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High gain and high extraction efficiency from a free electron laser amplifier operating in the millimeter wave regime

Description: Experiments at the Electron Laser Facility have generated peak microwave power of 180 MW at 35 GHz. The facility is operated as a single pass amplifier. Gain in excess of 30 dB/m has been observed up to saturation of the amplifier. For the 3 MeV, 850 Amp electron beam, the radiation corresponds to 7% energy extraction from the electron beam. Beyond saturation, the electron beam output power exhibits oscillations corresponding to the synchrotron motion of the trapped electrons in the ponderomotive well. In addition, the TE/sub 21/ and TM/sub 21/ modes have been studied and have power levels comparable to the fundamental. Third harmonic (105 GHz) radiation has been measured at power levels on the order of a few percent of the peak fundamental power.
Date: October 1, 1985
Creator: Orzechowski, T.J.; Anderson, B.R.; Fawley, W.M.; Prosnitz, D.; Scharlemann, E.T.; Yarema, S.M. et al.
Partner: UNT Libraries Government Documents Department

Enhancing the performance of a high-gain free electron laser operating at millimeter wavelengths

Description: A high-gain, high extraction efficiency, free electron laser (FEL) amplifier operating at the Experimental Test Accelerator (ETA) at 34.6 GHz has demonstrated a small signal gain of 13.4 dB/m. With a 30 kW input signal, the amplifier has produced a saturated output of 80 MW and a 5% extraction efficiency. Comparison of these results with a linear model at small signal levels indicates that the amplifier can deliver saturated output starting from noise, if the brightness of the electron beam is sufficiently high. The brightness of the ETA is far below that possible with optimized choice of practical design characteristics such as peak voltage, cathode type, gun electrode geometry, and focusing field topology. In particular, the measured brightness of the ETA injector is limited by plasma effects from the present cold, plasma cathode. As part of a coordinated theoretical and experimental effort to improve injector performance, we are using the EBQ gun design code to explore the current limits of gridless, relativistic, Pierce columns with moderate current density (>50 A/cm/sup 2/) at the cathode. The chief component in our experimental effort is a readily modified electron gun that will allow us to test many candidate cathode materials, types, and electrode geometries at field stresses up to 1 MV/cm. 8 references, 5 figures.
Date: October 25, 1984
Creator: Barletta, W.A.; Anderson, B.; Fawley, W.M.; Neil, V.K.; Orzechowski, T.J.; Prosnitz, D. et al.
Partner: UNT Libraries Government Documents Department

Construction tolerances for low loss, dielectric coated, metallic waveguide for transmission optical radiation

Description: The transmission of radiation, in a specific mode of interest for the IFELA, past a symmetric step in dielectric coating thickness has been calculated. The result shows that the transmission loss depends on the quantity (s/D)/sup 2/ and vanishes to first order in the ratio of the step s to the guide aperture D. With the reasonable assumption that this feature holds for all forms of surface imperfections, the attenuation length due to imperfections has been estimated. It is found that rms surface roughness of approx. 0.1 ..mu.. m leads to attenuation lengths of 25 km or greater.
Date: August 1, 1984
Creator: Sandweiss, J.
Partner: UNT Libraries Government Documents Department

Pierce-Wiggler electron beam system for 250 GHz GYRO-BWO: Final report

Description: This final report summarizes the design and performance of the VUW-8028 Pierce-Wiggler electron beam systems, which can be used to power high frequency gyro-BWO's. The operator's manual for this gyro-BWO beamstick is included as appendix A. Researchers at Lawrence Livermore National Laboratory (LLNL) are developing a gyro-BWO with a center frequency of 250 GHz, 6% bandwidth, and 10 kV peak output power. The gyro-BWO will be used to drive a free electron laser amplifier at LLNL. The electron beam requirements of the gyro-BWO application are: Small beam size, .100 inch at 2500 gauss axial magnetic field; a large fraction of the electron energy in rotational velocity; ability to vary the electrons' axial velocity easily, for electronic tuning; and low velocity spread i.e. little variation in the axial velocities of the electrons in the interaction region. 1 ref., 13 figs.
Date: January 1, 1989
Creator: Pirkle, D.R.; Alford, C.W.; Anderson, M.H.; Garcia, R.F.; Legarra, J.R. & Nordquist, A.L.
Partner: UNT Libraries Government Documents Department

