Ko J, Chung J
National Fusion Research Institute, Daejeon 34133, South Korea.
Rev Sci Instrum. 2017 Jun;88(6):063505. doi: 10.1063/1.4986461.
The safety factor profile evolutions have been measured from the plasma discharges with the external current drive mechanism such as the multi-ion-source neutral beam injection for the Korea Superconducting Tokamak Advanced Research (KSTAR) for the first time. This measurement has been possible by the newly installed motional Stark effect (MSE) diagnostic system that utilizes the polarized Balmer-alpha emission from the energetic neutral deuterium atoms induced by the Stark effect under the Lorentz electric field. The 25-channel KSTAR MSE diagnostic is based on the conventional photoelastic modulator approach with the spatial and temporal resolutions less than 2 cm (for the most of the channels except 2 to 3 channels inside the magnetic axis) and about 10 ms, respectively. The strong Faraday rotation imposed on the optical elements in the diagnostic system is calibrated out from a separate and well-designed polarization measurement procedure using an in-vessel reference polarizer during the toroidal-field ramp-up phase before the plasma experiment starts. The combination of the non-inductive current drive during the ramp-up and shape control enables the formation of the internal transport barrier where the pitch angle profiles indicate flat or slightly hollow profiles in the safety factor.
首次从韩国超导托卡马克先进研究装置（KSTAR）的具有外部电流驱动机制（如多离子源中性束注入）的等离子体放电中测量了安全因子分布的演变。通过新安装的运动斯塔克效应（MSE）诊断系统实现了这种测量，该系统利用在洛伦兹电场下由斯塔克效应诱导的高能中性氘原子的极化巴耳末α发射。25通道的KSTAR MSE诊断基于传统的光弹调制器方法，空间分辨率和时间分辨率分别小于2厘米（对于磁轴内除2至3个通道外的大多数通道）和约10毫秒。在等离子体实验开始前的环向场上升阶段，利用一个安装在真空室内的参考偏振器，通过一个单独且精心设计的偏振测量程序，对诊断系统中光学元件上施加的强法拉第旋转进行校准。上升阶段的非感应电流驱动与形状控制相结合，能够形成内部输运垒，在该输运垒中，螺距角分布表明安全因子呈平坦或略呈空心分布。
