Ion transport from collisions and finite guiding centre drift excursions

A study is made of the effects on ion transport of collisions and of finite drift excursions for a variety of guiding centre drift orbit shapes. The drift excursions Δx, where x denotes a normalized flux surface label, are calculated by solving the guiding centre drift equation for individual orbits. Collisions are described by a Fokker–Planck operator valid in all collisionality regimes. The operator describes the interaction between a test particle and a thermal plasma. The test particles represent the thermal ions of the plasma such that the collision operator is made to conserve particle number, momentum and energy. The momentum conservation leads to a new formulation of the ion heat flux from test particle calculations. General Monte Carlo type equations are derived from moments of the collision operator. These equations are solved in a two step computational approach. A plasma equilibrium based on a JET configuration is used in computations which scan a phase space of three dimensionless variables which characterize the guiding centre orbits. The time–space dependent contributions from the drifts across flux surfaces, as well as along field lines, are accumulated to yield the ion heat flux profile qi(x) characterizing a thermal, Ohmically heated plasma. The profile of this ion heat flux is different from those predicted by conventional neoclassical theories as it vanishes on the magnetic axis. The edge value is approximately a third of the experimental value determined from the total Ohmic heating rate. The electron heat flux qe(x), can in principle also be evaluated by the model, but requires a two order of magnitude increase in computing resources.

[1]  J. Bittencourt.  Transport Processes in Plasmas , 2004 .

[2]  M. Redi,et al.  Efficient evaluation of beam ion confinement in spherical tokamaks , 2003 .

[3]  Guiding Center Particle Simulation of Wide-Orbit Neoclassical Transport , 2001 .

[4]  L.-G. Eriksson,et al.  Dynamics of energetic ion orbits in magnetically confined plasmas , 2001 .

[5]  W.G.F. Core.  Non-standard particle orbits in a thermonuclear tokamak plasma , 2000 .

[6]  Drift orbit topology of fast ions in tokamaks , 2000 .

[7]  Per Helander,et al.  On neoclassical transport near the magnetic axis , 2000 .

[8]  O. Sauter,et al.  Neoclassical conductivity and bootstrap current formulas for general axisymmetric equilibria and arbitrary collisionality regime , 1999 .

[9]  Shaojie Wang.  Finite bootstrap current density and finite neoclassical reduction of electrical conductivity at the magnetic axis of a tokamak , 1998 .

[10]  Robert L. Miller,et al.  Steady State Tokamak Equilibria without Current Drive , 1997 .

[11]  Zhihong Lin,et al.  Large orbit neoclassical transport , 1997 .

[12]  K. Shaing,et al.  Electron transport processes close to magnetic axis in tokamaks , 1997 .

[13]  Effects of orbit squeezing on ion transport processes close to magnetic axis , 1997 .

[14]  K. Shaing,et al.  Ion transport process around magnetic axis in tokamaks , 1997 .

[15]  Zhihong Lin,et al.  Neoclassical transport in enhanced confinement toroidal plasmas , 1996 .

[16]  Per Helander,et al.  Monte Carlo operators for orbit‐averaged Fokker–Planck equations , 1994 .

[17]  Finite orbit effects in ICRF heated tokamak plasmas , 1992 .

[18]  F. Hinton,et al.  Effect of impurity particles on the finite-aspect ratio neoclassical ion thermal conductivity in a tokamak , 1986 .

[19]  L. Lao,et al.  Reconstruction of current profile parameters and plasma shapes in tokamaks , 1985 .

[20]  George H. Miley,et al.  Fast-ion thermalization in non-circular tokamaks with large-banana-width effects , 1981 .

[21]  D. McCune,et al.  New techniques for calculating heat and particle source rates due to neutral beam injection in axisymmetric tokamaks , 1981 .

[22]  Allen H. Boozer,et al.  Monte Carlo evaluation of transport coefficients , 1981 .

[23]  The topology of tokamak orbits , 1979 .

[24]  W. Horton,et al.  Properties of the Monte Carlo Lorentz collision operator , 1977 .

[25]  M. Rensink,et al.  A radial transport/Fokker-Planck model for a Tokamak plasma☆ , 1977 .

[26]  J. Cordey,et al.  Energetic particle distribution in a toroidal plasma with neutral injection heating , 1974 .

[27]  T. Stringer,et al.  Radial profile of alpha -particle heating in a Tokamak , 1974 .

[28]  J. Connor,et al.  The neo-classical transport theory of a plasma with multiple ion species , 1973 .

[29]  Marshall N. Rosenbluth,et al.  Plasma Transport in Toroidal Confinement Systems , 1972 .

[30]  M. Rosenbluth,et al.  EFFECT OF LONGITUDINAL ELECTRIC FIELD ON TOROIDAL DIFFUSION. , 1970 .

[31]  John M. Dawson,et al.  One‐Dimensional Model of a Lorentz Plasma , 1967 .

[32]  William M. MacDonald,et al.  Fokker-Planck Equation for an Inverse-Square Force , 1957 .