Nonlinear dynamics of tearing modes in the reversed field pinch

The results of investigations of nonlinear tearing‐mode dynamics in reversed field pinch plasmas are described. The linear instabilities have poloidal mode number m=1 and toroidal mode numbers 10≲n≲20, and the resonant surfaces are therefore in the plasma core. The nonlinear dynamics result in dual cascade processes. The first process is a rapid m=1 spectral broadening toward high n, with a simultaneous spreading of magnetic turbulence radially outward toward the field‐reversal surface. Global m=0 perturbations, which are driven to large amplitudes by the m=1 instabilities, in turn trigger the m=1 spectral broadening by back coupling to the higher n. The second process is a cascade toward large m and is mediated by m=2 modes. The m=2 perturbations have the structure of localized, driven current sheets and nonlinearly stabilize the m=1 modes by transferring m=1 energy to small‐scale dissipation. The calculated spectrum has many of the qualitative features observed in experiments.

[1]  Ian H. Hutchinson,et al.  The structure of magnetic fluctuations in the HBTX-1A reversed field pinch , 1984 .

[2]  H. R. Hicks,et al.  Nonlinear Destabilization of Tearing Modes , 1981 .

[3]  Richard A. Nebel,et al.  Sawteeth, magnetic disturbances, and magnetic flux regeneration in the reversed-field pinch , 1983 .

[4]  J. B. Taylor,et al.  Relaxation of toroidal plasma and generation of reverse magnetic fields , 1974 .

[5]  Z. G. An,et al.  Nonlinear interaction of tearing modes: A comparison between the tokamak and the reversed field pinch configurations , 1985 .

[6]  Resistive MHD studies of high β tokamak plasmas , 1981 .

[7]  E. Caramana,et al.  Numerical simulation of reversed-field pinch rising current operation , 1986 .

[8]  H. R. Strauss,et al.  Nonlinear, three‐dimensional magnetohydrodynamics of noncircular tokamaks , 1976 .

[9]  Benjamin A. Carreras,et al.  3D nonlinear calculations of resistive tearing modes , 1981 .

[10]  Tadashi Sekiguchi,et al.  Plasma Physics and Controlled Nuclear Fusion Research , 1987 .

[11]  H. Strauss.  The dynamo effect in fusion plasmas , 1985 .

[12]  Z. G. An,et al.  Theory of anomalous tearing mode growth and the major tokamak disruption , 1984 .

[13]  E. J. Caramana,et al.  Three‐dimensional magnetohydrodynamic studies of the reversed‐field pinch , 1985 .

[14]  D. D. Schnack,et al.  Nonlinear, single‐helicity magnetic reconnection in the reversed‐field pinch , 1983 .

[15]  A. A. Mirin,et al.  Compressibility as a feature of field reversal maintenance in the reversed‐field pinch , 1985 .