? Minimum beam gate? Use laser-ion time focus?

Micro – beam gate

UCx Transfer target line

Micro gate, (1μs) Requires high cavity voltage Note: Suitable for all (up to the limit allowed by surface ion <100/2 mass separator) contaminants

High resistance cavity concept

Sapphire tube DU = 20V (ext. heater) 0.5 mm Nb DU = 3V 1 mm Nb DU = 1V

The development of a thin Nb cavity, used in combination with micro-gating, enabled the discovery of 129Ag

Production of radioactive Ag beams with a Radioactive Ion-Beam Purification chemically selective laser ion source workshop Y. Jading et al., NIMB 126 (1997) 76-80 CERN, September 4th 2007 J. Lettry CERN ATB HRIBF Time structure studies

Ta Vapor Transport Tube 1000 Pre-pulse: ions produced in the extraction region 800 Cu data MC 600

400

Counts(a.u.) Ta cavity: 200 Φ3 x 30 mm 0 -40 0 40 80 120 160 200 240 280 Time (us)

Y. Liu, et al., NIMB 269 (2011) 2771-2780. Temporal behavior of RILIS (off-line @ RISIKO) • Goal: Comparison of time structure RILIS versus LIST • Starting with Rilis analysis by two step RIS of stable Yb

Pre-peaks Source-peaks Ionization within Ionization inside acceleration field the source

Time independent surface ionization Work by Sven Richter(PhD student, Mainz) 5μS beam gating test

Demonstration of 5 ms Gating 1000 50 45 5 ms Gate

35 800 30 25

Counts 20

600 10

0.00000 0.00005 0.00010 0.00015 0.00020

400 Time (s) Counts

200

0.00000 0.00002 0.00004 0.00006 0.00008 0.00010 Time (s)

Tom Day Goodacre (CERN, Manchester) – PhD work Influence of ion load in cavity

Bunch width increase at high current: But what about cavity voltage dependence of this effect? Beam gate test: investigate minimum gate width

2.0 Gating Limitations

Behlke Switch 1.8 Ideal Switch

1.6

1.4 Unreliable below 2 μs:

1.2 physical or technical limitation? Ratio to expected count rate count expected to Ratio 1.0

10 8 6 4 2 0 Duty Cycle (%) or gate time (ms) Pulsed heating

Pulsed LINE heating

U / V

16 Thin graphite @ 25% PWM

8 Thin graphite

4 Mz graphite, Thick graphite ? 600 W 2 Ta ionizer

75 150 300 I / A Possible benefits: • Increased voltage without requiring a thin and fragile cavity • Easier control for tests/characterization • Possibility to flush out surface ions before laser ionization • Overcome space charge/ion loading issues Potential issues: • Limited by separator acceptance: high cavity voltage = high energy spread • Induction in long cables: Physical rise/fall time limitations

Extract ions at time focus: ToFLIS

Carbon8V (amorphous) 100u

L = 37 mm

After fieldØ3 mm free region

atomic vapour source We are here

s D = 2s 3,7 cm 3,7 cm

Simulation: S.Rothe (CERN) Slides of V.I. Mishin (First LA3NET Topical workshop) Extract ions at time focus

acceleration region field free drift-region V E  τ +V L E=0 turn-around time t t0 1 t 0

t1 L

υ0 - initial thermal velocity 2vm0 τturn-around time = t1 – t0  m - mass of ions eE e - charge of electron

Slides of V.I. Mishin (First LA3NET Topical workshop) Combine LIST and ToFLIS?

Cavity exit sits inside RFQ Ion guide structure: Min cavity  repeller distance = minimum loss factor

Hot cavity with tubular heating connecter/heat shield

Quick switching of hot cavity heating polarity is under investigation Atom beam (and thermionic electrons) does not get deposited on a repeller surface = reduction of secondary ionization mechanisms

Drawing by Sven Richter (Mainz) Combine LIST and ToFLIS

78 78 81Rb/81Zn ratio Proton beam Ga/ Ni ratio (1.4 GeV, 2 μA) 1100000000 150000150 Switchable polarity 10000 1500 LIST mode: High Ω cavity 10 x higher selectivity LIST RFQ or e.g (thin (field free drift region) TOFLIS mode: glassy graphite) RILIS lasers 10 x higher efficiency

