Ion Source Development at RAL Dan Faircloth Including the work of: Scott Lawrie, Alan Letchford, Christoph Gabor, Phil Wise, Mark Whitehead, Trevor Wood, Mike Perkins, Mick Bates, David Findlay, Juergen Pozimski, Simon Jolly, Pete Savage, David Lee Dan Faircloth – Proton Meeting RAL Thursday 24 th MarchFaircloth

The ISIS Ion Source Penning H - ion source Surface plasma source (SPS) Dudnikov type 15 ml/min H 2 3 g/month Cs 20 day average lifetime

Mounting Flange Negative Ion Beam Mica Penning Pole Pieces 10mm Slit Aperture Plate Water Cooling Channels Source Body Air Cooling Channels Ceramic Spacer Copper Spacer Cathode Hollow Anode Discharge Region Extraction Electrode

H2H2 Negative Ion Beam Piezo Hydrogen Valve Caesium Oven Caesium Vapour Heated Transport Line Hollow Anode 50 A Discharge +17 kV Extraction Voltage 10 mm

H2H2 Negative Ion Beam Piezo Hydrogen Valve Caesium Oven Caesium Vapour Heated Transport Line Hollow Anode 50 A Discharge +17 kV Extraction Voltage Source Runs at 50 Hz Rep Rate 10 mm

Timing Time H 2 Gas Pulse ~ 200 μs Extraction Voltage Pulse ~ 250 μs Source Runs at 50 Hz Rep Rate Discharge Pulse ~ 600 μs H - Beam

Cathode Hydrogen Feed Heated Caesium Transport Line Air Cooling Source Body Hollow Anode Discharge Power Feed Thermocouples

Aperture Plate

Extraction Electrode Support Insulators Caesium Shields Extraction Mount

3 Sources at ISIS Operational Source 24 x 7 operation 20 day average lifetime μs pulse length 50 Hz 35 keV 35 RFQ Ion Source Development Rig Pre-test operational sources Problem solving FETS Source Experimental sources High current Long pulse 65 keV

FETS 65 kV high voltage platform

Laser Diagnostics Vessel 3 Solenoid LEBT Ion Source

+ Platform ground - 18 kV Pulsed extraction power supply Extraction electrode Aperture plate Extraction gap 90  Sector magnet Toriod 1 H - beam FETS Source Schematic Extraction electrode, coldbox and sector magnet all pulsed Coldbox 65 kV Platform DC power supply Post extraction acceleration gap Laboratory ground MΩ750 kΩ Protection electrode Ground plane Suppression electrode P.S.

FETS Source Dan Faircloth – ICIS 2009Faircloth

FETS source modifications Steady state calculation Computational fluid dynamic cooling calculation Cathode Surface Anode Surface ΔT= 73 ºC ΔT= 39 ºC Transient Calculation Finite Element Modelling 2.2 ms discharge at 50 Hz achieved with simple design changes 1. Extend discharge duty cycle

2. Discharge current FETS source modifications Experiments For each extraction condition there is a range of discharge currents that give minimum beam divergence 14 kV extraction voltage 2.2 mm extraction gap

1. Extend discharge duty cycle 3. Permanent magnet Penning field 2. Discharge current FETS source modifications Nd 2 Fe 14 B Permanent Magnets B To allow different extraction voltages the Penning field must be decoupled from the sector magnet field Permanent magnets are used to produce the produce the 0.15 – 0.25 T required for a stable discharge

1. Extend discharge duty cycle 3. Permanent magnet Penning field 2. Discharge current 4. Extraction FETS source modifications Voltage, Geometry and Meniscus Increase voltage from 17 to 25 kV Child-Langmuir 78 mA Widen plasma electrode aperture Meniscus Studies Decrease extraction jaw separation

1. Extend discharge duty cycle 3. Permanent magnet Penning field 2. Discharge current 4. Extraction 5. Analysing magnet FETS source modifications Magnet Redesign Dipole has a focusing component Magnetic Field Gradient Index, n Field gradient index 0 0.5T Field must be adequately terminated Significant improvement in emittance Size of good field region increased Beam expands under space charge Exact degree of compensation unknown Optimum field gradient index n = 1.2 determined by experiment

