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

Comparing RAL and FNAL H – Ion Sources

H – Ion Source Specifications ParameterISISFNAL TechnologyPenningMagnetron Beam current [mA] Arc current [A] Arc voltage [V] Arc pulse width [ μ s] Repetition rate [Hz]50 15 ExtractionTwo-stage: 18  36kV Two-stage: 25  65 kV Multi-stage: 18  750 kV One-stage: 35 kV Lifetime [month]~ 136 Existing Upgrade

Ion Source Development ISIS FNAL

FNAL Injector Upgrade

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

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

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

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

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

ISIS Ion Source R&D

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

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

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

VESPA Mk 1 Results

RAL & FNAL Collaboration

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

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

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

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