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Some applications of mirror-generated electric potentials to alternative fusion concepts

Description: Transient electrical potentials can be generated in plasmas by utilizing impulsive mirror-generated forces acting on the plasma electrons together with ion inertia to cause momentary charge imbalance. In the Mirrortron such potentials are generated by applying a rapidly rising (tens of nanoseconds) localized mirror field to the central region of a hot-electron plasma confined between static mirrors. Because of the loss-cone nature of the electron distribution the sudden appearance of the pulsed mirror tends to expel electrons, whereas the ion density remains nearly constant. The quasi-neutrality condition then operates to create an electrical potential the equipotential surfaces of which can be shown theoretically to be congruent with surfaces of constant B. An alternative way of generating transient potentials is to apply a pulse of high-power microwaves to a plasma residing on a magnetic field with a longitudinal gradient. This technique resembles one employed in the Pleiade experiments. At gigawatt power levels, such as those produced by a Free Electron Laser, the production of very high transient potentials is predicted. Fusion-relevant applications of these ideas include heavy-ion drivers for inertial fusion, and the possibility of employing these techniques to enhance the longitudinal confinement of fusion plasmas in multiple-mirror systems. 23 refs., 3 figs.
Date: September 24, 1990
Creator: Post, R.F.
Partner: UNT Libraries Government Documents Department

Proton laser accelerator by means of the inverse free electron laser mechanism

Description: The inverse free electron laser accelerator is considered to be a potential high gradient electron accelerator. In this accelerator electrons oscillating in the magnetic field of a wiggler can gain energy from a strong laser beam propagating collinearly. The same mechanism of acceleration can work for protons and all other heavier particles. One can expect that the proton acceleration will be less effective, as it is more difficult to wiggle a heavier particle. It is indeed so, but this less efficient coupling of the proton and laser beam is partly compensated by the negligible radiative losses. These losses impose restrictions on the electron acceleration above 100 Gev. 6 references, 2 figures.
Date: July 1, 1984
Creator: Zakowicz, W.
Partner: UNT Libraries Government Documents Department

Physics and design issues of a high gain FEL

Description: A series of viewgraphs is provided that summarize and illustrate some of the physics aspects and design issues of free electron lasers. Physics aspects include the coupling between electrons and light, electron beam properties that affect the free electron laser, and tapering of the wiggler. Design issues include focusing and mismatched electron orbit, as well as diffraction. Modelling of the free electron laser and scaling are also mentioned. (LEW)
Date: October 2, 1985
Creator: Prosnitz, D.
Partner: UNT Libraries Government Documents Department

An introduction to acceleration mechanisms

Description: This paper discusses the acceleration of charged particles by electromagnetic fields, i.e., by fields that are produced by the motion of other charged particles driven by some power source. The mechanisms that are discussed include: Ponderamotive Forces, Acceleration, Plasma Beat Wave Acceleration, Inverse Free Electron Laser Acceleration, Inverse Cerenkov Acceleration, Gravity Acceleration, 2D Linac Acceleration and Conventional Iris Loaded Linac Structure Acceleration. (LSP)
Date: May 1, 1987
Creator: Palmer, R.B.
Partner: UNT Libraries Government Documents Department

Preliminary studies of an infrared free-electron laser oscillator at the ATF(BNL)

Description: In this report, I present results of a theoretical 1-D model discussed by G. Dattoli, A. Reniere and myself. The validity of a steady-state analysis is discussed and some estimates are given of the effects introduced by the ''lethargy'' of the laser pulse due to the finite length of the e/sup /minus// pulse. Also, I present analytical expressions for the laser pulse in terms of supermodes (wave-packets of cavity modes), their evolution, physical width as well as the associated frequency spectrum. Next, I present results obtained with a 3-D code for the single pass, small-signal gain. In the appendix, I summarize the symbols used in this report. 2 refs., 6 figs., 3 tabs.
Date: October 19, 1988
Creator: Gallardo, J.C.
Partner: UNT Libraries Government Documents Department