1. Extend discharge duty cycle 3. Permanent magnet Penning field 2. Discharge current 4. Extraction 5. Analysing magnet 6. Post acceleration FETS source modifications Optimize Post Acceleration Gap Minimum emittance growth occurs for a post acceleration field of 9 kVmm kV PA Voltage Measured 355 mm from Ground Plane of PA Gap 11 kV PA Voltage25 kV PA Voltage Constant 10 kV Extraction Voltage 23 mA H - Beam Current 19 kV PA Voltage 55.0 mm PA Gap 9.2 mm PA Gap 2.5 mm PA Gap 2.0 mm PA Gap 12.5 kVmm kVmm kVmm kVmm kVmm kVmm kVmm kVmm kVmm kVmm kVmm kVmm kVmm kVmm kVmm kVmm - 1 Increasing Post Acceleration Gap Length Increasing Post Acceleration Voltage

Isolating Column 1×10 -4 mBar 6×10 -5 mBar Beam shutter Slit-slit scanners 5×10 -6 mBar Retractable Faraday Cup 2000 Ls -1 Turbo Pump Pepper pot or profile scintillator head Camera 7×10 -6 mBar Solenoid 3 Toroid3 Solenoid 2 Solenoid 1 Toroid 1 Toroid 2 4 × 800 Ls -1 & 1 x 400 Ls -1 Turbo Pumps Differential pumping and laser profile vessel 400 Ls -1 turbo pump Diagnostics vessel Toroid 4 Laser Diagnostics

Short Pulse Operation <1ms For pulse lengths shorter than 1 ms: 80 mA at the ground plane 60 mA at the entrance of the RFQ 0.3 πmm.mrads r.m.s normalised Results that follow are for 2 ms pulse lengths…

Vary Discharge Current- 20 to 50 A Discharge CurrentDischarge Voltage Discharge PowerDischarge Impedance H - Beam Current

1. Increased Plasma Density Increased H + and Cs + bombardment sputters Cs from cathode surface. More H - are stripped on their way to the extraction region. Possible Explanation of Droop:

2. Electrode Surface Temperature Rise Transient 3D FEA calculations of electrode surface temperature Higher discharge currents ↓ Greater surface temperature rise during the pulse ↓ Surface Cs coverage pushed away from optimum Discharge Power

Vary Discharge Rep Rate

Lower repetition rate ↓ More time between pulses ↓ Longer time for Cs coverage to build up

