K. Imasaki

Development of a compact high brightness X-ray source

Abstract Based on the concept of interacting electron with intense light stored in a supercavity, a compact and high brightness soft X-ray source has been proposed for lithography at ILT/ILE. For the purpose of enhancing the collision frequency of electron-photon beams, the idea of a combination of a supercavity pumped by a cw diode laser with an electrostatic dc accelerator has been put forward, for which a high average spectral brightness of 1.79×10 17 with a wavelength of 9.8 A, and a bandwidth of 0.17% can be expected. Two other upgraded systems for the production of high peak brightness X-ray radiation and high brightness γ-ray radiation have also been proposed, which are based on an ultrahigh power laser (2 TW, 5 ps) and a compact electron storage ring (300 MeV/89.3 mA). Meanwhile, the prototype laser undulator system and the current experiments on photon storage in a Fabry-Perot cavity pumped by a high power mode-locked Nd:YAG laser (25 MW, 89.25 MHz) are introduced.

Development of a modified wiggler for higher harmonic lasing of a free-electron laser

Abstract A modified wiggler, with enhanced harmonic fields, was developed for free-electron laser higher harmonic lasing. The harmonic wiggler field was produced by arranging high-permeability shims in the gap spacing of a four-block-per-period Halbach design wiggler. By this method, the 3rd harmonic wiggler field exceeded 18% of the fundamental field. The phasing of the harmonic field could be also controlled by the positioning of the shims.

A new FEL concept driven by a vacuum microfielf emitter

Abstract In order to reduce the scale and construction cost of free election lasers, it is necessary to investigate various new ideas with respect to electron beam generation, acceleration and radiation mechanism. In this paper, a microscale free electron laser is proposed which is driven by a very small diameter (less than a few μm) electron beam. The microscopic electron beam can be generated with a needle cathode, for an example, a Spindt cathode. By injecting the microscopic electron beam into a microdielectric channel, we generate radiations of several μm wavelength by Cherenkov emission, Smith-Purcell emission and so on. In the design of a microfield emitter FEL (MFE FEL). It is shown that a 2 mm long dielectric pipe with an electron beam of diameter 1 μm and with a current of 50 μA gives a one pass gain of 50% for a 10 μm wavelength radiation.

FEL experiment of the 5th harmonic generation with a modified wiggler

Abstract To enhance the FEL harmonic gain, we have developed a wiggler having a harmonic wiggler field. The modified wiggler consists of a conventional planar wiggler and high-permeability shims. Because of this simpleness, we can develop a wiggler having various types of modified fields, easily and economically. We show the design basis of the modified wiggler and examples of them which contain one harmonic field. Then, we introduce the FEL experiment of the 5th harmonic generation with a modified wiggler.

Compact high-brightness radiation sources

Abstract The feasibility of compact radiation sources using photon storage technology is discussed. Compact high-brightness radiation sources with photon energies from keV to more than 10 MeV can be realized by this method. These compact radiation sources will meet the requirements of applicatioins in lithography, angiography, fission product annihilation, intense positron source and so on.

Electrostatic microwiggler FEL

Abstract We propose here a new type of microwiggler in which a transverse electric field is applied to a relativistic electron beam. Not only the electrostatic wiggler works as a magnetic wiggler, but also the periodically arranged electrodes interact with the electron beam as a Smith-Purcell radiator. Inside the wiggler region, these radiations are multiply diffracted by the periodic structure, to constitute standing waves, to modulate and to bunch the beam.

Distributed feedback and gas-loaded FELs driven by induction linac SHVS

Abstract The induction linac SHVS at ILE, Osaka University, delivers a high current electron beam of 1.5–4.5 MeV energy to drive millimeter and submillimeter free electron lasers. In this article, we review the previous distributed feedback (DFB) FEL experiments and present a theoretical analysis of the output radiation spectrum. In the experiment, both the DFB and the wiggler were of a helical configuration. By employing the DFB structure, the output spectral intensity increases by factors of 3 ∼ 5 for radiation which satisfies the Bragg reflection condition. Future FEL experiments at ILE are also discussed, in which effects of the DFB and gas loading are investigated. These schemes are expected to make output spectra shorter and narrower and increase the gain. Furthermore, the numerical analysis of these FELs is presented in order to clarify the above-mentioned effects.

A 100 MW far-infrared free-electron laser driven by a 180 MeV RF-linac

Abstract The development of a 100xa0MW far-infrared free-electron laser oscillator is reported. By using a 180xa0MeV electron beam, this system will provide the high power and the rapid scanning of the broad wavelength range, 10–100xa0μm, to enhance the user programs. The intracavity power of several GWs will be used for Compton backscattering X- or γ-ray generation. To store such an intense radiation, the dynamics of the FEL oscillator with a coupling parameter μ c ⩽1, which is defined as the ratio of the slippage distance and the electron bunch length, was investigated experimentally on the operating mid-infrared system.

POP experiments of the photon-e-beam interaction in the supercavity

Abstract Use of the supercavity for photon storage had been proposed to enhance the interaction between lasers and e-beams (Compton scattering). To demonstrate the feasibility of this technology, proof-of-principle (POP) experiments are in progress. A supercavity with ∼99.99% reflectivity mirrors has been constructed to confine the LD-pumped Nd:YAG laser light. The confined photons will be used to interact with 100 kV CW electron beams. It is expected that the interaction will be enhanced by 10 4 times, resulting in a scattered photon flux as much as 2 × 10 7 photons s −1 rad −1 at the wavelength λ ∼ 0.4 μm.

Simulation of radiation build-up in an FEL oscillator: the effect of the electron beam micropulse shape

Abstract Using a one-dimensional multi-frequency simulation code, we have investigated how the radiation build-up time in an FEL oscillator depends upon the electron beam micropulse width and micropulse shape. From the simulation, it is found that in the Gaussian electron beam case when the electron beam micropulse width is shorter than the radiation wavelength, the radiation in the cavity builds up faster than in longer cases (because of the coherent spontaneous emission). But in the square electron beam pulse case, the spontaneous emission at the edge is much stronger than in the case of a Gaussian electron beam pulse, so the effect of coherent spontaneous emission is reduced. The radiation spectral intensity and temporal profiles have been evaluated for super Gaussian pulse shapes of a bunched electron beam.