R&D OF C-BAND PULSE COMPRESSION FOR SOFT X-RAY FEL

A compact Soft X-ray Free Electron Lasers facility is presently being constructed at SINAP, and 8 C-band accelerating structure unit are required for third-stage including 4 pulse compressors. The field mode of C-band SLED is TE0.1.15 with high quality factor Q, and the coupling coefficient is 8.5. Based on the design, the power pulse of klystron is compressed from 2.5μs to 0.5μs, and finally the power gain is about 3.1. In this paper, the details and simulation of 3-dB coupler, mode convertors and the resonant cavities are presented, meanwhile some cold test results of cavity are also analyzed at the end of this paper. INTRUDUCTION A compact soft X-ray Free Electron Laser facility is presently being constructed at shanghai institute of applied physics (SINAP), Chinese academy of science. This facility will be located to the shanghai synchrotron radiation facility which is a third generation light source in china. And it requires a compact linac with a high- gradient accelerating structure for a limited overall length less than 230m. The c-band technology is a good compromise for this compact facility and a c-and traveling-wave accelerating structure was already fabricated and tested at SINAP including a c-band pulse compression fir the cold mode measurerment. For it will enhance the peak RF power by expense of RF pulse length, so it will not increase the average power and at the same time reduce the total number of the klystron, it also increases the gradient of the accelerating structure, all of this have driven research in the c-band pulse compressor. And a SLED type RF compression scheme is proposed for the C-band RF system of the soft X-ray FEL and this scheme uses TE0.1.15 mode in the resonant cavity for high Q-value and high energy mutiplication. This scheme use TE0.1.15 mode in the storage cavity to compress an RF pulse into a short square high peak- power pulse for the course of R�¬ D study of the soft X- ray FEL. Figure 1 shows the schematic diagram. This scheme consists of one 3-db coupler, two mode convertors, and a pair of high-Q resonant cavities.