Extending ok5 wiggler operational limit at duke fel/higs facility
Since 2007 the HIGS facility has been operated to produce both linearly and circularly polarized gamma-ray beams using two FELs, the planar OK-4 FEL and helical OK-5 FEL. Presently, with the OK-5 FEL operating at 192 nm, we can produce circularly-polarized gamma-ray beams between 1 and 100 MeV for user applications. Gamma-ray production between 80 and 100 MeV required an extension of the OK-5 wiggler operation beyond the designed current limit of 3.0 kA. In 2009, we upgraded cooling and machine protection systems to successfully extend OK-5 operation to 3.5 kA. To realize HIGS gamma-ray operation beyond 100 MeV and ultimately toward 150 MeV (the pion-threshold energy), with various limitations of the VUV mirror technology, the OK-5 wigglers will need to be operated at an even higher current, between 3.6 and 4.0 kA. In this paper we present our technical solution to further extend the operation range of the OK-5 wigglers, and report our preliminary results with high-current wiggler operation.
