1. Injector Experimental Results John Schmerge, SSRL/SLAC April 24, 2002
Goals
Gun Test Facility Layout
Transverse Emittance
Longitudinal Emittance
Future Improvements/Conclusions
LCLS DOE Review, April 24, 2002
John Schmerge, SLAC

2. Experimental Goals Transverse Emittance Longitudinal Emittance Laser
en < 1.2 mm-mrad (projected)
Q = nC
Longitudinal Emittance
Dt < 10 ps
sg /g < 0.1%
Laser
sjitter < 1 ps
Temporal shape – flat-top
Elaser > 100 mJ (UV)
LCLS DOE Review, April 24, 2002
John Schmerge, SLAC

3. GTF Linac and Diagnostics
Analyzing
Magnet
Solenoid
Phosphor Screen
Faraday
Phosphor
YAG Screen
& OTR Screen
Cup
Screens &
Quadrupole
PCRF
Faraday
Phosphor
Screen &
Energy
Filter
Doublet
Gun
Cups
Toroids
3m S-Band
SLAC Linac
LCLS DOE Review, April 24, 2002
John Schmerge, SLAC

4. GTF Beamline
LCLS DOE Review, April 24, 2002
John Schmerge, SLAC

5. Major Differences between GTF and LCLS Injector
Laser
Nd:glass instead of Ti:saphire
20% energy fluctuations
Gun
Single RF power monitor
10 Hz operation
Beamline
90 cm gun to linac drift distance instead of 140 cm
Single linac section instead of two
No solenoid around the first linac section
LCLS DOE Review, April 24, 2002
John Schmerge, SLAC

6. Published Thermal Emittance for Cu
LCLS DOE Review, April 24, 2002
John Schmerge, SLAC

7. Emittance Measurement Technique at GTF
Quadrupole Scan Technique
Measure beam size vs quadrupole
current or strength.
counts
Background subtracted image
pixels
rms spot size calculation using projection cut off at 5% of maximum
LCLS DOE Review, April 24, 2002
John Schmerge, SLAC

8. Emittance vs Charge Parameters Egun = 110MV/m gun = 40 Rcat = 1mm
Bsol » 2.0kG
Elinac = 8.3 MV/m
LCLS DOE Review, April 24, 2002
John Schmerge, SLAC

9. Other Laboratories Published Results
LCLS DOE Review, April 24, 2002
John Schmerge, SLAC

10. QE vs Position QE = 3.6 ± 0.4 10-5 100 MV/m 40° injection
LCLS DOE Review, April 24, 2002
John Schmerge, SLAC

11. Improvements Data Acquisition and Analysis Beamline Pulse Shaping
Include space charge (20-25% reduction in reported e)
Use OTR screen instead of YAG screen for improved resolution
Beamline
Optimize gun field ratio and phase (minimum e near 30 degrees)
Optimize gun to linac matching
Eliminate 15 m focal length quadrupole in solenoid
Pulse Shaping
Improved transverse profile to reduce slice e
Laser temporal pulse shaping to reduce projected e
LCLS DOE Review, April 24, 2002
John Schmerge, SLAC

12. Longitudinal Emittance Measurement
Technique analagous to quadrupole scan of transverse emittance
Spectrometer
Booster
(vary fbooster)
Gun
Determine Longitudinal
f-Space at Linac Entrance
Energy Screen
Longitudinal : Measure Energy Spectra vs booster phase
Transverse: Measure Beam Size vs quad strength
LCLS DOE Review, April 24, 2002
John Schmerge, SLAC

13. Measurements Correlated Energy Spread DETotal = -ERF cos(fRF) Df =
Minimum
Energy
Spread
Maximum
Energy
Correlated Energy Spread
DETotal = -ERF cos(fRF) Df =
400 keV or 8 % FWHM
PARMELA predicts 2%
correlated energy spread
LCLS DOE Review, April 24, 2002
John Schmerge, SLAC

14. Path to Low Emittance Measurements at the GTF
Technology Challenge
Task
Advantage/Disadvantage
Spatially Uniform e-beam
Uniform cathode
Spatially flat laser
Demonstrated at GTF Reduces laser energy
Optimizing Gun Performance
Field/phase adjustments
Slice e measurements
Reduced slice e
Temporally Flat e-beam
Laser Pulse Shaping
E-beam measurement
Reduced projected e
Matching LCLS parameters at GTF
Klystron upgrade
Beamline modifications
Reduced e
LCLS DOE Review, April 24, 2002
John Schmerge, SLAC

15. Conclusions
1.5 mm projected emittance with 100 A beam measured at GTF with Gaussian temporal pulse shape
Measurements agree with PARMELA simulations
Emittance can be further reduced by:
Improved laser spatial uniformity
Improved solenoid with reduced quadrupole field
Optimize gun field, phase and linac matching
Emittance will be reduced using flat-top temporal laser pulse shape
Including space charge in analysis will reduce the reported emittance
Utilize OTR screens with improved resolution
LCLS DOE Review, April 24, 2002
John Schmerge, SLAC