FEL System Research Articles

Characteristics of the NIJI-IV FEL at the electron-beam energy of 263 MeV

Electron-beam qualities and characteristics of the FEL oscillation with the NIJI-IV FEL system were investigated at the low electron-beam energy of 263 MeV. The peak electron density at 263 MeV was suppressed due to instabilities in high electron-beam current, but it was about 40% higher than that at the normal electron-beam energy of 310 MeV below 4 mA. The maximum gain estimated from the measurements of the electron-beam qualities was about 1.5% at 4 mA. The measurement of the detuning curve suggests that the practical gain was about 0.8 times as low as the estimated value. Moreover, variation of the average FEL power versus the electron-beam current and the transverse profile was observed with a CCD camera system. The typical average power of the FEL was about 53 μ W at 3.2 mA and we were able to observe up to the TEM 03 mode.

NMR Studies of Drugs: Antipyrine and Analogs. I. Use of Achiral and Chiral Lanthanide Shift Reagents to Examine Hindered Rotation.

The 200 MHz 1H NMR spectra of the analgesic, antipyrine, 1, have been studied in CDC13 solution at ambient temperatures with the achiral lanthanide shift reagent (LSR) tris (6, 6, 7, 7, 8, 8, 8-heptafluoro-2, 2-dimethyl-3, 5-octanedionato) europium (III), Eu(FOD)3, 2, and with the chiral LSR, tris[3-(heptafluoropropylhydroxymethylene)-(+)-camphorato]europium(III), Eu(HFC)3, 3., Lanthanide-induced shift (LIS) magnitudes and broadening of selected signals are consistent with predominant LSR binding at the carbonyl oxygen with either 2 or 3. Of the different possible conformational regimes for the N-phenyl group of 1, our results appear to rule out a slow exchange limit (SEL) system with the N-phenyl coplanar with the heterocyclic ring. Perpendicular rings in an SEL regime can not be ruled out. A rapidly-rotating N-phenyl (fast exchange limit, FEL system) would also be consistent with observed results. Accurate chemical shifts for the aryl protons (overlapped in the 200 MHz spectrum of unshifted 1) are determined from spectra with added LSR by extrapolation to zero molar ratios of [LSR]:[1]. Relative slopes in the plots of chemical shift versus [LSR]:[1] molar ratios are calculated for each proton signal of 1.

Simulation study on efficiency enhancement of 10–140 GHz FEL with wiggler tapering and a prebunched e-beam

Efficiency enhancement with wiggler tapering and wiggler reductions with prebunching of e-beam in an induction linac-based FEL are assessed numerically in detail. The design of the wiggler with a prebunched beam is related to the upgrading of JAERI microwave FEL because it is crucial for the generation of extremely high-power RF pulse anticipated therein. Simulation studies to optimize the device parameters confirm that (1) an independent use of the prebunching is effective to reduce the rise distance of RF pulse along the wiggler, without significant enhancement of the saturation level, (2) wiggler tapering would lead to the extraction efficiency in energy as high as 50% when well optimized, and (3) the use of the optimized wiggler with the prebunched beam will realize a compact and high-power microwave FEL system. The tapering pattern depends on all of the FEL parameters and specifically on the initial distribution of the beam in phase space. The mechanisms involved such as the particle trapping in the ponderamotive potential well are discussed.

FEL system with the linear induction accelerator as the laser fusion reactor driver

An FEL based energy driver for inertial confinement fusion (ICF) is proposed. Construction of such a driver becomes possible due to application of a novel FEL amplifier scheme — a multi-channel, multi-stage FEL amplifier with a diaphragm focusing line. The driving beam for the FEL amplifier is generated by the linear induction accelerator. The laser system operates at the radiation wavelength of 0.5 μm with the total energy of laser flash of 1.5 MJ, pulse duration of 4 ns and repetition rate of 40 pulses/s. Total efficiency (i.e. conversion efficiency of net electrical power to the radiation power) of the proposed system is equal to 12%. The brightness of the output radiation is 10 22 W/cm 2 sr. The scale and the cost of the FEL based energy driver are close to those of the heavy ion fusion driver.

Gain enhancement for waveguide FEL systems using an optical klystron configuration

The application of an optical klystron configuration to waveguide free electron laser systems is proposed either as a gain enhancement scheme or as a way to reduce the beam current necessary for a given gain requirement. An analytical formulation is developed for these devices in the small signal regime. The feasibility of an optical klystron arrangement for FEL systems operating in the far infrared and submillimetre regions is studied. It is shown that with the excellent beam quality of electrostatic accelerators, the optical klystron scheme is an effective means to improve the small signal gain.

