| Paper |
Title |
Other Keywords |
Page |
| MOPPH016 |
Mode Couplings in a Raman Free-Electron-Laser with Ion-Channel Guiding
|
electron, space-charge, plasma, coupling |
75 |
| |
- B. Maraghechi, B. Maraghechi
IPM, Tehran
- T. Mohsenpour
AUT, Tehran
| |
The free-electron laser (FEL) theory in the collective or Raman regime relies on the unstable coupling between the radiation and the negative-energy space-charge wave. Due to the high density and low energy of electron beam a focusing mechanism like an axial magnetic field is usually required to guide the beam. We have shown in our previous study that, in addition to the above coupling that constitutes the regular FEL resonance, there are other unstable coupled-mode structures in the group II orbits. In the present analysis we are studying the mode-couplings when the electron beam is guided by an ion-channel. Using fluid model, a general dispersion relation of a FEL with a one-dimensional helical wiggler and an ion-channel guiding is derived. A numerical analysis of the general dispersion relation will be used to study interactions among all possible waves. In group II orbits, with relatively large wiggler induced velocities, new couplings between the negative and positive-energy space-charge waves as well as between the right and left circularly polarized electromagnetic waves are expected to be found. These instabilities are distinct from the usual FEL resonance.
|
|
|
|
| MOPPH020 |
Enhancement of a Coherent (Super Radiant) Emission in FEL by Means of Energy Modulation of an Emitting Short Electron Bunch
|
electron, radiation, simulation, electromagnetic-fields |
79 |
| |
- Yu. Lurie, Y. Pinhasi
CJS, Ariel
- A. Gover
University of Tel-Aviv, Faculty of Engineering, Tel-Aviv
| |
The developing techniques for generation of short bunches of relativistic electron beams enable construction of high-power, compact super-radiant free-electron lasers (FELs). Optimal efficiency of the super-radiant emission is achieved with ultra-short pulses (the beam duration is much less then the period of radiation). Unfortunately, the minimum duration of the pulse that can be achieved in practice is technologically limited, restricting the frequency of the radiation. We demonstrate that a super-radiant emission can be strongly enhanced by means of a proper energy modulation of the driving beam pulse, as suggested by A. Doria et al.*. In this way, a THz FEL source driven by short electron bunches generated by photo-cathode injection can be realized. Numerical simulations carried out using the WB3D code** show that linear energy modulation of a driving electron bunch enables one to increase the power of the super-radiant emission by a few orders of magnitude, approaching the power that can be achieved if ultra-short e-beam bunches are available. Possible limitations for the application of this method are also discussed, as well as the spectral purity of enhanced radiation.
* A. Doria et al., Phys. Rev. Lett. 80, 2841 (1998).** Y. Pinhasi, Yu. Lurie and A. Yahalom, Nucl. Instr. and Meth. in Phys. Res. A 475, 147 (2001).
|
|
|
|
| MOPPH044 |
Optical Beam Quality in Free-Electron Lasers
|
simulation, electron, laser, higher-order-mode |
134 |
| |
- P. Sprangle, J. Penano
NRL, Washington, DC
- H. Freund
SAIC, McLean
- B. Hafizi
Icarus Research, Inc., Bethesda, Maryland
| |
The quality of the FEL optical beam is an important consideration for many applications. The quantity M-squared is a single parameter that is used to quantify the higher-order transverse mode content of the beam. For steady state propagation in the paraxial limit, equations for the axial variation of the laser spot size and M-squared are derived. The quantity M-squared for the output of an FEL can also be determined by making measurements of the spot size at three locations and making use of the parabolic propagation law. We consider the optical beam quality for a MW-class amplifier. In this configuration the radiation is optically guided, maintaining a constant spot size through the wiggler, and is pinched at the wiggler exit. This leads to a relatively good optical beam quality, short growth length, short wiggler length, and good efficiency. Diffractive spreading of the FEL output beam can be sufficiently large to allow the first relay mirror to be close to the exit of the wiggler without exceeding the mirror damage intensity threshold, particularly in a grazing incidence configuration. The minimum distance to the relay mirror is shown to be inversely proportional to M-squared.
