HIGH BETA TOKAMAK RESEARCH

Columbia University will carry out new investigations of active control of the tokamak boundary using enhanced capabilities of the HBT-EP research facility to understand critical MHD effects in next generation advanced tokamaks and ITER. This research program continues the “High Beta Tokamak Research” project at Columbia University that has already made significant contributions to our understanding of magnetic confinement in the areas of passive and active control of MHD instabilities and has had significant impact on major experiments worldwide. With the installation of new diagnostic and control capabilities, HBT-EP research will undertake important new studies to understand critical MHD effects in next generation tokamaks and will expand interactions with the international tokamak community to complete critical ITER research tasks.

We will carry out this research using one of the world’s most extensive sensor and magnetic control system for tokamak studies [RSI 84, 063502 (2013)], including nonlinear control of non-axisymmetric magnetic perturbations on a microsecond timescale using a Graphics Processing Unit (GPU) [Nucl. Fusion 53, 073052 (2013); RSI 85, 045114 (2014)], and with unique capability for detailed measurements of SOL currents during applied resonant magnetic perturbations (RMPs), wall-touching kink modes, and plasma disruptions [Nucl. Fusion 57, 086035 (2017)]. This HBT-EP research program builds upon recent achievements that include: (i) using new scrape-off layer (SOL) current diagnostics that have measured helical SOL currents during MHD modes that directly impact MHD mode stability [Phys. Plasmas 14, 062505 (2007); Phys. Plasmas, 20, 082510 (2013); J Plasma Physics, 83, 1 (2017)], yet are rarely considered in stability analysis prior to disruptions; (ii) using the unique boundary structure of HBT-EP with movable wall segments and toroidally isolated vacuum chamber segments, which have detected details of the radial and poloidal profiles of the SOL currents for the first time; and (iii) achieving a robust and reliable H-Mode transition by applying a large bias to an electrode inserted into the edge of the plasma allowing the study of the influence of shear rotation and steep plasma pressure gradients on MHD instabilities, MHD active control, SOL currents, and disruption dynamics.

The research program is focused on three goals: (i) understanding the physics of SOL currents and interactions between the helical plasma edge and conducting boundary structures, (ii) testing new methods for measurement and mode control that integrate optical and magnetic detector arrays with both magnetic and SOL current feedback, and (iii) understanding fundamental MHD issues associated with disruptions, magnetic perturbations, and SOL currents. This HBT-EP research program will advance fundamental understanding of using both magnetic and edge current probe actuators, driven in response to both optical and magnetic sensors, and will advance mode control from present machines to DEMO.