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Speaker: N.W Eidietis, General Atomics, San Diego

Title: Prospects for Disruption Handling in a Commercial Tokamak Fusion Reactor

Abstract: Rapid termination of a tokamak discharge due to instability, termed a “disruption”, presents one of the greatest challenges to achieving an economically viable fusion reactor. Handling of these damaging transients, including prevention, mitigation, and resilient design, must be incorporated into future burning plasma tokamak designs at the same priority as core performance and steady state heat flux removal if the risk to capital investment due to catastrophic failure is to be reduced to economically acceptable levels. Disruption handling is typically executed along two paths: prevention and mitigation. Prevention requires avoiding unstable regimes, actively stabilizing instabilities if they do appear, or, if those steps should fail, terminating the plasma in a rapid but controlled ramp-down to remove the drivers of instability before it causes a disruption. Mitigation is a last resort that utilizes the injection of massive amounts of impurity to radiate the plasma thermal and magnetic energy as uniformly as possible throughout the vessel to avoid damaging concentrated thermal and mechanical loads. Extremely robust disruption prevention will be of paramount importance in to ensure high duty factor and capital return on the reactor investment. At the same time, successful prevention will face many challenges in a commercial reactor, as actuators will be far more limited, diagnostic access and reliability far less robust, the burning plasmas will be more self-organizing, and the expectation for mean time between failures far longer than in contemporary devices or ITER. Disruption mitigation is a highly undesirable outcome for a reactor, as it can reduce but is unlikely to prevent all damage. Hence, resilient design aims to sustain disruptions without long-term damage in the absence of active intervention. Several possibilities are presented: liquid metal divertors to sustain TQ thermal loads; sacrificial high-field-side limiters to prevent vertically unstable disruptions; and passive 3D conducting structures to prevent the formation of a RE beam. 

* This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Fusion Energy Sciences, using the DIII-D National Fusion Facility, a DOE Office of Science user facility, under Awards DE-FC02-04ER54698 and DE-SC0020299 .

Biography: Dr. Nicholas Eidietis received his PhD in Nuclear Engineering and Engineering Physics from the University of Wisconsin in 2007, and since that time has worked as a staff scientist in the Plasma Control and Operations Group at General Atomics. Dr. Eidietis’ research focuses upon tokamak control and disruption mitigation. He served as the group leader of the Disruption Mitigation Physics Group at the DIII-D National Fusion Program from 2013-2021, and is presently the chair of the Experimental Working Group for the ITER Disruption Task Force. Dr. Eidietis has developed real-time plasma and supervisory controllers for numerous tokamaks around the world, including DIII-D, EAST, KSTAR, and MAST-U.