ELIC Injector Working Group High-P, high-I source issues (DC) High-P, high-I EIC issues (RF) Experiments with BTLLPEG (Load Lock Gun) Modeling to support BTLLPEG Studies Conclusions and roadmap ELIC Meeting April 7, 2004 J. Grames

High-P, high-I source issues (DC) The foremost challenge for any high average current (mA’s) polarized electron source is maintaining the (suitably large initial) QE for a sufficiently long (1/e) duration. See Matt’s EIC workshop talk for more details. These challenges will may be met by understanding lifetime versus: radial laser spot location (primary emission site) active area (secondary emission sites) laser spot diameter (charge lifetime scaling) gun and beamline vacuum conditions (ionized residual gas) gun voltage (energy associated to ions accelerated to cathode) beam capture (electron loss impact on vacuum) laser wavelength (baseline emittance) Gas GaAs Active Area Effects associated with cathode degradation: QE gradient (transverse charge density modified) QE restoration (is ion damage reversible?) polarization reduction (is ion damage a term in depolarization) Laser Spot

High-P, high-I EIC issues (RF and time structure) Time Structure Schemes => set requirements of source injection compatible with EIC and ERL injection/extraction methods Microstructure surface charge limit on peak photocurrent high voltage required for bunch charge bunch dynamics beam polarization (average & along bunch) laser repetition rate (1497 or sub-harmonic) 3. Macrostructure impact on laser solution CW or pulse train (repetition rate or Q-switched)

Experiments in the ITS South Cave & EEL Lab Measurements aimed to answer: charge lifetime scaling (active area, spot location, spot size) ion-backbombardment vs. ion characteristics benchmark Parmela model, measure beam emittance Phase 1 BTLLPEG Measure polarization and add RF structure: addition of Wien filter, Mott polarimeter, RF deflector use modelocked ti:sapp lasers (bunch polarization, BPM’s) test surface charge limit Phase 2 BTLLPEG Phase 3 Upgrade At the point which the gun must be evolved: higher voltage to support bunch charge (500 kV?) electrode and beam optics improvements overall improved vacuum quality Laser R&D Q-switched mode-locked ti:sapp laser necessary for circulator ring proposal.

Modeling to support BTLLPEG Studies Simulations to support BTLLPEG lifetime studies: construct Parmela model for test beamline integrate electrode geometry into model develop improved laser profile and photocathode parameters benchmark against measurements Decrease beam loss through improved electrode geometry necessary to take advantage of charge lifetime scaling Ion implantation simulations to help disentangle lifetime vs: residual gas species and abundance ion energy (high voltage) Injector design: gun that can support high bunch charge What will injector look like?

Conclusions and roadmap for an ELIC gun/injector The stated lifetime measurements are needed to validate our strategy toward an ELIC injector design. Simulations are needed initially to support interpretation of the measurements and later to improve upon and extrapolate from our present test gun. Various injection/extraction schemes should be identified which can meet a range of gun and laser schemes ranging from modest to robust. These various layers of activity should have the strategy of converging upon a well refined parameter space to meet an ELIC gun/injector. A goal is to provide some level of technical guidance within 6 months, however, the needed developments for such a gun is likely 1-2 years.