Henrik Loos LCLS FAC Meeting 27 October RF Gun Status LCLS Facility Advisory Committee Meeting October 26, 2005 Mechanical design review (08/05) Commissioning plan Cathode development Response to FAC recommendations

Henrik Loos LCLS FAC Meeting 27 October RF Gun Mechanical Design Review Presentation of mechanical design with RF and thermal simulations. Mechanical design commended by review committee. Concerns Heating at cathode/gun RF joint and coupler irises. Damage from high flow in cooling channels. Recommendations Improve cooling design. RF reflection in waveguide pumping slots acceptable. Make two guns with tree sets of parts. Start load lock development program. Response Water flow rate lowered. Radii on ports increased to limit pulse heating. Cathode plate thickened.

Henrik Loos LCLS FAC Meeting 27 October Gun and Solenoid Courtesy of E. Jongewaard

Henrik Loos LCLS FAC Meeting 27 October Water Flow Velocity Reduction Courtesy of E. Jongewaard

Henrik Loos LCLS FAC Meeting 27 October Gun Commissioning Schedule Fabrication - 01/06 Scheduled in SLAC Klystron department. Cold test - 04/06 Characterize gun. Bead pull/drop measurement (use dummy cathode?). Cathode plate tuning with 1 st cathode. Cathode preparation - 06/06 Characterize 2 nd cathode. QE measurement, H + ion cleaning. Measure surface roughness & contaminants. Gun & Solenoid integration - 06/06 Assemble on common girder. Magnetic measurement with dummy cathode. Install cleaned 2 nd cathode and retune. Hot test - 08/06 Details follow. Installation & commissioning at S /06 See next presentation.

Henrik Loos LCLS FAC Meeting 27 October RF Gun Preparation Part of injector commissioning schedule

Henrik Loos LCLS FAC Meeting 27 October Gun Hot Test Objectives Vacuum bake to Torr. Stable 120 MV/m operation. Demonstrate 130 MV/m. Demonstrate 120 Hz operation (3.5 kW thermal load). Measure thermal distribution with low & high RF power. Measure Cell field balance at high RF power. Procedure Install assembly in Klystron department and bake. RF processing. Full characterization. Test temperature control?

Henrik Loos LCLS FAC Meeting 27 October Gun Hot Test Setup Hardware from GTF YAG/FC Solenoid power supply Thermal management Cooling without temperature feedback Track RF frequency with gun temperature Controls LLRF Parameter logging Algorithm for automatic processing To Klystron Wave GuideSolenoid GunValveYAG/FC Pump

Henrik Loos LCLS FAC Meeting 27 October Measurements for Gun Conditioning Gun temperatures (RTD’s) W/G and FC vacuum pressure Klystron drive power Gun forward/reflected power Half and full cell probes Dark current in FC Image of dark current (YAG) RF breakdowns

Henrik Loos LCLS FAC Meeting 27 October Open Issues Hot test schedule and location PEP test bunker in Klystron Department Available 08/06 Sector 20 Before, during, or after 2006 downtime (08/06-11/06) More details in next presentation Cooling water for gun Stand alone 4 kW chiller? Use facility water?

Henrik Loos LCLS FAC Meeting 27 October Cathode Development* Presently no process to improve and control QE of LCLS cathodes. No load lock in LCLS budget. Need for improved cathode installation procedure. Operational contamination requires in-situ cleaning. Avoid risky gun baking and laser cleaning *Courtesy of D. Dowell

Henrik Loos LCLS FAC Meeting 27 October In-Situ Cleaning Methods H-beam cleaning Use ~1keV H-beam. Cleans 1cm diameter area. Requires no reconfiguration of gun system. Benign to cathode surface. H-plasma cleaning Produce plasma inside gun volume. Plasma excitation with RF Only cleans region of high E-field. Plasma excitation with DC Only cleans region near electrodes.

Henrik Loos LCLS FAC Meeting 27 October H-Beam Cleaning Results & Installation on Gun Gun Solenoid H-ion Gun Valve LCLS Min QE 2x10 -5 at 255 nm See D. Dowell et al., FEL2005 Conf. Experimental results from SLAC Physical Electronics Lab

Henrik Loos LCLS FAC Meeting 27 October Proposed Three Step Plan Compare cathode surface processing with H + -beam vs. H + -plasma. Find best procedure to clean, transfer, and install cathodes for LCLS gun 1. Develop in-situ cleaner for LCLS gun 2. Thermal emittance measurement not part of this plan.

Henrik Loos LCLS FAC Meeting 27 October Laboratory Test (Part 1) Goals Comparison of H-beam and H-plasma cleaning. Find optimum materials and fabrication techniques. Simulation of cathode transfer and installation effects. Compare with theory. Plan Testing of small samples in SLAC PE lab. Uses existing surface diagnostics equipment. Construct H-plasma cleaner. Result Capability for H-beam and H-plasma cleaning & measured data.

Henrik Loos LCLS FAC Meeting 27 October Cathode Cleaning and GTF Test (Part 2) Goals Test robustness of cleaned cathodes for installation procedure and improve procedure for LCLS. Quantify effect of gun bake on QE. Plan Characterization and H-beam cleaning of GTF cathodes in SLAC PE lab. Transfer and test cathodes in GTF gun. Compare lab QE measurement with operational QE. Result Improved procedure for installing well characterized, clean LCLS cathodes.

Henrik Loos LCLS FAC Meeting 27 October In Situ Cleaning for LCLS Gun 2 (Part 3) Goals Design and build cleaner system for LCLS Gun 2. Find operating parameters for H + source. Plasma cleaning with RF, compare with bake. Plan Install and test system on existing chamber in PE lab. Move system to LCLS Gun 2 and test. Test with RF? Result Complete gun assembly with cleaner ready for installation at Sector 20.

Henrik Loos LCLS FAC Meeting 27 October Funding Status BCR requested for part 1. BCR in preparation for part 2. Request for part 3 when results from parts 1 and 2 available.

Henrik Loos LCLS FAC Meeting 27 October Response to FAC Recommendations Completion of second gun encouraged. Fabrication of second gun scheduled with first gun. Will be available as complete system with solenoid as fast backup at sector 20. Investigate gun wake field effects. Large energy spread in GTF gun contributed to pi-0 mode beating. Should not occur in LCLS gun with 15 MHz mode separation. PIC simulations planned for next year. Continue effort on H + ion cleaning of cathode. Budget modified to pursue cleaning and test on second gun. Develop permanent facility for gun testing. No decision made yet, but funding for GTF continued through FY2006.

Henrik Loos LCLS FAC Meeting 27 October Summary Gun mechanical design completed. Fabrication of gun scheduled. Commissioning plan in progress. Funding for cathode development underway.