Two-dimensional theory and simulation of free electron lasers

Description: Two-dimensional homogeneous theory of free-electron lasers with a wiggler magnetic field of constant wavelength is formulated. It has been found from the theory that waves propagating obliquely with respect to the electron beam are always unstable with appreciable growth rates; therefore, mode competition among the on-axis and off-axis modes is an important consideration in the design of the free-electron laser. Furthermore, electromagnetic waves with group velocities opposite to the direction of electron beam propagation are absolutely unstable if k/sub o/v/sub o/ > ..omega../sub pe/(1/..gamma../sup 3/2/ + 1/..gamma../sup 1/2/). Due to strong nonlinear saturation levels of the low-frequency absolute instability, the dynamics of the electron beam and the generation of the high-frequency electromagnetic radiation can be severely affected. Two-dimensional particle simulations show that the efficiency of generation of the on-axis high-frequency electromagnetic wave decreases significantly due to instability of the off-axis modes. In addition, complete disruption of the electron beam and laser oscillation due to the onset of the absolute instability have been observed in simulations.
Date: January 1, 1981
Creator: Kwan, T.J.T. & Cary, J.R.
Partner: UNT Libraries Government Documents Department

Universal scaling function for FEL gain

Description: We have developed an analytic calculation of FEL gain in the exponential regime taking into account the finite emittance, energy spread, focusing and betatron oscillation of the electron beam, and the diffraction and guiding of the radiation. The gain is expressed in terms of a universal scaling function with only three independent parameters. Excellent agreement is found with results of numerical simulation. 14 refs., 3 figs., 1 tab.
Date: January 1, 1990
Creator: Yu, L.H.; Krinsky, S. (Brookhaven National Lab., Upton, NY (USA)) & Gluckstern, R.L. (Maryland Univ., College Park, MD (USA). Dept. of Physics and Astronomy)
Partner: UNT Libraries Government Documents Department

Summary of Working Group on Storage Ring Collective Effects

Description: The purposes of this Workshop were to investigate the techniques available for the production of very low emittance electron beams, to explore the limitations of these techniques, and to consider new possibilities that might improve the present situation. Two uses for these low emittance beams are of interest here: to serve for a high energy linear collider, which requires very small beam sizes to achieve a suitable value for the luminosity; and to serve for a free-electron laser (FEL) in the short wavelength - say 40 A - regime, which requires both small transverse beam dimensions and a very low longitudinal emittance. This paper contains a brief summary of the main topics discussed by the Working Group on Storage Ring Collective Effects. In the case of the linear collider application, the use of a damping ring (DR) to reduce, by radiation damping, the emittance of an intermediate energy linac beam prior to its subsequent injection into the remaining high energy linac is considered. For FEL use, a high-gain device with a storage ring to damp the beam periodically between passages through a bypass section containing the long FEL undulator is considered. Such designs - at a longer wavelength of 400 A - are already available, but the shorter wavelength of interest here is much more of a challenge.
Date: June 1, 1987
Creator: Zisman, M.S.
Partner: UNT Libraries Government Documents Department

Optical guiding and beam bending in free-electron lasers

Description: The electron beam in a free-electron laser (FEL) can act as an optical fiber, guiding or bending the optical beam. The refractive and gain effects of the bunched electron beam can compensate for diffraction, making possible wigglers that are many Rayleigh ranges (i.e., characteristic diffraction lengths) long. The origin of optical guiding can be understood by examining gain and refractive guiding in a fiber with a complex index of refraction, providing a mathematical description applicable also to the FEL, with some extensions. In the exponential gain regime of the FEL, the electron equations of motion must be included, but a self-consistent description of exponential gain with diffraction fully included becomes possible. The origin of the effective index of refraction of an FEL is illustrated with a simple example of bunched, radiating dipoles. Some of the properties of the index of refraction are described. The limited experimental evidence for optical beam bending is summarized. The evidence does not yet provide conclusive proof of the existence of optical guiding, but supports the idea. Finally, the importance of refractive guiding for the performance of a high-gain tapered-wiggler FEL amplifier is illustrated with numerical simulations.
Date: January 1, 1987
Creator: Scharlemann, E.T.
Partner: UNT Libraries Government Documents Department

