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Free electron laser physical process code (FELPPC)

Description: 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, 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.
Date: February 1, 1995
Creator: Thode, L. E.; Chan, K. C. D. & Schmitt, M. J.
Partner: UNT Libraries Government Documents Department

High power free-electron laser concepts and problems

Description: Free-electron lasers (FELs) have long been thought to offer the potential of high average power operation. That potential exists because of several unique properties of FELs, such as the removal of ``waste heat`` at the velocity of light, the ``laser medium`` (the electron beam) is impervious to damage by very high optical intensitites, and the technology of generating very high average power relativistic electron beams. In particular, if one can build a laser with a power extraction efficiency 11 which is driven by an electron beam of average Power P{sub EB}, one expects a laser output power of P{sub L} = {eta} P{sub EB}. One approach to FEL devices with large values of {eta} (in excess of 10 %) is to use a ``tapered`` (or nonuniform) wiggler. This approach was followed at several laboratories during the FEL development Program for the Strategic Defense Initiative (SDI) project. In this paper, we review some concepts and technical requirements for high-power tapered-wiggler FELs driven by radio-frequency linear accelerators (rf-linacs) which were developed during the SDI project. Contributions from three quite different technologies - rf-accelerators, optics, and magnets - are needed to construct and operate an FEL oscillator. The particular requirements on these technologies for a high-power FEL were far beyond the state of the art in those areas when the SDI project started, so significant advances had to be made before a working device could be constructed. Many of those requirements were not clearly understood when the project started, but were developed during the course of the experimental and theoretical research for the project. This information can be useful in planning future high-power FEL projects.
Date: March 1, 1995
Creator: Goldstein, J. C.
Partner: UNT Libraries Government Documents Department

Achromatic and isochronous electron beam transport for tunable free electron lasers

Description: We have continued the study of a suitable electron beam transport line, which is both isochronous and achromatic, for the free electron laser being designed at Lawrence Berkeley Laboratory. A refined version of the beam transport optics is discussed that accommodates two different modes of FEL wavelength tuning. For the fine tuning involving a small change of the electron beam energy, sextupoles are added to cancel the leading nonlinear dispersion. For the main tuning involving the change of the undulator gap, a practical solution of maintaining the beam matching condition is presented. Calculation of the higher order aberrations is facilitated by a newly developed code. 11 refs., 4 figs., 3 tabs.
Date: September 1, 1991
Creator: Bengtsson, J. & Kim, K. J.
Partner: UNT Libraries Government Documents Department

Coherent pair creation as a positron source for linear colliders

Description: We propose a positron source for future linear colliders which uses the mechanism of coherent pair creation process from the collision of a high energy electron beam and a monochromatic photon beam. We show that there is a sharp spike in the pair-produced positron energy spectrum at an energy much lower than the primary beam energy. The transverse emittance is ``damped``, yielding final positrons with lower normalized emittance than the initial electrons. Numerical examples invoking conventional lasers and Free Electron Lasers (FEL) for the photon beams are considered.
Date: November 1, 1992
Creator: Chen, P. & Palmer, R. B.
Partner: UNT Libraries Government Documents Department

Inverse free-electron laser accelerator development

Description: The study of the Inverse Free-Electron Laser, as a potential mode of electron acceleration, has been pursued at Brookhaven National Laboratory for a number of years. More recent studies focused on the development of a low energy (few GeV), high gradient, multistage linear accelerator. The authors are presently designing a short accelerator module which will make use of the 50 MeV linac beam and high power (2 {times} 10{sup 11} W) CO{sub 2} laser beam of the Accelerator Test Facility (ATF) at the Center for Accelerator Physics (CAP), Brookhaven National Laboratory. These elements will be used in conjunction with a fast excitation (300 {mu}sec pulse duration) variable period wiggler, to carry out an accelerator demonstration stage experiment.
Date: June 1, 1994
Creator: Fisher, A.; Gallardo, J.; Steenbergen, A. van; Sandweiss, J. & Fang, J. M.
Partner: UNT Libraries Government Documents Department

