H– Ion Source Developmentat RAL & FNAL

PASI Meeting, RAL3rd 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

Parameter ISIS FNAL

Technology Penning Magnetron

Beam current [mA]

50 70 60 44

Arc current [A] 55 40 50 10

Arc voltage [V] 60 60 150 150

Arc pulse width [μs]

800 2200 80 230

Repetition rate [Hz]

50 50 15 15

Extraction Two-stage: 18 36kV

Two-stage:25 65 kV

Multi-stage:18 750 kV

One-stage:35 kV

Lifetime [month] ~ 1 3 6

Existing Upgrade

Ion Source DevelopmentISIS

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 UpgradesISIS Linac665 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