Ionization Effects - February 12, 2019
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Meeting Info
We will meet Tuesday February 12 at 11:00 am EST in TL 2236. Wiki: https://wiki.jlab.org/ciswiki/index.php/Ionization_Effects_-_February_12,_2019
For those calling in we'll use the Blue Jeans [1] audio conference system.
Meeting ID: 366850636# Meeting URL (for video and/or audio call in): http://bluejeans.com/366850636 Phone number (for audio call in): 1-888-240-2560
Topics
- Background Material
- PRAB (lifetime studies w/ bulk GaAs) media:high current lifetime_in print.pdf
- PSTP17 (lifetime study w/ GaAs/GaAsP) media:PSTP2017_Grames_v1.pptx media:PSTP2017_Grames_Final.pdf
Paper Outline
- Motivation for high polarization at high current
- Requires useful long operating lifetime (e.g. 2mA is 1200C/week)
- QE uniformity important for beam quality, especially parity violation experiments
- Applications: Electron Ion Collider (>50 mA), Polarized Positron Source (>10mA) or Moller Standard Model test (>0.2 mA)
- Experimental Conditions (GaAs/GaAsP, tee shape electrode w/ grounded anode, rf pulsed IR laser)
- Injector Test Facility (anode + vacuum)
- CEBAF (anode + vacuum + radiation + apertures + polarimetry)
- Results
- Injector Test Stand Results => 1mA and 4mA studies w/o polarimetry
- CEBAF QWeak performance applying laser scaling, then operating 1-2 years @ 0.2mA w/ online Compton polarimetry vs. QE
- CEBAF Scaling Experiment to achieve longest lifetime (>1000C) at >1 mA
- CEBAF Polarization Experiment to measure polarization up to 1mA
- Simulation Studies (IBSimu, GPT, Simion)
- Ion impact distribution at photocathode (#, energy, position) for CEBAF gun/geometry => show scaling depends upon optics
- Electron beam distribution and losses => validate radiation loss & vacuum load, useful to compare IBSimu w/ GPT model
- Ionization and secondaries distribution and total contribution to ions reaching cathode/anode gap
- Outlook & Conclusions
Background Material
- Ion impact degradation of GaAs photocathodes
- J. Grames, R. Suleiman, P. A. Adderley, J. Clark, J. Hansknecht, D. Machie, M. Poelker, and M. L. Stutzman, "Charge and fluence lifetime measurements of a DC high voltage GaAs photogun at high average current", Phys. Rev. ST Accel. Beams 14, 043501 (2011), media:high current lifetime_in print.pdf
- 2018 Experiment to exploit increase of laser area to achieve >100C at >1mA from high polarization photocathodes
- Joe Grames, Phil Adderley, John Hansknecht, Reza Kazimi, Matt Poelker, Daniel Moser, Marcy Stutzman, R. Suleiman Shukui Zhang "Milliampere beam studies using high polarization photocathodes at the CEBAF Photoinjector" media:PSTP2017_Grames_v1.pptx media:PSTP2017_Grames_Final.pdf