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Advancements in High-Current Polarized Electron Photogun Technology at CEBAF EIC

Explore the evolution of the CEBAF Load-Lock Polarized Electron Photogun by Joe Grames and Matt Poelker and its exciting directions for future development. Discover key features, current advancements, and potential technologies to enhance performance and longevity. With a focus on high current, high polarization, and improved lifetime, this research aims to push boundaries in electron beam technology.

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Advancements in High-Current Polarized Electron Photogun Technology at CEBAF EIC

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  1. CEBAF Load-Lock Polarized Electron Photogun Joe Grames & Matt Poelker (Jefferson Lab) Outline • Relevant EIC R&D • CEBAF e- source • gun evolution • high current & longer lifetime • high current & high polarization • Exciting directions

  2. Relevant EIC R&D • 200 kV gun for CEBAF NP • Qweak, PREX & other higher current experiments • Pursue enabling technologies • Inverted gun, ceramic insulators • FE elimination via HPR/EP/BCP • Polarized e- beam for e+ source • CEBAF at >1 mA for polarized positron source • Surface charge limit • Unpolarized e- beam for FEL/lightsources • DC gun at >10 mA • Lifetime vs. laser handling (spot size, incident/reflected power)

  3. CEBAF e- source: gun evolution ‘95-’97 ‘98-’99 ‘99-’07 ‘01-’05

  4. CEBAF e- source: today Installed July 2007 Operated since September 2007 • Key Features: • Smaller surface area • Electropolished and vacuum fired to limit outgassing • NEG-coated • Never vented • Multiple pucks (8 hours to heat/activate any photocathode) • Suitcase for installing new photocathodes (one day to replace all pucks) • Mask to limit active area, no more anodizing

  5. CEBAF e- source: current & lifetime Bulk GaAs w/ 532nm DC light • Improve vacuum • Reduce surface area • 400 C bake • Ion pump = Gas Source? • Limit “bad” electrons • Eliminate FE • Laser handling • Increase QE • Longer heat clean • Better vacuum • High-P Photocathode “HGUN” J. Grames et al., in AIP Conference Proceedings 915, p. 1037-1044 (2006).

  6. CEBAF e- source: high current & polarization • March 2007 • Superlattice high-P material (85%) • QE ~1% @ 780 nm • Fiber laser (499 MHz @ 780nm) • CEBAF-like Operation • I=0.25 mA (~20 C/day) • Measured Lifetime ~0.25-1 kC • (translates > 1 week running/spot) • EIC-like Operation • I=1 mA (~85 C/day) • Measured Lifetime ~0.2 kC • (translates ~few days running/spot) QE [%] J. Grames et al., in Proc. of the 2007 Particle Accelerator Conference, THPMS064, p. 3130.

  7. Exciting direction: inverted gun geometry • Medical x-ray technology • Ceramic not exposed to FE • Compact, no SF6 e Present design New design?

  8. CEBAF gun Exciting direction: eliminate field emission Investigate SRF-cavity technique “high pressure rinsing” M. Chetsova, K. Surles-Law New electrodes, including single crystal Niobium…

  9. Exciting direction: investing in design effort • To date => more QE, polarization or laser power • Now, opportunity to focus on cathode/anode design & first few meters of machine • Want to “get it right” the first time • Growing design/modeling expertise with PhD students: • Ken Surles-Law: 200kV gun • AshwiniJayaprakash: ILC gun • Jonathan Dumas: polarized positron source • Alicia Hofler: RF gun and genetic algorithm

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