Krychowiak M, Dodt D, Dreier H, König R, Wolf R
Max-Planck-Institut fur Plasmaphysik, Euratom Association, Wendelsteinstr. 1, 17491 Greifswald, Germany.
Rev Sci Instrum. 2008 Oct;79(10):10F512. doi: 10.1063/1.2956826.
For the W7-X stellarator a diagnostic system for measurement of local Z(eff) values from the visible bremsstrahlung continuum is foreseen. The method is based on passive, absolute measurement of the bremsstrahlung intensity along several lines of sight. In order to eliminate the spurious impact of other radiation sources of different spectral intensity distribution than the bremsstrahlung, like the line radiation, it is intended to spectrally resolve the detected radiation, e.g., by use of microspectrometers. The visible bremsstrahlung background can be extracted by making use of the 1/lambda(2) dependence of its intensity (expressed in unit Wm(3) sr nm) in the high temperature plasmas by using Bayesian data analysis techniques. In a second step, the local values of Z(eff) as a function of the effective plasma radius are derived by inversion, using different regularization methods, of the line-integrated bremsstrahlung signals with the knowledge of the magnetic flux surfaces. Inversion of the full model based on statistical methods allows taking into account all conceivable uncertainties accompanying Z(eff) measurement and provides uncertainties of the local Z(eff) values and valuable information on other uncertain parameters of the model. In this paper we show the first steps in developing a virtual Z(eff) diagnostic for W7-X which allows the optimization of the statistical model as well as of the future diagnostic setup.
对于W7-X仿星器，预计将开发一种用于从可见轫致辐射连续谱测量局部有效电荷数（Z(eff)）值的诊断系统。该方法基于沿多条视线对轫致辐射强度进行无源、绝对测量。为了消除与轫致辐射具有不同光谱强度分布的其他辐射源（如线辐射）的虚假影响，打算对检测到的辐射进行光谱分辨，例如使用微型光谱仪。在高温等离子体中，利用贝叶斯数据分析技术，通过利用其强度（以Wm(3) sr nm为单位表示）对波长的平方分之一（1/lambda(2)）的依赖性，可以提取可见轫致辐射背景。在第二步中，利用磁通量面的知识，通过对线积分轫致辐射信号进行反演，并使用不同的正则化方法，得出作为有效等离子体半径函数的局部Z(eff)值。基于统计方法对完整模型进行反演，可以考虑到Z(eff)测量中所有可能的不确定性，并提供局部Z(eff)值的不确定性以及关于模型其他不确定参数的有价值信息。在本文中，我们展示了为W7-X开发虚拟Z(eff)诊断的初步步骤，这允许对统计模型以及未来的诊断设置进行优化。