Open questions: Pulsed line heating feasibility? Minimum beam gate? Inverted line suppression factor? Physical construction Repeller Heat shielding of LIST Electrode < uS beam gate Replaced by Fast beam gate End plate inverted cavity UCx Transfer Fixed extraction field target line at time focus of ions

InvertedTOF RILIS line IonizeIonize inside inside cavityRFQ TOFLIST-RILIS Mode Mode selectivityrepeller 1/10 (?) INVERTED cavity Reduced LIST1 efficiency Standard cavity 10000>100(?) (?) loss polarity No efficiency loss polarity

Inverted line as an ion repeller

Pre-peak: Ions created at exit of cavity Standard cavity heating polarity

800 Inverted Line (2.2V)

600 Main peak (laser ions from cavity) has disappeared Suppression factor still has to be measured:

400 Is it as good as the LIST repeller? Counts

No surface ion background 200

0.00000 0.00005 0.00010 0.00015 0.00020 Time (s)

Tom Day Goodacre (CERN, Manchester) – PhD work Benefits of LIST + ToFLIS

Two LIST mode operating modes: 1 Inverted cavity polarity

• Offers high selectivity LIST operation but with the best possible laser/atom overlap (min LIST to repeller distance) for improved LIST mode efficiency. • Reduced background from secondary ionization mechanisms (no repeller). • Possibly better ion acceptance and transport in LIST (reduced RFQ fringe field effects in ionization region).

TOF-RILIS Mode 2 Standard cavity polarity • Replaces LIST ion-guide mode but: - Improved performance for high ion loads in hot cavity: better extraction for high ion currents due to high cavity voltage. - Still ~50x selectivity improvement over standard RILIS mode - No loss of RILIS efficiency

Another alternative laser/atom interaction region : Laser ionization inside a ‘standard’ FEBIAD type Arc-Discharge ion source

• Normally used for non surface- ionizing elements • Ar or Xe plasma with 130 eV electrons

3d drawing from Alberto Andrighetto’s talk last week Cathi Meeting Sept ‘14

First VADLIS demonstration • Laser ionization inside an arc discharge ion source ?? RILIS ionized gallium inside a modified VADIS

• Laser ionization efficiency for Ga was higher than VADIS efficiency under test conditions • Easy switching between VADIS and RILIS mode

• Pulsed anode enables new modes of operation to be investigated • Long laser ion survival/residence time indicates suitability for 2+ ionization or even optical pumping • RILIS in VADIS is the one step towards developing laser ionized refractory metal beams Two Modes of operation

RILIS 300 MODE No Lasers Laser Signal (background removed)

200 VADIS MODE

100 69Ga Ion Signal (pA) Signal Ion 69Ga

0 0 50 100 150 Anode Voltage (V) Tom Day Goodacre (CERN, Manchester) – PhD work RILIS@VADIS and VADLIS

VADIS aperture 1.5mm

178Hg Activity

Tom Day Goodacre (CERN, Manchester) – PhD work VADLIS Potential applications 1. As a RILIS cavity for selective 1+ ionization: • Operate VADIS with anode optimized for RILIS ions Feasibility: HIGH Ease to implement and test: Very Good Usefulness: immediate - Hg ionization for in-source RIS, RILIS compatibility with VADIS, MEDICIS source? 2. As a highly selective RILIS cavity: • Fast extraction + beam gating • Low work function anode + surface ion suppression with anode Feasibility: Undetermined Ease to implement and test: Good, but low work function anode may be non trivial. Usefulness: immediate - isobar reduction for RILIS beams is a long-standing issue. 3. For RILIS based 2+ ionization or optical pumping • Long residence time of laser ions • Are ions trapped in ‘inactive volume’? If so then good laser/ion overlap is likely. Feasibility: Undetermined Ease to implement and test: Good. Usefulness: undetermined – Could be useful for isobar reduction for RILIS Ba beams, depends on success of #1 + 2. Is useful as a diagnostic tool. VADLIS Potential applications

