Ballooning stability of JET high-beta discharges
The ballooning stability properties of the latest (July 1989) high-beta discharges produced at JET are analysed with the HBT code. One example of a discharge with a broad pressure profile is shown to be close to the ballooning stability limit in the region of the largest pressure gradient. The equilibrium that is marginally stable, with the same q-profile, shows that this limit is approached only locally but that much higher beta values are possible if the region of the large gradients can be increased towards the edge of the plasma. The evaluated high beta discharges with a peaked pressure profile, produced with or without the injection of a pellet, are shown to exceed the ballooning limit in the plasma centre by a factor of 1.5 to 2 if a montonic q-profile is assumed. The stabilising influence of raising q on axis is shown to be too small to stabilise this instability. Complete stabilisation can be obtained with a non-monotonic q-profile with relatively large negative shear in the plasma centre.
Bibliographic Reference: Report: Rijnhuizen Report 89-189 EN (1989) 33 pp.
Availability: Available from FOM-Institut voor Plasmafysica "Rijnhuizen", P.O. Box 7, 3430 AA Nieuwegein (NL)
Record Number: 199010699 / Last updated on: 1994-12-01
Original language: en
Available languages: en