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Publication# Stability limits for tokamak plasma with negative triangularity

Olivier Sauter, Laurent Villard, Holger Reimerdes, Antoine Pochelon, Andrei Martynov

2014

Conference paper

2014

Conference paper

Abstract

Negative triangularity tokamak plasmas are subject of an increased interest both in existing experiments and in studies of core physics as well as power handling relevant to the fusion demonstration power reactor. The ideal MHD stability calculations for the negative triangularity plasma extend the investigation of the TCV tokamak beta limits and edge stability to double null shapes, lower aspect ratio and negative shear. In case of the negative triangularity, the 2nd stability access is closed for ballooning modes and a well defined limiting pressure gradient profile exists in the positive shear region. The external kink mode stability limit can be obtained by rescaling the limiting profiles. H-mode discharges with upper negative triangularity in TCV demonstrate significant mitigation of type I ELM peak power losses. This is consistent with lower edge stability limits for the pedestal. For double null negative triangularity configurations higher pedestals can be stable due to higher shear at low pedestal current density. At the same time a destabilization of a whole range of fixed boundary modes takes place, once the Mercier criterion for localized modes is violated, implying possible changes in the ELM characteristics. In particular, the diamagnetic stabilization on the edge stability is much less effective than in a standard case when peeling-ballooning modes set pedestal height limit.

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Plasma stability

The stability of a plasma is an important consideration in the study of plasma physics. When a system containing a plasma is at equilibrium, it is possible for certain parts of the plasma to be disturbed by small perturbative forces acting on it. The stability of the system determines if the perturbations will grow, oscillate, or be damped out. In many cases, a plasma can be treated as a fluid and its stability analyzed with magnetohydrodynamics (MHD).

Tokamak

A tokamak (ˈtoʊkəmæk; токамáк) is a device which uses a powerful magnetic field to confine plasma in the shape of a torus. The tokamak is one of several types of magnetic confinement devices being developed to produce controlled thermonuclear fusion power. , it was the leading candidate for a practical fusion reactor. Tokamaks were initially conceptualized in the 1950s by Soviet physicists Igor Tamm and Andrei Sakharov, inspired by a letter by Oleg Lavrentiev. The first working tokamak was attributed to the work of Natan Yavlinsky on the T-1 in 1958.

Triangular matrix

In mathematics, a triangular matrix is a special kind of square matrix. A square matrix is called if all the entries above the main diagonal are zero. Similarly, a square matrix is called if all the entries below the main diagonal are zero. Because matrix equations with triangular matrices are easier to solve, they are very important in numerical analysis. By the LU decomposition algorithm, an invertible matrix may be written as the product of a lower triangular matrix L and an upper triangular matrix U if and only if all its leading principal minors are non-zero.

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Ontological neighbourhood

Stefano Coda, Justin Richard Ball

In this work, we study the impact of aspect ratio A = R 0 / r (the ratio of major radius R 0 to minor radius r) on the confinement benefits of negative triangularity (NT) plasma shaping. We use high-fidelity flux tube gyrokinetic GENE simulations and consi ...

Olivier Sauter, Stefano Coda, Justin Richard Ball, Alberto Mariani, Matteo Vallar, Filippo Bagnato

Negative triangularity (NT) scenarios in TCV have been compared to positive triangularity (PT) scenarios using the same plasma shapes foreseen for divertor tokamak test tokamak operations. The experiments provided a NT/PT L-mode pair and a PT H-mode with d ...

Olivier Sauter, Basil Duval, Stefano Coda, Benoît Labit, Alessandro Pau, Laurie Porte, Alexander Karpushov, Antoine Pierre Emmanuel Alexis Merle, Justin Richard Ball, Dmytry Mykytchuk, Filippo Bagnato

Carbon impurity transport is studied in the TCV tokamak using a charge exchange recombination diagnostic. TCVs flexible shaping capabilities were exploited to extend previous impurity transport studies to negative triangularity (delta < 0). A practical way ...