Millimeter Wave ESR Using Gyrotron as a Light Source

在毫米波领域，光谱研究一直不是很活跃，这主要是由于缺乏可用的光源。本项目利用研制的等离子体加热诊断回旋管作为毫米波ESR的光源，为W、D两个波段的ESR光谱仪设计制造了一种小尺寸电子枪、高Q腔的回旋管。尽管发生了超导磁体低温恒温器漏气、超导磁体电源故障、高压变压器损坏等事故，但研制的回旋管在W、D两个可供ESR使用的频段产生了93.9 GHz~146.2 GHz的强辐射。一些振荡模式可以在可获得的低阴极电流下连续激发，达到100 mA。在毫米波区域，ESR主要是通过传输过程中的吸收来观察到的，但本系统使用法布里-珀罗谐振器来精确测量W和D波段的…更多。在初步实验中，用后向振荡器代替回旋管，在室温下观测了一些低维晶格反铁磁体的ESR谱，并以DPPH为参照谱。所得到的各向异性g因子的粉末花样与相同样品的X带谱相比具有很高的分辨率。在本光谱仪中，通过在铁电驱动器上施加交流调制电压来精细地调节法布里-珀罗谐振腔的镜面间距。将调制后的探测器的相干输出反馈到致动器的驱动器，以保持谐振器的共振状态，从而从获得的吸收光谱中排除色散分量。处理后的信号实时显示并记录在计算机内存中的软件已经准备就绪，以回旋管为光源的毫米波ESR装置即将完成。用该装置对回旋管高压变压器进行修复后，很快就能获得分辨率较好的W、D波段的ESR谱。较少

Spectroscopic studies have not been so active in millimeter wave region mainly due to the lack of available light sources. In this project, the gyrotron developed for the plasma heating and diagnosis was utilized as the light source of the millimeter wave ESR.A gyrotron with small size electron gun and high Q cavity was designed and manufactured for ESR spectrometer of W and D bands. In spite of many accidents such as air leakage of the cryostat for the superconducting magnet, trouble of the power supply of the superconducting magnet and damage of the high voltage transformer, the developed gyrotron was proved to yield strong radiation of 93.9GHz-146.2GHz in W and D bands available for ESR. Some modes of oscillation may be excited continuously with attainable low cathode current as much as lOOmA.ESR in millimeter wave region has been mostly observed by the absorption during transmission, but the present system utilizes Fabry-Perot resonator for the precise measurements in W and D bands … More . For the preliminary test, a backward oscillator, instead of gyrotron, was used to observe ESR spectra at room temperature of some low dimensional lattice antiferromagnets together with a reference spectrum of DPPH. The obtained powder patterns with anisotropic g-factors are highly resolved compared with X band spectra of the same specimens. In the present spectrometer, the mirror spacing of the Fabry-Perot resonator is adjusted finely by applying an AC modulated voltage to a ferroelectric actuator. The coherent output of the detector with the modulation is fed back to the driver of the actuator so as to maintain the resonance condition of the resonator to exclude the dispersion component from the obtained absorption spectra. The software to display the processed signal in real time and to record in the memory of computer is ready for use.Thus, the millimeter wave ESR apparatus with light source of a gyrotron is near the completion. With the apparatus well resolved ESR spectra in W and D bands will be soon obtained after the high voltage transformer of the gyrotron will be repaired. Less