A quantitative comparison is made between the tearing-type modes observed in TFTR supershot plasmas and the nonlinear, neoclassical p: ssure gradient (Vp) driven tearing mode theory. Good agreement is found on the nonlinear magnetic island evolution of a single helicity mode {mjn = 3/2, 4/3 or 5/4, where m and n are the poloidal and toroidal mode numbers, respectively). Statistical data on the island width and growth rate are also found to be consistent with this theory. The results imply that the supershot plasmas are stable to the classical current-driven tearing modes.

No abstract

No abstract

Seed magnetic island formation due to a dynamically growing external source in toroidal confinement devices is modeled as an initial value, forced reconnection problem. For an external source whose amplitude grows on a time scale quickly compared to the Sweet-Parker time of resistive magnetohydrodynamics, the induced reconnection is characterized by a current sheet and a reconnected flux amplitude that lags in time the source amplitude. This suggests that neoclassical tearing modes, whose excitation requires a seed magnetic island, are more difficult to cause in high Lundquist number plasmas.

This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, rrcommendhtion, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof. c DISCLAIMER Portions of this document may be illegible in electronic image products. Images are produced from the best available original document.. .