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Status of High Current Ion Sources. Daniela Leitner Lawrence Berkeley National Laboratory

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Status of High Current Ion Sources Daniela Leitner Lawrence Berkeley National Laboratory October, 27th, Content Overview of available high current sources Requirements for
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Status of High Current Ion Sources Daniela Leitner Lawrence Berkeley National Laboratory October, 27th, Content Overview of available high current sources Requirements for underground accelerator Why ECR Ion Sources for NUSEL? Options for the NUSEL Accelerator Beam transport Areas for R&D 2 High current Ion sources Brief Overview MEVVA (Metal Vapor Vacuum Arc Ion Source) and Laser Evaporation Ion Sources Medium charge states High currents 100 ma no gases Pulsed Multicusp ion sources (Filament/ RF) and cathode based ion sources Single to low charge states High currents 100 ma Limited lifetime Microwave Sources Singly Charged Ions High currents 100 ma High Reliability Long Lifetime High charge ECR Ion sources (Electron Cyclotron Resonance) Medium to high charge state ions Medium currents (µa to ma) High Reliability Long Lifetime 3 What are the requirements for an underground injector system High Reliability Low Maintenance Easy Operation Flexibility change charge state to change energy beams from solid material and gases Low Power Consumption high voltage Platform High Stability 4 Why are ECR Ion Sources the ideal ion source type for NUSEL? AECR-U Injector at the 88- Inch Cyclotron as an example Runs 24 hours/day, 7 days/ week with minimum intervention Minimum maintenance (typically not required for years) Excellent Beam Stability High Reliability High intensities High flexibility Can produce ion beams from every element Good beam quality 5 How do ECR ion sources work Solenoid Coils ω e = B q m = ω rf microwave, gas ion extraction Plasma I ω rf2 M -1 I log B 1.5 Sextupole 6 ECR Ion source have been developed mainly for two areas high charge state ECR ion sources high charge states and low charge states 10-7 to 10-6 mbar, total current 1-5 ema Ar 8+ (2000 eµa) O 6+ (1500 eµa) several ma for light ions Beam transport challenging R&D area( RIA) Single Charged ECR ion source (Chalk River) single charge 10-3 to 10-2 mbar total current up to 130 ema* Beam transport challenging but demonstrated (LEDA) R&D area for high quality beams *J. Sherman, et. al. RSI, vol. 69, pp. 1003, LEDA has demonstrated 100 ma H + transported through CW RFQ low-energy demonstrator accelerator (LEDA) Proton beam current (ma) Proton fraction(%) Beam energy (kev) Discharge power (W) 2.45 GHZ Beam noise (%) Ion source emittance (πmm-mrad) to 800 ± (rms, normalized) *J. Sherman, et. al. RSI, vol. 69, pp. 1003, High Charge state ECR ion source development at LBNL n e ω rf 2 τ ion BL mirror I ω rf2 M -1 I P rf 1/3 ECR (1983) 0.4 T, 0.6 kw, 6.4 GHz AECR-U (1996) 1.7 T, 2.6 kw, GHz VENUS (2001) 4.0 T, 14 kw, GHz 9 The frequency scaling for the LBNL ECR ion sources 10 3 AECR-U 14 and 10 GHz LBL-ECR 6.4 GHz Argon Charge State 10 Most advanced ECR ion source is VENUS at LBNL Energy in MeV/amu PIG Evolution of the 88-Inch Cyclotron Performance for Heavy Ions at 1pnA ECR AECR-U 1995 VENUS Particle Mass in amu Produce the world most intense high charge state heavy ion-beams for the 88-Inch Cyclotron RIA R&D Ion Source 10 pµa U 30+ Driver Linac (to 400 MeV/nuc) Driver Ion Source Post Accelerator Target/ Ion Source Module Isotope Separator RFQ s Experimental Areas Fragmentation Fragmentation Separator Provide highest current high-charge state beams for the next generation heavy ion accelerators. 11 VENUS Components Superconducting Structure Beam Transport RIA R&D Source 10 pua U 30+ Conventional Components 1. Superconducting magnet structure forces a completely new ion source design, not an extension of an existing design. 