ENHANCEMENT OF HIGH-POWER MM WAVE RADIATION BY THE BEAM-PLASMA INSTABILITY IN A DIELECTRIC-LOADED WAVEGUIDE

1.理论分析(1)推导了强流单能线性相对论电子束(IREB)在有限磁场中等离子体填充介质衬里圆柱波导中激发波的色散关系。结果表明，除了可以在真空波导中激发的切伦科夫不稳定性和回旋切伦科夫不稳定性外，束流等离子体不稳定性也被激发。这些不稳定性是由于慢空间电荷波和慢回旋波在等离子体中与具有Trivelpich-Gould模的束流耦合所致。(2)数值分析了这些不稳定性的色散关系、导出频率和增长率。(3)当等离子体频率低于电子回旋频率时，由于等离子体的存在，切伦科夫不稳定性和回旋切伦科夫不稳定性的增长率没有增加。然而，当等离子体频率高于回旋频率时，两者在…中的增长率更多的不稳定性被提高，而且束-等离子体不稳定性的增长率也大大提高。(4)后一种不稳定性的增长率远远高于前者的增长率，我们可以期待基于这种机制的高功率宽频带辐射。实验(1)我们设计并制造了一个实验装置。等离子体是由注入到装置中的Ar气体与注入的IREB本身一起产生的。我们首先研究了IREB的传播，当Ar气压小于100mTorr时，观察到了电流放大现象。考虑到辐射测量的结果。我们认为这一现象是由束-等离子体不稳定性引起的。(2)我们观测到了宽带微波辐射。当Ar气压高于100mTorr时，总功率下降幅度较大。观测到的辐射光谱反映了整个不稳定性的贡献。这支持了Ar气压高于100mTorr时总功率的降低是由于束-等离子体不稳定性被抑制的观点。较少

1. THEORETICAL ANALYSIS(1) We derived a dispersion relation for waves excited by an intense monoenergetic linear relativistic electron beam (IREB) in a plasma-filled dielectric-lined cylindrical waveguide immersed in a finite magnetic field. Finding is that, in addition to the Cherenkov and cyclotron-Cherenkov instabilities which can be excited in a vacuum waveguide, the beam-plasma instabilities are also excited. These instabilities are due to coupling of slow space-charge waves and slow cyclotron waves on the beam with Trivelpiece-Gould modes in the plasma.(2) We analyzed numerically the dispersion relation and derived frequencies and growth rates of these instabilities.(3) When the plasma frequency is lower than the electron cyclotron frequency, enhancement of the growth rates of the Cherenkov and the cyclotron-Cherenkov instabilities due to presence of the plasma are not observed. However, when the plasma frequency is higher than the cyclotron frequency, the growth rates of both in … More stabilities are enhanced, and, moreover, the growth rates of the beam-plasma instabilities are also much enhanced.(4) The growth rates of the latter instabilities are much higher than the growth rates of the former instabilities and we can expect high-power radiation based on this mechanism with broad frequency band.2. EXPERIMENTS(1) We designed and manufactured an experimental device. A plasma was produced by ionizing argon gas introduced into the device with the injected IREB itself. We studied IREB propagation first, and observed current amplification phenomenon when the argon pressure was less than about 100 mTorr. Taking into account results of radiation measurement. we think that this phenomenon is caused by the beam-plasma instabilities.(2) We observed broadband microwave radiation. The total power decreased much for the argon pressure higher than about 100 mTorr. The spectrum of the observed radiation shows contribution from the whole instabilities. This supports the idea that decrease of the total power for the argon pressure above 100 mTorr is due to suppression of the beam-plasma instabilities. Less