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Optical analysis of high power free electron laser resonators

Description: The first part of this paper briefly describes the optics code used at Los Alamos National Laboratory to do optical analyses of various components of a free electron laser. The body of the paper then discusses the recent results in modeling low frequency gratings and ripple on the surfaces of liquid-cooled mirrors. The ripple is caused by structural/thermal effects in the mirror surface due to heating by optical absorption in high power resonators. Of interest is how much ripple can be permitted before diffractive losses or optical mode distortions become unacceptable. Preliminary work is presented involving classical diffraction problems to support the ripple study. The limitations of the techniques are discussed and the results are compared to experimental results where available.
Date: January 1, 1987
Creator: Knapp, C.E.; Viswanathan, V.K.; Appert, Q.D.; Bender, S.C. & McVey, B.D.
Partner: UNT Libraries Government Documents Department

Storage ring design optimization for FEL operation

Description: An electron beam in a storage ring seems to be a perfect driver for a free electron laser. The understanding of storage rings is very well advanced to project designs with high peak current, small beam sizes and short damping times. Since the beam is recycled after passage through the optical cavity we can expect a relatively high overall efficiency. On the other hand, however the fact that we do want the beam to circulate and interact with the laser field every turn puts a limit on the allowable perturbation of the beam due to the laser field. This limits the peak laser power we can get from a storage ring beam. The main advantage of a storage ring for FEL operation therefore is realized for continuous high power laser generation. In this paper we discuss some of the limitations in storage ring beam parameter as they pertain to FEL operation. The interaction of a FEL field with the beam, however, is not discussed here.
Date: November 1, 1982
Creator: Wiedemann, H.
Partner: UNT Libraries Government Documents Department

Free-electron laser-fusion drivers for inertial-confinement fusion

Description: The use of tapered wiggler, free electron lasers as drivers for inertial confinement fusion requires an electron beam source which must meet specific and stringent requirements. The characteristics of ICF targets are combined with those of the free electron laser to obtain a general set of requirements and to define parameter tradeoffs. In particular, low beam emittance is essential to the system. A conceptual point design of an ICF-FEL driver is discussed.
Date: January 1, 1980
Creator: Schlitt, L.G.
Partner: UNT Libraries Government Documents Department

An alternative strategy for low specific power reactors to power interplanetary spacecraft, based on exploiting lasers and lunar resources

Description: A key requirement setting the minimum electric propulsion performance (specific power ..cap alpha../sub e/ = kW/sub e//kg) for manned missions to Mars is the maximum allowable radiation dose to the crew during the long transits between Earth and Mars. Penetrating galactic cosmic rays and secondary neutron showers give about 0.1-rem/day dose, which only massive shielding (e.g., a meter of concrete) can reduce significantly. With a humane allowance for cabin space, the shielding mass becomes so large that it prohibitively escalates the propellant consumption required for reasonable trip times. This paper covers various proposed methods for using reactor power to propel spacecraft. 7 refs., 6 figs., 1 tab.
Date: February 2, 1989
Creator: Logan, B.G.
Partner: UNT Libraries Government Documents Department

Robust rf control of accelerators

Description: The problem of controlling the variations in the rf power systems can be effectively cast as an application of modern control theory. Two components of this theory are obtaining a model and a feedback structure. The model inaccuracies influence the choice of a particular controller structure. One can design wither a variable, adaptive controller or a fixed, robust controller to achieve the desired objective. The adaptive control scheme usually results in very complex hardware; and therefore, shall not be pursued. In contrast, the robust control method leads to simplified hardware. However, robust control requires a more accurate mathematical model of the physical process than is required by adaptive control. Our research at the Los Alamos National Laboratory (LANL) and the University of New Mexico has led to the development and implementation of a new rf power feedback system. In this paper, we report on our research progress. In section one, the robust control problem for the rf power system and the philosophy adopted for the beginning phase of our research is presented. In section two, results of our proof-of-principle experiments are presented. In section three, we describe the actual controller configuration that is used in LANL FEL physics experiments. The novelty of our approach is that the control hardware is implemented directly in rf without demodulating, compensating, and then remodulating.
Date: January 1, 1990
Creator: Johnson, W.J.D. (Los Alamos National Lab., NM (USA)) & Abdallah, C.T. (New Mexico Univ., Albuquerque, NM (USA))
Partner: UNT Libraries Government Documents Department

