Development of the JAERI FEL driven by a superconducting accelerator

A prototype for a quasi-CW, and high-average power free electron laser (FEL) driven by a 15 MeV superconducting RF linac has been developed, and constructed at Tokai, JAERI. Expected cryogenic (stand-by loss <3.5 W at 4.5 K) and accelerating fields´ performances (Eacc ~7 MV/m and Q~2×10⁺⁹) of four JAERI superconducting accelerator modules have been demonstrated, and installed them in the FEL accelerator vault. A beam test and commissioning of the JAERI superconducting RF linac as an FEL driver have been successfully performed to get an electron beam ranging from 10 to 20 MeV with nearly full transmision. FEL opticals and beam transport elements around the undulator, which have been already assembled, are now under commissioning. Spontaneous emission in the wavelength of 20 μm to 80 μm or longer has been observed by using the Ge(Cu) and Ge(Ga) detectors and fast current amplifier system