Charge Lifetime Improvement After Biasing Gun2 Anode by Josh Yoskowitz
Explore the charge lifetime improvement after biasing Gun2 anode, showcasing ion production and photocathode bombardment. Follow the timeline of measurements and future work for a simulation benchmarking project presented in the 2019 Polarized Sources Workshop.
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Charge Lifetime Improvement After Biasing Gun2 Anode Josh Yoskowitz
Ion Production and Photocathode Bombardment Electron beam ionizes residual gas Ions accelerate back towards the negatively biased photocathode and strike it, resulting in QE decay Biasing the anode repels downstream ions, reducing the number of ions that strike the photocathode, resulting in slower QE decay and a larger photocathode lifetime Anode Cathode Ions Ions e-beam
Timeline 5/16 - Performed measurements during the last SAD, which demonstrated no observable difference to the beam orbit, beam size or beam timing after applying a small <1000 V bias to the gun anode. 6/15 Start of run 6/15 to 7/25 Ran beam with anode grounded at 0V Total charge extracted: ~65C 7/25-8/8 (30 min to bias anode and verify no impact to Parity Quality Beam) Ran beam with anode biased at +961V Total charge extracted: ~62C 8/8-8/12 (10 min to ground anode) Ran beam with anode grounded at 0V Total charge extracted: 22C
Present/Future work Will continue running with anode grounded until the total charge extracted is ~180C (in ~1 week), then the anode bias will be brought back to +961V to complete (OFF, ON, OFF, ON) measurements. These measurements are being used to benchmark a simulation of ion generation and photocathode bombardment in our photo-guns. The results will be presented in September at the 2019 Polarized Sources, Targets and Polarimeters Workshop.
