Numerical modeling of diffusive heat transport across magnetic islands and local stochastic field

The heat diffusion across magnetic islands is studied numerically and compared with analytical results. For a single island, the enhanced radial heat diffusivity, χr, due to the parallel transport along the field lines is increased over a region of about the island width w. The maximum enhanced heat conductivity at the rational surface is proportional to w2(χ‖χ⊥)1∕2 for sufficiently high values of χ‖∕χ⊥, where χ‖∕χ⊥ is the ratio between the parallel and the perpendicular heat diffusivity. For low ratios of χ‖∕χ⊥, however, the maximum value of χr is proportional to w4χ‖. In a locally stochastic magnetic field, χr is again proportional to w4χ‖ for low χ‖∕χ⊥, which is in agreement with the analytical results. With increasing χ‖∕χ⊥,χr is dominated first by the additive effect of individual islands and then by the field ergodicity.

[1]  A. Donné,et al.  Effect of the dynamic ergodic divertor in the TEXTOR tokamak on MHD stability, plasma rotation and transport , 2005 .

[2]  R. Balescu,et al.  Transport in sheared stochastic magnetic fields , 1997 .

[3]  R. Fitzpatrick,et al.  Helical temperature perturbations associated with tearing modes in tokamak plasmas , 1995 .

[4]  M E Fenstermacher,et al.  Suppression of large edge-localized modes in high-confinement DIII-D plasmas with a stochastic magnetic boundary. , 2004, Physical review letters.

[5]  R. Bickerton.  REVIEW ARTICLE: Magnetic turbulence and the transport of energy and particles in tokamaks , 1997 .

[6]  A. Boozer,et al.  Particle diffusion in tokamaks with partially destroyed magnetic surfaces , 1982 .

[7]  A. Schilham,et al.  Test particle transport in perturbed magnetic fields in tokamaks , 1999 .

[8]  Sibylle Günter,et al.  Numerical modeling of nonlinear growth and saturation of neoclassical tearing modes , 2004 .

[9]  L. L. Lao,et al.  High beta tokamak operation in DIII-D limited at low density/collisionality by resistive tearing modes , 1997 .

[10]  Sibylle Günter,et al.  Modelling of heat transport in magnetised plasmas using non-aligned coordinates , 2005 .

[11]  H. Zohm,et al.  High-confinement regime at high beta(N) values due to a changed behavior of the neoclassical tearing modes. , 2001, Physical review letters.

[12]  P. Liewer.  Measurements of microturbulence in tokamaks and comparisons with theories of turbulence and anomalous transport , 1985 .

[13]  Observation of spontaneous neoclassical tearing modes , 2002 .

[14]  K. Lackner,et al.  Interactions between neoclassical tearing modes , 2000 .

[15]  Sibylle Günter,et al.  Seed island of neoclassical tearing modes at ASDEX Upgrade , 1999 .

[16]  G. Gantenbein,et al.  The physics of neoclassical tearing modes and their stabilization by ECCD in ASDEX Upgrade , 2001 .

[17]  J. Callen,et al.  Unified fluid/kinetic description of plasma microinstabilities. Part I: Basic equations in a sheared slab geometry , 1992 .

[18]  M. Rosenbluth,et al.  Electron heat transport in a tokamak with destroyed magnetic surfaces , 1978 .

[19]  P. Ghendrih,et al.  REVIEW ARTICLE: Theoretical and experimental investigations of stochastic boundaries in tokamaks , 1996 .

[20]  Harold P. Furth,et al.  Finite‐Resistivity Instabilities of a Sheet Pinch , 1963 .

[21]  N. T. Gladd,et al.  Electron temperature gradient driven microtearing mode , 1980 .

[22]  Calculation of the Kolmogorov entropy for motion along a stochastic magnetic field , 1979 .

[23]  McGuire,et al.  Observation of nonlinear neoclassical pressure-gradient-driven tearing modes in TFTR. , 1995, Physical review letters.

[24]  E. Strumberger.  The stochastic edge region of W7-X , 1999 .

[25]  L. Napolitano.  Materials , 1984, Science.

[26]  K. F. Mast,et al.  Disruptions in JET , 1989 .

[27]  Sibylle Günter,et al.  Influence of neoclassical tearing modes on energy confinement , 1999 .

[28]  G. Giruzzi,et al.  Modeling of the stabilization of neoclassical tearing modes by localized radio frequency current drive , 2000 .

[29]  J. Krommes,et al.  Plasma transport in stochastic magnetic fields. Part 3. Kinetics of test particle diffusion , 1983, Journal of Plasma Physics.

[30]  Perkins,et al.  Fluid moment models for Landau damping with application to the ion-temperature-gradient instability. , 1990, Physical review letters.

[31]  T. H. Stix.  Plasma transport across a braided magnetic field , 1978 .

[32]  J. Callen,et al.  Global energy confinement degradation due to macroscopic phenomena in tokamaks , 1990 .

[33]  S. Günter,et al.  Numerical modeling of linear drift-tearing mode stability , 2003 .