Nonlocal Transport in the Reversed Field Pinch

Spizzo, G. ; White, R. B. ; Cappello, S. ; Marrelli, L.

关键词: DIFFUSION;    DISTRIBUTION;    INCLINATION;    KINETICS;    MAGNETIC FIELDS;    MAGNETIC SURFACES;    RANDOM PHASE APPROXIMATION;    REPRODUCTION;    SCATTERING;    SIMULATION;    TOMOGRAPHY;    TRAJECTORIES;    TRANSPORT Diffusion;    ParticleReversed Field Pinch;    Transport Theory;   

DOI  :  10.2172/965276
RP-ID  :  PPPL-4458
PID  :  OSTI ID: 965276
Others  :  TRN: US0904245

学科分类：原子、分子光学和等离子物理

美国|英语

来源: SciTech Connect

【 摘 要 】

Several heuristic models for nonlocal transport in plasmas have been developed, but they have had a limited possibility of detailed comparision with experimental data. Nonlocal aspects introduced by the existence of a known spectrum of relatively stable saturated tearing modes in a low current reversed field pinch offers a unique possibility for such a study. A numerical modelling of the magnetic structure and associated particle transport is carried out for the reversed-field pinch experiment at the Consorzio RFX, Padova, Italy. A reproduction of the tearing mode spectrum with a guiding center code1 reliably reproduces the observed soft X-ray tomography. Following particle trajectories in the stochastic magnetic field shows the transport across the unperturbed flux surfaces to be due to a spectrum of Levy flights, with the details of the spectrum position dependent. The resulting transport is subdiffusive, and cannot be described by Rechester-Rosenbluth diffusion, which depends on a random phase approximation. If one attempts to fit the local transport phenomenologically, the subdiffusion can be fit with a combination of diffusion and inward pinch2. It is found that whereas passing particles explore the stochastic field and hence participate in Levy flights, the trapped particles experience normal neoclassical diffusion. A two fluid nonlocal Montroll equation is used to model this transport, with a Levy flight defined as the motion of an ion during the period that the pitch has one sign. The necessary input to the Montroll equation consists of a time distribution for the Levy flights, given by the pitch angle scattering operator, and a distribution of the flight distances, determined numerically using a guiding center code. Results are compared to experiment. The relation of this formulation to fractional kinetics is also described.