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New source for the new injector

New source for the new injector. Current sources. Sources used in the Cockcroft-Walton accelerators:. 1978 to present H- magnetron Slit aperture 50+ mA to linac. Current sources. Cockcroft- Walton magnetron source lifetime and beam quality. Cs inlet at beginning of run.

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New source for the new injector

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  1. New source for the new injector

  2. Current sources Sources used in the Cockcroft-Walton accelerators: • 1978 to present H- magnetron • Slit aperture • 50+ mA to linac

  3. 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

  4. Current sources Magnetron source lifetime and beam quality Low power efficiency and high arc current lead to short lifetime due to cathode erosion

  5. New source Source vacuum cube • source mounted in a 10” vacuum cube • twin turbo (2400 l/s for H2)

  6. New round aperture magnetron ion source extractor ~11in anode cover plate round anode aperture gas valve Cs tube spherical cathode dimple cathode connections

  7. Extractor Pulser Current pulser design uses a 4PR250C tube, unfortunately only one manufacturer extractor voltage LEBT toroid • 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 200usec arc PW toroid DS of RFQ chopped beam

  8. 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 beam current extractor voltage

  9. 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 – 300V) Arc modulator Heater power supplies 50kV isolation transformer

  10. perveance • 94mA at 35kV, max seen so far • on the same order as BNL • current density less than BNL data taken from LEBT toroid so it’s about 10mA lower than what is coming out of the source

  11. 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 35kV, the ratio is 1/1 • Source impedance ~11 Ohms

  12. Extraction gap studies • This study was an attempt to determine what the ideal extraction gap would be. • Three different gaps tried, ranging from 4.4mm to 4.9mm, 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/d2 )

  13. Extraction gap studies 30kV extraction • The smallest gap size has the largest emittance • Within the error of the measurement, the 2 largest gaps have roughly the same emittance

  14. 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 <30kV 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.

  15. 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: • plan to start up with the short can source • minimize boiler temp asap * 11A arc current  >70% RFQ transmission efficiency These will certainly change as we learn how to operate this style of source !

  16. Still need to: • build a 2nd 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 and on…………

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