Numerical determination of injector design for high beam quality

Description: The performance of a free electron laser strongly depends on the electron beam quality or brightness. The electron beam is transported into the free electron laser after it has been accelerated to the desired energy. Typically the maximum beam brightness produced by an accelerator is constrained by the beam brightness deliverd by the accelerator injector. Thus it is important to design the accelerator injector to yield the required electron beam brightness. The DPC (Darwin Particle Code) computer code has been written to numerically model accelerator injectors. DPC solves for the transport of a beam from emission through acceleration up to the full energy of the injector. The relativistic force equation is solved to determine particle orbits. Field equations are solved for self consistent electric and magnetic fields in the Darwin approximation. DPC has been used to investigate the beam quality consequences of A-K gap, accelerating stress, electrode configuration and axial magnetic field profile.
Date: October 15, 1985
Creator: Boyd, J.K.
Partner: UNT Libraries Government Documents Department

Cherenkov and transition radiation diagnostics for high energy free-electron lasers

Description: Electron Beam diagnostics based on imaging techniques using Cherenkov conversion screens and intensified video cameras should be adaptable to the developing high-energy free-electron lasers (FEL) driven by radio frequency powered linear accelerators. The high beam energies (60-150 MeV) and the peak currents (100s of amps) anticipated should also make optical transition radiation intensities sufficient for these techniques. The distinctive features of the two light generation mechanisms will be summarized and a few diagnostic examples will be cited.
Date: January 1, 1987
Creator: Lumpkin, A.H.
Partner: UNT Libraries Government Documents Department

Design requirements and calculated performance of an XUV FEL oscillator operating on a higher harmonic

Description: We study, using numerical simulation methods, the design requirements for the electron beam, wiggler, and optical resonator of an extreme-ultraviolet (XUV, 100 nm {ge} {lambda} {ge} 10 nm) free-electron laser oscillator operating on a higher harmonic. Our previous theoretical studies of an XUV FEL oscillator have assumed operation at the fundamental wavelength. Higher harmonic operation is attractive because the energy of the electrons can be reduced, thus reducing the cost of the linac. A further reduction in beam energy is possible with the use of short-period wigglers: in the present work, we use the expected properties of pulsed-wire wigglers. Operation of an FEL oscillator on the third harmonic has been experimentally demonstrated at Stanford University and Los Alamos, and this mode of operation may also be both possible and desirable for an XUV device. 12 refs., 2 tabs.
Date: January 1, 1990
Creator: Goldstein, J.C.; Warren, R.W. & Newnam, B.E.
Partner: UNT Libraries Government Documents Department

Subharmonic triple buncher for a high-efficiency free-electron laser

Description: A high-efficiency free-electron laser oscillator experiment is being constructed at Los Alamos National Laboratory. A buncher system has been designed to deliver 30-ps, 5-nC electron bunches to a 20-MeV standing-wave linac at the 60th subharmonic of the 1300-MHz accelerator frequency. The first 108.3-MHz buncher cavity accepts a 5-ns, 5-A peak current pulse from a triode gun. Following a 120-cm drift space, a second 108.3-MHz cavity is used, primarily to enhance the bunching of the trailing half of the bunch. A 1300-MHz cavity with 20-cm drift spaces at each end completes the beamline components. The bunching process continues into the linac's first three accelerating cells. Two thin iron-shielded lenses and seven large-diameter solenoids provide axial magnetic fields for radial focusing.
Date: January 1, 1983
Creator: Fraser, J.S.
Partner: UNT Libraries Government Documents Department

