6D Phase Space Measurements at the SLAC Gun Test Facility

Abstract

Proposed fourth generation light sources using SASE FELs to generate short pulse, coherent X-rays require demonstration of high brightness electron sources. The Gun Test Facility (GTF) at SLAC was built to test high brightness sources for the proposed Linac Coherent Light Source at SLAC. The GTF is composed of an Sband photocathode rf gun with a Cu cathode, emittance compensating solenoid, single 3 m SLAC linac section and e-beam diagnostic section with a UV drive laser system. The longitudinal emittance exiting the gun has been determined by measuring the energy spectrum downstream of the linac as a function of the linac phase. The e-beam pulse width, correlated and uncorrelated energy spread at the linac entrance have been fit to the measured energy spectra using a least square error fitting routine. The fit yields a pulse width of 2.9 ps FWHM for a 4.3 ps FWHM laser pulse width and 2% rms correlated energy spread with 0.07% rms uncorrelated energy spread. The correlated energy spread is enhanced in the linac to allow slice emittance measurements by conducting a quadrupole scan in a dispersive section. The normalized slice emittance has been measured to be as low as 2 mm-mrad for beams with peak currents up to 150 A (300 pC with a laser pulse length of 1.8 ps) while the full projected emittance is 3 mm-mrad.

Development of PUNDA (Parametric Universal Nonlinear Dynamics Approximator) Models for Self-Validating Knowledge-Guided Modelling of Nonlinear Processes in Particle Accelerators \& Industry

“…The purpose of the analysis is to identify the longitudinal/transverse beam matrix at the exit of the linac. It is noted that these are not the same as those at the gun exit, because of continued evolution of the bunch as it drifts from the gun to the linac [13,16].…”

“…rate of accumulation = in by flow − out by flow − substrate consumption (46) where substrate consumption can be modeled as substrate concentration, x 2 , multiplied by a consumption rate for the substrate 16 , µ s .…”

“…16 The consumption rate is sometimes modeled as the ratio of the production rate to the yield of the bioreaction [28]. For this study however we adopted a more direct approach identifying the consumption rate directly from measured fermentation data.…”

Parametric modeling of transverse phase space of an rf photoinjector

“…The measurement technique, known as quadrupole scan [2], measures the transverse size of the beam as a function of quadrupole strength. The purpose of the analysis is to identify the transverse beam matrix at the quadrupole doublet [1,5]. …”

Optimum electron distributions for space charge dominated beams in photoinjectors

“…For copper cathode, the "thermal emittance" per unit spot radius is 0.3 mm.mrad per mm. Several electron beam based measurements have shown that the "cathode emittance" for copper cathode is closer to 0.6 mm.mrad per mm radius [10][11][12][13]. The electron beam measurements show that the value for the Cs 2 Te "cathode emittance" is 0.6mm.mrad per mm [14] which is also larger than the "thermal emittance" estimated to be 0.43 mm.mrad per mm [15].…”