13 nm advanced SASE free electron laser with a quasi-stable optical klystron configuration

Abstract For soft X-ray projection lithography, we propose a 13 nm advanced SASE FEL with a quasi-stable optical klystron configuration. To shorten the wiggler length and decrease the overall size of the FEL system, we put forward the concept of quasi-stable operation of an asymmetric optical klystron. With a similar tolerance, our advanced SASE FEL can cut down the magnetic length of a single-pass SASE FEL from 37.12 to 20.3 m at the saturation power 42.8 MW (3D corrected), at the cost of an energy-modulated e-beam bunch and an adjustable dispersion magnet system. The detail analyses are based on the Pellegrini's scaling law and the one-dimensional FEL simulation code ILT1D.

Temporal and spectral evolution of a storage ring FEL source: experimental results on Super-ACO and new theoretical approach

Abstract Because of the complex interaction in a storage ring FEL system (SRFEL + storage ring), SRFELs show various phenomena. Conventional theoretical models, such as the super-modes model, can not treat the dynamic behavior of the SRFELs, or do not contain spectral effects. In this paper, a new simulation model is presented, which enables the study of temporal and spectral behavior of a SRFEL. Novel is that this model starts from the spontaneous emission spectrum, which is specially important for small gain FELs. The simulation results are compared with the experimental observations of the Super-ACO FEL. We have also used the simulation code to study the response of the laser to perturbation on the beam. These results provide meaningful aspects for designing new storage rings.

Gain measurements on a waveguide FEL amplifier with pre-bunched electron beam

Abstract A recently proposed theory suggests that a synchronous, pre-bunched electron beam should amplify radiation with a power gain which is inversely proportional to the square root of the input power. We have measured the power gain experimentally for a waveguide FEL system using a 1 mA nominal low-voltage (55.5 kV) electron beam, pre-bunched in a waveguide cavity. The gain in the wiggler has been observed as a function of the beam energy, beam current and wiggler waveguide input power; and good agreement with theory was obtained.

FEL based energy driver for inertial confinement fusion

An FEL based energy driver for inertial confinement fusion (ICF) is proposed. The key element of the scheme is a free electron laser system. Novel technical solutions reveal a possibility to construct the FEL system operating at a radiation wavelength λ = 0.5 μm and providing a flash energy E = 1 MJ and brightness 4 × 10 22 W cm −2sr −1 within the steering pulse duration 0.1–2 ns. The totalenergy efficiency of the proposed ICF energy driver is about 11% and repetition rate is 40 Hz. It is shown that the FEL based ICF energy driver may be constructed at the present level of accelerator technique R&D.

A computer model of the energy-current loss instabilities in a recirculating accelerator system

The computer program called ESRA (energy stability in a recirculating accelerator FELs) has been written to model bunches of particles in longitudinal phase space traversing a recirculating accelerator and the associated rf changes and aperture current losses. This code addresses stability issues and determines the transport, noise, feedback and other parameters for which these FEL systems are stable or unstable.A representative system is modeled, the Novosibirisk high power FEL race-track microtron for photochemical research. The system is stable with prudent choice of parameters.

Basic consideration on high power free-electron lasers

An FEL amplifier to generate a laser power of the order of TW at 4 μm wavelength is investigated for a γ-γ collider. A concept of an amplifier chain consisting of a phase-displacement deceleration FELs is proposed to increase the FEL efficiency and to mitigate the requirement for the beam energy spread. The feasibility of the driving linac for the FEL system is also discussed.

Electromagnetically pumped free-electron laser in the scheme of separate interaction space from pump wave generator

The theory of an electromagnetically pumped free-electron laser in the scheme of a separate interaction space from the pump wave generator is developed, taking into account the transverse inhomogeneity of incident and scattered waves, and the presence of a magnetic field of 20 kG focusing the particles. The nonlinear computation results, including the coupling coefficients, the excitation curves, powers and efficiency, etc., are obtained on a set of input parameters of our recently established accelerator and FEL system with a pulse high-current relativistic electron beam (600 kV, 3 kA, 70 ns). An experiment is demonstrated in which the relativistic backward wave corrugation oscillator provides a TM/sub 01/ pump wave with the power of 100 MW at 3 cm wavelength and connects with a smooth tube interaction section to produce stimulated scattering radiation with integral power of 1 MW at 38 mm wavelengths. Also, the numerical and the measured results are compared and discussed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

On a possibility to construct a high luminosity 2 × 5 GeV photon collider at SLC

Physical principles of operation of the high energy photon linear colliders (PLC) based on the Compton backscattering of laser photons on high energy electrons are discussed. The main emphasis is put on the analysis of a possibility to construct the PLC with the center of mass energy 3–10 GeV at the Stanford Linear Collider (SLC) facility. It is shown that it can be done with minor modifications of the existing facility by installation of new injector, kicker magnet and two-stage free electron laser. Proposed FEL system consists of a tunable FEL oscillator (λ ∼ 10–30 μm, output power ∼ 10 MW) with subsequent amplification of the master signal in a FEL amplifier up to the power ∼ 3 × 10 11W. The FEL parameters are optimized, restrictions on the electron beam and FEL magnetic system parameters are formulated and the ways of the possible technical realization are discussed. It is shown that the FEL based photon collider at SLC, providing luminosity of colliding γγ beams L γγ ∼ 10 34 cm −2 s −1, may be constructed at the present level of acceleration technique R&D. It will be a unique instrument for precision studying of the charmonium and bottomonium physics as well as τ-lepton physics providing ∼10 2 polarized τ-leptons per second. At the same time the photon linear collider at SLC will serve as a reliable test base for constructing the future TeV-range photon linear colliders.

