以亚毫米波回旋管为辐射源的等离子体散射测量
Plasma scattering measurement using a submillimeter wave gyrotron as a radiation source
摘要：
等离子体散射测量是观测等离子体中激发的低频密度涨落的有效方法。测量的空间分辨率、波数分辨率和信噪比取决于探测光束的波长范围、大小和强度。良好准直的亚毫米波波束适合于提高空间和波数分辨率。由于高频回旋管的高功率输出能力，它的应用对提高测量的信噪比是有效的。与分子蒸汽激光器不同，回旋管产生具有TEMn模式结构的发散辐射束。因此，有必要将输出辐射转换成高斯光束。准光学天线是用于所考虑的转换系统的合适元件，因为它适用于几种TE 0 n和TE 1 n模式。为了将回旋管应用于等离子体散射测量，我们将回旋管的输出功率（P= 110 W，f= 354 GHz）稳定到DP/P<1%，Df<10 kHz的水平。减小阴极电位的波动可以稳定回旋管的输出。
英文摘要：
Plasma scattering measurement is effective technique to observe low frequency density fluctuations excited in plasma. The spatial and wave number resolutions and the S/N ratio of measurement depend on the wavelength range, the size and the intensity of a probe beam. A well-collimated, submillimeter wave beam is suitable for improving the spatial and wave number resolutions. Application of high frequency gyrotron is effective in improving the S/N ratio of the measurement because of its capacity to deliver high power. Unlike the molecular vapor lasers, the gyrotrons generate diverging beam of radiation with TEmn mode structure. It is therefore necessary to convert the output radiation into a Gaussian beam. A quasi-optical antenna is a suitable element for the conversion system under consideration since it is applicable to several TE0n and TE1n modes. In order to apply the gyrotron to plasma scattering measurement, we have stabilized the output (P=110W, f=354GHz) of gyrotron up to the level (DP/P<1 %, Df<10 kHz). The gyrotron output can be stabilized by decreasing the fluctuation of the cathode potential.
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