An electron beam injector for pulse compression experiments

Description: An electron beam injector has been constructed to study the physics of longitudal pulse compression in the University of Maryland electron beam transport experiment. The injector consists of a variable-perveance gridded electron gun followed by three matching lenses and one induction linac module. It produces a 50 ns, 40 mA electron pulse with a 2.5 to 7.5 keV, quadratically time-dependent energy shear. This beam will be injected into the existing 5-m long periodic transport channel with 38 short solenoid lenses. With the given beam parameters and initial conditions the pulse will be compressed by a factor of 4 to 5 before reaching the end of the existing solenoid channel. This paper reports on the design features and the measured general performance characteristics of the injector system including its mechanical, electrical, and beam-optical properties.
Date: January 1, 1990
Creator: Wang, J.G.; Boggasch, E.; Kehne, D.; Reiser, M.; Shea, T. & Wang, D.X.
Partner: UNT Libraries Government Documents Department

Design overview of a highly stable infrared free electron laser at LBL

Description: An infrared free electron laser (IRFEL) is being designed for the Chemical Dynamics Research Laboratory (CDRL) at LBL. The FEL is based on a 50 MeV RF linac operating in synchronization to the Advanced Light Source (ALS), and will produce intense (100 {mu}J per micropulse), narrow bandwidth (narrower than 0.1%) radiation between 3 {mu} and 50 {mu}. In the design, we pay particular attention to the FEL stability issues and require that the fluctuations in electron beam energy and in timing be less then 0.05% and 0.1 ps respectively. The FEL spectrum can then be stabilized to about 10{sup {minus}3}, or if grating is used, to 10{sup {minus}4}. We discuss various sources of fluctuations in the gun, the bunchers and the accelerator sections, as well as the feedback and feedforward schemes to reduce these fluctuations. The accelerator structure is chosen to be of the side coupled, standing wave type for easier control. The beam transport is made isochronous to avoid the coupling between the energy and the timing fluctuations. 12 refs., 1 fig.
Date: November 1, 1990
Creator: Kim, K.J.; Berz, M.; Chattopadhyay, S.; Gough, R.; Kim, C.; Kung, A.H. et al.
Partner: UNT Libraries Government Documents Department

Influence of the synchrotron radiation on particle dynamics in a rectangular undulator

Description: This paper is concerned with the synchrotron radiation from an undulating electron beam in a rectangular waveguide. It is shown analytically and numerically that the radiated energy spectrum may differ significantly from the free space result when the undulator length divided by the Lorentz factor of the electron beam is larger than the transverse size of the waveguide. The undulator radiation is identified with the awake field in beam instabilities. The concepts of wake function and impedance are introduced to formulate the present problem in the same manner as the beam instability problem. It is shown that the obtained impedances satisfy the Panofsky-Wenzel theorem and other properties inevitable for wake fields. 5 refs., 2 figs.
Date: March 1, 1989
Creator: Chin, Yong Ho
Partner: UNT Libraries Government Documents Department

