G. Ingold

Design of a harmonic generation FEL experiment at BNL

We present design parameters of a harmonic generation FEL experiment to be carried out at the Accelerator Test Facility (ATF) at BNL. This experiment out as a proof-of-principle for the proposed UV-FEL Users Facility at BNL. In the experiment we plan to triple the frequency of a CO{sub 2} seed laser by utilizing two superconducting wigglers and a dispersive section. The first wiggler will be used in conjunction with the CO{sub 2} seed laser to generate a ponderomotive force that will bunch the electron beam. The bunching will then be enhanced by the dispersion section. The second wiggler, tuned to the third harmonic of the seed laser will follow. In the beginning of the second wiggler the bunched beam will produce super-radiant emission (characterized by a quadratic growth of the radiated power), then the radiation will be amplified exponentially. The last part of the wiggler will be tapered. We plan to study the evolution of the various radiation growth mechanisms as well as the coherence of the tripled and exponentially amplified radiation. 12 refs.

Performance of the Brookhaven Photocathode RF Gun

The Brookhaven Accelerator Test Facility (ATF) uses a photocathode rf gun to provide a high-brightness electron beam intended for FEL and laser-acceleration experiments. The rf gun consists of 1{1/2} cells driven at 2856 MHz in {pi}-mode with a maximum cathode field of 100 MV/m. To achieve long lifetimes, the photocathode development concentrates on robust metals such as copper, yttrium and samarium. We illuminate these cathodes with a 10-ps, frequency-quadrupled Nd:YAG laser. We describe the initial operation of the gun, including measurements of transverse and longitudinal emittance, quantum efficiencies, and peak current. The results are compared to models.

The performance of a superconducting micro-undulator prototype

Abstract We report on the performance of a prototype of a superferric micro-undulator. The micro-undulator consists of a continuous winding of niobium-titanium wire wound on a low-carbon-steel yoke. It is about three periods long with a period of 8.8 mm and a gap of 4.4 mm. The undulator achieves a peak magnetic field on axis of over0.5 T. Asymmetry of the field pattern due to a dipole component was identified, analyzed and a correction has been applied to the undulator ends to produce a symmetric field distribution. Within the precision of the measurement the field pattern produced by the superferric undulator needed no correction.

Fabrication of a high-field short-period superconducting undulator

Abstract The visible free electron laser (FEL) experiment at the accelerator test facility (ATF) at Brookhaven National Laboratory is designed to utilize the high brightness beam from a laser-photocathode rf gun injected into a 50 MeV S-band linac in conjunction with a 8.8 mm period undulator. The undulator is designed to provide a 0.5 T field on axis which is reached at a current 15% below the quench current. It consists of 3 contiguous sections. We discuss the field errors by evaluating the trajectory wander and the optical phase error. Whereas undulator sections with low errors can be built as machined without any shimming or trimming, special care has to be taken during the assembly of a full length device.

Performance of a superconducting, high field subcentimeter undulator

A Superconducting 8.80mm wavelength undulator is under construction for the 500nm Free-Electron Laser at the Accelerator Test Facility (ATF) at Brookhaven National Laboratory. We present results on the design, construction and performance of this novel undulator structure. A field on axis of 0.51T has been measured for a 4.40mm gap, with a current 20% below the quench current. Our simple design focuses on minimizing the accumulation of errors by minimizing the numbers of parts and by using a ferromagnetic yoke. The magnetic field error is less than 0.30% rms as manufactured (without shimming). The third harmonic content is less than 0.1% of the fundamental.

Status of the visible Free-Electron Laser at the Brookhaven Accelerator Test Facility

Abstract The 500 nm free-electron laser (FEL) at the accelerator test facility (ATF) of the Brookhaven National Laboratory is reviewed. We present an overview of the ATF, a high-brightness, 50-MeV, electron accelerator and laser complex which is a users facility for accelerator and beam physics. A number of laser acceleration and FEL experiments are under construction at the ATF. The visible FEL experiment is based on a novel superferric 8.8 mm period undulator. The electron beam parameters, the undulator, the optical resonator, optical and electron beam diagnostics are discussed. The operational status of the experiment is presented.

Magnetic field measurements of a superconducting undulator for a harmonic generation FEL experiment at the NSLS

An 18 mm period, 0.54 Tesla, 8 mm gap superconducting undulator with both horizontal and vertical focusing has been-built and tested. This magnet, which is fabricated in 25 cm length sections, is being tested for use in the radiator section (total magnet length of 1.5 m) of the Harmonic Generation Free Electron Laser experiment at the National Synchrotron Light Source-Accelerator Test Facility at Brookhaven National Lab, in collaboration with Grumman Corp. The measurement system is outlined, sources and estimates of errors are described, and some magnetic field data are presented and discussed.<<ETX>>

A superconducting short period undulator for a harmonic generation FEL experiment

A three stage superconducting (SC) undulator for a high gain harmonic generation (HGE) FEL experiment in the infrared is under construction at the NSLS in collaboration with Grumman Corporation. A novel undulator technology suitable for short period (6-40 mm) undulators will be employed for all three stages, the modulator, the dispersive section and the radiator. The undulator triples the frequency of a 10.4 /spl mu/m CO/sub 2/ seed laser. So far a 27 period (one third of the final radiator) prototype radiator has been designed, built and tested.<<ETX>>

Analysis of the superconducting wiggler magnets for the ATF Harmonic Generation FEL experiment

In this paper, we consider the superconducting wiggler magnet under construction for the High Gain Harmonic Generation experiment (HGHG) at the Accelerator Test Facility (ATF) at BNL. This wiggler consists of an energy modulation section, a dispersion magnet and a radiator section. We present an analysis of the dispersion magnet and the end effects in the other wiggler sections. The purpose of the dispersion magnet is to convert energy modulation of the electron beam into spatial bunching. For the dispersion magnet, we discuss the physical requirements, analyze the magnetic design, determine the focusing properties, and consider the effect of departures from ideal behavior on the FEL gain. In the modulator and radiator wigglers we analyze the effects due to the ends of the wiggler and discuss their correction. In addition, the localized field produced by a trim coil for horizontal beam steering is investigated.

Theoretical analysis of iron-bore superconducting undulators

Abstract The unavoidable undulator field errors due to machining tolerances of the yokes lead to a reduction of the gain in comparison to the case computed with an ideally perfect undulator. We describe a mathematical model of errors in iron-dominated micro-undulators introduced by manufacturing tolerances. Explicit expressions for the perturbation fields are derived. We use these fields to calculate the first, second and phase integrals describing the effects on the electron trajectory. We conclude that the intrinsic tolerances achievable with wire electric discharge machining do not significantly affect the performance of the Accelerator Test Facility free-electron laser.