Geometrical effects in X-mode scattering
Geometrical effects in X-mode scattering
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X 模式散射中的几何效应
DOI：
10.1017/s0022377800012411
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发表时间：
1987
影响因子：
2.5
通讯作者：
N. Bretz
中科院分区：
文献类型：
--
作者：
N. Bretz
将微波散射扩展为磁约束等离子体中长波长密度波动探测的一种技术是考虑几乎垂直于场的特殊（x模）波的发射和散射。当入射频率小于电子回旋加速器频率时，该模式可以穿透等离子体频率的普通模式截止，并避免托卡马克等离子体典型密度梯度造成的显著畸变。在更熟悉的情况下，入射波和散射波是普通的，散射是垂直于场的各向同性。然而，由于x模偏振取决于频率比和射线与磁场的夹角，因此入射波和散射波之间的耦合是复杂的。为了解释仅由密度波动引起的散射，必须从观测到的散射中展开这个几何形状因子。这里计算了垂直于磁场散射的特殊情况下的几何因子。在普通模式截止点以上的频率，散射是相对各向同性的，而在普通模式截止点以下的频率，在正反方向上都有最小值，在大约为普通模式截止点密度的一半时趋于零。
One technique to extend microwave scattering as a probe of long-wavelength density fluctuations in magnetically confined plasmas is to consider the launching and scattering of extraordinary (X-mode) waves nearly perpendicular to the field. When the incident frequency is less than the electron cyclotron frequency, this mode can penetrate beyond the ordinary mode cut-off at the plasma frequency and avoid significant distortions from density gradients typical of tokamak plasmas. In the more familiar case, where the incident and scattered waves are ordinary, the scattering is isotropic perpendicular to the field. However, because the X-mode polarization depends on the frequency ratios and the ray angle to the magnetic field, the coupling between the incident and scattered waves is complicated. This geometrical form factor must be unfolded from the observed scattering in order to interpret the scattering due to density fluctuations alone. The geometrical factor is calculated here for the special case of scattering perpendicular to the magnetic field. For frequencies above the ordinary-mode cut-off the scattering is relatively isotropic, while below cut-off there are minima in the forward and backward directions which go to zero at approximately half the ordinary-mode cut-off density.