Storage-ring FEL for the vuv

Description: A free-electron laser for the vuv operating in a storage ring requires an electron beam of high density and low energy spread and a short wavelength, narrow-gap undulator. These conditions tend to produce longitudinal and transverse beam instabilities, excessive beam growth through multiple intrabeam scattering, and a short gas-scattering lifetime. Passing the beam only occasionally through the undulator in a by-pass straight section, as proposed by Murphy and Pellegrini, allows operation in a high-gain, single-pass mode and a long gas-scattering lifetime. Several storage ring designs have been considered to see how best to satisfy the several requirements. Each features a by-pass, a low-emittance lattice, and built-in wigglers for enhanced damping to counteract the intra-beam scattering. 15 references, 3 figures, 2 tables.
Date: September 1, 1984
Creator: Peterson, J.M.; Bisognano, J.J.; Garren, A.A.; Halbach, K.; Kim, K.J. & Sah, R.C.
Partner: UNT Libraries Government Documents Department

Center for X-Ray Optics, 1986

Description: The Center for X-Ray Optics has made substantial progress during the past year on the development of very high resolution x-ray technologies, the generation of coherent radiation at x-ray wavelengths, and, based on these new developments, had embarked on several scientific investigations that would not otherwise have been possible. The investigations covered in this report are topics on x-ray sources, x-ray imaging and applications, soft x-ray spectroscopy, synchrotron radiation, advanced light source and magnet structures for undulators and wigglers. (LSP)
Date: July 1, 1987
Creator: Available, Not
Partner: UNT Libraries Government Documents Department

Brightness and coherence of radiation from undulators and high-gain free electron lasers

Description: The purpose of this paper is to review the radiation characteristics of undulators and high-gain free electron lasers (FELs). The topics covered are: a phase-space method in wave optics and synchrotron radiation, coherence from the phase-space point of view, discussions of undulator performances in next-generation synchrotron radiation facility and the characteristics of the high-gain FELs and their performances. (LSP)
Date: March 1, 1987
Creator: Kim, Kwang-Je
Partner: UNT Libraries Government Documents Department

Emittance correction of photocathode gun

Description: The standard emittance calculation removes linear correlations between transverse displacement r and the divergence r{prime}. Higher order correlations remain and they are responsible for a substantial area in phase space which corresponds to the calculated emittance. Time dependent correlations are identified and different procedures (transverse and longitudinal laser shaping, rf quadrulope) are proposed to remove them. The Brookhaven National Laboratory rf gun has been studied; however, in order to more clearly demonstrate the desired effects, the accelerating field and bunch length have been assumed to be more optimistic than the present operating values. This approach reduces the realizable emittance by a factor of 5 with respect to the value before the correction. 9 refs., 5 figs., 1 tab
Date: January 1, 1990
Creator: Gallardo, J.C. (Brookhaven National Lab., Upton, NY (USA)) & Palmer, R.B. (Brookhaven National Lab., Upton, NY (USA) Stanford Linear Accelerator Center, Menlo Park, CA (USA))
Partner: UNT Libraries Government Documents Department

Quadrupole magnets measurement

Description: A rotating coil setup is designed for quadrupole magnet measurement at the Accelerator Test Facility (ATF); Hall probe measurement was also performed for one of each type of quadrupole magnet. Both mechanical and magnetic properties of the quadrupole magnets were measured, the results are reported here. 5 refs., 12 figs., 12 tabs.
Date: January 1, 1991
Creator: Wang, Xijie (California Univ., Los Angeles, CA (USA). Center for Advanced Accelerators Physics) & Sylvester, C. (Brookhaven National Lab., Upton, NY (USA))
Partner: UNT Libraries Government Documents Department

