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Title: Spheromak Impedance and Current Amplification

Abstract

It is shown that high current amplification can be achieved only by injecting helicity on the timescale for reconnection, {tau}{sub REC}, which determines the effective impedance of the spheromak. An approximate equation for current amplification is: dI{sub TOR}{sup 2}/dt {approx} I{sup 2}/{tau}{sub REC} - I{sub TOR}{sup 2}/{tau}{sub closed} where I is the gun current, I{sub TOR} is the spheromak toroidal current and {tau}{sub CLOSED} is the ohmic decay time of the spheromak. Achieving high current amplification, I{sub TOR} >> I, requires {tau}{sub REC} <<{tau}{sub CLOSED}. For resistive reconnection, this requires reconnection in a cold zone feeding helicity into a hot zone. Here we propose an impedance model based on these ideas in a form that can be implemented in the Corsica-based helicity transport code. The most important feature of the model is the possibility that {tau}{sub REC} actually increases as the spheromak temperature increases, perhaps accounting for the ''voltage sag'' observed in some experiments, and a tendency toward a constant ratio of field to current, B {proportional_to} I, or I{sub TOR} {approx} I. Program implications are discussed.

Authors:
; ;
Publication Date:
Research Org.:
Lawrence Livermore National Lab., CA (US)
Sponsoring Org.:
US Department of Energy (US)
OSTI Identifier:
15004646
Report Number(s):
UCRL-ID-147087
TRN: US0304915
DOE Contract Number:  
W-7405-ENG-48
Resource Type:
Technical Report
Resource Relation:
Other Information: PDF-FILE: 16 ; SIZE: 0.5 MBYTES; PBD: 31 Jan 2002
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; 72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; AMPLIFICATION; DECAY; FEEDING; HELICITY; IMPEDANCE; TRANSPORT

Citation Formats

Fowler, T K, Hua, D D, and Stallard, B W. Spheromak Impedance and Current Amplification. United States: N. p., 2002. Web. doi:10.2172/15004646.
Fowler, T K, Hua, D D, & Stallard, B W. Spheromak Impedance and Current Amplification. United States. doi:10.2172/15004646.
Fowler, T K, Hua, D D, and Stallard, B W. Thu . "Spheromak Impedance and Current Amplification". United States. doi:10.2172/15004646. https://www.osti.gov/servlets/purl/15004646.
@article{osti_15004646,
title = {Spheromak Impedance and Current Amplification},
author = {Fowler, T K and Hua, D D and Stallard, B W},
abstractNote = {It is shown that high current amplification can be achieved only by injecting helicity on the timescale for reconnection, {tau}{sub REC}, which determines the effective impedance of the spheromak. An approximate equation for current amplification is: dI{sub TOR}{sup 2}/dt {approx} I{sup 2}/{tau}{sub REC} - I{sub TOR}{sup 2}/{tau}{sub closed} where I is the gun current, I{sub TOR} is the spheromak toroidal current and {tau}{sub CLOSED} is the ohmic decay time of the spheromak. Achieving high current amplification, I{sub TOR} >> I, requires {tau}{sub REC} <<{tau}{sub CLOSED}. For resistive reconnection, this requires reconnection in a cold zone feeding helicity into a hot zone. Here we propose an impedance model based on these ideas in a form that can be implemented in the Corsica-based helicity transport code. The most important feature of the model is the possibility that {tau}{sub REC} actually increases as the spheromak temperature increases, perhaps accounting for the ''voltage sag'' observed in some experiments, and a tendency toward a constant ratio of field to current, B {proportional_to} I, or I{sub TOR} {approx} I. Program implications are discussed.},
doi = {10.2172/15004646},
journal = {},
number = ,
volume = ,
place = {United States},
year = {2002},
month = {1}
}

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