Time Variation of Emittance: 25 Hz 50 A discharge

500 Current (μA) Current (μA) µs Horizontal Vertical Beam Current Normalised RMS Emittance ( π mm mrad)

500 Current (μA) Current (μA) µs Horizontal Vertical Beam Current Normalised RMS Emittance ( π mm mrad)

500 Current (μA) Current (μA) µs Horizontal Vertical Beam Current Normalised RMS Emittance ( π mm mrad)

500 Current (μA) Current (μA) µs Horizontal Vertical Beam Current Normalised RMS Emittance ( π mm mrad)

500 Current (μA) Current (μA) µs Horizontal Vertical Beam Current Normalised RMS Emittance ( π mm mrad)

500 Current (μA) Current (μA) µs Horizontal Vertical Beam Current Normalised RMS Emittance ( π mm mrad)

500 Current (μA) Current (μA) µs Horizontal Vertical Beam Current Normalised RMS Emittance ( π mm mrad)

500 Current (μA) Current (μA) µs Horizontal Vertical Beam Current Normalised RMS Emittance ( π mm mrad)

500 Current (μA) Current (μA) µs Horizontal Vertical Beam Current Normalised RMS Emittance ( π mm mrad)

500 Current (μA) Current (μA) µs Horizontal Vertical Beam Current Normalised RMS Emittance ( π mm mrad)

500 Current (μA) Current (μA) µs Horizontal Vertical Beam Current Normalised RMS Emittance ( π mm mrad)

500 Current (μA) Current (μA) µs Horizontal Vertical Beam Current Normalised RMS Emittance ( π mm mrad)

500 Current (μA) Current (μA) µs Horizontal Vertical Beam Current Normalised RMS Emittance ( π mm mrad)

500 Current (μA) Current (μA) µs Horizontal Vertical Beam Current Normalised RMS Emittance ( π mm mrad)

500 Current (μA) Current (μA) µs Horizontal Vertical Beam Current Normalised RMS Emittance ( π mm mrad)

500 Current (μA) Current (μA) µs Horizontal Vertical Beam Current Normalised RMS Emittance ( π mm mrad)

500 Current (μA) Current (μA) µs Horizontal Vertical Beam Current Normalised RMS Emittance ( π mm mrad)

500 Current (μA) Current (μA) µs Horizontal Vertical Beam Current Normalised RMS Emittance ( π mm mrad)

500 Current (μA) Current (μA) µs Horizontal Vertical Beam Current Normalised RMS Emittance ( π mm mrad)

500 Current (μA) Current (μA) µs Horizontal Vertical Beam Current Normalised RMS Emittance ( π mm mrad)

500 Current (μA) Current (μA) µs Horizontal Vertical Beam Current Normalised RMS Emittance ( π mm mrad)

500 Current (μA) Current (μA) µs Horizontal Vertical Beam Current Normalised RMS Emittance ( π mm mrad)

500 Current (μA) Current (μA) µs Horizontal Vertical Beam Current Normalised RMS Emittance ( π mm mrad)

500 Current (μA) Current (μA) µs Horizontal Vertical Beam Current Normalised RMS Emittance ( π mm mrad)

500 Current (μA) Current (μA) µs Horizontal Vertical Beam Current Normalised RMS Emittance ( π mm mrad)

500 Current (μA) Current (μA) µs Horizontal Vertical Beam Current Normalised RMS Emittance ( π mm mrad)

500 Current (μA) Current (μA) µs Horizontal Vertical Beam Current Normalised RMS Emittance ( π mm mrad)

500 Current (μA) Current (μA) µs Horizontal Vertical Beam Current Normalised RMS Emittance ( π mm mrad)

500 Current (μA) Current (μA) µs Horizontal Vertical Beam Current Normalised RMS Emittance ( π mm mrad)

500 Current (μA) Current (μA) µs Horizontal Vertical Beam Current Normalised RMS Emittance ( π mm mrad)

500 Current (μA) Current (μA) µs Horizontal Vertical Beam Current Normalised RMS Emittance ( π mm mrad)

500 Current (μA) Current (μA) µs Horizontal Vertical Beam Current Normalised RMS Emittance ( π mm mrad)

500 Current (μA) Current (μA) µs Horizontal Vertical Beam Current Normalised RMS Emittance ( π mm mrad)

500 Current (μA) Current (μA) µs Horizontal Vertical Beam Current Normalised RMS Emittance ( π mm mrad)

500 Current (μA) Current (μA) µs Horizontal Vertical Beam Current Normalised RMS Emittance ( π mm mrad)

500 Current (μA) Current (μA) µs Horizontal Vertical Beam Current Normalised RMS Emittance ( π mm mrad)

500 Current (μA) Current (μA) µs Horizontal Vertical Beam Current Normalised RMS Emittance ( π mm mrad)

500 Current (μA) Current (μA) µs Horizontal Vertical Beam Current Normalised RMS Emittance ( π mm mrad)

500 Current (μA) Current (μA) µs Horizontal Vertical Beam Current Normalised RMS Emittance ( π mm mrad)

500 Current (μA) Current (μA) µs Horizontal Vertical Beam Current Normalised RMS Emittance ( π mm mrad)

Time variation of Emittance Parameters for different conditions: Phase space rotation caused by decompensation of the beam HORIZONTAL VERTICAL Normalised RMS Emittance Twiss Alpha Twiss Beta

IB8π2εHεVIB8π2εHεV Beam Brightness =

ISIS Source around the World Chinese Spallation Neutron Source ESS Bilbao

CERN SLHC-pp Source THE CHALLENGE: Over 3 times increase in power Over 100 times increase in d.f.

Modelling and Prototyping

1.2 ms pulse length at 50 Hz 50 kW plasma stable

The Future Up-rated power supplies Better understanding of the plasma - PhD research project with JAI - Optical spectroscopy - Plasma modelling Scaled source Understand lifetime limitations

Thank you for your attention Questions, Comments?