There are a number of codes that; can calculate the performance of a free-electron laser (FET) in three;dimensions with nonideal electron beams, wigglers, and optics. Unfortunately, these codes can be very computationally intensive. So, given the large number oi parameters associated with an FEL, it is often impractical to utilize such. a large-scale code to develop a preliminary design, To overcome this problem, we developed a reduced FEL model that is sufficiently accurate to provide a realistic performance estimate, while, at tile same time, the algorithm is sufficiently efficient to investigate a large number of parameter variations. The low-level algorithms design the wiggler, determine the effective energy distribution of the electron beam inside the wiggler, determine the small-signal gain, determine the saturation gain and efficiency, and design the optics.

Even at the conceptual level, the strong coupling between subsystem elements complicates the understanding and design of a free electron laser (FEL). Given the requirements for high- performance FELs, the coupling between subsystems must be included to obtain a realistic picture of the potential operational capability. The concept of an Integrated Numerical Experiment (INEX) was implemented to accurately calculate the coupling between the FEL subsystems. During the late 1980's, the INEX approach was successfully applied to a large number of accelerator and FEL experiments. Unfortunately, because of significant manpower and computational requirements, the integrated approach is difficult to apply to trade-off and initial design studies. However, the INEX codes provided a base from which realistic accelerator, wiggler interaction, optics, and control models could be developed. The Free Electron Laser Physical Process Code (FELPPC) includes models developed from the INEX codes, provides coupling between the subsystem models, and incorporates application models relevant to a specific study. In other words, FELPPC solves the complete physical process model using realistic physics and technology constraints. FELPPC can calculate complex FEL configurations including multiple accelerator and wiggler combinations. When compared with the INEX codes, the subsystem models have been found to be quite accurate over many orders-of-magnitude. As a result, FELPPC has been used for the initial design studies of a large number of FEL applications: high-average-power ground, space, plane, and ship based FELs; beacon and illuminator FELs; medical and compact FELs; and XUV FELs.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

We examine the effects of random magmetic field errors on the performance of a free electron laser. We report a modification of the straightest wiggler orbit operating point (SWOOP) theory for two very high efficiency systems. The first system utilizes a gapless pulsed cryogenic wiggler and the second a continuous wave gapless superconduction wiggler. We further show a method to improve the choice of separation of correctors. To establish this method we show that corrected steering errors, BPM errors and gap misadjustments are errors similarly construed as phase errors (ESCAPE). The corrected steering errors also have a component that requires retuning of the wiggler and this task is relegated to unoptimized SWOOP. Without this retuning, these errors are emittance cannot be removed by returning except for the resonant particle. The remaining part of the field errors are similar to similar to an effective emittance, but because the steering errors are homogeneous and the emittance is inhomogeneous, the phase errors and behave like a random force in the KMR potential. In a returned wiggler, the effective energy broadening from emittance is responsible for the initial trapping and the field errors are responsible for the detrapping. This work constitutes a complete high-efficiency model of phase, gap and corrected steering errors for an enmsemble of the free electron lasers. The classical bound-free transition, the detrapping phenomenon, is treated as the Kramers problem.

It is shown that a cw electromagnetic wiggler can be constructed from chilled high-purity copper that is capable of delivering higher magnetic field strengths and vector potential, aw, than either permanent magnet or superconducting wigglers. A model calculation with a 90 MeV beam lasing at 1.7 μm showed a 20% higher arnw than a superconducting system, giving a 23% shorter wiggler period and 16% higher efficiency. Experimental measurements of magnetoresistive effects in copper are included in this paper.

Even at the conceptual level, the strong coupling between the laser subsystem elements, such as the accelerator, wiggler, optics, and control, greatly complicates the understanding and design of a free-electron laser (FEL). Given the requirements for a high-performance FEL, the coupling between the laser subsystems must be included in the design approach. To address the subsystem coupling, we implemented the concept of an integrated numerical experiment (INEX). Unique features of the INEX approach are consistency and numerical equivalence of experimental diagnostics. The equivalent numerical diagnostics mitigate the major problem of misinterpretation that often occurs when theoretical and experimental data are compared. A complete INEX model has been applied to the 10-micrometers high-extraction-efficiency experiment at Los Alamos and the 0.6-micrometers Burst Mode experiment at Boeing Aerospace. In addition, the agreement between INEX and the experiments is very good. With the INEX approach, it now appears possible to design high-performance FELs for numerous applications. The first full-scale test of the INEX approach is the Los Alamos High-Brightness Accelerator FEL (HIBAF) experiment. Implementation and experimental validation of the INEX concept are discussed.