An analysis of the saturation of a high gain FEL

Description: We study the saturated state of an untapered free electron laser in the Compton regime, arising after exponential amplification of an initial low level of radiation by an initially monoenergetic, unbunched electron beam. The saturated state of the FEL is described by oscillations about an equilibrium state. Using the two invariants of the motion, and certain assumptions motivated by computer simulations, we provide approximate analytic descriptions of the radiation field and electron distribution in the saturation regime. We first consider a one-dimensional approximation, and later extend our approach to treat an electron beam of finite radial extent. Of note is a result on the radiated power in the case of an electron beam with small radius.
Date: December 1, 1992
Creator: Gluckstern, R. L.; Okamoto, Hiromi & Krinsky, S.
Partner: UNT Libraries Government Documents Department

Field profile and loading measurements on higher order modes in a two cell 500 MHz superconducting structure

Description: The Infrared Free Electron Laser, being designed at LBL as part of the Chemical Dynamics Research Laboratory, is based on a 500 MHz superconducting linac driver that consists of five 4-cell structures of the CERN/DESY type. A 500 MHz, 2-cell version of this structure is being used in a joint Stanford/LBL/BNL program to study accelerator issues relevant to the FEL applications. As part of this study, field profile and loading measurements of higher order modes have been made on the prototype structure.
Date: August 1, 1992
Creator: Barry, W.; Edighoffer, J.; Chattopadhyay, S. & Fornaca, S.
Partner: UNT Libraries Government Documents Department

Undulators for short wavelength FEL amplifiers

Description: Issues critical to the design of undulators for use in short wavelength FEL amplifiers, such as attainable on-axis field strength, device compactness, field quality, required magnetic gap, and strong focusing schemes, are discussed. The relative strength of various undulator technologies, including pure permanent magnet, hybrid, warm electromagnetic, pulsed, and superconducting electromagnetic devices in both helical and planar configurations are reviewed. Favored design options for proposed short wavelength FELs, such as the Linac Coherent Light Source at SLAC and the DUV Free-Electron Laser at BNL, are presented.
Date: August 1, 1994
Creator: Schlueter, R.
Partner: UNT Libraries Government Documents Department

Laser field assisted photoemission using femtosecond laser pulses

Description: Photoemission from Cu mirror at a laser fluence of 10{sup 11} W/cm{sup 2}, 300 fs, pulse is investigated for various angles of incidence, intensities and polarizations. Electron emission is enhanced by {approximately} 20 from s to p polarization and by 4 on changing the angle of incidence from 0 to 73 degree.
Date: November 1, 1992
Creator: Srinivasan-Rao, T.; Fischer, J. & Tsang, T.
Partner: UNT Libraries Government Documents Department

Finite pulse effects in self-amplified-spontaneous emission

Description: The authors study the effects of the electron density profile on self-amplified-spontaneous-emission (SASE). A general formalism in the linear regime is developed by deriving the coupled Maxwell-Klimontovich equations for an arbitrary density profile and including the effects of the energy spread, diffraction, and the betatron oscillation. An explicit solution is obtained for the one-dimensional (1-D) case. The temporal and the spectral intensity profiles of SASE depend linearly on the initial electron correlation function. The correlation function consists of two terms, a term giving rise to the usual spontaneous radiation and its amplification to SASE, and a term representing the coherent bunched beam effect. The latter term has been neglected so far in the treatments of SASE, but it could be significant when there is a variation in the electron density at a length scale comparable to the wavelength. The theory reproduces the well-known results when the electron density is uniform. It also reproduces a recent theory for a finite top-hat density profile and a vanishing energy spread.
Date: September 1, 1994
Creator: Kim, Kwang-Je & Hahn, Sang June
Partner: UNT Libraries Government Documents Department

Ultraviolet free-electron laser (uv FEL) facility at Brookhaven National Laboratory

