Ralph A. Cover

In search of a meaningful field-error specification for wigglers

Abstract The quality of a wiggler field is often characterized by its rms deviation from the ideal. This deviation, however, is a poor predictor of actual system performance, particularly in light of the possibilities for optimized error ordering. An alternative field-quality characterization in terms of trajectory wander and cumulative phase shake shows greatly improved correlation with performance.

Statistical variation of FEL performance due to wiggler field errors

Abstract Numerical simulations are used to demonstrate that large statistical variations in peak spontaneous emission and small-signal gain are obtained for FEL wigglers with the same rms field error, but different error distributions. Results demonstrate the need for a wiggler specification which reflects the effect of error ordering on FEL performance.

FEL performance with pure permanent-magnet undulators having optimized ordering

Abstract The degradation of FEL performance by field errors can be greatly mitigated in a pure permanent-magnet undulator by appropriate ordering of magnets. Monte Carlo techniques have been used to obtain such optimized ordering for various systems. The resulting performance improvement has been evaluated using the Rocketdyne simulation code FELOPT.

Three Dimensional Modeling Of Free-Electron Lasers Using Rigorous Wave Propagation

The essential features of generalized numerical models developed at Rocketdyne to compute rigorously the 3 D transverse mode structure of free-electron laser oscillators are presented. The oscillator may consist of a conventional standing or a traveling wave cavity, or may be more complex, and contain intracavity grazing optical elements. Numerical resolution needed to (1) compute the gain due to a spatially distributed electron beam and (2) propagate the electromagnetic field when coupled to this gain are discussed with illustrative examples.

Effects Of Gain Displacements On A Tapered Wiggler Free-Electron Laser

The performance of a low gain, free-electron laser (FEL) operating in the Compton regime is evaluated in the presence of e-beam displacements in planes parallel or perpendicular to the FEL linearly polarized wiggler magnetic field. In this fully coupled, nonlinear formalism, the gain is described by a 3-D extension of the Kroll-Morton-Rosenbluth (KMR) equations and evaluated by using optical fields that are propagated numerically between sections of the wiggler (and the oscillator) using the Gardner-Fresnel-Kirchhoff (GFK) algorithm. The oscil-lator extraction efficiency, optical gain, and the 3-D transverse mode and gain distributions are computed in the absence of slippage between the optical and e-beam pulses, using standard iterative techniques for obtaining resonator solutions. The influence of local off-axis magnetic fields and betatron oscillations on individual particles is included in the gain computations.

FEL Amplifier Performance In The Compton Regime

The Kroll-Morton-Rosenbluth equations of motion for electrons in a linearly polarized, tapered wiggler are utilized to describe gain in free-electron laser amplifiers. The three-dimensional amplifier model includes the effects of density variation in the electron beam, off-axis variations in the wiggler magnetic field, and betatron oscillations. The input electromagnetic field is injected and subsequently propagated within the wiggler by computing the Fresnel-Kirchhoff diffraction integral using the Gardner-Fresnel-Kirchhoff algorithm. The injected optical beam used in evaluating amplifier performance is initially a Gaussian which in general may be astigmatic. The importance of the above effects on extraction effi-ciency is computed both with rigorous three-dimensional electromagnetic wave propagation and a Gaussian treatment of the field.

Simulations of the Rocketdyne free-electron laser with a 4 m wiggler

Abstract Rocketdyne is assembling a high-brightness 78 MeV FEL. After full development the laser will be capable of an average output of greater than 1 kW. Performance calculations using the Rocketdyne FELOPT code are presented for a 1.06 μm system.

Rocketdyne FEL for power beaming using a regenerative amplifier

The Rocketdyne free-electron laser (FEL) being presently developed for operation in the visible to one-micron regime is described, with particular attention given to some of the principal optics and atmospheric propagation issues. The paper describes the system assembly and discusses the performance requirements for power beaming, the resonator design, and the basic ideas and calculations involved in the beam propagating through the atmosphere and tilt corrections. This FEL will be capable of an average output of greater than 1 kW in the near infrared. The laser system has an ability of scaling to power levels required for beaming power to space platforms.

Enhanced performance from high-extraction-efficiency free electron lasers

Abstract Tapering either wiggler wavelengths or wiggler magnetic fields has been used to enhance the extraction efficiency of free electron lasers. For high-extraction-efficiency systems, the electron beam dynamics and thus the system performance can depend on the method of tapering. It is shown that tapering the wiggler wavelength could yield better results for a high-extraction-efficiency system. If aperturing of the optical field by the wiggler becomes significant, a double-taper scheme is proposed that could improve results over a magnetic-field-tapered system.

Transverse mode control in high gain free electron lasers with grazing incidence, unstable ring resonators☆

Abstract Grazing incidence, ring resonators have been proposed [1,2] to alleviate the problem of inordinately high irradiance on the intracavity optics in free electron lasers. Such resonators are also relatively compact, and consequently their alignment tolerances are more manageable. In this paper we present the transverse mode characteristics of an unstable, grazing incidence ring resonator under high gain conditions, and examine the issue of transverse mode control as a function of key resonator parameters.