Demonstrating H – Beam Focussing Using an Elliptical Einzel Lens Scott Lawrie on behalf of the ISIS Low Energy Beams Group TueO5
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Demonstrating H– Beam Focussing Using an Elliptical Einzel Lens
Scott Lawrie
on behalf of the ISIS Low Energy Beams Group
TueO5
Contents
• Introduction to VESPA
• Plain diode extraction
• Emittance scanner resolution
• Einzel lens design and HV sparking solutions
• Results and comparison with simulations
• Other work
Present ISIS Ion Source Setup
Sector magnet in cold box
Refrigerant pipes on HV
feedthroughs
Main flange
Ion source flange
Magnet coil and yoke
35 kV insulator
Post-acceleration
electrode and toroid
Drawbacks: • 220 mm path from emission
to toroid collimation • Unknown space charge
compensation • No possibility of plasma
diagnostics • Complicated • Power supplies near
maximum output
Legacy: • Reliable • 50 mA beam current • 50 Hz, up to 2 ms • ~30 day lifetime • Quick to replace • 30 years operational
experience
VESPA (Vessel for Extraction and Source Plasma Analyses)
Benefits: • 100 mm path length from
emission to toroid no beam-loss
• Simpler & cheaper • Plasma diagnostics • Space for additional lens and
deflector • Variable geometry • Variable focussing • Flexible perveance
Main flange
35 kV insulator
Ion source flange
Post-acceleration
electrodes and toroid
Purpose: • Understand plasma • Emission spectroscopy • Improve beam transport • High efficiency • Greater Reliability • Increase source lifetime
VESPA (Vessel for Extraction and Source Plasma Analyses)
Main flange
35 kV insulator
Ion source flange
Post-acceleration
electrodes and toroid
Einzel assembly replaced with large orifice for
plain diode extraction
Plain Diode Extraction
Emittance Scanner Resolution
Norm. RMS εH = 0.24 π mm mrad
Norm. RMS εV = 0.13 π mm mrad
Improve Scanner
Resolution
Norm. RMS εH = 0.39 π mm mrad
Norm. RMS εV = 0.36 π mm mrad
Improve Scanner
Resolution
Einzel Lens Design and Spark Mitigation
Einzel Lens Design and Spark Mitigation
Einzel Lens Design and Spark Mitigation
Prototype solution of moving insulator legs and power cable much further from beam
Einzel Lens Design and Spark Mitigation
Slim-line extraction electrode increases distance to einzel
Einzel Lens Design and Spark Mitigation
Fully engineered einzel support including shielded insulators
Einzel Lens Design and Spark Mitigation
Remove excess large surfaces and move cable away from HV region
H– Beam Current
Emittance Variation with Einzel Voltage
0.0 kV Einzel
Horizontal
Vertical
Simulation
Measurement
Emittance Variation with Einzel Voltage
Next Steps
• More einzel lens measurements
• Further reduce spark rate
• Steering & chopping
• Caesium deposition monitoring using 4 x QCMs
• Lifetime studies at reduced arc current
• 2 x Scaled Ion Source
• ISIS Medium Energy Beam Transport (MEBT)
ISIS Long Shutdown MEBT Preparation
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