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Disruption Avoidance on TFTR

Dennis Mueller, Michael G. Bell, Eric Fredrickson, Alan C. Janos, Forrest C. Jobes, Larry C. Johnson, E. John Lawson, Robert Marsala, David Kingston Owens, Hyeon Park, Alan T. Ramsey, Thomas Senko, Hironori Takahashi, Gary Taylor, King-Lap Wong

Fusion Science and Technology / Volume 30 / Number 2 / Pages 251-257

November 1996


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Disruptions on the Tokamak Fusion Test Reactor (TFTR), especially those occurring at high stored energy, result in lost experimental run time because many discharges are required to regain wall conditions necessary for good plasma performance. A variety of disruption types have been observed on TFTR. These include density-limit disruptions, those caused by a high influx of impurities, those occurring during the current ramp-down, those resulting from locked modes, and those occurring at high normalized β(βN = βTaBT/Ip). A combination of operational experience and limiter development has helped to avoid many potential disruptions. However, the experimental goal of high fusion power production engenders the risk of high-βN disruptions. A system to limit βN by reducing the neutral beam power as a preprogrammed βN limit is reached is now in use to help avoid high-βN disruptions. Operational issues of disruption avoidance, the βN feedback system, the limitations and possible improvements of the system are discussed.

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