P roduction of an intense, high quality submillimeter wave probe-beam and its application to plasma scattering measurements

准光传输线的设计基于354 GHz的回旋管输出，以实现等离子体散射。该系统由准光天线和椭圆镜组成，准光天线用于将输出转换为线偏振光束，椭圆镜用于准直光束。尽管产生的束流形状与计算结果不同，但产生的束流大小(58 mm*55 mm)与计算结果(42 mm*67 mm)基本一致。我们已在美国国家核聚变科学研究所用这种强流束流研究了致密螺旋系统(CHS)等离子体中等离子体散射引起的低频密度涨落。在上谱中发现了一个约150 kHz的峰值。虽然由等离子体参数推导出的电子漂移波的频率从100 kHz变化到300 kHz，但观测到的峰值频率没有变化。这表明峰值不仅仅是由于电子漂移波。高频回旋管在亚毫米波长(f=302 GHz)提供中等的连续波输出(P=20W)。时间分辨频率测量表明，连续波输出的频率起伏电平在2 MHz以内。CW输出的频率由主体的电势调制来调制。120V的峰峰值可以产生29 MHz的调频。

The design of the quasi-optical transmission line was based on gyrotron output at 354 GHz in order to carry out plasma scattering. This system consists of a quasi-optical antenna to convert the output into an linearly-polarized beam and an elliptical mirror to collimate the beam. Although the beam shape of the beam produced is different from that of calculated result, the size of the beam produced (58mm*55mm) is in broad agreement with that of the calculated result (42mm*67mm).We have used this intense beam to study low frequency density fluctuations by plasma scattering in Compact Helical System (CHS) plasmas at the National Institute for Fusion Science. A peak is found around 150 kHz in the upper spectrum. Although the frequency of the electron drift waves deduced from the plasma parameters changed from 100 kHz to 300 kHz, the observed peak frequency did not change. This suggests that the peak is not merely due to the electron drift waves.A high frequency gyrotron delivers moderate cw outputs (P=20W) at submillimeter wavelengths (f=302GHz). Time resolved frequency measurements show that the frequency fluctuation levels of the cw outputs are within 2MHz. The frequency of the cw output is modulated by the potential modulation of the body. A peak-to-peak value of 120V can produce the frequency modulation of 29MHz.