Stable Alfven Wave Dynamo Action in the Reversed Field Pinch
Werley, Kenneth Alan
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https://hdl.handle.net/2142/70892
Description
Title
Stable Alfven Wave Dynamo Action in the Reversed Field Pinch
Author(s)
Werley, Kenneth Alan
Issue Date
1984
Department of Study
Nuclear Engineering
Discipline
Nuclear Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Nuclear
Abstract
Previous theoretical work has suggested that Alfven waves may be related to the anomalous toroidal magnetic flux generation and extended (over classical expectations) discharge times observed in the reversed field pinch. This thesis examines the dynamo action of stable Alfven waves as a means of generating toroidal flux, (PHI)(,z). Recent advances in linear resistive MHD stability analysis are used to calculate the quasi-linear dynamo mean electromotive force, , of Alfven waves. This emf is incorporated into a one-dimensional transport and mean-field evolution code. The changing equilibrium is then fed back to the stability code to complete a computational framework that self-consistently evaluates a dynamic plasma dynamo. This technique is readily extendable to other plasmas in which dynamic stable mode action is of interest. Such plasmas include Alfven wave current-drive and plasma heating for fusion devices, as well as astrophysical and geophysical dynamo systems.
Static quasi-linear Alfven wave calculations have shown that dynamo emfs on the order of(' )(eta)J are possible. This suggested a possible explanation of RFP behavior and a new (externally driven) mechanism for extending operation and controlling field profiles (possibly reducing plasma transport). This thesis demonstrates that the dynamo emf can quickly induce plasma currents whose emf cancels the dynamo effect. Thus, the ability of Alfven waves to provide significant dynamo action is greatly reduced. Consequently, single wave dynamo action is too weak to explain ZT-40 behavior. However, multiple mode action can increase the dynamo effect, not by increasing the dynamo emf, but by reducing the induction rate of the cancelling current. This is accomplished by reducing the curvature of the dynamo emf {B(' )=(' )-(DEL)xE(r)}. A new dimensionless parameter, X {defined as the dynamo-to-resistive ratio of ((PHI)(,z)) times (the induction time)}, estimates the (PHI)(,z) generation capability of a given emf. Heavily damped modes provide the largest X values. However, when steadily maintained, their emfs change drastically. Thus, detailed external drive boundary condition studies are required to evaluate the feasibility of external drive.
This thesis also contains extensive studies of resistive Alfven wave properties. This includes behavior versus spectral location, magnetic Reynolds number and wave number.
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