The Advanced Test Accelerator (ATA) experience

Description: On January 26, 1990 at 20:03:30, the Advanced Test Accelerator (ATA) was turned off with the shot counter reading 12,425,999. During the interval between 1985 and 1990 there were eight major experiments performed at ATA. Three of these experiments were for the Free Electron Laser program, and five were for the Charged Particle Beam (CPB) program. The five experiments were: Spring 1985 Propagation Experiment (April 1985), December 1985 20m Propagation Experiment (December 1985), Open Air Experiment (March--June 1987), Beam Transport Experiment (Spring 1988), and Multi Pulse Propagation Experiment (September 89--January 90). Several new technologies such as the rise time sharpener, the Beam Director, and the Fast Corrector Coil were also developed. Experiments for diagnostic development such as the transition radiation studies were also conducted. In this report the major experiments will be revisited; their highlights and shortcomings will be outlined. The current view on the understanding of lead pulse stability and CPB feasibility will be discussed.
Date: October 1, 1990
Creator: Chambers, F.W.
Partner: UNT Libraries Government Documents Department

Status of the Los Alamos Free-Electron Laser

Description: Since the initial oscillator experiments were completed last year, the Los Alamos FEL has undergone some major modifications and additions in preparation for the next set of experiments. The laser performance is projected to be substantially enhanced, the rf energy-recovery technique will be demonstrated, and FEL physics measurements will be expanded. The accelerator is now being tuned with very promising performance. The above experiments will be completed during the next year.
Date: January 1, 1985
Creator: Watson, J.M.
Partner: UNT Libraries Government Documents Department

Experimental characteristics of a high-gain free-electron laser amplifier operating at 8-mm and 2-mm wavelengths

Description: The Electron Laser Facility (ELF) at the Lawrence Livermore National Laboratory (LLNL) uses a high-current induction linac (3.5 MeV, 1000 A), in conjunction with a pulsed electromagnetic wiggler (4.0 M, 4000 G), to operate a free electron laser (FEL) that produces intense radiation in the microwave regime (2 to 8 mm). ELF is a high-gain, single-pass amplifier, using a commercial microwave source as an oscillator input (200 W-50 kW). Previous experiments at 35 GHz produced exponential gains of 40 dB/m, peak powers exceeding 1 GW, and beam-to-rf conversion efficiencies of 34%. Recent experiments at 140 GHz have demonstrated exponential gains of 22 dB/m, peak powers exceeding 50 MW, and total gains of 65 dB. In this paper, we describe the experimental results at these two frequencies and compare then with the predictions of simulation codes.
Date: June 8, 1987
Creator: Throop, A.L.; Orzechowski, T.J.; Anderson, B.R.; Chambers, F.W.; Clark, J.C.; Fawley, W.M. et al.
Partner: UNT Libraries Government Documents Department

Free electron lasers using stable-unstable ring resonators

Description: The free electron laser (FEL) simulation code FELEX is used to examine the operation of stable-unstable FEL resonators. These resonators are stable along one transverse axis and unstable along the orthogonal transverse axis. The simulations utilize a ring resonator with an intracavity focus in the unstable plane near the center of the wiggler (close to the same axial position as the waist in the stable plane) thereby enhancing the coupling between the optical and electron beams. Asymmetric output scraping is performed in the back leg of the ring using a reflective mirror inserted from one side of the unstable axis. Resonators with relatively low equivalent Fresnel number (/vert bar/N/sub eq//vert bar/ less than or equal to 10) and magnification (/vert bar/M/sub x//vert bar/ approx. = 1.2) are examined. Optical characteristics including the cavity mode profile at various positions inside the resonator are shown. 8 refs., 8 figs.
Date: January 1, 1989
Creator: Schmitt, M.J. & Paxton, A.H.
Partner: UNT Libraries Government Documents Department

Intensity-induced absorption in ZnSe

Description: In a particular sample of ZnSe, working at 10 ..mu..m, a nonlinear absorption was observed that was generated by light intensities greater than 100 MW/cm/sup 2/. This absorption was subsequently bleached by light intensities over 600 MW/cm/sup 2/. This result was obtained using 10-ps pulses from the Los Alamos National Laboratory Free-Electron Laser. 5 refs., 4 figs.
Date: January 1, 1988
Creator: Sollid, J.E.; Feldman, D.W.; Phipps, C.R. Jr. & Warren, R.W.
Partner: UNT Libraries Government Documents Department