Description: The proposal for a Ultraviolet Free-Electron Laser Facility UV-FEL grew from the realization that neither existing lasers or synchrotrons, nor the third generation synchrotron radiation sources now under construction address all of the needs of scientists interested in the ultraviolet region of the spectrum, particularly with respect to the combination of continuous wavelength selection, high peak power and short pulse duration. Several workshops have been held at BNL and elsewhere which explored applications and source requirements in the 5 to 30 eV range. A critical requirement determined was is for very high peak power and short wavelength, especially for applications in chemical physics and non-linear optics. The need for wavelength tuning with the ease and agility to which synchrotron radiation users have become accustomed has also been strongly emphasized. With these initial parameters in mind, the accelerator physics staff set about devising ways to produce this radiation. Their design is for an FEL that has unique characteristics both in terms of possible applications, and in the range of radiation it could produce. In addition, the proposed location of the UV-FEL adjacent to the NSLS means that pump-probe experiments involving radiation from both sources will be possible. Each successive design has been reviewed in consultation with potential users in an iterative process to arrive at the present proposal design.
Date: December 31, 1992
Creator: Johnson, E. D. & Sutherland, J. C.
Partner: UNT Libraries Government Documents Department

An inverse free electron laser accelerator experiment

Description: A free electron laser was configured as an autoaccelerator to test the principle of accelerating electrons by stimulated absorption of radiation ({lambda} = 1.65mm) by an electron beam (750kV) traversing an undulator. Radiation is produced in the first section of a constant period undulator (1{sub w1} = 1.43cm) and then absorbed ({approximately} 40%) in a second undulator, having a tapered period (1{sub w2} = 1.8 {minus} 2.25cm), which results in the acceleration of a subgroup ({approximately} 9%) of electrons to {approximately} 1MeV.
Date: December 31, 1992
Creator: Wernick, I. & Marshall, T. C.
Partner: UNT Libraries Government Documents Department

Particle dynamics in a wave with variable amplitude. Progress report

Description: Our past research efforts led to the derivation of the adiabatic invariant in spatially varying accelerator structures, to the calculation of the loss of the invariant due to trapping, and to a method for determining transverse invariants using a nonperturbative approach to the Hamilton-Jacobi equation. These research efforts resulted in the training of two graduate students who are now working in the area of accelerator physics.
Date: January 1, 1992
Creator: Cary, J. R.
Partner: UNT Libraries Government Documents Department

Performance and upgrades of the NSLS storage rings and photon sources

Description: The usefulness of synchrotron radiation sources is not only determined by current, energy and magnetic field but also orbit stability and lifetime. The status and developments at NSLS in storage ring performance are discussed. Efforts at NSLS to look toward the future in source development are presented. In particular, small gap undulator development and studies toward development of UV Free Electron Laser at the Accelerator Test Facility are described. 5 refs., 2 figs., 1 tab.
Date: December 31, 1991
Partner: UNT Libraries Government Documents Department

Report from the NSLS workshop: Sources and applications of high intensity uv-vuv light

Description: A workshop was held to evaluate sources and applications of high intensity, ultra violet (UV) radiation for biological, chemical, and materials sciences. The proposed sources are a UV free electron laser (FEL) driven by a high brightness linac and undulators in long, straight sections of a specially designed low energy (400 MeV) storage ring. These two distinct types of sources will provide a broad range of scientific opportunities that were discussed in detail during the workshop.
Date: December 31, 1990
Creator: Johnson, E. D. & Hastings, J. B.
Partner: UNT Libraries Government Documents Department

Proposed ultraviolet free-electron laser at Brookhaven National Laboratory: A source for time-resolved biochemical spectroscopy

