自由电子激光辐射频谱测量

文章描述了在环形电子束和实心电子束自由电子激光(FEL)研究中,测量辐射频谱使用的两种方法——波导色散线和带通滤波器谱仪。介绍了测量系统的组成和特点,给出了测量结果:环形束FEL试验。辐射频率在27—38GHz内可调:实心束FEL试验,辐射频谱带宽～1.2GHz。

RADIATION SPECTRUM MEASUREMENTS IN THE FREE ELECTRON LASERS

In this paper, two approaches of FEL spectral measurements are described. One is conducted by using a wave-guide dispersive line and the other by a band-pass filter spectrometer. The dispersive line system consists of a microwave horn, a standard rectangular wave-guide of 150m long, an attenuator, a crystal detector, and a probe to obtain a reference signal. In order to avoid electromagnetic disturbance, the probe is of a dually shielded construction. The bandpass filter spectrometer consists of many directional couplers, band-pass filters, attenuators and a common crystal detector. In fact it is a spectrometer of many channels and the configuration is elaborately designed. The signal of each channel is displayed on a fast oscillocope. Of course, the band-pass spectrometer can be operated with only one channel. In that case, spectral diagnoses are performed by placing different band-pass filters each time and the spectra must be assembled from successive shots. The resolution is determined by the band width of the band-pass filter. And so. good results of the measurments are obtained with many shots and band-filters with narrow band widths. We have performed two FEL experiments on the EPA-74 accelerator. The first experiment is operated in Raman regime using an annular beam (-1kA), which has a 4cm diameter and a thicknees of 1mm and propagates through a drift tube of 5.2cm I. D. . 28-38GHz radiation frequencies are measured by a wave-guide dispersive line with B1 from 5 to 8kGs. Bw from 0.6 to 0. 9kGs. and the electron energy Ee = 0. 5MeV.The second experiment is performed with a solid electron beam of 5mm diameter( 300A ). The beam propagates through a drift tube of 1.6 cm I. D.. In that case, we have observed radiation frequencies ranging from 25to33GHz. which are obtained by the band-pass filter spectrometer with B1=8kGs. Bw from 0.6 to 1kGs and Ee = 0. 6MeV.