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Resistive pressure driven RFP modes are not removed by heat conduction effects
KTH, School of Electrical Engineering (EES), Fusion Plasma Physics. KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.ORCID iD: 0000-0001-6379-1880
KTH, School of Electrical Engineering (EES), Fusion Plasma Physics. KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
2012 (English)In: 39th EPS Conference on Plasma Physics 2012, EPS 2012 and the 16th International Congress on Plasma Physics: Volume 3, 2012, 2012, 1690-1693 p.Conference paper, Published paper (Refereed)
Abstract [en]

During the last decade it has been shown theoretically, numerically and experimentally that current driven, resistive tearing modes can be significantly suppressed in the reversed-field pinch (RFP). In these advanced scenarios, the confinement time can be enhanced by a factor 5-10. Pressure driven resistive instabilities (g-modes) still stand in the way, however, for high RFP confinement. Classical theory [1] shows that the unfavourable RFP curvature inevitably leads to unacceptably large linear growth rates even at high Lundquist numbers. Later theory [2] demonstrates, however, that the classical assumption of adiabatic plasma energy dynamics is inaccurate. The reason is that anomalously large experimental perpendicular heat conduction, together with strong parallel heat conduction, to a certain extent outbalance the pressure terms of the plasma energy equation. Resulting resistive length scales appear to extend the resistive layer at the resonance to allow for fully stable, finite beta RFP configurations. In the present work we show theoretically that the latter result is limited to low beta only and that it scales unfavourably with Lundquist number. Numerical solution, using a novel time-spectral method [3] of the linearised resistive MHD initial-value equations including heat conduction, ohmic heating and resistivity, supports the analytical results

Place, publisher, year, edition, pages
2012. 1690-1693 p.
National Category
Fusion, Plasma and Space Physics
Identifiers
URN: urn:nbn:se:kth:diva-105504Scopus ID: 2-s2.0-84876917604ISBN: 978-162276981-0 (print)OAI: oai:DiVA.org:kth-105504DiVA: diva2:571193
Conference
39th EPS Conference on Plasma Physics and 16th Int. Congress on Plasma Physics, Stockholm, Sweden, 2-6 July 2012
Note

QC 20130115

Available from: 2012-11-21 Created: 2012-11-21 Last updated: 2013-09-10Bibliographically approved
In thesis
1. Pressure driven instabilities in the reversed-field pinch: numerical and theoretical studies
Open this publication in new window or tab >>Pressure driven instabilities in the reversed-field pinch: numerical and theoretical studies
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

According to classical linearized resistive magnetohydrodynamics theory, pressuredriven modes are unstable in the reversed-field pinch (RFP) due to unfavorable magnetic field line curvature. The result is based on the assumption of an adiabatic energy equation where anisotropic thermal conduction effects are ignored as compared to convection and compression. In this thesis the effects of heat conduction in the energy equation have been studied. We have examined these effects on the linear stability of pressure-driven resistive modes using boundary value theory (Δ´ ) and a novel initial-value full resistive MHD code employing the Generalized Weighted Residual Method (GWRM). In the Δ´ method, a shooting technique is employed by integrating from the resistive layer to boundaries. The GWRM method, on the other hand, is a time-spectral Galerkin method in which the fully linearized MHD equations are solved. For detailed computations, efficiency requires the temporal and spatial domains to be divided into subdomains. For this purpose, a number of challenging test cases including linearized ideal MHD equations are treated.

Numerical and analytical investigations of equilibria reveal that thermal conduction effects are not stabilizing for reactor relevant values of Lundquist number, S0, and normalized pressure, βθ, for tearing-stable plasmas. These studies show that growth rate scales as  γ~_ S0−1/5 , which is weaker than for the adiabatic case, γ~_ S0−1/3.

A numerical study of optimized confinement for an advanced RFP scenario including ohmic heating and heat conduction, is also part of this thesis. The fully nonlinear resistive MHD code DEBSP has been employed. We have identified, using both Δ´ and GWRM methods, that the observed crash of the high confinement is caused by resistive, pressure-driven modes.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2013. xi, 56 p.
Series
Trita-EE, ISSN 1653-5146 ; 2013:017
Keyword
Fusion plasma, thermonuclear, Reversed-field pinch, resistive MHD, resistive g modes, thermal conduction, the boundary value theory
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:kth:diva-121345 (URN)978-91-7501-722-8 (ISBN)
Public defence
2013-05-17, Sal F3, Lindstedtsvägen 26, KTH, Stockholm, 14:00 (English)
Opponent
Supervisors
Note

QC 20130503

Available from: 2013-05-02 Created: 2013-04-29 Last updated: 2013-05-02Bibliographically approved

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Scheffel, Jan

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