4. Refractory metal ion beams at ISOLDE: • Extract refractory metals as volatile molecules • Which molecule? • Investigate operating mode options: • Break-up molecule with VADIS + RILIS ionize atom? • Ionize molecule and/or break up in VADIS + non-resonant laser dissociation? • Investigate operating cycle/options: • Reduced anode voltage • Pulsed anode (with DC offset option)

Feasibility: Speculative, but will be more clear after development of #1-3 Ease to implement and test: Difficult – this is a very complex project Usefulness Alternative approach for surface ionized isobars of 112-118Ba

Ba: IP 5.21 eV

Risks of contamination:

Cs: IP 3.89 eV In: IP 5.78 eV

Tom Day Goodacre (CERN, Manchester) – PhD work Solution: Hot cavity 2+ resonance ion ionization

Tom Day Goodacre (CERN, Manchester) – PhD work Ba 2+ to prevent Cs and In contamination

2+ Ba halves the charge to mass ratio

Shifts the Ba on the mass spectrum away from isobaric contamination

Orders of magnitude signal-noise improvement

Tom Day Goodacre (CERN, Manchester) – PhD work Switch to 2+ Ba?

Elements with isotopes mass 56-59

Titanium 6.82eV Vanadium 6.75 eV Chromium 6.77 eV Manganese 7.43eV Iron 7.9eV Cobalt 7.88eV Nickel 7.64eV Copper 7.73eV Zinc 9.39 eV

None of these are efficiently surface ionized!

Tom Day Goodacre (CERN, Manchester) – PhD work World’s first hot cavity resonance ion-ionization! Success! 1.2% of Surface ions ionized

Room for improvement:

• Ensure saturation of 2nd step

• New laser for non resonant ionisation

Tom Day Goodacre (CERN, Manchester) – PhD work GISELE results SIMION simulation

Extraction and ion optics Ion distribution at the detector

Detection

Dipole Extraction and ion optics

Jose Luis Time profile distribution HENARES (GANIL) Low intensity beam profiler

60 Horizontal axis 50 120Sn

20 Intensity [au] Intensity

0 -15 -12 -9 -6 -3 0 3 6 9 12 15 The emission-Foil Monitor (EFM) and general view Distance [mm]

70 300 Vertical axis Simulation 60 120Sn 250 50 Time Structure 200 Acquisition 40

150 30 ofcounts

Intensity [au] Intensity 20 100

10 Number

50 0 -15 -12 -9 -6 -3 0 3 6 9 12 15 0 Distance [mm] 0 10 20 30 40 50 60 TOF [µs] Horizontal and vertical profiles of 120Sn Jose Luis Time profile distribution HENARES (GANIL) vs. Current simulation JL. Vignet Proceedings of IBIC2013, Oxford, UK Future plans

New low work function materials: Carbides ZrC, TaC, HfC, TiC

LISBET_v0: LISBET_v1: Diameter 7 mm, Length 60 mm Diameter 7 mm, Length 35 mm

LISBET_v2: LISBET_v3: Diameter 3 mm, Length 60 mm Diameter 3 mm, Length 35 mm Jose Luis HENARES (GANIL) SUMMARY 4 – Selectivity

1. Unfortunately the conditions needed for extraction of short lived species (high temperature, reliable materials), make the target/transfer line an effective surface ion source: Obtaining an ISOBAR free RILIS ion beam is not trivial for many isotopes.

1. Selective production or atom transport cannot always be applied.

1. RILIS selectivity relies on surface ionization suppression or surface-ion suppression.

1. A universal solution has not been established but many effective methods have been tried and tested (LIST, fast beam gating, 2+ ionization, etc).

