Post on 24-Feb-2016
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Dan Bollinger AD/Proton Source
New source for the new injector
Dan Bollinger AD/Proton Source Dan Bollinger AD/Proton Source
1978 to present H- magnetron• Slit aperture• 50+ mA to linac
Sources used in the Cockcroft-Walton accelerators:
Current sources
Dan Bollinger AD/Proton Source Dan Bollinger AD/Proton Source
Cockcroft- Walton magnetron source lifetime and beam quality
Typical source aging
Cs inlet completely blocked with cathode material
Cs inlet at beginning of run
Hydrogen inlet almost completely blocked after 3 months of operation
Current sources
Dan Bollinger AD/Proton Source Dan Bollinger AD/Proton Source
Magnetron source lifetime and beam quality
Parameter Value
Arc Current 50A
Arc Voltage 150V
Extractor Voltage 15-18kV
Power efficiency 6.7 mA/kW
Beam Current 50mA
Emittance(entrance of DTL)
ex 2.8 pi mm mradey 4.0 pi mm mrad
Duty factor 0.12%
Average lifetime 3.5 months
Low power efficiency and high arc current lead to short lifetime due to cathode erosion
Current sources
Dan Bollinger AD/Proton Source Dan Bollinger AD/Proton Source
Source vacuum cube
• source mounted in a 10” vacuum cube• twin turbo (2400 l/s for H2)
New source
Dan Bollinger AD/Proton Source Dan Bollinger AD/Proton Source
New round aperture magnetron ion source
~11in
gas valve
Cs tube
cathode connections
round anode aperture
extractor
anode cover plate
spherical cathode dimple
Dan Bollinger AD/Proton Source Dan Bollinger AD/Proton Source
Extractor Pulser
Current pulser design uses a 4PR250C tube, unfortunately only one manufacturer
•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
extractor voltage
LEBT toroid
toroid DS of RFQchopped beam
Dan Bollinger AD/Proton Source Dan Bollinger AD/Proton Source
Extractor Pulser
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
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.
extractor voltage
beam current
Dan Bollinger AD/Proton Source Dan Bollinger AD/Proton Source
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
Dan Bollinger AD/Proton Source Dan Bollinger AD/Proton Source
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
Dan Bollinger AD/Proton Source Dan Bollinger AD/Proton Source
electron to H- ratio
• 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
data was taken in middle of flattop
Dan Bollinger AD/Proton Source 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 4.4mm to 4.9mm, in the test stand.• Coarse perveance and emittance were measured• Hope to run with the largest gap possible to reduce sparking
Extracted beam current slightly lower with larger extraction gap. ( should scale as 1/d2 )
cathodeanode
extractor
extractiongap
45
Dan Bollinger AD/Proton Source Dan Bollinger AD/Proton Source
Extraction gap studies
• The smallest gap size has the largest emittance• Within the error of the measurement, the 2 largest gaps have roughly the same emittance
30kV extraction
Dan Bollinger AD/Proton Source Dan Bollinger AD/Proton Source
emittance as a function of arc current studyMotivated 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.
Dan Bollinger AD/Proton Source 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 11A
Arc Voltage 150V
Extractor Voltage 35kV
Power efficiency 48 mA/kW
Beam Current 80mA
Emittance (end of LEBT)
ex 0.2 pi mm mrad ey 0.3 pi mm mrad
Extraction Gap Size 4.9mm
Cathode temp 380C
Source body temp 290C
Cs boiler temp 120C
Parameter Value
Rep Rate 15Hz
Arc PW 200us
Extracted beam PW 80us
Duty Factor 0.3 %
These will certainly change as we learn how to operate this style of source !
•plan to start up with the short can source•minimize boiler temp asap
* 11A arc current >70% RFQ transmission efficiency
Dan Bollinger AD/Proton Source Dan Bollinger AD/Proton Source
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…………