Induction accelerators and free-electron lasers at LLNL: Beam Research Program

Description: Linear induction accelerators have been developed to produce pulses of charged particles at voltages exceeding the capabilities of single-stage, diode-type accelerators and at currents too high rf accelerators. In principle, one can accelerate charged particles to arbitrarily high voltages using a multistage induction machine. The advent of magnetic pulse power systems makes sustained operation at high repetition rates practical, and high-average-power capability is very likely to open up many new applications of induction machines. In Part A of this paper, we survey the US induction linac technology, emphasizing electron machines. We also give a simplified description of how induction machines couple energy to the electron beam to illustrate many general issues that designers of high-brightness and high-average-power induction linacs must consider. We give an example of the application of induction accelerator technology to the relativistic klystron, a power source for high-gradient accelerators. In Part B we address the application of LIAs to free-electron lasers. The multikiloampere peak currents available from linear induction accelerators make high-gain, free-electron laser amplifier configurations feasible. High extraction efficiencies in a single mass of the electron beam are possible if the wiggler parameters are appropriately ''tapered'', as recently demonstrated at millimeter wavelengths on the 4-MeV ELF facility. Key issues involved in extending the technology to shorter wavelengths and higher average powers are described. Current FEL experiments at LLNL are discussed. 5 refs., 16 figs.
Date: February 15, 1989
Creator: Briggs, R.J.
Partner: UNT Libraries Government Documents Department

Stability and performance of CDRL-FEL (Chemical Dynamics Research Laboratory-Free Electron Laser)

Description: We study the performance of a proposed infrared free electron laser at Lawrence Berkeley Laboratory, which would be a user facility and therefore has a unique set of requirements in intensity, spectrum and stability. The output performance in intensity and spectrum, and methods to optimize the performance, are studied in detail. The effect of the electron beam fluctuation on FEL stability is carefully evaluated to set a tolerance for the accelerator design. Use of intracavity gratings is studied as a means of further improving the spectral purity and stability. 19 refs., 12 figs., 2 tabs.
Date: November 1, 1990
Creator: Kim, K.J. & Xie, M.
Partner: UNT Libraries Government Documents Department

Intense microwave generation using free-electron lasers

Description: In this paper, I will describe a free-electron laser amplifier which operated in the microwave regime. This device, called the Electron Laser Facility (ELF), used an electron beam generated by a Linear Induction Accelerator (LIA). ELF operated as a single pass amplifier at 35 and 140 GHz. Because the device had no cavity, we could study the FEL physics independent of cavity considerations. With a sufficiently large input signal, growth of the signal from noise on the beam did not influence the performance. This device demonstrated significant gain and allowed us to investigate such FEL phenomenon as saturation and synchrotron oscillation of the electrons trapped in the ponderomotive well. We were also able to study the phase shift of the radiation due to the real part of complex gain of the FEL. Because the interaction takes place in a waveguide, the FEL can couple to several spatial modes at a given frequency. The bunched electrons can radiate at harmonics of the fundamental and in this experiment we studied the evolution of the third harmonic. In this paper, I will describe the Electron Laser Facility. I will discuss the FEL performance with regard to gain, saturation, phase evolution, mode coupling and harmonic generation, I will briefly discuss a switching technique which allows the LIA to run at high average power. When driven by such a device, and FEL can produce high average power radiation. We will present the design for such a device which can be used to heat a tokamak plasma. This device is designed to operate at 250 GHz and produce an average power of 2 MW.
Date: September 1, 1990
Creator: Orzechowski, T.J.
Partner: UNT Libraries Government Documents Department

Injector modeling and achievement/maintenance of high brightness

Description: Viewgraphs for the workshop presentation are given. The presentation has three fundamental parts. In part one the need for numerical calculations is justified and the available computer codes are enumerated. The capabilities and features of the DPC computer code are the focal point in this section. In part two the injector design issues are discussed. These issues include such things as the beam optics and magnetic field profile. In part three the experimental results of two injector designs are compared with DPC predictions. 8 figs.
Date: October 1, 1985
Creator: Boyd, J.K.
Partner: UNT Libraries Government Documents Department