We report our initial measurements of bright (high-charge, low-emittance) electron beams generated at the Los Alamos high brightness accelerator FEL (HIBAF) facility. Normalized emittance values of less than 50π mm mrad for charges ranging from 0.7 to 8.7 nC were obtained for single micropulses at a y-waist and at an energy of 14.7 MeV. These measurements were part of the commissioning campaign on the HIBAF photoelectric injector. Macropulse measurements have also been performed and are compared with integrated numerical experiment (INEX) calculations.

In this paper we review the accelerator design of the high brightness accelerator FEL (HIBAF) at Los Alamos National Laboratory and analyze its actual performance. HIBAF is the first high-brightness high-current (several hundred amperes) accelerator built using a photoelectric injector. We discuss the design philosophy and the integrated numerical experiment (INEX) design tool, and describe the accelerator components. Currently, the machine has only been operated at intermediate energies near 15 MeV. We use the INEX computer code package to examine the accelerator performance by comparing the measurements with simulations at that energy. The accelerator should be able to reach the design goal of 300 A current with the normalized 90% transverse emittance of less than 50-pi-mm mrad for a 5 nC bunch after reaching the final energy of 40 MeV.

The INEX (integrated numerical experiment) numerical model is applied to the 0.6 μm FEL oscillator at the Boeing laboratory in Seattle, WA. This sytem consists of a 110 MeV L-band rf linac, a beam transport line from the accelerator to the entrance of the wiggler, the 5.0 m THUNDER variable-taper wiggler, and a near-concentric two-mirror optical oscillator. Many aspects of the model for the electron beam accelerator and transport line agree with experimental measurements. Predictions for lasing performance are compared with data obtained in May and June 1989, using a mild-tapered wiggler. We obtain good agreement with the achieved extraction efficiency, while ID pulse simulations reproduce the observed sideband instability.

The HIBAF 40 MeV accelerator and beam transport have been designed and studied with ISIS and PARMELA simulations. The nominal beam parameters for a 5 nC pulse are an emittance of 40π mm mrad, 300 A peak current, and an energy spread of 0.25%. We will discuss the major design issues and report on performance expectations.

The 10 μm Los Alamos free-electron laser (FEL) facility is being upgraded. The conventional electron gun and bunchers have been replaced with a much more compact, 6 MeV photoinjector accelerator. By adding existing parts from previous experiments, the primary beam energy will be doubled to 40 MeV. With the existing 1 m wiggler (λw = 2.7 cm) and resonator, the facility can produce photons with wavelengths from 3 to 100 μm when lasing on the fundamental mode and produce photons in the visible spectrum with short-period wigglers or harmonic operation. After installation of a 150° bend, a second wiggler will be added as an amplifier. The installation of laser transport tubes between the accelerator vault and an upstairs laboratory will provide experimenters with a radiation-free environment for experiments. Although the initial experimental program of the upgraded facility will be to test the single-accelerator master-oscillator/power amplifier configuration, some portion of the operational time of the facility can be dedicated to user experiments.

Under the influence of space charge or longitudinal wake fields, transporting an electron beam through a long undulator can cause a degradation of beam quality. Using the PARMELA code, including longitudinal wake-field and space-charge contributions, we simulate a beam bunch that travels through the undulator. The electron beam is focused in both planes with the parabolic pole faces of the undulator. The effect of space charge on the beam envelope is also calculated using the K-V (Kapchinskij-Vladimirskij) envelope equation.

The nonideal characteristics of the electron beam have largely determined the performance of all free electron laser (FEL) oscillators that have operated up to the present time. A realistic quantitative theoretical assessment of FEL oscillator performance must therefore include a viable representation of the electron beam's characteristics, as well as the properties of the wiggler magnet and the optical resonator. This paper presents results of integrated numerical modeling of the Los Alamos FEL oscillator, using as input to the 3-D FEL simulation code FELEX, a numerically-generated electron pulse obtained from the accelerator code PARAMELA as a solution of a full model of the Los Alamos accelerator system (electron gun, accelerator cavities, and beam transport line).

