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Title:Computational Studies of Ohmic Heating in the Spheromak
Author(s):Olson, Richard Edward
Department / Program:Nuclear Engineering
Discipline:Nuclear Engineering
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Engineering, Nuclear
Abstract:Time-dependent computational simulations using both single-fluid O-D and two-fluid 1 1/2-D models are developed for and utilized in an investigation of the ohmic heating of a spheromak plasma. The plasma density and composition, the applied magnetic field strength, the plasma size, and the plasma current density profile are considered for their effects on the spheromak heating rate and maximum achievable temperature. The feasibility of ohmic ignition of a reactor-size spheromak plasma is also contemplated.
The ratio between the externally applied magnetic field strength, B(,e), and the plasma particle density--plasma radius product, nr(,p), is proposed as a key parameter in the determination of the spheromak plasma heating rates and temperature limits. If B(,e)/nr(,p) is too large, excessive magnetic fluctuation will limit the plasma heating. A low B(,e)/nr(,p) will result in excessive radiation losses. In general, the optimum parameter regime for spheromak heating is found to be centered at B(,e)/nr(,p) (TURN) 1-5 x 10('-20) Wb.
The radiation losses and temperature limits in the high density (low B(,e)/nr(,p)) regime are found to be especially sensitive to the plasma composition. In particular, concentrations of (TURN)1% oxygen and (TURN)0.1% iron place significant limitations on the maximum achievable plasma temperature and cause an enhancement of poloidal flux surface decay. Ideal soft-(beta) limits and resistive interchange instabilities provide additional limitations on the heating in small, low-field spheromaks.
The relationship between the initial current profile shape and the temperature profile evolution has been considered. Although a flat initial current density profile is desirable, excessive "flatness" will lead to the evolution of a hollow temperature profile, hence an enhanced transfer of energy to the edge region of the plasma and increased energy losses.
This work has also led to new ideas concerning the ohmically ignited spheromak reactor, concept, the stabilization of spheromak tilting, the origin and effects of magnetic fluctuations, the nature of resistive interchange braided-field transport, the inductive recovery of magnetic energy in an expansion chamber, and the computational solution of the Grad-Shafranoy equilibrium equation.
Issue Date:1983
Description:183 p.
Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1983.
Other Identifier(s):(UMI)AAI8324614
Date Available in IDEALS:2014-12-16
Date Deposited:1983

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