New source for the new injector Dan Bollinger
New source for the new injector Dan Bollinger AD/Proton Source
Current sources Sources used in the Cockcroft-Walton accelerators: 1978 to present H- magnetron • Slit aperture • 50+ m. A to linac Dan Bollinger AD/Proton Source
Current sources Cockcroft- Walton magnetron source lifetime and beam quality Cs inlet at beginning of run Typical source aging Cs inlet completely blocked with cathode material Hydrogen inlet almost completely blocked after 3 months of operation Dan Bollinger AD/Proton Source
Current sources Magnetron source lifetime and beam quality Parameter Value Arc Current 50 A Arc Voltage 150 V Extractor Voltage 15 -18 k. V Power efficiency 6. 7 m. A/k. W Beam Current 50 m. A Emittance (entrance of DTL) ex 2. 8 pi mm mrad ey 4. 0 pi mm mrad Duty factor 0. 12% Average lifetime 3. 5 months Dan Bollinger AD/Proton Source Low power efficiency and high arc current lead to short lifetime due to cathode erosion
New source Source vacuum cube • source mounted in a 10” vacuum cube • twin turbo (2400 l/s for H 2) Dan Bollinger AD/Proton Source
New round aperture magnetron ion source extractor gas valve Cs tube cathode connections round anode aperture spherical cathode dimple Dan Bollinger AD/Proton Source anode cover plate ~11 in
Extractor Pulser Current pulser design uses a 4 PR 250 C tube, unfortunately one manufacturer extractor voltage • This tube seems to be current limited and has a limited lifetime of ~4. 5 months • Small flattop when arc turns on prior to extraction pulse • Need about 200 usec arc PW Dan Bollinger AD/Proton Source LEBT toroid DS of RFQ chopped beam
Extractor Pulser DTI solid state switches We tried ½ of our solid state chopper pulser as an extractor. It worked very well with fast rise time and good flattop. With DTI switches • Fast rise time • Very good flattop • Solid State • Fewer failures? • might be able to run with shorter arc PW which would lower the duty factor and cathode erosion Dan Bollinger AD/Proton Source beam current extractor voltage
Source electronics HV rack Computer for D/A and A/D + fiber optic communication S&H for arc current and voltage Thermocouple readbacks Gas valve pulser Arc power supply (0 – 300 V) Arc modulator Heater power supplies 50 k. V isolation transformer Dan Bollinger AD/Proton Source
perveance • 94 m. A at 35 k. V, max seen so far • on the same order as BNL • current density less than BNL data taken from LEBT toroid so it’s about 10 m. A lower than what is coming out of the source Dan Bollinger AD/Proton Source
electron to H- ratio data was taken in middle of flattop • Study assumed that the total current the extractor pulser sees is the sum of the electron current and the H- current • At 35 k. V, the ratio is 1/1 • Source impedance ~11 Ohms Dan Bollinger AD/Proton Source
Extraction gap studies • This study was an attempt to determine what the ideal extraction gap would be. • Three different gaps tried, ranging from 4. 4 mm to 4. 9 mm, in the test stand. • Coarse perveance and emittance were measured • Hope to run with the largest gap possible to reduce sparking anode cathode extractor extraction gap 45 Extracted beam current slightly lower with larger extraction gap. ( should scale as 1/d 2 ) Dan Bollinger AD/Proton Source
Extraction gap studies 30 k. V extraction • The smallest gap size has the largest emittance • Within the error of the measurement, the 2 largest gaps have roughly the same emittance Dan Bollinger AD/Proton Source
emittance as a function of arc current study Motivated by a paper written by S. R. Lawrie, Dan Faircloth, A. P. Letchford, C. Gabor, and J. K. Pozmiski “Plasma meniscus and extraction electrode studies of the ISIS H- ion source” Test stand data taken <30 k. V extraction Preliminary LEBT scan cathode Shape of plasma meniscus affects the divergence of the extracted beam and is affected by the arc current/plasma density. Dan Bollinger AD/Proton Source
Start-up source parameters These are the source parameters that we plan to use for commissioning the RFQ after it is installed in the Linac: Parameter Value *Arc Current 11 A Rep Rate 15 Hz Arc Voltage 150 V Arc PW 200 us Extractor Voltage 35 k. V Extracted beam PW 80 us Power efficiency 48 m. A/k. W Duty Factor 0. 3 % Beam Current 80 m. A Emittance (end of LEBT) ex 0. 2 pi mm mrad ey 0. 3 pi mm mrad Extraction Gap Size 4. 9 mm Cathode temp 380 C Source body temp 290 C Cs boiler temp 120 C • plan to start up with the short can source • minimize boiler temp asap * 11 A arc current >70% RFQ transmission efficiency These will certainly change as we learn how to operate this style of source ! Dan Bollinger AD/Proton Source
• • Still need to: build a 2 nd source optimize anode/extraction aperture new longer Cs tubes machined HV isolation boxes built build HV rack umbilical cord (possibly PVC) try gas valve feedback loop design/build HVPS controls extractor/Lens • • Studies different anode/extractor apertures optimize extraction gap Cs boiler temp extraction timing minimize emittance maximize transmission efficiency monitor Cs deposition on extractor cone an on and on………… Dan Bollinger AD/Proton Source
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