Field error lottery

Description: The level of field errors in an FEL is an important determinant of its performance. We have computed 3D performance of a large laser subsystem subjected to field errors of various types. These calculations have been guided by simple models such as SWOOP. The technique of choice is utilization of the FELEX free electron laser code that now possesses extensive engineering capabilities. Modeling includes the ability to establish tolerances of various types: fast and slow scale field bowing, field error level, beam position monitor error level, gap errors, defocusing errors, energy slew, displacement and pointing errors. Many effects of these errors on relative gain and relative power extraction are displayed and are the essential elements of determining an error budget. The random errors also depend on the particular random number seed used in the calculation. The simultaneous display of the performance versus error level of cases with multiple seeds illustrates the variations attributable to stochasticity of this model. All these errors are evaluated numerically for comprehensive engineering of the system. In particular, gap errors are found to place requirements beyond mechanical tolerances of {plus minus}25{mu}m, and amelioration of these may occur by a procedure utilizing direct measurement of the magnetic fields at assembly time. 4 refs., 12 figs.
Date: January 1, 1990
Creator: Elliott, C.J.; McVey, B. (Los Alamos National Lab., NM (USA)) & Quimby, D.C. (Spectra Technology, Inc., Bellevue, WA (USA))
Partner: UNT Libraries Government Documents Department

A high gain free electron laser amplifier design for the Alcator-C tokamak. [FRED]

Description: We describe an improved wiggler tapering algorithm and the resulting wiggler design for a high-gain free electron laser amplifier to be used for plasma heating and current drive experiments in the Alcator-C tokamak. Unlike the original, this new design limits the growth of the shot noise to insignificant levels. The design goal of at least 8 GW of peak power in the TE/sub 01/ mode was achieved with a 3 kA electron beam with energies in the 7 to 9 MeV range and a beam brightness of 10/sup 5/ A/(rad-cm)/sup 2/. The wiggler was 5 m long with a wiggler wavelength of 8 cm.
Date: February 1, 1987
Creator: Jong, R.A.
Partner: UNT Libraries Government Documents Department

Investigation of metal coatings for the free electron laser

Description: We are investigating the deposition and characteristics of metal coatings for use in environments such as the Free Electron Laser where the radiation resistance of metal coatings could prove to be of great benefit. We have concentrated our initial efforts on silver laminate coatings due to the high reflectance of silver at 1 micron wavelength. Our initial laminate coatings have utilized thin layers of titanium oxide to break up the columnar structure of the silver during electron-beam deposition on fused silica substrates. Our initial results on equal coating thickness samples indicate an improvement in damage threshold that ranges from 1.07 to 1.71 at 351 nm.
Date: January 1, 1985
Creator: Scott, M.L.; Arendt, P.N.; Springer, R.W.; Cordi, R.C. & McCreary, W.J.
Partner: UNT Libraries Government Documents Department

Compact rf-linac free-electron lasers

Description: Design studies using the INEX simulation methods are presented for an infrared compact rf-linac-driven FEL. The possibility of such a device relies upon two technological advances: a very bright electron beam from a linac with a photocathode injector, and a short-period, high-field wiggler. 10 refs., 6 figs., 3 tabs.
Date: January 1, 1989
Creator: Goldstein, J.C.; Sheffield, R.L.; Carlsten, B.E. & Warren, R.W.
Partner: UNT Libraries Government Documents Department

