R. Nagai

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.

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.

Potential applications of high-Tc superconductors to FEL accelerator components

Abstract After the discovery of the new metal-oxide superconductivity with higher onset temperatures in late 1986, a feasibility study for superconductor devices (cavity resonator, transmission line, antenna, magnetic shield, focusing lens and so on) as FEL accelerator components was started at JAERI Tokai in March 1987. The present status of the feasibility study will be discussed.

Study of HOM Instability of the JAERI ERL-FEL

Abstract The free-electron laser (FEL) linac has been modified to the energy recovery linac (ERL) at the Japan Atomic Energy Research Institute (JAERI) to achieve the higher power FEL of the next stage of 5-10kW. We review transverse instabilities and present experimental data on transverse beam breakup (BBU) obtained at the JAERI ERL-FEL. We compare measurement with simulation.