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Static current profile control and RFP confinement
KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.ORCID iD: 0000-0001-6379-1880
University of Wisconsin.
KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
2013 (English)In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 53, no 11, 113007- p.Article in journal (Refereed) Published
Abstract [en]

Static current profile control (CPC) is shown numerically to substantially enhance plasma confinement in the reversed-field pinch (RFP). By suitable application of an auxiliary electric field and adjustment of its internal location, width and amplitude, strongly decreased levels of dynamo fluctuations are obtained. The simulations are performed using a fully non-linear, resistive magnetohydrodynamic model, including the effects of ohmic heating as well as parallel and perpendicular heat conduction along stochastic field lines. The importance of controlling the parallel current profile in the core plasma to minimize the effects of tearing modes on confinement is thus confirmed. A near three-fold increase in energy confinement is found and poloidal plasma beta increases by 30% from 0.20 to 0.27. The edge heat flux is reduced to a third of that of the conventional RFP. The high-confinement phase is interrupted here by a crash, characterized by a rapid decrease in confinement. A detailed study of the crash phase is carried out by the standard Delta' theory and a fully resistive linearized time-spectral method; the generalized weighted residual method. The analysis suggests that the instability is caused by pressure-driven, resistive g-modes. Inclusion of anisotropic thermal conduction reduces the linear growth rates. As compared with our earlier numerical studies of CPC in the RFP, employing feedback control, the present static control scheme should be more easily implemented experimentally.

Place, publisher, year, edition, pages
Institute of Physics (IOP), 2013. Vol. 53, no 11, 113007- p.
Keyword [en]
Reversed-Field Pinch, Current Drive, High-Beta, Fluctuation, Reduction
National Category
Fusion, Plasma and Space Physics
URN: urn:nbn:se:kth:diva-121596DOI: 10.1088/0029-5515/53/11/113007ISI: 000326684400008ScopusID: 2-s2.0-84887107572OAI: diva2:619227

QC 20131209

Available from: 2013-05-02 Created: 2013-05-02 Last updated: 2013-12-09Bibliographically 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.
Trita-EE, ISSN 1653-5146 ; 2013:017
Fusion plasma, thermonuclear, Reversed-field pinch, resistive MHD, resistive g modes, thermal conduction, the boundary value theory
National Category
Fusion, Plasma and Space Physics
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)

QC 20130503

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

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