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CEBAF Guns July 1999 - Present

In July 1999, significant progress was made in photocathode technology at CEBAF, culminating in a new Load Lock Gun system by Spring 2006. This system facilitates rapid loading and preparation of GaAs cathodes, achieving unprecedented lifetimes and high polarization levels (~85%) with low RF structures. Key advancements include the integration of a powerful laser setup, advanced vacuum systems, and innovative ion pump configurations. Goals include enhancing current output (up to 10 mA) for future collider facilities such as JLab ELHC and BNL eRHIC, supporting precision tests of the standard model.

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CEBAF Guns July 1999 - Present

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  1. CEBAF Guns July 1999 - Present

  2. Cathode (GaAs) 4 days to load, bake, prepare new photocathode Anode Laser - e -100 kV Cs (F.E.) NF 3 (leaky) Present JLab “Vent/Bake” Polarized Electron Gun

  3. New Load Lock Gun Assembled & Running Spring ‘06 Goal: 8 hours swap photocathode Present: ~12 hours Heat/activation chamber x4 Small bake Load region NEG-coated HV chamber Suitcase

  4. Experimental Setup Faraday Cup (450 C bake) Laser (1 W @ 532 nm) & attenuators High Voltage (-100 kV) NEG pipe Activation (Cs/NF3, Mask=5 mm) Solenoid Centering Spot Size Adjustment 7 Precision Ion Pump Supplies 350 mm 1500 mm Load lock port (GaAs on puck)

  5. Benchmarking the NEW Load Lock Gun (2006-2007) • CEBAF ~2500 C/year • LL Gun ~ 2500 C/week • No RF structure • Low-P wavelength • Demonstrated world best • GaAs lifetimes, & up to 10 mA 13 mA!

  6. Future: High Current & High Polarization Programs Qweak to test standard model >200 mA at 85% polarization Proposed e-/ion collider facilities JLab ELIC (>1 mA), BNL eRHIC (>50 mA) Circulator <1 C/day Linac >100 C/day ~20 C/day

  7. Fiber-based Laser Superlattice GaAs: Layers of GaAs on GaAsP chekc 100 nm 14 pairs No strain relaxation QE ~ 1% Pol ~ 85% @ 780 nm Now: High Current & High Polarization Ingredients: Good gun, good photocathode, powerful laser NEW Load Lock Gun

  8. Friday, Saturday & Sunday • Brief opportunity to use one of the fiber lasers, before installed into CEBAF on Monday: • Superlattice high-P material (85%) • Very good QE ~1% in New Gun • First running with 499 MHz RF • Qweak Demonstrated • 250 mA (2 days, 70 C) • Lifetime 250-1000 C • (translates > 1 week running/spot) • ELIC Circulator Ring Demonstrated • 1 mA (10 hr, 30 C) • Lifetime ~200 C

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