Abstract
Recent work has shown the possibility of generating self-shaped ellipsoidal beams with properties commensurate with the requirements of future light sources such as free-electron lasers and inverse Compton sources. In this so-termed ``blowout'' regime, short laser bunches are transformed via photoemission into short electron bunches which then self-consistently evolve into nearly uniform-density ellipsoids under space-charge forces. We report here on the first blowout studies conducted in collaboration between the UCLA Particle Beam Physics Lab and the Photo Injector Test Facility, Zeuthen (PITZ). The measurements conducted at the PITZ photoinjector facility examine the evolution of 750 pC, 2.7 ps FWHM electron bunches born in an L-band photoinjector and subsequently accelerated through a nine-cell L-band booster for a resulting energy of 12 MeV. These measurements represent the first observations of self-shaped ellipsoid evolution under postinjector acceleration, a key step in demonstrating the utility of such self-shaped beams at higher energy, where the advantages in both transverse and longitudinal and transverse phase space may be exploited in creating very high brightness beams.
Highlights
The prevailing method for producing high brightness beams has been until recently a combination of the emittance compensation process [1,2] with a nearly uniformly filled cylindrical electron beam
This trait is most suitable for the emittance compensation process, in which the transverse phase space distributions of different longitudinal slices of the beam may be approximated as thin lines of differing orientation in phase space; compensation refers to the realignment of these lines
It has been shown that the shape due to space-charge expansion is maintained even through postphotoinjector acceleration. We note that this is a first test of the blowout regime in the context of lower-field L-band photoinjectors, which will undoubtedly play a major role in future high average power free-electron lasers
Summary
The prevailing method for producing high brightness beams has been until recently a combination of the emittance compensation process [1,2] with a nearly uniformly filled cylindrical electron beam. The uniformly filled cylindrical electron beam is used in an attempt to create a beam whose space-charge forces are linear in distance from the axis This trait is most suitable for the emittance compensation process, in which the transverse phase space distributions of different longitudinal slices of the beam may be approximated as thin lines of differing orientation in phase space; compensation refers to the realignment of these lines. A novel approach to the creation of uniformly filled ellipsoidal beams was introduced by Serafini, where an initially short laser pulse was used to illuminate a cathode and the subsequently emitted electron beam was allowed to expand longitudinally under space-charge forces [6]. We begin with a description of the experiment and the simulations leading to its design and follow with a presentation of data collected and a discussion of results and future work
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