1. Even if surface ions are suppressed, electron impact (inc. beta-decay) must be considered.

1. Laser ionization inside an arc discharge ion source may open the doors to several new laser ion source configurations for different applications. Acknowledgements

Thank you for your attention V. Fedosseev, S. Rothe, D. Fink, T. Kron, T. Day Goodacre, V. Mishin, R. Rossel, S. Richter, D. Fedorov, M. Seliverstov, P. Molkanov, K. Wendt

Tom Day Goodacre (CERN), New recruit: Matthieu Veinhard (CERN) Jose Henares (GANIL), New recruit: lara hijazi (GANIL) + EN-STI-ECE: Alessandro MASI, Sergio BATUCA, Mark BUTCHER Nathalie LECESNE, + EN-STI-RBS: CREPIEUX Bernard, MARZARI Stefano, STORA Thierry, Jose Luis HENARES (GANIL) GILES Tim, BARBERO Ermanno, SEIFFERT Christoph RILIS RELATED DEVELOPMENTS: RECENT PUBLICATIONS

An ion guide laser ion source for isobar-suppressed rare isotope beams http://scitation.aip.org/content/aip/journal/rsi/85/3/10.1063/1.4868496

Ionization of short-lived isotopes in a hot cavity – Numerical simulations http://www.sciencedirect.com/science/article/pii/S0042207X13004090

The in-gas-jet laser ion source: Resonance ionization spectroscopy of radioactive atoms in supersonic gas jets http://www.sciencedirect.com/science/article/pii/S0168583X12007525

First application of the Laser Ion Source and Trap (LIST) for on-line experiments at ISOLDE http://www.sciencedirect.com/science/article/pii/S0168583X13007180

Development of a resonant laser ionization gas cell for high-energy, short-lived nuclei http://www.sciencedirect.com/science/article/pii/S0168583X12006465

RILIS cavity tests at off-line mass separator

A simplified laser system is setup at the off-line ISOLDE mass separator – producing Ga ion beams for testing RILIS cavities pA – meter Faraday cup and MCP detector l – meter on movable holder

Vertical deflector

Nd:YAG Ti:Sa SHG/THG/FHG

RILIS Ti:Sa Laser System Delay Behlke generator switch

10 kHz DC Master clock V-source

Nd:YAG Narrow laser-ion bunch width + micro beam gate tests Solid-state switch Ga mass ~ 500 V @ 10 kHz marker l2 = lNd:YAG RILIS 1 l1 = lTiSa ionization 3 High Ω cavities: scheme 1. Thin graphite  2. Pyrolytic graphite – being tested  Ga 3. Sigradur ‘glassy’ graphite ☐ – under construction 4. Pulsed heating for higher voltage ☐ -under investigation

300 Model Voigt 5 us beam gating test Equation y = nlf_voigt(x,y0,xc,A,wG,wL);

Reduced Chi-S 21.57725 1000 6.5 V qr Adj. R-Square 0.99118 Voigt Fit Value Standard Error Peak1(H) y0 0.80691 0.13008800 Peak1(H) xc 2.92636E-5 9.17292E-9The fast beam gate is capable of 200 Peak1(H) A 0.00151 1.06434E-5 Peak1(H) wG 4.92994E-6 6.68324E-8 Peak1(H) wL 5.8493E-7 9.11171E-8 Peak1(H) FWHM 5.25016E-6 1.80362E-8a1μs beam gate! 600 Laser-ion Peak2(H) y0 0.80691 0.13008 Peak2(H) xc 1.29282E-4 9.32479E-9 Peak2(H) A 0.00151 1.0731E-5This would give a 100 x time structure: Peak2(H) wG 4.99076E-6 6.687E-8 Peak2(H) wL 5.24769E-7 9.18146E-8400

Counts Peak2(H) FWHM 5.27728E-6 1.82598E-8 Counts 100 5 μS FWHM! surface ion suppression!

Challenge200 : make a 1μs wide laser ion bunch. 0 0 Required pulsed cavity heating 0.0000 0.0001 0.0002 and0.00000 possibly0.00002 0.00004ToFLIS0.00006 technique0.00008 0.00010 Time (s) Time (s) Correcting for energy spread caused by high cavity voltage Exploit the time dependent laser-ion energy within the ion bunch High voltage cavity + micro beam gating + drift tube extractor with voltage ripple Pulsed heating: 0-30 V, 25% duty factor Proton beam (1.4 GeV, 2 μA)

REMOVE energy spread from laser ions

At least DOUBLE the energy spread of surface ions

Additional selectivity increase due to good mass separator acceptance of only laser ions! Available elements so far

85 At