K.Yamada, N.Sei, H.Ohgaki, T.Mikado, T.Yamazaki(*)
Electrotechnical Laboratory (*)Kyoto University
Storage-ring FELs have substantial advantages, such as good coherence, good
focusability and easy synchronization with the synchrotron
radiation from bending magnets or other insertion devices, compared with
linac-based SASE FELs. This feature enables them to be
excellent tools for both excitation and measurement in photon-related physics
and chemistry. At the Electrotechnical laboratory,
efforts to shorten the FEL wavelength have been made using a compact storage
ring NIJI-IV. By improving the performance in both storage
ring and the cavity mirrors, the NIJI-IV FEL can cover the wavelength range
from 595 nm to 212 nm. Taking in to account the
state-of-the-art dielectric-mirror technology, we are aiming our tentative goal
for FEL lasing at 150 nm. The laser gain presently
obtained is insufficient to reach lasing below 200 nm, considering the rapid
reduction of the mirror reflectance through degradation of
dielectric multiplayer mirrors. To enhance the laser gain, we already
introduced a new RF system into the NIJI-IV to shorten the bunch
length and started to design low-impedance type ring vacuum chambers to
minimize anomalous bunch lengthening through longitudinal
microwave instability. Here we discuss about the lasing characteristics in the
UV - VUV expected on the NIJI-IV FEL system.
