Drive Laser & RF Gun Status LCLS Week October 25, 2005

1. Drive Laser & RF Gun StatusLCLS WeekOctober 25, 2005 Drive Laser* Project status Normal incidence for gun Launch system design RF Gun Mechanical design review (08/05) Commissioning plan Cathode development *Courtesy of S. Gilevich

2. Drive Laser Project Status • Contract for Drive Laser was awarded to Thales Lasers. • Design review was held October 18 – 20. • Construction of the S20 drive laser facility is underway. • Old building has been demolished. • Requirements for electrical and water systems were defined based on Thales laser system requirements. • Design of the electrical system is near completion. • Beneficial occupancy is planned for the end of February 2006. • The laser beam transport tubes were installed. • Laser safety system design is underway. Review in 11/05. • Design of the optical tables completed. Procurement process started. • Optical Design of Launch System for normal incidence completed.

3. Project Status Cont’d • Design of the active beam steering stabilization system started. • Test is planned in Building 407 and parts are ordered. • Draft of drive laser commissioning schedule put together. • R&D effort of collaborators continues. • LLNL completed modeling of the UV temporal pulse shaping. A spatially flat-top IR beam needed to obtain efficient, temporally uniform UV pulses. • Temporal diagnostics designs are finished. For UV and blue measurements TG FROG is proposed. Orders are placed. • ANL performed spatial shaping of broadband IR pulses using the Newport aspheric beam shaper. Optimum shaping conditions were defined. It was shown that quality of shaping strongly depends on bandwidth. • Work on a collaboration with INFN and Elettra started.

4. gun solenoid cathode laser injection cross vacuum valve Normal Incidence Design • Grazing incidence optics add risk to laser shaping. • Wakes from dual in-vacuum mirrors tolerable. Drawing compliments of R.F. Boyce & T. Osier

5. Transport and Launch System • Objectives • Flat-top beam on cathode. • Beam radius on cathode from 0.6 to 1.5 mm by variable magnification. • Features • Aspheric beam shaper in IR for UV generation. • Shaping and zoom system in upstairs laser bay. • Shaped UV is imaged with variable magnification into relay system to photocathode.

6. Layout Vacuum cell Zoom Beam shaper UV converter Virtual Cathode Transport tube Table in the tunnel Steering system Photocathode Active Steering Stabilization

7. Beam Profile on the CathodeZEMAX Modeling

8. Laser Summary • First LCLS injector item – Laser transport tubes were installed. • Design of the gun has been changed to normal incidence. It significantly simplifies the optical set-up and makes the beam shaping less problematic. • Manufacturing of the Drive Laser and R&D work according to the schedule.

9. 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.

10. Gun and Solenoid Courtesy of E. Jongewaard

11. Water Flow Velocity Reduction Courtesy of E. Jongewaard

12. 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 1st cathode. • Cathode preparation - 06/06 • Characterize 2nd 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 2nd cathode and retune. • Hot test - 08/06 • Details follow. • Installation & commissioning at S20 - 11/06 • See next presentation.

13. Gun Hot Test • Objectives • Vacuum bake to 10-10 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?

14. 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 Pump Gun Valve YAG/FC To Klystron Wave Guide Solenoid Pump

15. 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

16. 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?

17. 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

18. 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.

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

20. 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. • BCR requested (Part 1) or in preparation (Part 2).

21. SLAC PE Lab. 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.

22. 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.

23. 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.

24. Summary • Gun mechanical design completed. • Fabrication of gun scheduled. • Commissioning plan in progress. • Funding for cathode development underway.