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…………