Electromagnetic Wiggler Research Articles

Generation of microwave free-electron laser radiation using sheet electron beam and planar electromagnetic wiggler

An experimental study of sheet electron beam propagation through a planar electromagnetic wiggler and generation of microwave radiation by free-electron laser action has been carried out. The space charge dominated sheet electron beam of energy /spl sim/100-200 keV, current 50-150 A, and pulsewidth of 100-150 ns was propagated through a 20-period planar electromagnetic wiggler. Significant enhancement in the beam transmission through the wiggler was observed as the wiggler magnetic field was increased, even though the operating regime of the beam is space charge dominated. Generation of microwave radiation in E-band (60-90 GHz) was also observed when the sheet electron beam is injected through the niggler in the presence of wiggler magnetic field.

Low-voltage infrared free-electron lasers based on gyrotron-powered RF wigglers

Designs are presented for infrared free-electron lasers (FEL's) with gyrotron-powered electromagnetic wigglers and relatively low voltage electron beams. The use of an electromagnetic wiggler formed by a quasi-optical gyrotron, where the radiation is coupled into a corrugated waveguide, has the potential for substantial increases of FEL gain compared to an open mirror system. Designs for proof-of-principle low-voltage infrared FEL experiments based on both radio-frequency (RF) linear accelerator and electrostatic accelerator technology are presented together with point designs for portable systems covering the infrared windows in the atmosphere.

Propagation of sheet electron beam through a planar, five-period electromagnetic wiggler

An experimental study on the propagation of a sheet electron beam of energy ∼200 keV, current ∼80–250 A, and pulse duration of ∼100–150 ns through a planar five-period electromagnetic wiggler has been carried out as a part of the development of a pulsed, high-power mm wave free-electron laser. Beam focusing is observed for peak wiggler magnetic fields up to 2.5 kG, and enhancements in propagated beam current efficiencies by 40%–65% are found for different values of the initial beam current.

First lasing, capabilities, and flexibility of FIREFLY

Abstract FIREFLY is a free electron laser (FEL) designed to produce picosecond pulses of intense light between 10 and 100 μm. It uses an inexpensive electromagnetic wiggler and variable outcoupling to provide maximum flexibility for user experiments. FIREFLY first lased on November 23, 1994, and has now operated successfully from 15 to 65 μm. It has lased in both a traditional undulator configuration and as an optical klystron, and has also operated in the undulator configuration on the third harmonic. During initial tests FIREFLY reached theoretical extraction efficiency for fundamental, third harmonic, and optical klystron operation, and demonstrated wavelength switching between adjacent peaks in the gain spectrum of an optical klystron for the first time.

Characterization of a novel elliptically polarized wiggler

We report on the initial characterization of an elliptically polarized wiggler built by a collaboration between the Advanced Photon Source, the Budker Institute of Nuclear Physics, and the National Synchrotron Light Source. The wiggler has recently been installed in the X13 straight section of the NSLS X-Ray ring. The device consists of a vertical permanent-magnet wiggler and a horizontal electromagnet wiggler. The electromagnets allow the wiggler to produce on-axis circularly polarized soft x-rays with the capability of AC modulation of the polarization. The maximum switching frequency that can be reached is 100 Hz. The degree of circular polarization of the radiation from the wiggler was characterized by making magnetic circular dichroism measurements using the X13A soft x-ray beamline. For a horizontal deflection parameter, K x, of 1.6, the dichroism effects at the Fe L 2,3 edges indicate a degree of circular polarization of approximately 75% using an aperture with a vertical acceptance of 87 μrad. Because both the left- and right-circularly polarized photons traverse identical paths through the beamline optical system, significantly smaller intensity fluctuations associated with switching of the polarization were observed than are typically possible at bending magnet beamlines. This, together with the relatively fast modulation rate, means that it will now be feasible to perform a variety of experiments that have not been possible using bending magnet sources.

Design of a far infrared FEL with an electromagnetic wiggler

Design of a far infrared FEL with an electromagnetic wiggler

High flux and high resolution beamline for elliptically polarized radiation in the vacuum ultraviolet and soft x-ray regions

A dedicated beamline with a broad energy range of photons and with high flux and a high degree of circular polarization has been designed for the ELETTRA storage ring. The beamline exploits the circularly polarized radiation produced by an electromagnetic elliptical wiggler and cover the (5–1200) eV photon energy range using a double-incidence spherical grating monochromator.