Description: Brookhaven National Laboratory is designing an ultraviolet free- electron laser (UV-FEL) user facility that will provide pico-second and sub-picosecond pulses of coherent ultraviolet radiation for wavelengths from 300 to 75 nm. Pulse width will be variable from abut 7 ps to {approx} 200 fs, with repetition rates as high as 10{sup 4} Hz, single pulse energies > 1 mJ and hence peak pulse power >200 MW and average beam power > 10 W. The facility will be capable of ``pump-probe`` experiments utilizing the FEL radiation with: (1) synchronized auxiliary lasers, (2) a second, independently tunable FEL beam, or (3) broad-spectrum, high-intensity x-rays from the adjacent National Synchrotron Light Source. The UV-FEL consists of a high repetition rate recirculating superconducting linear accelerator which feeds pulses of electrons to two magnetic wigglers. Within these two devices, photons from tunable ``conventional`` laser would be frequency multiplied and amplified. By synchronously tuning the seed laser and modulating the energy of the electron beam, tuning of as much as 60% in wavelength is possible between alternating pulses supplied to different experimental stations, with Fourier transform limited resolution. Thus, up to four independent experiments may operate at one time, each with independent control of the wavelength and pulse duration. The UV-FEL will make possible new avenues of inquiry in time studies of diverse field including chemical, surface, and solid state physics, biology and materials science. The experimental area is scheduled to include a station dedicated to biological research. The complement of experimental and support facilities required by the biology station will be determined by the interests of the user community. 7 refs., 5 figs.
Date: February 1, 1992
Creator: Johnson, E. D.; Sutherland, J. C. & Laws, W. R.
Partner: UNT Libraries Government Documents Department

Adaptive optimization and control using neural networks

Description: Recent work has demonstrated the ability of neural-network-based controllers to optimize and control machines with complex, non-linear, relatively unknown control spaces. We present a brief overview of neural networks via a taxonomy illustrating some capabilities of different kinds of neural networks. We present some successful control examples, particularly the optimization and control of a small-angle negative ion source.
Date: October 22, 1993
Creator: Mead, W. C.; Brown, S. K.; Jones, R. D.; Bowling, P. S. & Barnes, C. W.
Partner: UNT Libraries Government Documents Department

Two-gigawatt burst-mode operation of the intense microwave prototype (IMP) free-electron laser (FEL) for the microwave tokamak experiment (MTX)

Description: The MTX explored the plasma heating effects of 140 GHz microwaves from both Gyrotrons and from the IMP FEL wiggler. The Gyrotron was long pulse length (0.5 seconds maximum) and the FEL produced short-pulse length, high-peak power, single and burst modes of 140 GHZ microwaves. Full-power operations of the IMP FEL wiggler were commenced in April of 1992 and continued into October of 1992. The Experimental Test Accelerator H (ETA-II) provided a 50-nanosecond, 6-MeV, 2--3 kAmp electron beam that was introduced co-linear into the IMP FEL with a 140 GHz Gyrotron master oscillator (MO). The FEL was able to amplify the MO signal from approximately 7 kW to peaks consistently in the range of 1--2 GW. This microwave pulse was transmitted into the MTX and allowed the exploration of the linear and non-linear effects of short pulse, intense power in the MTX plasma. Single pulses were used to explore and gain operating experience in the parameter space of the IMP FEL, and finally evaluate transmission and absorption in the MTX. Single-pulse operations were repeatable. After the MTX was shut down burst-mode operations were successful at 2 kHz. This paper will describe the IMP FEL, Microwave Transmission System to MTX, the diagnostics used for calorimetric measurements, and the operations of the entire Microwave system. A discussion of correlated and uncorrelated errors that affect FEL performance will be made Linear and non-linear absorption data of the microwaves in the MTX plasma will be presented.
Date: October 6, 1993
Creator: Felker, B.; Allen, S. & Bell, H.
Partner: UNT Libraries Government Documents Department

Photoemission using femtosecond laser pulses

Description: Successful operation of short wavelength FEL requires an electron bunch of current >100 A and normalized emittance < 1 mm-mrad. Recent experiments show that RF guns with photocathodes as the electron source may be the ideal candidate for achieving these parameters. To reduce the emittance growth due to space charge and RF dynamics effects, the gun may have to operate at high field gradient (hence at high RF frequency) and a spot size small compared to the aperture. This may necessitate the laser pulse duration to be in the subpicosecond regime to reduce the energy spread. We will present the behavior of metal photocathodes upon irradiation with femtosecond laser beams, comparison of linear and nonlinear photoemission, and scalability to high currents. Theoretical estimate of the intrinsic emittance at the photocathode in the presence of the anomalous heating of the electrons, and the tolerance on the surface roughness of the cathode material will be discussed.
Date: October 1, 1991
Creator: Srinivasan-Rao, T.; Tsang, T. & Fischer, J.
Partner: UNT Libraries Government Documents Department