2. VENUS serves as test bed to understand the transport of high current heavy ion beams 12 Venus at 18 GHz out performances AECR-U especially for heavy ions Bi performance Xe performance 150 Bi - VENUS Bi - AECR 150 VENUS AECR Charge State Charge State 13 High performance fully permanent magnet ECR ion source (commercially available) 2 ma of H+ 150 eµa O eµa of Ar High Frequency 14.5 GHz Fully permanent magnet Compact, but Performance limited Ovens difficult Beam transport difficult Compact RF system (Traveling Wave Tube) Power limited (400 W) Especially suitable for high voltage platforms 14 High performance fully permanent magnet ECR ion source (continue) 700 mm Very tight injection for oven inserts 500 mm Permanent magnets imply very narrow extraction (beam blow up due to space charge) Ref.: C. Bieth, J. L. Bouly, J. C. Curdy, S. Kantas, P. Sortais, P. Sole, and J. L. Vieux-Rochaz Rev. Sci. Instrum. 71, 899 (2000) 15 A conventional ECR Ion source offers more operational flexibility and higher intensities than fully permanent sources AECR-U Ions Source Radial probe (direct insertion) Radial oven Radial oven Off-axis axial Oven MIVOC Chamber(Metal Ions from Volatile compounds) 16 Comparison of highest performance conventional and fully permanent ECR ion sources SNANOGAN (compact) AECR-U 14 GHz RIKEN 18 Data GHz Argon Charge State 17 Beam Transport 18 Multi Charged ECR Ion Beam Transport Ar 1+ Ar 5+ Space charge dominated beams Ar 16+ Charge state distribution for each species present at extraction (each contribution must be taken into account correctly) Different focusing properties for each M/Q Emittance contribution due to the high solenoid field at the extraction 19 The ECR Ion Source Emittance dominated by the magnetic field at extraction 30 kv, 238 U 20+, xx' rms norm ε = r2 B 1 MAG 0 M Q Magnetic Field Dominates Emittance for given M/Q above M/Q=1 B 0 0.07 T M/Q=5 B 0 0.15 T M/Q=30 B 0 0.38 T Therefore the ion source emittance for every ECR ions is dominated by the magnetic field at extraction M. Leitner et al: Design of the Extraction System and Beamline of the Superconducting ECR Ion Source VENUS,Proc. of the 2001 Particle Accelerator Conference (PAC 2001), Chicago, Illinois, June VENUS Low Energy Beam Transport LEBT-Design 25 ma proton-equivalent current at 30 kv extraction voltage 21 Emittance Measurements combined with Ion Beam simulations are essential for understanding the ion beam transport for ECR ion source 0.2 theoretical emittance (1rms) due to the magnetic field X [mrad] 220euA Ar kev 0.10 pi mm mrad Plasma stability Tuning Optics 0.05 X [mm] Essential for providing very high quality beams as required for precision measurements RIA R&D will provide an essential data base for the beam transport 22 Experimental requirements are needed for the optimum design of the injector Injector system type (Power and Space available ) Intensity needed Energy range Ion species? Purity of Ions CW or pulsed Timing (chopping) Beam quality Beam Noise Stability Spot size High Intensity single charge Ion Source Maybe required for some low cross section experiments High charge state ECR Conventional/permanent magnet Charge state can vary to change energy Charge state selection Beam transport 23 Conclusion and areas for R&D ECR sources are ideal sources for an underground accelerator Demonstrated performance record on accelerator High Reliability and Flexibility Have to decide which kind of ECR is best suited (depends mainly on intensity required) R&D (simulations and experiments) for the ECR ion beam transport would be beneficial To assure very high quality beams Build injector system to measure beam parameter overlap with RIA R&D 24
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