Disruptions and density limits
Current understanding of disruptions in tokamaks is reviewed. Five different types of disruptions are identified: density limit, low q, current rise, beta-limit and vertical instability. Density limit disruptions have been most studied. Contraction of temperature profile due to radiative cooling in the plasma edge is the dominant initiating mechanism in most cases. Disruptions determine operational limits of tokamaks, particularly current density. Reducing the probability of disruptions by avoiding these operational limits could reduce the potential performance of an experiment. Some discharges appear even though they are well away from operational limits. These random disruptions are due to equipment failure, particle impurities and quasi-stationary mhd activity induced during the current rise phase. Operational limits in density and current are presented as the Hugill diagram. Most tokamaks are in agreement with the broad features. Density limits vary over a wide range and are clearly dependent on radiation cooling of the plasma edge. The B(t)/R scaling in density limits implied by Hugill diagram is now recognised as misleading. Higher values of the Murakami parameter nR/B(t) can be obtained at low B(t) values than at high B(t).
Bibliographic Reference: Report: JET-P(88)27 EN (1988)
Availability: Available from the Publications Officer, JET Joint Undertaking, Abingdon, Oxon. OX14 3EA (GB)
Record Number: 198910003 / Last updated on: 1994-12-01
Original language: en
Available languages: en