N. Kikuzawa

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.

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.

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.

Control System Upgrade of JAERI ERL-FEL

Abstract The control system used for the JAERI ERL-FEL is a PC-based distributed control system that has been in operation since 1992. Since an interface bus of the PCs is peculiar, interface boards for the PCs are difficult to obtain in recent years. Thus we have been developing the CAMAC controller with μIJTRON operating system to replace the old PCs connected with CAMAC. We will introduce a Java and CORBA environment in the new control system. The control system upgrade, including hardware upgrading and applications rewriting, is described in this paper. PACScodes: 41.60.Cr, 07.05.Dz

Design and performance of the JAERI superconducting linac for high-power free-electron laser

A superconducting rf linac has been required to realize high-duty operation and low-electricity consumption for a high-average-power and high-efficiency free-electron laser (FEL). The JAERI FEL superconducting linac consists of a 250 kV electron gun, a subharmonic normal-conducting buncher (SHB) of 83.3 MHz, and two single-cell and two five-cell superconducting cavities of 499.8 MHz. The gun was typically operated around 200 kV to reduce space-charge effects. A combination of the SHB and the two single-cell cavities enabled a high-current beam of more than 10 A by utilizing a thermionic cathode and a grid pulser. The full width at half maximum bunch length and energy resolution were measured to be 22 ps and 1% or less, respectively. The measured results agreed with calculations utilizing the modified PARMELA code. This showed the validity of the linac design for the FEL. With this beam quality, high-average FEL power of 0.1 kW at a 24–28 μm wavelength was obtained in a quasi-cw mode.

Intense ultrashort pulse generation using the JAERI far-infrared free electron laser

An intense ultrashort optical pulse has been quasi-continuously generated using a superconducting RF linac-based free-electron laser at a wavelength of 22.5 μm. The pulse shape and width are measured by second-order optical autocorrelation with a birefringent Te crystal. At synchronism of the optical resonator, the pulse shape is a smooth single pulse with an FWHM width of 255 fs and energy of 74 μJ. A train of subpulses is developed by increasing the desynchronism of the optical resonator. The measured results are in good agreement with numerical simulation.

Development of an Optical Resonator with High-Efficient Output Coupler for the JAERI Far-Infrared Free-Electron Laser

An optical resonator with a high-efficient output coupler was developed for the JAERI far-infrared free- electron laser. The optical resonator is symmetrical near-concentric geometry with an insertable scraper output coupler. As a result of the development of the optical resonator, the JAERI-FEL has been successfully lased with averaged power over 1kW. Performance of the optical resonator with the output coupler was evaluated at optical wavelength of 22 μm by using an optical mode calculation code. The output coupling and diffractive loss with a dominant eigen-mode of the resonator were calculated using an iterative computation called Fox-Li procedure. An efficiency factor of the optical resonator was introduced for the evaluation of the optical resonator performance. The efficiency factor was derived by the amount of the output coupling and diffractive loss of the optical resonator. It was found that the optical resonator with the insertable scraper coupler was the most suitable to a high-power and high-efficient far-infrared free-electron laser.