Novel probe for determining the size and position of a relativistic electron beam

Description: In order to determine the size and position of a relativistic electron beam inside the wiggler magnetic field of a Free Electron Laser (FEL), we have developed a new probe which intercepts the electron beam on a high Z target and monitors the resulting bremsstrahlung radiation. The probe is designed to move along the entire three meters of the wiggler. This FEL is designed to operate in the microwave region (2 to 8 mm) and the interaction region is an oversized waveguide with a cross section 3 cm x 9.8 cm. The axial probe moves inside this waveguide. The probe stops the electron beam on a Tantalum target and the resulting x-rays are scattered in the forward direction. A scintillator behind the beam stop reacts to the x-rays and emits visible light in the region where the x-rays strike. An array of fiber optics behind the scintillator transmits the visible light to a Reticon camera system which images the visible pattern from the scintillator. Processing the optical image is done by digitizing and storing the image and/or recording the image on video tape. Resolution and performance of this probe will be discussed.
Date: July 23, 1984
Creator: Orzechowski, T.J.; Koehler, H.; Edwards, W.; Nelson, M. & Marshall, B.
Partner: UNT Libraries Government Documents Department

Analysis of undulator field errors for XUV FELs (extreme ultraviolet free electron lasers)

Description: This report discusses a number of magnetic field errors for extreme ultraviolet free electron lasers. Longitudinal coherence phase is one important parameter. For long undulators, beam wander is the important criterion; for segmented undulators with short segments, longitudinal coherence is the important criterion. An effective way to control files errors is shown to be segmentation of the undulator. Sample calculations are given. 10 refs., 13 figs., 1 tab. (JDH)
Date: January 1, 1987
Creator: Elliott, C.J. & McVey, B.D.
Partner: UNT Libraries Government Documents Department

XUV free-electron laser development at Los Alamos

Description: Free-electron lasers (FELs) for the vacuum-ultraviolet and soft x-ray spectral regions (together termed the XUV) are being designed at Los Alamos for integration into a future national UV/XUV FEL user facility for scientific experimentation. As proposed, this facility would consist of a sequence of up to 15 FEL oscillators and amplifiers, driven by a single, rf-linear accelerator, that will generate broadly tunable, picosecond-pulse, coherent radiation over the range from 1 to 400 nm. Below 300 nm, the peak- and average-power output of these FEL devices should surpass the capabilities of any existing, continuously tunable photon sources by many orders-of-magnitude. We describe the design parameters and predicted output of these FELs and make comparison with synchrotron radiation sources. Brief mention is given to our recent progress in developing the three primary components (electron beam, magnetic undulator, and resonator mirrors). 30 refs., 2 figs., 3 tabs.
Date: January 1, 1988
Creator: Newnam, B.E.
Partner: UNT Libraries Government Documents Department

Optical guiding in a free electron laser

Description: The coherent interaction between an optical wave and an electron beam in a free electron laser (FEL) is shown to be capable of optically guiding the light. The effect is analyzed using a two-dimensional approximation for the FEL equations, and using the properties of optical fibers. Results of two-dimensional (cylindrically symmetric) numerical simulations are presented, and found to agree reasonably well with the analytically derived criterion for guiding. Under proper conditions, the effect can be large and has important applications to short wavelength FEL's and to directing intense light.
Date: October 16, 1984
Creator: Scharlemann, E.T.; Sessler, A.M. & Wurtele, J.S.
Partner: UNT Libraries Government Documents Department

Proposed UV-FEL user facility at BNL

Description: The NSLS at Brookhaven National Laboratory is proposing the construction of a UV-FEL operating in the wavelength range from visible to 1000{angstrom}. Nano-Coulomb electron pulses will be generated at a laser photo-cathode RF gun at a repetition rate of 10 KHz. The 6 ps pulses will be accelerated to 250 MeV in a superconducting linac. The FEL consists of an exponential growth section followed by a tapered section. The amplifier input is a harmonic of a tunable visible laser generated either by nonlinear optical material or the non-linearity of the FEL itself. The FEL output in 10{sup {minus}4} bandwidth is 1 mJ per pulse, resulting in an average power of 10 watts. The availability of radiation with these characteristics would open up new opportunities in photochemistry, biology and non linear optics, as discussed in a recent workshop held at BNL. 10 refs., 4 figs., 1 tab.
Date: January 1, 1990
Creator: Ben-Zvi, I.; Di Mauro, L.F.; Krinsky, S.; White, M.G. & Yu, L.H.
Partner: UNT Libraries Government Documents Department

