High Current Tokamak Protection Switch

One of the major remaining technical hurdles facing tokamaks, a leading architecture for fusion systems, is that plasma disruptions can result in the generation of high current beams of relativistic electrons (10s of MeV). These beams are called Runaway Electrons (RE). In advanced fusion machines, Runaway Electrons can cause severe damage to plasma-facing surfaces of a tokamak structure. This catastrophic destruction includes melt damage, coolant leaks, and loss of vacuum.High field tokamaks, which will be required for commercial fusion power, will be even more susceptible to damage from RE than present-day systems such as ITER. Even if these events occur rarely, they could hamper fusion machines from reaching commercial viability. To prevent these events from damaging tokamaks, a non-axisymmetric coil can be excited to disrupt the magnetic field and prohibit formation of such relativistic electron beams. Diversified Technologies, Inc. (DTI) is working under a Small Business Innovative Research (SBIR) grant from the Department of Energy
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(DOE) to develop a fast-acting high current switch and vacuum feedthrough controlling a magnetic coil. When passively switched ON, this will disrupt formation of the relativistic beams, and prevent damage to the plasma facing surfaces. As part of the switch design, protective circuits are integrated to ensure proper switch operation.The full-scale switch and feedthrough will be installed in a working fusion device for full-scale tests. This effort is in collaboration with MIT and General Atomics (GA) for future installation on the GA fusion device (DIII-D) as a prototype.