A relatively high gain ( approximately=25 to 40%) free-electron laser (FEL) with an optical ring resonator is simulated using the code FELEX. The laser system corresponds to the 'burst mode' FEL. The ring consists of paraboloids, grazing incidence hyperboloids, and a grating rhomb. The wiggler is 5 m in length and has an adjustable taper, while the electron beam is produced by an RF linac. The optical elements of the ring together with the FEL interaction in the wiggler are modeled in three spatial dimensions to investigate the system from start-up to saturation. Both single-frequency and finite-pulse simulations are performed. >

It is pointed out that the energy spread of a beam bunch induced in a linear accelerator can be reduced to a minimum if the amplitude and the phase of the RF voltage are optimized. The energy spread is induced by the longitudinal wakefield and by the sinusoidal profile of the accelerating voltage acting on the beam. The cavity shape, the bunch profile, and the charge in the bunch determine the wake function. In order to have an approximately constant net voltage acting across the beam bunch, the amplitude and the phase of the RF voltage are optimized. The minimum energy spread, the required RF voltage, and the required RF phase are calculated as a function of the net charge and the length of the bunch. To determine the effect of cavity shape on the minimum energy spread, the optimization was performed for several types of cavities. The optimization shows that the energy spread can be reduced by a factor of 3 for the Energy Recovery Experiment (ERX)-type cavity and the Modular Component Technology Development (MCTD)-type cavity by adjusting the amplitude and the phase of the RF voltage. This is done by increasing RF voltage and phase. However, the ERX-type cavity is superior because it requires a third of the voltage of the MCTD to attain the same energy spread

A numerical simulation capability has been developed to model the physics and realistic design constraints of free electron laser oscillators driven by rf linear accelerators. Two computer codes have been written, FELEX and FELP. The code FELP is a one spatial dimension code with essentially unlimited time or spectral resolution. The codes are complementary and their use is dependent upon the problem being addressed. The code FELP is used to model optical and electron micropulse structure, broadband noise, and the sideband instability. The code FELEX models accelerator generated electron beam distributions, the transport of these distributions through wigglers with misalignments and field errors, self-consistent interaction with the optical field, and propagation of the optical field through resonators with realistically modelled components. FELEX is routinely used to match resonator designs to the optical parameters of the electron beam, and used to investigate the physics of 3-D micropulse effects. Some details of the codes will be presented along with various examples of simulation results.

Simulation of the generation of a relativistic electron beam in a foil diode configuration and the subsequent intense microwave generation resulting from the formation of the virtual cathode is presented. The oscillating virtual cathode and the trapped beam electrons between the real and the virtual cathodes were found to generate microwaves at two distinct frequencies. Generation of high-power microwaves with about 10% efficiency might reasonably be expected from such a virtual-cathode configuration.

A new high-voltage scaling based on Kilpatrick's criterion is presented that suggests that voltages more than twice the Kilpatrick limit can be obtained with identical initial conditions of vacuum and surface cleanliness. The calculations are based on the experimentally observed decrease in secondary electron emission with increasing ion impact energy above 100 keV. A generalized secondary-emission package has been developed to simulate actual cavity dynamics in conjunction with our 2½-dimensional fully electromagnetic particle-in-cell code CEMIT. The results are discussed with application to the suppression of vacuum breakdown in rf accelerator devices.

Previous investigations on the two-stream and filamentation instabilities are based on either the electrostatic or the ordinary-mode approximation. A general relativistic dispersion formulation is presented to study these two instabilities for a scattered electron beam propagating a collisional, bi-Maxwellian plasma. New analytical results that apply to a general beam distribution are obtained for the stability boundary of the filamentation instability. The general dispersion relation uncovers the inadequacy in applying the ordinary-mode approximation in a frame other than the rest frame of the plasma. Analytical expressions for the the growth rates of the filamentation modes in various parameter regimes are obtained. Finally, numerical comparisons are made between the general dispersion results and the earlier results based on the electrostatic and ordinary-mode approximations.