Emittance studies at the Los Alamos National Laboratory Free-Electron Laser

Description: Recent emittance studies at the Los Alamos FEL have indicated several areas of concern in the linac and beamline feeding the wiggler. Four emittance growth mechanisms of special importance have been studied. First, a rapid growth of the electron beam's emittance immediately after the spherical gridded Pierce gun resulted, in part, from the long time required for our pulsing electronics to ramp the grid voltage up at the start and down at the end of the pulse, which created a pulse with a cosine-like current distribution as a function of time. The growth was compounded by the extremely small radial beam size (almost a waist) leaving the gun. In addition, we saw evidence of electrostatic charging of the insulators in the gun, reducing the quality of the electron beam further. Second, the action of the solenoidal focusing fields in the low-voltage bunching region was studied, and criteria for a minimum emittance growth were established. Third, maximum misalignment angles and displacements for various elements of the beamline were calculated for the desired low emittance growth. Finally, emittance growth in the horizontal dimension through the nonisochronous bend caused by varying energy depression on the particles due to longitudinal wake fields was both calculated and observed. In addition, we measured energy depressions caused by the wake fields generated by various other elements in the beamline. Strategies were developed to relieve the magnitude of these wake-field effects. 10 refs., 12 figs.
Date: January 1, 1987
Creator: Carlsten, B.E.; Feldman, D.W.; Lumpkin, A.H.; Stein, W.E. & Warren, R.W.
Partner: UNT Libraries Government Documents Department

Free electron laser variable bridge coupler

Description: The Los Alamos free-electron laser (FEL) is being modified to test a scheme for recovering most of the power in the residual 20-MeV electron beam by decelerating the microbunches in a linear standing-wave accelerator and using the recovered energy to accelerate new beam. A variable-coupler low-power model that resonantly couples the accelerator and decelerator structures has been built and tested. By mixing the TE/sub 101/ and TE/sub 102/ modes, this device permits continuous variation of the decelerator fields relative to the accelerator fields through a range of 1:1 to 1:2.5. Phase differences between the two structures are kept below 1/sup 0/ and are independent of power-flow direction. The rf power is also fed to the two structures through this coupling device. Measurements were also made on a three-post-loaded variable coupler that is a promising candidate for the same task.
Date: January 1, 1985
Creator: Spalek, G.; Billen, J.H.; Garcia, J.A.; McMurry, D.E.; Harnsborough, L.D.; Giles, P.M. et al.
Partner: UNT Libraries Government Documents Department

Gain physics of rf-linac-driven xuv free-electron lasers

Description: In an rf-linac-driven xuv free-electron laser oscillator, the gain depends on the details of the shape of the electron beam's phase-space distribution, particularly the distribution of electrons in the transverse (to the direction of propagation) position and velocity coordinates. This strong dependence occurs because the gain in this device is inhomogeneously broadened. Our previous theoretical studies have assumed that the transverse phase space distribution is a product of uncorrelated Gaussian functions. In the present work, we shall present the results of a theoretical study of the gain for non-Gaussian phase-space distributions. Such distributions arise either from a better representation of the electron beam from an rf-linac or from an emittance filter applied to the beam after the linac.
Date: January 1, 1986
Creator: Goldstein, J.C.; McVey, B.D. & Newnam, B.E.
Partner: UNT Libraries Government Documents Department

Free-electron laser results

Description: The Los Alamos free-electron laser (FEL) amplifier experiment was designed to demonstrate high efficiency for transfer of energy from an electron beam to a light beam in the magnetic field of a tapered wiggler. Initial results indicate an energy transfer consistent with theory. Distinct groups of decelerated electrons as well as accelerated electrons are clearly present in the energy spectrum of electrons emerging from the wiggler when the laser light is present. The observed energy decrease for the electrons captured in the decelerating bucket is approx. 6% and the average decrease of the entire energy distribution is approx. 2% for the conditions of these initial measurements.
Date: January 1, 1981
Creator: Stein, W.E.; Brau, C.A.; Newnam, B.E.; Warren, R.W.; Winston, J. & Young, L.M.
Partner: UNT Libraries Government Documents Department