Plasma-loaded free-electron laser with an electromagnetic wave wiggler and axial guide field

A fluid model is used to study the effects of background plasma in an electromagnetically pumped free-electron laser with an axial guide field. The dispersion relation is derived, and the growth rate is formulated for the Raman regime. Numerical calculations are also carried out for both fast electromagnetic wave and whistler wigglers propagating opposite to the relativistic electron beam. In the case of a fast wave wiggler, the background plasma can enhance the growth rate considerably, and a much larger growth rate can be obtained around cyclotron resonance ωi∼Ω0, where ωi is the angular frequency of pump wave, and Ω0 represents the cyclotron frequency of the background plasma electrons. However, in the case of a whistler wiggler, the growth rate decreases rapidly as the plasma density increases, and a considerable decrease also occurs when ωi is near Ω0.

Chaotic electron trajectories in electromagnetic wiggler free-electron laser with a guide magnetic field

The Hamiltonian for an electron travelling through a large-amplitude backward electromagnetic wave, an axial guide magnetic field and radiation field is formulated. Poincare surface-of-section plots show that this Hamiltonian is non-integrable, and leads to chaotic trajectories. Equilibrium conditions are derived in the limit where the radiation field approaches zero. Compared to conventional FEL, the total energy of the system at pondermotive resonanceE c is large, while the electron's critical energyγ c is low for electromagnetic wiggler FEL. Moreover, the threshold wave amplitude (A r=A c) of beam chaoticity is found at lower values of the radiation field amplitude compared to magnetostatic wiggler FEL. Previous features confirmed that electromagnetic wiggler FEL can operate more coherently and more efficiently at moderated particle's energy compared to magnetostatic wiggler FEL.

Designs for an infrared free-electron laser based on gyrotron-powered electromagnetic wigglers

The possibility of developing gyrotron-powered electromagnetic wiggler free-electron laser (FEL) oscillators is of considerable interest for reducing the electron energy required for operation in the infrared spectrum. This paper considers the design of a 10.6 /spl mu/m electromagnetic wiggler FEL experiment based on the University of California at Santa Barbara (UCSB) 6 MeV electrostatic accelerator. Both waveguide and quasioptical wiggler resonator configurations are considered. A prescription for optimizing the gain of a waveguide electromagnetic wiggler FEL is derived and the nonlinear regime is treated by relating the electromagnetic wiggler FEL equations-of-motion to the universal normalized FEL equations. Point designs are given showing accelerator, gyrotron, and output parameters for 10.6 /spl mu/m Proof-of-Principle FEE experiments based on both waveguide gyrotron and quasioptical gyrotron wigglers. Designs are given for both a 5- and a 2-A FEL electron beam. >

Long-pulse, low-voltage infrared free-electron laser

Free-electron lasers (FEL's) have been developed as powerful IR sources at several sites around the world. This paper considers the design of a relatively compact, low-cost, tunable IR FEL based on a 3-MeV electrostatic accelerator and a submillimeter-wavelength electromagnetic wiggler. The system should be sufficiently portable for use in the field, and applications such as remote sensing and industrial processing are envisioned. The wiggler is powered by a second-harmonic quasioptical gyrotron. A prescription for optimizing the gain of an electromagnetic wiggler FEL is derived and the nonlinear regime is treated by relating the electromagnetic wiggler FEL to the universal normalized FEL equations. A point design is given showing accelerator, gyrotron, and output parameters for a system capable of operating over the entire 3-13-/spl mu/m wavelength atmospheric windows. A wide range of output characteristics is available. >

INFLUENCE OF UNTRAPPED ELECTRONS ON THE SIDE-BAND INSTABILITY OF ELECTROMAGNETIC WIGGLER FREE ELECTRON LASER

Influence of untrapped electrons on the sideband instability of electromagnetic Wiggler free electron laser (EM一FEL) is analyzed in detail with single-particle theory. The dispersion equation is derrived by applying the methode in Ref.[1]，and detailed discussions are carried out, some conclusions are drawn.

A tunability enhanced electromagnetic wiggler

This paper outlines a design technique for attaining much larger on-axis magnetic field tuning ranges in accurate, high magnetic field electromagnetic wigglers than have been heretofore possible. The general theory of “tunability enhancement” is described, followed by specific application to the magnetics design of the wiggler for the intense microwave prototype (IMP) free electron laser at the Lawrence Livermore National Laboratory.