|
|
|
|
| TUAAU04 |
On the Design Implications of Incorporating an FEL in an ERL
|
electron, controls, laser, acceleration |
273 |
| |
- G. Neil, S. V. Benson, D. Douglas, P. Evtushenko, T. Powers
Jefferson Lab, Newport News, Virginia
| |
Encouraged by the successful operation of the JLab Demo in 1998, many high current ERLs are now being designed with not only short pulse synchrotron beamlines but also FELs. Such inclusion has major implications on magnet quality, rf feedback requirements, wiggler design, srf cavity QL, halo, etc. Measurements on the JLab ERL FEL have identified new challenges. The JLab Upgrade was designed with a 160 MeV beam of 10 mA in 75 MHz, 300 fs bunches. FEL designers set transverse emittance and longitudinal bunching, but to accommodate an FEL in our ERL also means setting stringent phase stability requirements of (<6x10-9/fm rms) based on a desired FEL detuning tolerance of 1.2 microns. Recovered beam RF loading on the subsequent accelerated beam complicates satisfying these requirements. Gain in the rf feedback limits the accuracy of energy stability when loaded Qs are ~107 . Energy recovery to <10 MeV sets magnetic field tolerances at 10-4. We present measurements on the JLab ERL showing how to set system requirements to tolerate such FEL lasing.
|
|
|
Slides
|
|
Talk
|
|
|
| TUPPH008 |
Harmonic Lasing Characterization at Jefferson Lab
|
laser, electron, simulation, free-electron-laser |
323 |
| |
- S. V. Benson, M. D. Shinn
Jefferson Lab, Newport News, Virginia
| |
Harmonic lasing is normally suppressed because of lasing at the fundamental wavelength. It can, however, be achieved by using any of several methods that suppress fundamental lasing. In this paper we discuss two methods used at Jefferson Lab. The first is to use the characteristics of dielectric coatings to allow harmonic lasing at cavity lengths longer than the synchronous length for the fundamental. The second is to use a dielectric coating that has little reflectivity at the fundamental. This allows us to directly compare fundamental and harmonic lasing with the same optical resonator and electron beam. We present measurement carried out at Jefferson Lab using the IR Upgrade FEL operating at 0.54, 0.93, 1.04, 1.6, and 2.8 microns in which both schemes are used to produce lasing at both the 3rd and 5th harmonic of the fundamental.
|
|
|
|
| TUPPH009 |
A Design Study of a FIR/THz-FEL for High Magnetic Field Research
|
radiation, linac, resonance, electron |
327 |
| |
- M. Tecimer, L. C. Brunel, J. van Tol
NHMFL, Tallahassee, Florida
- G. Neil
Jefferson Lab, Newport News, Virginia
| |
Presently a conceptual design work for a NIR-FIR FEL system at the NHMFL/FSU is being undertaken. The system is intended to combine high magnetic field research with an intense, tuneable photon source, spanning the spectral region ~2–1000 microns. Here, we present a design study involving the FIR/THz part of the NHMFL FEL design proposal. The suggested long-wavelength FEL encompasses in the first phase a thermionic injector (similar to that in use at the Forschungszentrum-Rossendorf ELBE facility) with a planned ~2 mA average current and a ~10 MeV superconducting rf linac module operating at 1.3 GHz. The broadband outcoupling over the envisaged FIR/THz spectral range (100–1100 microns) is accomplished by adopting a single (variable height slot) outcoupler in a waveguided cavity. Besides the performance predictions of the suggested long-wavelength FEL, techniques for the generation of high peak power, nanoseconds long THz pulses (for magnetic resonance applications) are also reported.
