LCLS Gun Commissioning Status

1
LCLS Gun Commissioning Status PlansDavid H.
DowellLCLS Injector Commissioning Workshop
October 9, 2006

• Status of gun fabrication and testing
• Gun test results
• Characterization of magnetic components
• Systems to be commissioned
• The 3-Pass Commissioning Plan
• Summary

2
Gun Fabrication and Testing Process

• Fabricate parts
• Cold test sub assemblies and clamped parts
• Machine and measure for resonance and field
  balance
• Braze and weld final assembly
• Low power RF and cathode tests
• Furnace bake at 500deg C
• Assemble and configure for high power RF test
  (hot test)
• Vacuum bake of assembly in Klystron test vault
• Perform hot test
• Vacuum qualification of gun
• Alignment of assembly with CMM
• Install at S20

3
RF Gun Fabrication and Cold RF Testing Finished
Preparing for High-Power Tests
Gun only pictures
CAD cut away view of gun interior
4
RF Field Balance Measured Using Bead Drop
Technique
Data compliments J. Wang, ATR Dept., SLAC
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Gun Design and Measured Specifications
RF Parameters Design Measured
fp (GHz) 2.855987 2.855999
Q0 13960 14062
ß 2.1 2.03
Mode Sep. ?f (MHz) 15 15.17
Field Balance 1 1
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LCLS RF Gun Beam Side
dual rf power feeds
focusing solenoid
beam port Attach 2-km linac here
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LCLS RF Gun Cathode Side
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Description of gun magnet system

• Gun solenoid SOL1
• Bucking coil SOL1BK
• X,Y dipole correctors
• XC00YC00 (inside SOL1)
• Normal skewed quad correctors CQ01SQ01
  (inside SOL1)
• Field maps and calibrations measured

9
Gun Solenoid and Dipole Corrector Magnetic
Measurements
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Bucking Coil Magnetic Measurements
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What were commissioning
e- to L0A

• Q 1 nC
• f 120 Hz
• G 120 MV/m
• gex,y 1 mm
• Dt 10 ps
• I 100 A
• E 6 MeV

spec. dipole
UV laser
e-
solenoid
YAG screens
RF gun
cathode
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The Gun Gun-to-Linac Region with the Drive
Laser Launch Optics
Laser tube from laser room
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CAD Model of the Drive Laser Launch Optics (top
view)
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Schematic of Drive Laser Launch Optics
Laser beam from drive laser
Virtual in-vacuum mirror camera
lens
Virtual cathode camera
M2
M1
Polarizer
Virtual image of in-vacuum mirror
mirrors used to steer laser on cathode
Wave plate
BS2
BS beam splitter
BS1
Joule meter
shutter (BCS), rate control
To the Gun window and in-vacuum mirror
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Gun and Gun-to-Linac Components
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Injector Commissioning Philosophy

• Commissioning plan is organized into three passes
  through the injector
• Tasks 2.3.3 1st pass
• Pre-beam and beam-based hardware software
  checkout
• Tasks 2.3.4 2nd pass
• First-order optics
• Tasks 2.3.5 3rd pass
• Full beam characterization and optimization
• In each pass the beam is transported from the gun
  through DL1 and BC1 stopping at the beam dump,
  TD-11.

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The Injector Commissioning Schedule and the
3-Pass Plan
Approximation of real schedule!
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Pass 1 Pre-Beam Commissioning
RF Processing and Water RF Controls

• Characterize and test gun water system controls
• Water system only, no RF
• Control loop bandwidth
• Temp stability
• RF processing with resonance control (water
  LLRF)
• Test of LLRF phase/amplitude controls (4-gun
  probes) (0.1deg s-band, 0.1)
• Measure recovery time after trip
• Interaction between LLRF water controls

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Pass 1 Commissioning
Setting RF Centering Laser in SOL1. Then
continue transport thru L0a, L0b ending at BXS to
set the injector beam energy

• Use fast diode at gun to time laser in rf
  envelope
• Set launch phase within rf period
• SOL1 at nominal field, scan laser phase until
  beam observed on YAG01
• Meas. base width of charge vs. laser phase (is it
  correct?, i.e. 110deg)
• Locate zero crossing set laser phase to 30deg
• Center laser beam on SOL1
• Vary SOL1 current move laser on cathode until
  there is no motion on YAG01
• Observe beam on YAG02, vary SOL1 current move
  laser until there is no motion
• Record settings on virtual cathode, virtual
  mirror, etc.

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Pass 2 Commissioning
Overview of Second Pass Gun/GTL Commissioning
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Pass 2 Commissioning
Second Pass Commissioning Details of Gun/GTL
Optimization, 1st of 3 parts

• Calibration of charge and energy diagnostics
• Alignment procedure for energy measurements
• Measurements of gun beam energy

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Pass 2 Commissioning
Second Pass Commissioning Details of Gun/GTL
Optimization, 2nd of 5 parts

• Schottky scan to determine QE and presence of
  satellite laser pulses
• Charge vs. laser energy to measure QE and
  linearity (no space charge limit of emission)
• QE uniformity measurement by rastering laser beam

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Pass 2 Commissioning
Second Pass Commissioning Details of Gun/GTL
Optimization, 3rd of 5 parts

• Determination of emission uniformity by imaging
  cathode onto YAG01 and YAG02
• Thermal emittance by solenoid scan at different
  gun fields
• Divergence of beam at cathode by
  parallel-to-point imaging at YAG02
• Confirm parallel-to-point optics by varying laser
  radius
• Repeat at different gun fields

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Pass 2 Commissioning
Second Pass Commissioning Details of Gun/GTL
Optimization, 4th of 5 parts

• Beam alignment and calibration checks of BXG and
  quads
• Gun beam energy and energy spread vs. laser phase
• Low charge, short bunch
• Low charge, 10ps bunch
• High charge, 10ps bunch

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Pass 2 Commissioning
Second Pass Commissioning Details of Gun/GTL
Optimization, 5th of 5 parts

• Beam-based feedback systems tested and enabled
• First emittance and bunch length measurements

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Pass 3 Commissioning
Third Pass Commissioning Details of Gun/GTL
Optimization

• Integrated operation with entire injector
• Projected and slice emittance optimization (Gun
  solenoid laser shape)
• Longitudinal phase space measurements

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Summary of Gun Commissioning Status Plans

• Gun fabrication and cold testing completed
• Gun meets all design goals
• All magnetic components calibrated and
  characterized
• Gun integrated with solenoid and waveguide
  assembly
• Installed in test vault at Klystron
• First bake of assembly (gun vacuum in high 10-10
  Torr)
• High-power RF (hot) testing has begun
• Final vacuum qualification alignment performed
  after Hot-Testing
• Gun on schedule for Dec06 installation
• Commissioning will be done in three passes
• Pass 1 Pre-beam checkout and beam-based checkout
• First transport beam through entire injector
  BC1 to TD-11
• Pass 2 First-order optics
• Characterize components and beam throughout
  injector
• Pass 3 Full beam Characterization
• Optimize beam quality