FEL oscillation on TERAS

In the laser oscillation experiment on the storage ring TERAS, the improvement of the beam quality is quite important due to the extremely low gain of the TERAS FEL system. A second harmonic rf cavity (Landau cavity) is installed in TERAS to suppress the beam instability which degrades the beam quality. By observing the beam parameters, such as energy spread and transverse beam sizes systematically, it was proved that the Landau cavity is effective to improve the beam quality at a beam current less than ∼7 mA/bunch. A Q-switching experiment was carried out by changing the frequency (171.62 MHz) of the rf, fed to the main rf cavity, by 500 Hz with a modulation frequency of 2.2 Hz. The oscillation behavior was changed from a random-pulse manner, to a periodic oscillation and the peak power was increased by a factor of ∼5 with the Q-switching operation.

Development of a compact FEL system with a wide wavelength range

A compact FEL system is developed at ILT/ILE, Osaka, Japan. The wavelength range from mm to several μm in infrared and soft X-ray generation using a laser undulator is expected.

Optical modes in a partially waveguided cavity

The behavior of the optical beam in an FEL cavity is well understood in both the long- and short-wavelength limits. At long wavelengths the optical mode interacts strongly with the walls, which act as a waveguide. At short wavelengths the optical beam in an FEL is undisturbed by the walls; it propagates as a simple Gaussian. We are interested in the intermediate regime, where, as the wavelength increases, the optical mode grows and begins to feel the influence of the walls, causing the mode shape to distort and losses to occur. Using a Fox-Li technique to propagate in free space and a decomposition of the Gaussian beam into waveguide modes inside the undulator, we calculate the changes in mode shape and cavity losses as the wavelength increases. The resulting theory and numerical calculations are an important consideration for the design of mid- to far-infrared FEL systems.

Design and experiment of a far-infrared FEL

To design a FEL system, we have developed a three-dimensional simulation code including nonlinear effects such as interaction of electrons with laser fields. The code can calculate the motion of electrons and the variation of laser fields in a wiggler. It can simulate processes of bunching of electrons, and amplification and saturation of laser fields. This code, however, cannot include the effects of inhomogeneity of the wiggler field and beam misalignment. To estimate the gain reduction due to the above effects, we have also developed a linear simulation code based on Madey's theorem including the following effects: actual wiggler field, beam envelope, energy spread, and electron beam misalignment to the wiggler axis. The FEL system we have designed consists of a 20 MeV, 100 mA rf linac and a wiggler with 6 cm pitch, 28 periods and 2.5 kG peak field. The simulation results show that the FEL system has about 30% gain and several MW output power at 37 μm laser wavelength. Our FEL system has been completed and experiments have been started.

Evaluation of compact FELs operating at 0.4 micron wavelength

Microwiggler operation for proposed compact free electron laser devices are simulated to explore the wider use of harmonics in order to reach optical wavelengths with moderate-to-low electron beam energy. We show the gain degradation due to energy spread and strong field saturation effects to demonstrate the advantages of using harmonics in order to reduce size and complexity of FEL systems.

Self-mode-locked oscillator-amplifier FEL configuration

We propose a new method for achieving high output power from tunable FEL systems. In the master oscillator/power amplifier (MOPA) geometry the output power can be raised above the damage threshold of the oscillator optics. However, when a single electron beam is used, the electron beam quality is degraded by the oscillator interaction, lowering the extraction efficiency of the amplifier. When the positions of the oscillator and amplifier are reversed (the PAMO geometry) the amplifier uses a fresh electron beam, but one must find a way to ensure adequate gain in the oscillator. Our PAMO scheme uses the laser/electron beam interaction in the amplifier, along with a proper choice of the optical delay between oscillator and amplifier, to bring the oscillator-amplifier system into a self-mode-locked state. In this state the pulse trains from the oscillator and amplifier are synchronized so that both FEL sections use fresh electron pulses. We present a theoretical description of our PAMO scheme, describe our one-dimensional numerical simulations of its performance as a function of FEL operating conditions, and show that self-mode-locking can be achieved using existing FEL hardware.

140 GHz microwave FEL experiments using ELF-II

We describe the modeling, the experimental facility and the initial operating results for ELF-II, an induction-linac-based free-electron laser designed to produce up to 2 GW of peak power at 140 GHz ELF-II is the initial configuration of an FEL system which will eventually produce up to 2 MW of average power at a frequency of 250 GHz, for use in plasma heating experiments in the Microwave Tokamak Experiment.