|
|
|
|
| TUPPH013 |
Electrodynamical Properties of a Volume Free Electron Laser with a ''Grid'' Resonator
|
lattice, electron, laser, free-electron-laser |
335 |
| |
- A. Gurinovich, V. G. Baryshevsky
Belarussian State University, Scientific Research Institute of Nuclear Problems, Minsk
| |
The electrodynamical properties of a crystal-like artificial periodic structure (a photonic crystal), formed by a periodic structure built from the metallic threads ("grid" volume resonator) is considered. Peculiarities of passing of electromagnetic waves with different polarizations through such a volume resonator are discussed. It is shown that the frequency spectrum of diffraction (Smith-Purcell) radiation is such a resonator appears splitted due to the complex anomalous Doppler effect. Specific features of a Volume Free Electron Laser (VFEL)*,** with a ''grid'' resonator for different frequency ranges are analyzed. Possibility of development of tunable radiation source in THz range is particularly discussed. The equations, which describe lasing of VFEL with a ''grid'' resonator (photonic crystal)***, are obtained. Estimation of the resonator durability to the heating by the electron beam is done.
* V. G.Baryshevsky, K. G. Batrakov, A. A. Gurinovich et al., NIM 483A (2002) 21. ** V. G. Baryshevsky, NIM A 445 (2000) 281. *** V. G. Baryshevsky et.al. LANL e-print archive: physics/0409125
|
|
|
|
| TUPPH018 |
New Resonator for the Israeli FEL
|
radiation, electron, coupling, controls |
349 |
| |
- A. Faingersh, J. Dadoun, Kh. Garb, A. Gover, Y. Socol
University of Tel-Aviv, Faculty of Engineering, Tel-Aviv
- G. G. Denisov, M. Y. Shmelyov
IAP/RAS, Nizhny Novgorod
- M. Einat, B. Kapilevich, B. Litvak, Y. Pinhasi, A. Yahalom
CJS, Ariel
| |
The Israeli FEL resonator was re-designed in order to reduce the overall round-trip losses and achieve control on the radiation output-coupling. In its new configuration, the resonator consists of overmoded corrugated rectangular waveguide and two radiation mode splitters, separating the high-energy e-beam from the laser radiation. The electron input splitter is based on Talbot effect in an overmoded rectangular waveguide. The radiation out-coupling is done in the output splitter. It is based on novel design and it combines Talbot effect between two parallel plates with free space propagation, and focusing by two curved cylindrical mirrors in a confocal imaging scheme. The waveguide and the splitters were tested experimentally, showing improved performance in comparison with the former resonator. The measured unloaded Q-factor of the new version is increased by a factor of ~ 3, attaining up to Q=30,000. Accordingly, the round-trip losses are ~15%. Rotating grids control the radiation out-coupling allowing wide variation for maximization of the radiation output power and extraction efficiency. The design layout and the testing results are presented.
|
|
|
|
| TUPPH028 |
The Research of FIR-FEL in CAEP
|
electron, gun, cathode, brightness |
386 |
| |
- X. Yang, X. Jin, M. Li, W. Li, Z. Xu
CAEP/IAE, Mianyang, Sichuan
| |
The research of FIR-FEL has been undertaken about 10 years in CAEP and first lasing at center wavelength 115·10-6 m was observed in March 2005. The facility consists of RF-gun, alpha magnet, L-band SW accelerator, beam transport line, wiggler, optical cavity and measurement system. At present, a high brightness photo cathode RF-gun is commissioning, the cathode material is Cs2Te. This injector will be used in the FIR-FEL project in the second half of this year. In this paper, the design consideration, the system layout, some experimental results are introduced.
