M. Sawamura

First demonstration of energy-recovery operation in the JAERI superconducting linac for a high-power free-electron laser

An energy-recovery linac (ERL) for a high-power free-electron laser (FEL) has been designed and constructed at Japan Atomic Energy Research Institute (JAERI). The construction of the ERL was completed and first energy-recovery operation and first FEL lasing have been demonstrated. We present the design overview and the performance of the JAERI-ERL. Future plans towards a 10-kW FEL are also described.

Status of the JAERI FEL - beam test for injection system

Abstract The injection system of the JAERI superconducting linac for far infrared FEL oscillation was installed and commissioned. The characteristics of the electron beam measured, so far, are as follows: an electron beam of 100 mA with 4 ns bunch length was extracted from the gun at the accelerating voltage of 180–220 kV. The beam was compressed tentatively to less than 70 ps at the end of the transport line by preliminary operation of both the sub-harmonic buncher and the buncher.

Design of energy-recovery transport for the JAERI FEL driven by a superconducting linac

Abstract A high-average power free-electron laser driven by a superconducting linac has been developed in Japan Atomic Energy Research Institute (JAERI), and stable laser output over 0.1 kW in infrared region is now available. For further increasing of FEL output power, installing energy-recovery transport has been planned. The lattice design for the energy-recovery transport is discussed in the present paper. It is found that a recirculation transport, which fulfills the requirements for energy acceptance and isochronicity, can be realized by adding another triple-bend arc to the existing beam line.

Improved performance of the JAERI injection and free electron laser system

Abstract Several modifications have been made for the JAERI Free Electron Laser (FEL) system in order to extract greater average lasing power. The electron gun was improved to produce an electron beam with 1 ns pulse width, 600 mA peak current, amplitude fluctuation less than 1% and timing jitter less than 0.1 ns. In addition, the 180° bending arc was modified to match the beam envelope inside the undulator. After these modifications, we obtained an FEL power of 180 W in macro-pulse average at wavelength of 23 μm .

An optical resonator with insertable scraper output coupler for the JAERI far-infrared free-electron laser

Abstract The performance of an optical resonator featuring an insertable scraper output coupler was evaluated for the JAERI far-infrared free-electron laser. An efficiency factor of the resonator was introduced for evaluation. The efficiency factor was derived from the amount of the output coupling and diffractive loss of the optical resonator, which were calculated by using an optical mode calculation code, using the iterative computation called Fox–Li procedure. As a result of the evaluation, it was found that the insertable scraper coupler was the most suitable for the far-infrared free-electron lasers.Dependencies of insertion direction and scraper radius were also investigated to find out the optimum geometry of the insertable scraper coupler. It was found that the optimum direction of the scraper was parallel to the wiggling plane of the electron beam and the efficiency of the optical resonator increased with the enlargement of the scraper radius.

Performance of the undulator for JAERI FEL project

Abstract A newly designed hybrid undulator (DFTH-1), whose field termination parts are a novel implementation of the displacement-free termination scheme, has been constructed for the JAERI FEL project. The field termination part of the undulator was designed to minimize the electron trajectory walkoff by using the 3D magnetic field computational code named ELF/Magic. The DFTH-1 undulator could reduce the walkoff by one third of that of the conventional hybrid undulator with non-steering termination.

Status of the JAERI FEL system

Abstract An overview of the JAERI (Japan Atomic Energy Research Institute) FEL program and its status are described. Design and construction of the JAERI FEL system based on a superconducting linac are in progress, aiming at FEL oscillation in the 10–20 μm infrared wavelength region. A part of the vacuum system, a subharmonic buncher have been fabricated.

JAERI quasi-cw, and high-average power free electron laser driven by a superconducting rf linac

Abstract We have developed and constructed a prototype for a quasi-cw, and high-average power free electron laser driven by a superconducting rf linac at the Japan Atomic Energy Research Institute (JAERI), Tokai. We have successfully demonstrated expected performances of the JAERI 250 keV electron gun and bunching system, and completed an extension to an old 5.5 MV electrostatic accelerator building as an FEL accelerator vault in the 1991 Japanese fiscal year. All solid state rf amplifiers, liquid He refrigerators, a hybrid undulator and vacuum pumping stations are ready for use now. The first superconducting accelerator module is now under preparation for a cold rf test, and the other three modules are now under assembly. A description and the latest results of the JAERI superconducting rf linac FEL will be discussed, and reported in detail.

Design concept for the second phase project of the JAERI free electron laser facility

Abstract We present a conceptual design of the second phase project of the JAERI FEL facility. The FEL project is planned with the electron beam accelerated by low-frequency superconducting cavities to accomplish high average output laser power. While in the first phase the project the FEL wavelength is in far infrared region, in the second phase it is planned to ge in the near-infrared or shorter range.

Optical resonator matching for JAERI free electron laser

An optical resonator length of free electron lasers must be exactly matched with the frequency of the repeated electron beam from the accelerator driver so the incident electron beam can overlap with stored light pulses in the resonator. We made the exact resonator length matching by injecting ultrashort laser light pulses in the resonator as external clock signals. The external laser was a mode-locked Ti:Sapphire laser with 80 fs pulse width and synchronized with the accelerator clock signals. With the simultaneous use of a streak camera and a photo diode, we succeeded in making the quick matching within an accuracy of 1 μm or less in a direct and exact manner.