a OneDimensional Plasma and Impurity Transport Model for Reversed Field Pinches.
Abstract
A onedimensional plasma and impurity transport model to study impurity behavior in Reversed Field Pinch (RFP) fusion plasmas is developed. A coronal nonequilibrium model is used for impurities. The impurity model is incorporated into an existing onedimensional plasma transport model creating RFPBI, a selfconsistent multispecies plasma transport model. Neutral deuterium particles were treated using a onedimensional (slab) model of neutral transport. RFPBI was applied to study ZT40M and MST, and to examine steady state behavior of ZTH based on the design parameters. A parallel algorithm for the impurity transport equations was also implemented and tested to determine speedup and efficiency. Quasisteady state simulation of ZT40M show that between 3% to 33% of ohmic heating is required to maintain T_{i} >=q T_{e } depending on the assumptions used for ion thermal conduction, the recycle source deposition profile, and the ion heating profile. The model can simulate a wide range of radiation percentages from 20% to 90% of the input power in ZT40M. Typical ZT40M particle confinement times of 0.6 ms and a radiation fraction of 20% can be modeled using an impurity diffusion coefficient, D _{z}, of 1013 m^2 /s, and 2% oxygen and 0.25% nickel impurities. A krypton seeded experiment with 90% radiation fraction is consistent with 4% oxygen, 2.1% nickel and 3.5% krypton, and D_{z} ~ 20 m^2/s. Anomalous thermal conduction was introduced by adding to the classical crossfield expression a fraction of classical parallel thermal conduction, i.e., f_1kappa_{ e }. The phenomenological model is consistent with a stochastic core for the RFP and quantitatively reproduces observed behavior in which beta_theta remains constant over a wide range of radiation fractions. The model has a form similar to the Rechester Rosenbluth model for thermal conduction due to stochastic field line diffusion given by chi_ {RR} ~ (a/L_{corr})Sigma( delta B/B)^2. To achieve design parameters of ZTH, it was necessary to decrease f_1 by factors of about 2040 below typical ZT40M values. It corresponds to a scaling requirement for delta B/B ~ S^{1/2} or better. For time dependent calculations with iron as the impurity, parallel processing using geometric domain decomposition applied to the impurity solver on an IBM 3090/600S shows that a speedup of 2.79 is achievable with four processors.
 Publication:

Ph.D. Thesis
 Pub Date:
 1991
 Bibcode:
 1991PhDT.........7V
 Keywords:

 Engineering: Nuclear; Physics: Fluid and Plasma; Engineering: Electronics and Electrical;
 Algorithms;
 Impurities;
 Plasma Composition;
 Plasma Pinch;
 Plasmas (Physics);
 Reverse Field Pinch;
 Transport Theory;
 Mathematical Models;
 Parallel Processing (Computers);
 Simulation;
 Plasma Physics