Experimental Observation of Cyclotron Superradiance from an Intense Relativistic Electron Beam.

利用4级自加速技术，将宽度为10 ns、能量为0.55 MeV的强流相对论电子束注入均匀磁场中的圆柱形波导，获得了宽度为1 ns、能量为1.1 MeV的超短脉冲高功率电子束。当电磁波群速度与束流电子速度一致时，观察到较窄频谱的强辐射微波，而束宽为10 ns时，微波频谱出现多个剩余峰。粒子模拟程序KARAT也表明束宽对辐射谱有影响，束流电子与电磁波相互作用的漂移管长度也会发生变化。辐射微波的输出功率随着1 ns和10 ns的光束呈指数增长。1ns光束的微波输出功率比10ns光束的微波输出功率增加得快。然而，在40厘米的长度饱和。经过60cm的传输，1ns光束的输出功率比10ns光束的输出功率大10倍，表明实验中观察到了回旋超辐射。应研究输出功率对束流的依赖关系。

An ultrashort pulsed high power electron beam with width of 1 ns and energy of 1.1 MeV was obtained from an intense relativistic electron beam with width of 10 ns and energy of 0.55 MeV using 4-stage autoacceleration.The ultrashort pulsed electron beam with width of 1 ns was injected into a cylindrical waveguide immersed in a uniform magnetic field. Intense radiated microwaves with narrow frequency spectrum were observed when the group velocity of the electromagnetic wave coincided with the beam electron velocity, while, the microwave spectrum with the beam with width of 10 ns showed many surplus peaks. The particle simulation code KARAT also indicated that the beam width affected the radiation spectrum.The length of the drift tubes where the beam electrons interacted with the electromagnetic waves was changes. The output power of the radiated microwave increased exponentially with 1 ns and 10 ns beams. The output power of the microwave from 1 ns beam increased more rapidly than that from 10 ns beam. However, that saturated at the length of 40 cm. After 60 cm propagation, the output power from the 1 ns beam was 10 times larger than that from 10 ns beam.These results suggest that the cyclotron superradiance was observed in the experiment. The dependence of the output power on the beam current should be investigated.