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

Experimental Goals Transverse Emittance Longitudinal Emittance Laser en < 1.2 mm-mrad (projected) Q = 0.2-1 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

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

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

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

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

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

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

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

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

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

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

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

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

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