Use of a miniature Toroidal Grating Monochromator on the FEL Undulator at the NSLS

Description: The use of a miniature Toroidal Grating Monochromator is described which we intend to use to monochromatize the radiation from the free electron laser (FEL) Undulator at the NSLS. Some of the properties of Undulators are described with reference to the design of beamlines and review the properties of TGM's. The results of ray tracing a beamline using such a device and estimates of the expected flux are given.
Date: January 1, 1984
Creator: Johnson, P.D.; Hulbert, S.L. & Howells, M.R.
Partner: UNT Libraries Government Documents Department

Proposed extended tuning range for the Los Alamos mid-infrared adjustable, coherent light experiment (MIRACLE) Facility

Description: The Los Alamos Free-Electron Laser (FEL) Facility has been in operation as an oscillator in the 10..mu..m wavelength regime since 1983. Operations from 10 to 45..mu..m have been recently demonstrated which would provide a new applications capability: A Mid-Infrared Adjustable Coherent Light Experiment (MIRACLE) Facility. We propose to extend this tunability from 3 to 160..mu..m by upgrading the injector, accelerator, and resonator cavity. Potential applications in material science (high-temperature superconductors) and biophysics (DNA spectroscopy) for this wavelength regime are briefly addressed. 7 refs., 2 figs., 2 tabs.
Date: January 1, 1988
Creator: Lumpkin, A.H.; Feldman, D.W.; Warren, R.W.; Stein, W.E.; Watson, J.M.; Sollid, J.E. et al.
Partner: UNT Libraries Government Documents Department

The next generation of RF-FEL (Free-Electron Laser) diagnostics: Synchroscan and dual-sweep streak camera techniques

Description: Time-resolved experiments on rf-linac driven free-electron laser (FEL) experiments have recently been extended to displaying both the submicropulse and submacropulse effects. By using a synchroscan sweep on a streak camera key rf phase effects can be studied, and an additional dual sweep feature can provide this information during the macropulse. Successful measurements to date on the Los Alamos and Boeing FELs include electron-beam micropulse bunching during a macropulse, phase stability effects, micropulse elongation and transit time in a photoinjector, drive-laser phase stability, and FEL output evolution. Several of these measurements are the first of their kind on a FEL system 7 refs., 10 figs., 1 tab.
Date: January 1, 1990
Creator: Lumpkin, A.H.
Partner: UNT Libraries Government Documents Department

High-current-density, high brightness cathodes for free electron laser applications

Description: This report discusses the following topics: brightness and emittance of electron beams and cathodes; general requirements for cathodes in high brightness electron guns; candidate cathode types; plasma and field emission cathodes; true field emission cathodes; oxide cathodes; lanthanum hexaborides cathodes; laser driven thermionic cathodes; laser driven photocathodes; impregnated porous tungsten dispenser cathodes; and choice of best performing cathode types.
Date: June 1, 1987
Creator: Green, M.C. (Varian Associates, Palo Alto, CA (USA). Palo Alto Microwave Tube Div.)
Partner: UNT Libraries Government Documents Department

High-efficiency free-electron laser results

Description: Results obtained with a tapered-wiggler free-electron laser demonstrate the concepts proposed by Morton for enhanced efficiency and show deceleration of electrons by as much as 7%, and extraction of more than 3% of the total electron-beam energy as laser energy when the laser is operated as an amplifier. The experiment is presently being reconfigured to examine its performance as a laser oscillator.
Date: January 1, 1983
Creator: Boyer, K.; Baru, C.A.; Newnam, B.E.; Stein, W.E.; Warren, R.W.; Winston, J.G. et al.
Partner: UNT Libraries Government Documents Department