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H – Ion Source Development at RAL & FNAL

H – Ion Source Development at RAL & FNAL. PASI Meeting, RAL 3 rd April 2013. Scott Lawrie & Dan Faircloth (RAL) Dan Bollinger (FNAL). Contents. Comparing FNAL & RAL ion sources FNAL Injector Upgrade Present status RAL FETS VESPA Collaboration Conclusion.

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H – Ion Source Development at RAL & FNAL

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  1. H– Ion Source Developmentat RAL & FNAL PASI Meeting, RAL 3rd April 2013 Scott Lawrie & Dan Faircloth(RAL) Dan Bollinger (FNAL)

  2. Contents • Comparing FNAL & RAL ion sources • FNAL • Injector Upgrade • Present status • RAL • FETS • VESPA • Collaboration • Conclusion

  3. Comparing RAL and FNAL H– Ion Sources

  4. H– Ion Source Specifications Existing Upgrade

  5. Ion Source Development FNAL ISIS

  6. FNAL Injector Upgrade

  7. Replace Cockroft-Waltons • Two 750 kV Cockroft-Walton multipliers • 40 years old • Daily tuning needed • Regular maintenance • Expensive repairs • Experts soon retiring

  8. 2 x BNL-type magnetron H– ion sources on slider 750 keV 4-rod RFQ Linac Tank 1 Two-solenoid magnetic LEBT with additional gas focussing 700mm MEBT (4 x quads, 1 x re-buncher, 1 x einzel-chopper)

  9. New H– Magnetron Circular aperture Single-stage extraction Re-entrant mounting

  10. Extracted Beam Studies Arc Current (A) Excellent power efficiency (50 mA/kW) Best RFQ transmission for 11 A arc > 6 months lifetime

  11. Reduce Extractor Breakdowns • Pressure too low  Paschen minimum • Reduce pumping speed • Extractor heavily damaged • Change from Mo to W • Low B-field  plasma leak • Increase strength of permanent magnets Before After

  12. ISIS Ion Source R&D

  13. Injector Upgrades ISIS Linac 665 keV pre-injector ~2.5 m long Front End Test Stand (FETS) 3 MeV pre-injector ~12 m long

  14. FETS Ion Source Progress • 60 mA flat-top high duty factor beam at: • 50 Hz, 1 ms pulse length; or • 25 Hz, 2 ms pulse length • 96% transmission through LEBT • 0.35 π mm mrad RMS norm. emittance • Studies continue on improving: • Beam alignment and repeatability • Reliability and robustness to HV breakdowns

  15. Vessel for Extraction and Source Plasma Analyses: VESPA • Study and improve ISIS/FETS ion source • Plasma • Beam Transport • Reliability/Longevity • Staged design • Cost effective • Well informed

  16. VESPA Mk 1 Results

  17. RAL & FNAL Collaboration

  18. Caesium Trapping • Caesium is necessary: • Sustain plasma • Enhance H– production • Reduce e–/H– ratio • But causes problems: • HV breakdowns • Electrode sputtering • Dangerous to handle FNAL & RAL collaborating to understand trapping of Cs from source

  19. Optical Spectroscopy • Non-invasive plasma diagnostic • ISIS & FNAL sources are small • Measure emission spectrum • Can determine many things • Plasma density • Electron temperature • Hydrogen to caesium ratio • Space- and time-resolved • Both ISIS & FNAL are pursuing

  20. Conclusions • H– ion sources are actively researched • FNAL & ISIS ion sources have similar traits • Sensible for labs to collaborate • Share plasma and beam diagnostics • Improve ion source efficiency & lifetime  Both facilities benefit

  21. FNAL Einzel-Chopper Lens pulsed to -38 kV MOSFET switches ~100 ns rise time

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