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A Hybrid Ion Source Concept for a Proton Driver Front-End

ICFA-HB 2004 Workshop. A Hybrid Ion Source Concept for a Proton Driver Front-End R. Keller , P. Luft, M. Regis, J. Wallig M. Monroy, A. Ratti, and D. Syversrud Lawrence Berkeley National Laboratory, Berkeley, CA, USA and

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A Hybrid Ion Source Concept for a Proton Driver Front-End

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  1. ICFA-HB 2004 Workshop A Hybrid Ion Source Conceptfor a Proton Driver Front-End R. Keller, P. Luft, M. Regis, J. WalligM. Monroy, A. Ratti, and D. SyversrudLawrence Berkeley National Laboratory, Berkeley, CA, USA and R. Welton and D. AndersonSNS-Oak Ridge National Laboratory, Oak Ridge, TN, USA Bensheim, Oct. 21, 2004

  2. Acknowledgments John Staples LBNL 2 & 13-MHz rf matching Richard Pardo ANL Microwave ECR ion source Bob Scott ANL Microwave ECR ion source

  3. Background Sources of intense H- beams are needed for future Proton Driversthat include Accumulator Rings Specifically, the Spallation Neutron Source (SNS) needs to pursue cutting-edge technology in areas critical to accelerator operation • To ensure adequate performance • Linac and Ring commissioning • 1.44-MW production beam • Future power upgrade towards 3 MW and higher • Ion source and beam-formation system constitute such an area • H- beam production is particularly complex and challenging • R&D investment in this area is highly cost effective Develop ion sources with highest levels of performance and reliability • First phase of work aims at improving reliability and availabilityof the plasma generator (the “ion source proper”) • At least 500 hours of time-between-services

  4. Original SNS Ion Source and LEBTAreas for Improvement Plasma Generation Beam Formation Electron Dumping LEBT

  5. HYBRIS Development Plan • Abandon standard SNS 2 & 13-MHz rf technology, including • Internal, porcelain coated antenna • 2-MHz amplifier and impedance matcher • Main-plasma generation by pulsed d.c. discharge • Proven to work for H- production with filaments (e. g. KEK, JAERI) • Sustain main discharge by microwave-driven plasma cathode • No need for thermionic filaments • No build-up of surface-poisoning deposits • 2.45-GHz ECR plasma generators have proven extremely long lifetime and reliability as proton sources (e. g. LANL-LEDA, CEA Saclay) • Attempts to produceintense H- beamsdirectlyin ECR ion source were moderately successful (~1mA beam current, e. g. TRIUMF, CEA Saclay) • Controlling electron energy in main discharge vessel will be crucial

  6. Performance Parameters • Established SNS ion-source performance • ~55 mA at about 0.1% duty factor • 51 mA transported through LEBT, RFQ, and MEBT • 2.5 weeks with 33 mA at 7.4% d. f. through LEBT • 0.12 p mm mrad normalized rms emittance • 60 mA at 1.2 ms, 20 Hz through LEBT • Modified cesium collar/outlet aperture (see ICFA-HB 2002) • 0.35 p mm mrad normalized rms emittance • Ultimate HYBRIS performance goals • 75 mA peak H- beam current • 0.25 p mm mrad normalized rms emittance • 12% duty factor • 2 months interval between services

  7. HYBRIS Layout

  8. HYBRIS Electrical Circuit 0 - 20 sccm 0 - 100 sccm Cesium Collar/ Outlet Ion Extractor Faraday Cup Microwave Chamber Electron Extractor Discharge Cathode Discharge Chamber Electron Dump Waveguide HV Break ECR H- 60 Hz 1 ms 1W - + - + - + - + - + 150 V 20 kV 150 V 6 kV 50 kV 1 A 0.1 A 5 A 0.4 A 0.2 A Hot Deck

  9. Envisaged Operational Parameters

  10. Status of HYBRIS Development • 2.45-GHz ECRIS obtained on loan from Argonne Nat. Lab. • Chalk River Nat. Lab. model • Test stand assembled • Discharge pulser received from SNS and tested • Baseline test with rf-driven SNS prototype ion source performed • Capacitive rf impedance matcher worked very well • ECR ion source operated • Immediately produced intense electron beam • Electron beam current limited by uncooled extractor tube • So far, operated barely above ECR threshold for 2.45 GHz • HYBRIS extraction chamber built and assembled • Modified, cooled, extractor tube • First test imminent • Still a low-budget effort

  11. HYBRIS ECR Discharge Vessel Electron Extraction H- Discharge Vessel

  12. HYBRIS Test Stand Tuner Directional CouplersHV Break Dummy Load Magnet Coils Vacuum Tank

  13. Future Developments • Optimize ECR discharge chamber as a plasma cathode • Simplify magnetic field generation • Use one solenoid coil only - or permanent magnets • Reduce electron extraction voltage • Reduce distance between ECR and H- discharge chambers • Electron dumping mechanism • LEBT layout

  14. Summary • Hybrid Ion Source under development • Aimed at producing high-current H- beamsat high duty factor with very high reliability • Combining three well proven concepts • Pulsed d.c. main discharge • Microwave-driven plasma cathode • H- production chamber of existing SNS ion source • H- ion production still to be demonstrated • Principal unproven issue is control of the electron temperature in the H- production chamber • Areas of future developments identified

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