Experience with photoinjector at ATF Vitaly Yakimenko October 11, 2006 LCLS ICW2006

Laser uniformity

Standardized BPM (zoom lens with doubler and 20 cm achromat) Old style Min zoom Max zoom Work distance [mm] 155 160 Field of view [mm] 18x13 59x37 11x7 Relative intensity [a.u.] 279 60 62 Resolution [ln/mm] center 20 6 29 edge 14 4 Pixel Calibration [mm/pix] 24x29 77x91 14x17 Image

Laser alignment on the cathode Emittance degrades from 1mm to 1.5mm for 200mm shift from the “centered” position Laser profile on the cathode after 10 holes mask: e-beam after the gun: RF phase optimized to enhance distortions Laser “centered” on the cathode Laser moved ~200mm

Four step to improve emittance (FEL 2001, Darmstadt) Stability of the driving laser and RF Optimization of the drive laser (Mg plug cathode with Qe~0.25% is used to reduce laser load) Accelerating gradient in the RF GUN and operating phase Beam based alignment of the focusing quads to transport beam thought the linac center. CCD Images of the 0.5 nC /60 MeV beam after linac

BPM resolution limit Beam images taken consequently with the six different diagnostics under stable experimental conditions (the charge Q ~ 500 pC). µm Electron beam horizontal spot size as a function of charge, measured with the scintillating diagnostics and the OTR.

Fitting the beam size using multiple BPMs to resolve emittance BPMs were used to measure beam sizes >200 mm and quads for smaller sizes Focusing properties of the transport line were extensively studied for the tomographic phase space rotation.

New Capabilities: Digital Mirror Array Study underway to allow generation of flattop beams with <5% P-P variation Shaping of an Optical Beam Intensity Profile -2nd order output 2nd order output Input Signal Mirror tilt axis