The Los Alamos Photoinjector Program

Description: Free-electron lasers (FELS) require electron beams of high peak brightness. In this presentation, we describe the design of a compact high-brightness electron source for driving short-wavelength FELs. The experiment uses a laser-illuminated Cs/sub 3/Sb photoemitter located in the first rf cavity of an injector linac. The photocathode source and associated hardware are described. The doubled YAG laser (532 nm), which is used to drive the photocathode, produces 75-ps micropulses at 108-MHz repetition rate and peak powers of approximately 300 kW. Diagnostics include a pepper-pot emittance analyzer, a magnetic spectrometer, and a 4-ps resolution streak camera. Present experiments give the following results: micropulse current amplitude of 100 mA to 400 A, beam emittances ranging from 10 n.mm.mrad to 40 n.mm.mrad, an energy spread of +-3%, and peak current densities of 600 A/cm/sup 2/. A brief discussion on the possible applications of this very bright and compact electron source is presented. 16 refs., 5 figs., 1 tab.
Date: September 1, 1987
Creator: Sheffield, R.L.; Gray, E.R. & Fraser, J.S.
Partner: UNT Libraries Government Documents Department

Linac-driven XUV free-electron laser

Description: Use of an rf linear accelerator as the electron source for a free-electron laser operating in the extreme ultraviolet wavelength range from 100 nm to at least as low as 50 nm appears feasible. Peak and average power outputs of greater than 100 kW and 50W, respectively, are predicted.
Date: January 1, 1983
Creator: Newnam, B.E.; Goldstein, J.C.; Fraser, J.S. & Cooper, R.K.
Partner: UNT Libraries Government Documents Department

Limitations on the use of the pulsed-wire field-measuring technique

Description: As wigglers become longer and the wavelength of the light they produce becomes shorter, the requirements for magnetic field uniformity and precision of wiggler construction become more severe. Techniques used to measure magnetic fields and to estimate the performance of wigglers are now being pushed to their limits in precision and are generally awkward and time consuming in practice. A new field-error measurement technique has been developed that has the usual advantages of a null technique, demonstrates high sensitivity to field errors, and is rapid and simple to employ. With this technique, it appears practical to use computer control to both measure and correct field errors. In a particularly attractive application, these measuring and correcting steps could be carried out on a daily basis for an operational wiggler, which is mounted under vacuum in its optical cavity. In this way, changes in the fields caused by aging or by thermal or radiation-induced deterioration effects could be rapidly identified and corrections could be instituted without significant interruption to normal operations. The principles and limitations of ths technique will be described and examples given of various implementations that have been examined experimentally. 10 refs., 2 figs., 2 tabs.
Date: September 1, 1987
Creator: Warren, R.W.
Partner: UNT Libraries Government Documents Department

Los Alamos free-electron laser

Description: During the past year the Los Alamos free-electron laser (FEL) oscillator has demonstrated high peak and average power (10 MW and 6 kW), broad-wavelength tunability (9 to 35 ..mu..m), and near-ideal optical quality (0.9 Strehl ratio). An electron energy-extraction efficiency of 1% was measured. The predicted production of synchrotron sidebands also was observed in the broadened optical spectrum. As shorter wavelengths and higher powers are pursued, higher currents with improved beam quality will be required. Advanced injectors and energy-recovery systems are being developed to meet these demands. 17 refs., 6 figs., 3 tabs.
Date: January 1, 1985
Creator: Watson, J.M.
Partner: UNT Libraries Government Documents Department

Los Alamos free electron laser: accelerator performance

Description: The Los Alamos free electron (FEL) laser oscillator has successfully operated over a wavelength range from 9 to 11 ..mu..m with a peak output power of 5 MW and an average output power of 6 kW over a 70-..mu..s pulse length. The FEL is driven by a conventional rf linear accelerator operating at 1.3 GHz with a nominal energy of 20 MeV. Particularly important parts of the beamline are the electron gun, the subharmonic and fundamental-bunching systems, the accelerator, the feedback controllers, the steering and focusing systems, the Cherenkov radiators used as beam-position monitors, and the slow and fast deflectors used with the diagnostic spectrometer at the exit of the beamline. We will discuss problems and present the performance of these components. 10 references, 12 figures, 2 tables.
Date: January 1, 1984
Creator: Warren, R.W.; Stein, W.E.; Lynch, M.T.; Sheffield, R.L. & Fraser, J.S.
Partner: UNT Libraries Government Documents Department