Preparation for propagation and absorption experiments in MTX

Description: Preparatory calculations of microwave transmission through the MTX access duct, propagation of the waves through the plasma and the resulting power deposition profile on a calorimeter located on the tokamak inside wall have been performed. The microwave transmission calculations include the relative phase slippage of waveguide modes in the duct to determine the spatial structure of the wavefront at the duct exist. Ray-tracing calculations show substantial spreading of the beam in the poloidal direction at densities above 1.5 /times/ 10/sup 20/ m/sup /minus/3/, well within the range of the experiments. Initial experiments with low or high toroidal field (cyclotron resonance outside the plasma) will investigate both diffraction and refraction effects, without absorption. Estimates of the fractional absorption of the beam in the initial experiments with the cyclotron resonance at the plasma axis have also been made. 4 refs., 3 figs.
Date: April 1, 1989
Creator: Byers, J.A.; Cohen, R.H.; Fenstermacher, M.E.; Hooper, E.B.; Meassick, S.; Rognlien, T.D. et al.
Partner: UNT Libraries Government Documents Department

High threshold HR (highly reflective) coatings at 1064 nm

Description: We have conducted as extensive series of laser damage measurements on highly reflective (HR) dielectric coatings which have yielded 1064-nm thresholds as high as 40 J/cm{sup 2} for 8- to 10-ns pulses at pulse-repetition frequencies (PRF) of 10 Hz. Moreover, by laser conditioning these coatings with subthreshold pulses, the thresholds of some coatings were raised to levels exceeding 70 J/cm{sup 2}. These are the highest threshold dielectric HR coatings that we have tested in this regime. The coatings were originally developed to produce HR-overcoated metal mirrors for free-electron-laser (FEL) applications at high PRF. Our tests included coatings deposited on both dielectric substrates and molybdenum (Mo) substrates. In each category we also examined coatings with a pre-coat of Mo between the substrate and the HR stack. The improved dielectric HR stacks effectively shielded the Mo from the laser irradiation so that the thresholds of virtually all Mo samples exceeded levels of the best dielectric-enhanced and dielectric-HR-coated metal mirrors we have tested to date. In addition to the low PRF measurements, we also conducted 1064-nm damage tests at 6-kHz PRF using 65-ns pulses from the Kilroy damage test facility. The coatings survived thermal loading of fluences ranging from 2 to 10 J/cm{sup 2} with respective small spot sizes on the order of 1.2 to 0.3 mm (1/e{sup 2} diameter). 6 refs., 3 figs.
Date: December 17, 1990
Creator: Rainer, F.; DeMarco, F.P.; Hunt, J.T.; Morgan, A.J. (Lawrence Livermore National Lab., CA (USA)); Mott, L.P.; Marcelja, F. et al.
Partner: UNT Libraries Government Documents Department

High-average-power millimeter-wave FEL (free-electron laser) for plasma heating using the ETA-II accelerator

Description: The Microwave Tokamak Experiment (MTX) is under construction at LLNL to investigate the feasibility of intense, pulsed microwave radiation for plasma heating on future ignition tokamaks. A high-average-power free-electron laser (FEL) will use the Experimental Test Accelerator (ETA-II), a linear induction accelerator, in combination with an advanced high-field wiggler, to produce 1-2 MW of power at 1-2-mm wavelengths for periods of up to 0.5s. The design of the FEL, termed the intense microwave prototype (IMP), is described, along with the status and major issues associated with the status and major issues associated with the experiment. 10 refs., 8 figs., 4 tabs.
Date: March 10, 1989
Creator: Throop, A.L.; Atkinson, D.P.; Clark, J.C.; Deis, G.A.; Jong, R.A.; Nexsen, W.E. et al.
Partner: UNT Libraries Government Documents Department

ECH on the MTX (Microwave Tokamak Experiment)

