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一、引 言 在目前托卡马克等离子体诊断中,采用垂直多道干涉仪测量等离子体电子密度时,由于等离子体水平位移的影响,使得测量信号在沿大环半径方向的分布是非对称的。这就要求采用非对称的Abel变换来给出等离子体电子密度的空间分布。一种常用的非对称Abel变换是分离变量法,它的基本思想是把测量信号分成对称元和非对称的权函数,对称部分采用标准的Abel变换,变换的结果乘上非对称的权函数。这种方法实际上是假定了等离子体电子密度弦积分值的不对称性与局部的不对称性是相同的;而且对称部分采用标准的Abel变换,如Barr的方法,Bockasten方法等。这些方法是把等离子体看成一个个同心圆,没有考虑到等离子体水平位移引起的弦长变化。本文采用一种新的变换方法,这种方法的特点是考虑到等离子体位移的实际情况。
I. INTRODUCTION In the current tokamak plasma diagnosis, the vertical multichannel interferometer is used to measure the plasma electron density, and the distribution of the measurement signal in the radial direction along the large ring is asymmetric due to the influence of the horizontal displacement of the plasma. This requires the use of asymmetric Abel transform to give the plasma electron density of the spatial distribution. A common asymmetric Abel transform is a separation-variable method. Its basic idea is to divide the measurement signal into symmetric elements and asymmetric weight functions. The symmetrical part adopts the standard Abel transform, and the result of the transform is multiplied by an asymmetric weight function. This method actually assumes that the asymmetry of the plasma electron density chord integral value is the same as the local asymmetry; and the symmetric part adopts the standard Abel transform, such as Barr’s method, Bockasten’s method and so on. These methods treat the plasma as one concentric circle without taking into account the change in chord caused by the horizontal displacement of the plasma. In this paper, a new transformation method is adopted. The characteristic of this method is taking into account the actual situation of plasma displacement.