Image courtesy of General Atomics
Precise real-time steering of microwaves drives current at location of a Neoclassical Tearing Mode, causing it to shrink and disappear.
Feedback controlled steering mirrors are used to precisely aim microwave beams in real time to catch and subdue neoclassical tearing modes on DIII-D tokamak plasmas. The microwaves drive current in the plasma at specific locations that shrink these instabilities, which if left to grow would limit plasma performance or cause the discharge to terminate.
Neoclassical tearing modes can increase energy transport and hinder the performance of high performance fusion plasmas, such as those that will be produced in ITER. They can sometimes also grow large enough to terminate the plasma discharge. The DIII-D results show promise in demonstrating how the problem of these instabilities can be solved in ITER with the least power and energy from the microwave heating system, thereby maintaining high fusion performance, by use of these advanced feedback and control techniques.
Research at the DIII-D National Fusion Facility involving scientists from General Atomics, Princeton Plasma Physics Laboratory, and Columbia University has demonstrated the basis of efficient, real-time control of neoclassical tearing modes (NTMs), providing confidence that these instabilities can be controlled in ITER. This result builds on previous results that showed that precise alignment of electron cyclotron current drive (ECCD) with the location of the NTM will lead to stabilization of this instability. The research has combined several advanced control technologies to achieve robust NTM suppression: real-time steering of mirrors that control the ECCD deposition location, real-time ECCD power control, and real-time internal current profile determination. Combining these technologies allows rapid deployment of ECCD soon after NTM detection, thereby reducing the ECCD power requirement for suppression by a factor of two. This reduced power requirement may be important in ITER in achieving high gain (fusion power/power input) operation.
DOE Office of Science, Fusion Energy Sciences
E. Kolemen et al., “State-of-the-Art Neoclassical Tearing Mode Control in DIII-D Using Real-time Steerable Electron Cyclotron Current Drive Launchers”, 24th IAEA Fusion Energy Conference, PD/1-1.
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