An optical-input Maximum Likelihood Estimation feedback system demonstrated on tokamak horizontal equilibrium control

A readily parallelized Maximum Likelihood Estimation (MLE) algorithm with linear computational complexity is demonstrated in real time using only measurements from an extreme ultraviolet (EUV) diagnostic to control the horizontal position of a tokamak plasma. A set of trial emissivity profiles are parameterized by the control quantity of interest ( R m ), and the MLE is identified from the profile which minimizes the signal reconstruction residual. The algorithm depends on an empirically determined likelihood function with exponential form. EUV emission ( λ ≈ 15 eV-1 keV) is captured in a poloidal plane by four 16-channel AXUV diodes mounted at different poloidal angles with radial and angular resolution sufficient to discern plasma equilibrium evolution in HBT-EP. Calculations of the plasma major radius by the system are consistent within diagnostic uncertainty for the majority of the discharge with those of: a weighted average of vertical soft X-ray or EUV chords, magnetic sensors, and an equilibrium reconstruction. The feedback system corrects for a horizontal displacement of the major radius equal to 20% of the plasma minor radius by adjusting the vertical field produced from 40 in-vessel control coils in real time. The MLE calculation is performed on a GPU in a 15 μ s cycle, with similar performance in this application to a simple weighted average of vertical chords. Results demonstrate horizontal position control using magnetic actuators and an optical observer.

一种具有线性计算复杂度且易于并行化的最大似然估计（MLE）算法仅使用极紫外（EUV）诊断的测量值实时控制托卡马克等离子体的水平位置。一组试验发射率分布由感兴趣的控制量（$R_m$）参数化，并且从使信号重建残差最小的分布中识别出MLE。该算法依赖于一个经验确定的指数形式的似然函数。极紫外发射（$\lambda\approx15\ eV - 1\ keV$）由四个16通道AXUV二极管在极向平面内捕获，这些二极管安装在不同的极向角度，其径向和角度分辨率足以分辨HBT - EP中的等离子体平衡演化。该系统对等离子体大半径的计算在诊断不确定度范围内，对于大多数放电与以下几种方法的结果一致：垂直软X射线或EUV弦的加权平均值、磁传感器以及平衡重建。反馈系统通过实时调整40个内部控制线圈产生的垂直场，校正等于等离子体小半径20%的大半径水平位移。MLE计算在图形处理单元（GPU）上以$15\ \mu s$的周期进行，在该应用中其性能与垂直弦的简单加权平均值相似。结果证明了使用磁驱动器和光学观测器进行水平位置控制。