H. Suk

Bunch length measurement of picosecond electron beams from a photoinjector using coherent transition radiation

Abstract The bunch length of an electron beam derived from the UCLA Saturnus photoinjector has been measured using a 45° CTR foil. The sudden change of electrons boundary conditions cause them to radiate (transition radiation) with the spectral power entirely dependent upon the degree of coherency, which strongly relates to the beam size. A polarizing Michelson interferometer allowed measurement of the auto-correlation of the coherent transition radiation signal. An analysis method was developed to compensate for undetected low-frequency radiation and systematically extract the bunch length information for a specific beam model. This analysis allowed observation of pulse lengthening due to the space charge, as well as compression with the variation of the RF injection phase. The hypothesis of a satellite beam has been also tested using this analysis.

The Neptune photoinjector

Abstract The RF photoinjector in the Neptune advanced accelerator laboratory, along with associated beam diagnostics, transport and phase-space manipulation techniques are described. This versatile injector has been designed to produce short-pulse electron beams for a variety of uses: ultra-short bunches for injection into a next-generation plasma beatwave acceleration experiment, 2 space-charge dominated beam physics studies, plasma wake-field acceleration driver, plasma lensing, and free-electron laser microbunching techniques. The component parts of the photoinjector, the RF gun, photocathode drive laser systems, booster linac, RF system, chicane compressor, beam diagnostic systems, and control system, are discussed. The present status of photoinjector commissioning at Neptune is reviewed, and proposed experiments are detailed.

Plasma source test and simulation results for the underdense plasma lens experiment at the UCLA Neptune Laboratory

The planned plasma lens experiment at the UCLA Neptune Laboratory is described. In the experiment, electron beams with an energy of 16 MeV, a charge of 4 nC, and a pulse duration of 30 ps [full-width at half-maximum (FWHM)] are designed to be produced from the 1.625-cell photoinjector radio-frequency gun (f=2.856 GHz) and PWT linac in the Neptune. The generated beams are passed through a thin plasma with a density of low 10/sup 12/ cm/sup -3/ range and a thickness of a few centimeters. For this experiment, a LaB/sub 6/-based discharge plasma source was developed and tested. In this paper, the overview of the planned plasma lens experiment and the test results of the plasma source for various conditions are presented. In addition, computer simulations with a 2-1/2 dimensional particle-in-cell code (MAGIC) were performed and the simulation results are shown.

Underdense plasma lens experiment at the UCLA Neptune Laboratory

An underdense plasma-lens experiment is planned at the UCLA Neptune Laboratory. For this experiment, a LaB/sub 6/-based discharge plasma source was developed and tested. Test results of the plasma source show that it can provide satisfactory Ar plasma parameters for underdense plasma lens experiments, i.e., a density in the low 10/sup 12/ cm/sup -3/ range and a thickness of a few cm. In the plasma chamber a YAG slab and a Cherenkov radiator are placed for electron beam diagnostics so that both time-integrated and time-resolved information will be obtained and compared with the MAGIC code (2 and 1/2 dimensional particle-in-cell) simulations. In this paper, the planned experiment including test results of the plasma source, diagnostics and MAGIC simulation results is presented.

Commissioning and measurements of the Neptune photo-injector

The photo-injector for the Neptune Advanced Accelerator Laboratory is introduced. Its component parts, including the radio frequency gun, photo-cathode drive laser system, booster linac, RF system, chicane compressor, beam diagnostics, and control system are described. The injector is designed to produce high brightness, short pulse electron beams. Measurements of the photo-injector beams including quantum efficiency, emittance, pulse length, and pulse compression are presented.

Commissioning of the Neptune photoinjector

The status of the RF photoinjector in the Neptune advanced accelerator laboratory is discussed. The components of the photoinjector: the RF gun and booster linac, chicane compressor, and beam diagnostic systems are described. Measurement techniques used to diagnose the short pulse length, high brightness beam are detailed and measurements of emittance and pulse compression are given. The effect of the pulse compressor on transverse emittance is explored.

Test results of the plasma source for underdense plasma lens experiments at the UCLA Neptune Lab

A plasma source was developed at UCLA for planned underdense plasma lens experiments, where the plasma density is less than the electron beam density. The argon plasma, produced by a discharge between a LaB6 cathode at 1330 °C and a tantalum anode, is confined by a solenoidal magnetic field and flows transversely across the electron beam path. Extensive test of the plasma source is under way for various conditions before it is assembled with the UCLA photocathode-based electron linac. In particular, different longitudinal (with respect to the electron beam) plasma profiles and effective plasma lengths can be obtained by adjusting the moveable sliding door between the plasma source and the transverse beamline. Test results of the plasma source are presented.

Longitudinal energy-spread evolution due to radiation cooling in a compact electron recirculator

Abstract The analytical solution for electron energy in a compact radiation-cooling recirculator is obtained. Based on the analytical solution, the evolution of a longitudinal energy distribution function is calculated. From the obtained energy distribution function, a longitudinal energy spread is obtained. An example for a Gaussian energy distribution is shown in the race-track-type cooling recirculator with a bending radius of 33.4 cm at both ends. In this example, where the initial mean beam energy and the current are 100 MeV and 100 A, respectively, it is shown that the initial relative energy spread of 2.5% is reduced to less than 1.0% after 2 million turns in the cooling recirculator.