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Comparative Analysis of H– Ion Source Development between RAL and FNAL at PASI Meeting 2013

This presentation details the advancements and comparisons of H– ion source technologies between RAL and FNAL, shared during the PASI meeting on April 3, 2013. Key highlights include the current status of ion source specifications, ongoing injector upgrades, and collaborative studies to enhance ion source efficiency and reliability. The discussion addresses the challenges of existing technologies, particularly regarding maintenance and upgrades of aging equipment, and outlines significant research findings on plasma diagnostics, caesium trapping, and beam dynamics improvements.

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Comparative Analysis of H– Ion Source Development between RAL and FNAL at PASI Meeting 2013

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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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