D.W. Rule

Comparative analysis of optical-transition-radiation-based electron-beam emittance measurements for the Los Alamos free-electron laser

Abstract A series of measurements have been performed to determine the emittance of the electron beam of the LANL FEL. These measurements were made both before and after installation of a photoelectric injector on the LANL linac. An optical-transition-radiation (OTR) interferometer was used to determine the beam divergence while simultaneously using the beam spot imaged in OTR to determine the spatial profile at a beam waist. We have developed two methods to analyze the OTR interference patterns in order to determine the beam divergence from the observed interference-fringe visibility. The first method relies on a simple analytical model in which a Gaussian beam divergence is convolved with the OTR interference pattern for a single particle. The second method uses a numerical convolution of the phase-space distribution in beam angle and energy with the single-particle OTR interference pattern. The six-dimensional phase space used to simulate the experimental OTR patterns was produced by the particle code PARMELA which was run for the beam parameters appropriate for the two sets of experiments. We present a comparison of these two methods with each other and with the experimental observations. The effects of both the beam divergence and the beam energy spread on the emittance measurement is illustrated.

Initial optical-transition radiation measurements of the electron beam for the Boeing free-electron-laser experiment☆

Abstract The potential for characterization of electron beams at ∼ 100 MeV at the Boeing Free Electron Laser (FEL) facility by optical-transition radiation (OTR) techniques has been demonstrated as an important complement to other diagnostic means. Electron beam properties such as spatial profile and position, current intensity, emittance and energy were studied using OTR. Initial examples including transport through the 5 m wiggler and the resolution of Cherenkov radiation and spontaneous-emission radiation competitive sources are discussed.

Optical-transition radiation measurements for the Los Alamos and boeing free-electron laser experiments

Abstract Optical-transition radiation (OTR) measurements of the electron-beam emittance have been performed at a location just before the wiggler in the Los Alamos free electron laser (FEL) experiment. Beam profiles and beam divergence patterns from a single macropulse were recorded simultaneously using two intensified charge-injection device (CID) television cameras and an optical beam splitter. Both single-foil OTR and two-foil OTR interference experiments were performed. Preliminary results are compared to a reference variable quadrupole, single-screen technique. New aspects of using OTR properties for pointing the e-beam on the FEL oscillator axis, as well as measuring e-beam emittance are addressed.

Developments in on-line, electron-beam emittance measurements using optical-transition radiation techniques

Abstract We have developed image analysis software to facilitate the analysis of optical-transition radiation (OTR) patterns generated by the electron beam from the Los Alamos free-electron laser facility. The software can be used for beam alignment, beam profile and angular divergence measurements, and the programs run on an IBM AT microcomputer. The programs and their use are described and some results shown.

Developments In On-line, Electron-beam Emittance Measurements Using Optical-transition Radiation Techniques

We have developed image analysis software to facilitate the analysis of optical-transition radiation (OTR) patterns generated by the electron beam from the Los Alamos free-electron laser facility. The software can be used for beam alignment, beam profile and angular divergence measurements, and the programs run on an IBM AT microcomplater. The programs and their use are described and some results shown.

Optical transition radiation measurements of the Los Alamos free electron laser driver

The authors have used the optical transition radiation (OTR) generated by the LANL FEL (Los Alamos National Laboratory free-electron laser) electron beam transiting a single mirrored quartz foil, and a two-foil OTR interferometer, to measure the electron beams divergence and spot size. Two gated intensified CID cameras are employed to monitor the OTRs angular and spatial distributions simultaneously. This method allows a determination of the x and y emittances of the beam, when the beam is focused to an x or y waist, at a single position in the beam line. Both time-integrated and time-resolved measurements are possible with such a system. Time-integrated results are compared with those obtained by measuring the beam spot size as a function of magnetic quadrupole focusing strength, which inherently requires multiple beam pulses.<<ETX>>

Emittance measurements of FEL accelerators using optical transition radiation methods

Measurements of the emittance of the Boeing free electron laser accelerator operating at 107 MeV, were performed using optical transition radiation (OTR). The results of the three measurement methods, measurement of beam spot size as a function of magnetic quadrupole focusing strength, two screen beam spot measurements, and beam spot-divergence measurements using an OTR interferometer, are compared and shown to be in excellent agreement.<<ETX>>

Initial Nonintercepting Measurements of Subpicosecond Bunches Using Coherent Diffraction Radiation

We report initial measurements of the subpicosecond (sub-ps) bunch structure in a 40 MeV linac beam using the autocorrelation of far infrared (FIR) coherent diffraction radiation (CDR). Since the radiation was generated as the charged particles passed through a slit or aperture in a metal screen oriented at 45 degrees to the beam direction, this is a nonintercepting technique. A compact Michelson interferometer was used to obtain the autocorrelation of the backward CDR with a Golay cell used as the FIR-mm wave detector. The longitudinal shape was calculated from the autocorrelation using the minimal phase approximation. A model was developed and used to calculate the CDR spectral emissions. The experimental results, analysis, and model are presented. Complementary measurements were also made with coherent transition radiation (CTR).

Initial electron-beam characterizations for the Los Alamos APEX facility☆

The ongoing upgrade of the Los Alamos Free-Electron Laser (FEL) Facility involves the addition of a photoelectric injector (PEI) and acceleration capability to about 40 MeV. The electron-beam and high-speed diagnostics provide key measurements of charge, beam position and profile, divergence emittance, energy (centroid, spread, slew, and extraction efficiency), micropulse duration, and phase stability. Preliminary results on the facility include optical transition radiation interferometer measurements of divergence (1 to 2 mrad), FEL extraction efficiency (0.6 {plus_minus} 0.2%), and drive laser phase stability (< 2 ps [rms]). 10 refs.

Comparative Analysis Of Optical-transition-radiation-based Electron-beam Emittance Measurements For The Los Alamos Free-electron Laser

A series of measurements have been performed to determine the emittance of the electron beam of the LANL FEL. These measurements were made both before and after installation of a photoelectric injector on the LANL lmac. An optical-transition-radiation (OTR) interferometer was used to determine the beam divergence while simultaneously using the beam spot imaged in OTR to determine the spatial profile at a beam waist. We have developed two methods to analyze the OTR interference patterns in order to determine the beam divergence from the observed interference-fringe visibility. The first method relies on a simple analytical model in which a Gaussian beam divergence is convolved with the OTR interference pattern for a single particle. The second method uses a numerical convolution of the phase-space distribution in beam angle and energy with the single-particle OTR interference pattern. The six-dimensional phase space used to simulate the experimental OTR patterns was produced by the particle code PARMELA which was run for the beam parameters appropriate for the two sets of experiments. We present a comparison of these two methods with each other and with the experimental observations. The effects of both the beam divergence and the beam energy spread on the emittance measurement is illustrated.