|
|
|
|
| TUPPH032 |
Development of Powerful FEMs for X, Ka and W Bands for Physical and Industrial Applications
|
radiation, electron, controls, linac |
390 |
| |
- M. Einat
CJS, Ariel
- N. S. Ginzburg, N. Yu. Peskov, M. I. Petelin
IAP/RAS, Nizhny Novgorod
- A. Gover, Y. Socol
University of Tel-Aviv, Faculty of Engineering, Tel-Aviv
- A. Kaminsky, S. Sedykh
JINR, Dubna, Moscow Region
- J. Lucas
University of Liverpool, Liverpool
| |
FEMs are among the main sources of powerful microwave pulses from X to W-bands. Interest to such sources is caused by the large number of potential physical and industrial applications, requiring a wide variety of the radiation parameters. The new generation of the accelerators (SLAC, CERN) requires sources of ~100 MW pulse RF power at 30-38 GHz with a narrow spectrum. Material processing stations require kW-level average power. Alternatively, spectroscopic and biological experiments require lower power but for a specific frequency spectrum. The possibility to develop such sources is being studied at Tel-Aviv University, IAP RAS, JINR and The University of Liverpool within the framework of the INTAS collaboration project. Three successful FEM experiments have been carried out:- Electrostatic-accelerator driven 70-130 GHz Tandem-FEM with kW-level pulse power (Tel-Aviv University.)
- Linac-driven 30-GHz FEM-oscillator with pulse RF power of ~ 20 MW (JINR + IAP RAS)
- Sub-relativistic e-beam industrial FEM tunable over X-band with output power up 1 kW (The University of Liverpool).
The presentation summarizes the progress in the development of FEMs and their applications.
|
|
|
|
| TUPPH071 |
Simulation of Mirror Distortion in Free-Electron LASER Oscillators
|
simulation, electron, vacuum, emittance |
477 |
| |
- H. Freund
SAIC, McLean
- S. V. Benson, M. D. Shinn
Jefferson Lab, Newport News, Virginia
| |
Thermal distortion in cavity mirrors in high-power FELs can alter mode quality and degrade performance. Hence, it is important to be able to predict the character of the distortions to model their effect on FEL performance. To this end, we address these key issues by developing modeling and simulation tools that can accomplish these goals, and then benchmarking the simulation against observations on the 10 kW-Upgrade experiment at the Thomas Jefferson National Accelerator Facility. The modeling and simulation will rely on the MEDUSA code, which is a 3-D FEL simulation code capable of treating both amplifiers and oscillators in both the steady-state and time-dependent regimes. MEDUSA employs a Gaussian modal expansion, and treats oscillators by decomposing the modal representation at the exit of the wiggler into the vacuum Gaussian resonantor modes and then analytically propagating these modes through the resonator back to the entrance of the wiggler in synchronism with the next electron bunch. Knowledge of the power loading on the mirrors allows us to model the mode distortions using Zernicke polynomials and this technique has been incorporated into MEDUSA.
|
|
|
|
| THAAU03 |
A Scalloped Electron Beam Free-Electron Laser
|
electron, radiation, emittance, simulation |
509 |
| |
- D. C. Nguyen
LANL, Los Alamos, New Mexico
- W. B. Colson
NPS, Monterey, California
- H. Freund
SAIC, McLean
| |
Typical high-gain FEL amplifiers employ an electron beam that is matched to the wiggler so that the envelope remains constant throughout the wiggler. This paper describes a novel approach in which the electrons undergo natural betatron scalloping motion along the wiggler because the beams are deliberately mismatched at the wiggler entrance. We present an analysis of the electron scalloping motion and the FEL interaction with a scalloped electron beam. For a representative set of beam and wiggler parameters, we discuss the effect of the pinching the electron beams on the interaction in the FEL and on the focusing and propagation of the FEL radiation.