Description: The Microwave Tokamak Experiment (MTX) at LLNL is investigating the heating of high density Tokamak plasmas using an intense pulse FEL. Our first experiments, now beginning, will study the absorption and plasma heating of single FEL pulses (20 ns pulse length and peak power up to 2 GW) at a frequency of 140 GHz. A later phase of experiments also at 140 GHz will study FEL heating at 5 kHz rate for a pulse train up to 50 pulses (35 ns pulse length and peak power up to 4 GW). Future operations are planned at 250 GHz with an average power of 2 MW for a pulse train of 0.5 s. The microwave output of the FEL is transported quasi-optically to the tokamak through a window-less, evacuated pipe of 20 in. diameter, using a six mirror system. Computational modelling of the non-linear absorption for the MTX geometry predicts single-pass absorption of 40% at a density and temperature of 1.8 /times/ 10/sup 20/m/sup /minus/3/ and 1 keV, respectively. To measure plasma microwave absorption and backscatter, diagnostics are available to measure forward and reflected power (parallel wire grid beam-splitter and mirror directional couplers) and power transmitted through the plasma (segmented calorimeter and waveguide detector). Other fast diagnostics include ECE, Thompson scattering, soft x-rays, and fast magnetic probes. 8 refs., 2 figs.
Date: April 1, 1989
Creator: Stallard, B.W.; Byers, J.A.; Hooper, E.B.; Makowski, M.A.; Meassick, S.; Rice, B.W. et al.
Partner: UNT Libraries Government Documents Department

Economics of induction linac drivers for radiation sources

Description: Recent developments in high reliability components for linear induction accelerators (LIA) make possible the use of LIAs as large-scale, economical sources of radio-frequency (rf) power for many applications. One particularly attractive example of interest to high energy physicists is a ''two-beam accelerator'' version of a linear e/sup +/-e/sup -/ collider at TeV energies in which the LIA is configured as a monolithic relativistic klystron operating at 10 to 12 GHz. Another example of keen interest to the fusion community is the use of the LIA to drive a free-electron laser operating at 200 to 500 GHz for use in heating fusion plasma via electron resonance cyclotron heating. This paper briefly describes several potential uses of LIA radiation sources. It discusses the physical basis for scaling our present experience with LIAs to the operating characteristics applicable to large-scale sources of rf power and synchrotron radiation. 14 refs., 6 figs., 1 tab.
Date: June 15, 1987
Creator: Barletta, W.A.
Partner: UNT Libraries Government Documents Department

Simulation of a standing-wave free-electron laser

Description: The standing-wave free-electron laser (FEL) differs from a conventional linear-wiggler microwave FEL in using irises along the wiggler to form a series of standing-wave cavities and in reaccelerating the beam between cavities to maintain the average energy. The device has been proposed for use in a two-beam accelerator (TBA) because microwave power can be extracted more effectively than from a traveling-wave FEL. The standing-wave FEL is modeled in the continuum limit by a set of equations describing the coupling of a one-dimensional beam to a TE{sub 01} rectangular-waveguide mode. Analytic calculations and numerical simulations are used to determine the time variation of the reacceleration field and the prebunching required so that the final microwave energy is the same in all cavities. The microwave energy and phase are found to be insensitive to modest spreads in the beam energy and phase and to errors in the reacceleration field and the beam current, but the output phase appears sensitive to beam-energy errors and to timing jitter.
Date: September 1, 1990
Creator: Sharp, W.M. (Lawrence Livermore National Lab., CA (USA)); Sessler, A.M.; Whittum, D.H.; Wurtele, J.S. (Lawrence Berkeley Lab., CA (USA)); McDermott, D. & Luhmann, N. (California Univ., Los Angeles, CA (USA))
Partner: UNT Libraries Government Documents Department

Electron beam optics for the FEL experiment and IFEL experiment

Description: Electron beam transport system parameters for the FEL experiment and for the FEL experiment are given. The perturbation of the interaction region'' optics due to wiggler focussing is taken into account and a range of solutions are provided for relevant Twiss parameters in the FEL or IFEL region. Modifications of the transport optics in specific sections of the overall beam transport lines, for reasons of enhanced diagnostic capability or enhanced beam momentum analysis resolution, is also presented.
Date: January 1, 1990
Creator: van Steenbergen, A.
Partner: UNT Libraries Government Documents Department