A new method for measuring the magnetic field in a microwiggler based on magnetic tape recording

The new generation of FELs should be more compact than present designs. One important way to achieve this size reduction is to use microwigglers. Measurements and mapping of the magnetic field inside electromagnetic microwigglers is at present a difficult task because of the small dimensions of the microwiggler, the requirement for high spatial resolution in the measurement of the magnetic field, and the need to obtain a fast response since the field-producing pulse may be of short duration. We present a new method for quick measurement and mapping of the microwiggler field. Like the pulsed wire method [1,2], it gives in one measurement the magnetic field variation along the entire length of the electromagnetic wiggler. In addition it is possible to also measure, instantaneously, the distribution of the magnetic field across the lateral dimension of the wiggler. Our method is based on the use of a magnetic recording tape which is inserted into the gap of the electromagnetic microwiggler. The maximum local magnetic field produced during the driving-current pulse is recorded on the tape at all axial and lateral positions. The tape containing the recorded magnetic field can then be read (and “heard”) by an ordinary tape recorder.

New results and applications for the quasioptical gyrotron*

The quasioptical gyrotron (QOG), which features an open resonator formed by a pair of spherical mirrors instead of the conventional gyrotron waveguide cavity, has been under development at the U. S. Naval Research Laboratory as a tunable high power millimeter-wave source for tokamak plasma heating, advanced radars, and power beaming. Results have recently been obtained for a quasioptical gyroklystron (QOGK) realized by the addition of an open-mirror prebunching resonator driven by an 85 GHz, 1.5 kW extended interaction oscillator. Efficiency enhancement by mode priming has been investigated, and efficiencies up to 19% have been obtained by increasing the frequency detuning of the operating mode. An overall efficiency of 30% was obtained by the addition of a simple depressed collector. Phase-locked operation was demonstrated at a power of 57 kW and efficiency of 16%. The high circulating power in the QOG resonator is currently being considered for use as an electromagnetic wiggler for compact infrared free-electron lasers. The QOG is also promising as a source for an active sensor of upper atmosphere trace impurities.

A cryogenic cw electromagnetic wiggler

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

A magnetic circuit model for electromagnet wigglers

A simple analytical model of electromagnetic wigglers for free electron lasers has been derived from a magnetic circuit transmission line. The model can deal with the problems of leakage from core to core, the effects of size and position of the exciting coils, and takes account of the finite permeability of the magnet iron. The onset of saturation effects can be predicted.

INEX simulations of the optical performance of the AFEL

Abstract The AFEL (advanced free-electron laser) Project at Los Alamos National Laboratory is presently under construction. The project's goal is to produce a very high brightness electron beam which will be generated by a photocathode injector and a 20 MeV rf linac. Initial laser experiments will be performed with a 1 cm period permanent magnet wiggler which will generate intense optical radiation near a wavelength of 3.7 μm. Future experiments will operate with “slotted-tube” electromagnetic wigglers (formerly called “pulsed-wire” wigglers). Experiments at both fundamental and higher harmonic wavelengths are planned. This paper presents results of INEX (integrated numerical experiment) simulations of the optical performance of the AFEL. These simulations use the electron micropulse produced by the accelerator/beam transport code PARMELA in the 3-D FEL simulation code FELEX.

A magnetic circuit model for electromagnet wigglers

A simple analytical model of electromagnet wigglers for free electron lasers has been derived from a magnetic circuit transmission line. The model can deal with the problems of leakage from core to core, the effects of size and position of the exciting coils, and takes account of the finite permeability of the magnet iron. The onset of saturation effects can be predicted.

FEL design using the CEBAF linac

Abstract The applicability of the high quality, continuous electron beam from the CEBAF accelerator to free electron laser (FEL) research and photon production has been examined. A simple electromagnetic wiggler utilizing the output of the CEBAF injector (modified to include a new, continuous pulse train, high brightness photoemission gun) would produce output powers of ∼ 1 kW CW in the 45-20 μm wavelength range. With a similar 6 cm wavelength EM wiggler of twice the length with a 400 MeV beam from the North Linac comparable laser output could be achieved at wavelengths around 200 nm. Analysis to date includes conceptual design optimization and more detailed modeling of the optimized parameter space. Program plans as well as designs for the two FELs are presented.