Transcript RF Gun Update

RF Gun Status
LCLS Facility Advisory Committee Meeting
October 26, 2005
Mechanical design review (08/05)
Commissioning plan
Cathode development
Response to FAC recommendations
27 October 2005
LCLS FAC Meeting
1
Henrik Loos
[email protected]
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.
27 October 2005
LCLS FAC Meeting
2
Henrik Loos
[email protected]
Gun and Solenoid
Courtesy of E. Jongewaard
27 October 2005
LCLS FAC Meeting
3
Henrik Loos
[email protected]
Water Flow Velocity Reduction
Courtesy of E. Jongewaard
27 October 2005
LCLS FAC Meeting
4
Henrik Loos
[email protected]
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.
27 October 2005
LCLS FAC Meeting
5
Henrik Loos
[email protected]
RF Gun Preparation
Part of injector commissioning schedule
27 October 2005
LCLS FAC Meeting
6
Henrik Loos
[email protected]
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?
27 October 2005
LCLS FAC Meeting
7
Henrik Loos
[email protected]
Gun Hot Test Setup
Hardware from GTF
Pump
Gun Valve
YAG/FC
Solenoid power supply
YAG/FC
Thermal management
To Klystron
Cooling without temperature
feedback
Track RF frequency with gun
temperature
Controls
Wave Guide
27 October 2005
LCLS FAC Meeting
Solenoid
LLRF
Parameter logging
Algorithm for automatic
processing
Pump
8
Henrik Loos
[email protected]
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
27 October 2005
LCLS FAC Meeting
9
Henrik Loos
[email protected]
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?
27 October 2005
LCLS FAC Meeting
10
Henrik Loos
[email protected]
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
27 October 2005
LCLS FAC Meeting
11
Henrik Loos
[email protected]
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.
27 October 2005
LCLS FAC Meeting
12
Henrik Loos
[email protected]
H-Beam Cleaning Results & Installation on Gun
0.01
3
1 10
4
1 10
5
1 10
6
1 10
7
QE
1 10
H-ion Gun
LCLS Min QE
2x10-5 at 255 nm
200
initial
0.63mC
2.07mC
3.03mC
10.23mC
Experimental
results from
SLAC Physical
Electronics Lab
27 October 2005
LCLS FAC Meeting
260
240
220
Wavelength (nm)
280
300
6
Work Function (eV)
180
Gun Solenoid
5.5
5
0
1"
2"
3"
Scale
4.5
4
0
2
4
6
8
10 12
Integrated H-ion Charge (mC)
13
See D. Dowell et al., FEL2005 Conf.
Henrik Loos
[email protected]
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.
27 October 2005
LCLS FAC Meeting
14
Henrik Loos
[email protected]
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.
27 October 2005
LCLS FAC Meeting
15
Henrik Loos
[email protected]
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.
27 October 2005
LCLS FAC Meeting
16
Henrik Loos
[email protected]
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.
27 October 2005
LCLS FAC Meeting
17
Henrik Loos
[email protected]
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.
27 October 2005
LCLS FAC Meeting
18
Henrik Loos
[email protected]
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.
27 October 2005
LCLS FAC Meeting
19
Henrik Loos
[email protected]
Summary
Gun mechanical design completed.
Fabrication of gun scheduled.
Commissioning plan in progress.
Funding for cathode development underway.
27 October 2005
LCLS FAC Meeting
20
Henrik Loos
[email protected]