HYBRIS: R. Keller Page 1 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 R. Welton and D. Anderson SNS-Oak Ridge National Laboratory, Oak Ridge, TN, USA Bensheim, Oct. 21, 2004 ICFA-HB 2004 Workshop

HYBRIS: R. Keller Page 2 Acknowledgments John StaplesLBNL2 & 13-MHz rf matching Richard PardoANLMicrowave ECR ion source Bob ScottANLMicrowave ECR ion source

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

HYBRIS: R. Keller Page 4 Original SNS Ion Source and LEBT Areas for Improvement Plasma Generation Beam Formation Electron DumpingLEBT

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

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

HYBRIS: R. Keller Page 7 HYBRIS Layout

HYBRIS: R. Keller Page 8 HYBRIS Electrical Circuit V 20 kV 150 V 6 kV 50 kV 1 A 0.1 A 5 A 0.4 A 0.2 A Hot Deck 60 Hz 1 ms 1  sccm sccm ECR H - HV Break WaveguideMicrowave Chamber Electron Extractor Discharge Cathode Discharge Chamber Cesium Collar/ Outlet Electron Dump Ion ExtractorFaraday Cup

HYBRIS: R. Keller Page 9 Envisaged Operational Parameters

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

HYBRIS: R. Keller Page 11 HYBRIS ECR Discharge Vessel Electron Extraction H - Discharge Vessel

HYBRIS: R. Keller Page 12 HYBRIS Test Stand Tuner Directional Couplers HV Break Dummy Load Magnet Coils Vacuum Tank

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

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