Analysis of a high brightness photo electron beam with self field and wake field effects

Description: High brightness sources are the basic ingredients in the new accelerator developments such as Free-Electron Laser experiments. The effects of the interactions between the highly charged particles and the fields in the accelerating structure, e.g. R.F., Space charge and Wake fields can be detrimental to the beam and the experiments. We present and discuss the formulation used, some simulation and results for the Brookhaven National Laboratory high brightness beam that illustrates effects of the accelerating field, space charge forces (e.g. due to self field of the bunch), and the wake field (e.g. arising from the interaction of the cavity surface and the self field of the bunch).
Date: December 31, 1991
Creator: Parsa, Z.
Partner: UNT Libraries Government Documents Department

40-{angstrom} FEL designs for the PEP storage ring

Description: We explore the use of the 2.2-km PEP storage ring at SLAC to drive a 40-{Angstrom} free-electron laser in the self-amplified spontaneous emission configuration. Various combinations for electron-beam and undulator parameters, as well as special undulator designs, are discussed. Saturation and high peak, in-band, coherent power (460 MW) are possible with a 67-m, hybrid permanent-magnet undulator in a ring bypass. A 100-m, cusp-field undulator can achieve high average, in-band, coherent power (0.25 W) in the main ring. The existing, 25.6-m, Paladin undulator at LLNL, with the addition of optical-klystron dispersive sections, is considered for both peak and average power. 35 refs., 4 figs., 1 tab.
Date: December 31, 1991
Creator: Fisher, A. S.; Gallardo, J. C.; Nuhn, H. D.; Tatchyn, R.; Winick, H. & Pellegrini, C.
Partner: UNT Libraries Government Documents Department

Towards short wavelengths FELs workshop

Description: This workshop was caged because of the growing perception in the FEL source community that recent advances have made it possible to extend FEL operation to wavelengths about two orders of magnitude shorter than the 240 nm that has been achieved to date. In addition short wavelength FELs offer the possibilities of extremely high peak power (several gigawatts) and very short pulses (of the order of 100 fs). Several groups in the USA are developing plans for such short wavelength FEL facilities. However, reviewers of these plans have pointed out that it would be highly desirable to first carry out proof-of-principle experiments at longer wavelengths to increase confidence that the shorter wavelength devices will indeed perform as calculated. The need for such experiments has now been broadly accepted by the FEL community. Such experiments were the main focus of this workshop as described in the following objectives distributed to attendees: (1) Define measurements needed to gain confidence that short wavelength FELs will perform as calculated. (2) List possible hardware that could be used to carry out these measurements in the near term. (3) Define a prioritized FEL physics experimental program and suggested timetable. (4) Form collaborative teams to carry out this program.
Date: December 1, 1993
Creator: Ben-Zvi, I. & Winick, H.
Partner: UNT Libraries Government Documents Department

Scientific opportunities for FEL amplifier based VUV and X-ray research

Description: It has become increasingly clear to a wide cross section of the synchrotron radiation research community that FELs will be the cornerstone of Fourth Generation Radiation Sources. Through the coherent generation of radiation, they provide as much as 12 orders of magnitude increase in peak power over the third generation storage ring machines of today. Facilities have been proposed which will extend the operating wavelength of these devices well beyond the reach of existing solid state laser technology. In addition, it appears possible to generate pulses of unprecedented brevity, down to a few femtoseconds, with mJ pulse energies. The combination of these attributes has stimulated considerable interest in short wavelength FELs for experiments in chemical, surface, and solid state physics, biology and materials science. This paper provides a brief overview of how the features of these FEL`s relate to the experimental opportunities.
Date: December 31, 1994
Creator: Johnson, E. D.
Partner: UNT Libraries Government Documents Department