|
|
|
|
Slides
|
|
|
Talk
|
|
|
| THBAU04 |
Stair-Step Tapered Wiggler for High-Efficiency FEL
|
electron, extraction, simulation, synchrotron |
545 |
| |
- D. C. Nguyen
LANL, Los Alamos, New Mexico
- H. Freund
SAIC, McLean
| |
A new concept of a high-efficiency wiggler called the stair-step tapered wiggler is presented. The stair-step tapered wiggler differs from the traditional continuously tapered wigglers in that there are several uniform wiggler segments with decreasing wiggler periods (or decreasing Krms). Thanks to the relatively large ponderomotive potential in each segment, a substantial fraction of the electrons is captured while the electrons execute synchrotron motion down the energy scale. This leads to high FEL extraction efficiencies and partial optical guiding in the tapered wiggler sections. The stair-step tapered wiggler provides other advantages, such as ease of fabrication and flexibility in the taper rate. Numerical simulations using the code MEDUDA* will be presented to show the high-efficiency performance of a representative FEL with a stair-step tapered wiggler.
* H. P. Freund, S. G. Biedron, and S. V. Milton, IEEE J. Quantum Electron. 36, 275 (2000)
|
|
|
|
Slides
|
|
|
Talk
|
|
|
| THPPH040 |
Study on Focusing Property of New Type Wiggler and SASE-FEL Experiment at the ISIR, Osaka University
|
focusing, electron, radiation, permanent-magnet |
672 |
| |
- S. Kashiwagi, G. Isoyama, R. Kato
ISIR, Osaka
- H. Sasaki, K. Tsuchiya, S. Yamamoto
KEK, Ibaraki
| |
We have developed a new type of wiggler based on the edge-focusing wiggler for free electron laser (FEL) in the infrared region at the Institute of Scientific and Industrial Research (ISIR), Osaka University. The strong focusing (SF) scheme is adopted for the new wiggler in order to keep the beam size small along the wiggler. The period length of the wiggler is 60 mm, the number of periods is 32, and the total length is 1.938 m, including end magnet blocks for the orbit compensation. The wiggler consists of four FODO cells for double focusing. Focusing elements and defocusing elements are incorporate with single wiggler periods with edge angles of +5 and -5 degrees, respectively, and they are separated by three normal wiggler periods. The focusing properties of the SF wiggler for FEL and SASE are studied using a high-intensity electron beam at ISIR L-band linear accelerator. Optics parameters of electron beam are changed at the entrance of the SF wiggler, and the profiles of the electron beam are measured using screen monitors at several points along the wiggler. We will present the result of the beam experiments using the focusing wiggler in this conference.
|
|
|
|
| THPPH056 |
Initial Search for 9-keV XTR from a 28-GeV Beam at SPPS*
|
radiation, photon, background, diagnostics |
714 |
| |
- A. H. Lumpkin
ANL, Argonne, Illinois
- J. B. Hastings
SLAC, Menlo Park, California
- D. W. Rule
NSWC, West Bethesda, Maryland
| |
The potential to use x-ray transition radiation (XTR) as a beam diagnostic and coherent XTR (CXTR) as a gain diagnostic in an x-ray FEL was proposed previously. At that time we noted that the unique configuration of the SLAC Sub-picosecond Photon Source (SPPS) with its known x-ray wiggler source, a special three-element x-ray monochromator, x-ray transport line, and experimental end station with x-ray detectors made it an ideal location for an XTR feasibility experiment. A test of XTR intensity with respect to the x-rays emitted by the SPPS wiggler was proposed. The three-element monochromator was first adjusted to transport 9-keV or 1.3-Angstrom x rays from the SPPS wiggler source to the camera. The expected source strength in the bandpass of the monochromator was about 2x107 photons per 3 nC electron pulse, and our calculated XTR intensity was about 103 photons. We first successfully imaged the SPPS x-ray beam with the ANDOR x-ray CCD by using an Al-foil attenuation of 4x103. The wiggler gap was then opened, and x-ray images recorded with the Ti foils out for background evaluation and with the Ti foils inserted to search for XTR. Initial images will be presented.
|
|
|
|
| THPPH059 |
Energy Modulation of the Electrons by the Laser Field in the Wiggler Magnet: Analysis and Experiment
|
electron, laser, radiation, resonance |
725 |
| |
|
|