RF Gun Status LCLS Facility Advisory Committee Meeting October 26, 2005

1
RF Gun StatusLCLS Facility Advisory Committee
MeetingOctober 26, 2005

• Mechanical design review (08/05)
• Commissioning plan
• Cathode development
• Response to FAC recommendations

2
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.

3
Gun and Solenoid
Courtesy of E. Jongewaard
4
Water Flow Velocity Reduction
Courtesy of E. Jongewaard
5
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 - 12/06
• See next presentation.

6
RF Gun Preparation

• Part of injector commissioning schedule

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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?

8
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

Gun
Valve
YAG/FC
Pump
To Klystron
Wave Guide
Solenoid
Pump
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Measurements for Gun Conditioning

• Gun temperatures (RTDs)
• 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

10
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?

11
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
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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.

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H-Beam Cleaning Results Installation on Gun
Experimental results from SLAC Physical
Electronics Lab
See D. Dowell et al., FEL2005 Conf.
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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.

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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.

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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.

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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.

18
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.

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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.

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Summary

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