Experimental and Theoretical Stability Limits of Highly Elongated Tokamak Plasmas

Hofmann, F.; Sauter, O.; Reimerdes, H.; Furno, I.; Pochelon, A.

doi:10.1103/physrevlett.81.2918

Cited by 37 publications

(33 citation statements)

References 24 publications

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“…This figure suggests that β N and q * are parameters well suited for describing the dependence of the profileoptimized no-wall stability limit on safety factor across plasma aspect ratio. This finding extends early analytic treatments of the tokamak current limit [18] to more realistic profiles and appears to be consistent with experimental stability data [19,20] at high normalized current I P /aB t0 from standard aspect ratio tokamaks.…”

supporting

confidence: 71%

Unified Ideal Stability Limits for Advanced Tokamak and Spherical Torus Plasmas

Menard¹,

Bell²,

Bell³

et al. 2003

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Ideal magnetohydrodynamic stability limits of shaped tokamak plasmas with high bootstrap fraction are systematically determined as a function of plasma aspect ratio. For plasmas with and without wall stabilization of external kink modes, the computed limits are well described by distinct and nearly invariant values of a normalized beta parameter utilizing the total magnetic field energy density inside the plasma. Stability limit data from the low aspect ratio National Spherical Torus Experiment is compared to these theoretical limits and indicates that ideal non-rotating plasma no-wall beta limits have been exceeded in regimes with sufficiently high cylindrical safety factor. These results could impact the choice of aspect ratio in future fusion power plants. Introduction -The superconducting advanced tokamak [1, 2] is presently the leading candidate for producing an efficient magnetic fusion reactor. Alternative concepts such as the compact stellarator [3,4] and spherical torus [5][6][7] are also actively being pursued as possible improvements to the advanced tokamak. The advanced tokamak (AT) and spherical torus (ST) reactor concepts have several features in common. In particular, both rely on the neoclassical bootstrap current [8] to sustain nearly all of the plasma current and on stabilization of pressure-driven external kink modes to achieve sufficiently high beta (ratio of plasma kinetic pressure to magnetic pressure) to produce power efficiently. The AT and ST reactor concepts have been independently optimized for various physics and engineering constraints and arrive at notably different plasma aspect ratio and beta. This difference has motivated the present work which seeks to understand how the theoretical ideal magnetohydrodynamic (MHD) stability limits of the AT and ST are linked. More generally, aspect ratio invariants of stability are sought.The first equilibrium regime studied consists of fully self-driven plasmas utilizing a close-fitting conducting wall to stabilize external kink modes. The stability limits of this regime represent the maximum achievable beta for this class of equilibrium at any aspect ratio given the present understanding of the relevant physics. The second regime studied consists of plasmas with a self-driven current fraction of 50% and no conducting wall stabilization of the external kink mode. The stability limits of this regime have largely been experimentally realized in present-day tokamaks [9] but have only recently been realized in relatively new ST experiments. Finally, the no-wall current limit is studied for typical AT and ST configurations. These studies show that the degeneracy

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supporting

confidence: 71%

Unified Ideal Stability Limits for Advanced Tokamak and Spherical Torus Plasmas

Menard¹,

Bell²,

Bell³

et al. 2003

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“…Plasma shape is one of the fundamental parameters in a tokamak that strongly influences plasma properties and performance, placing also strong constraints on technological and construction choices in machine design. Increasing the elongation allows higher plasma current and also influences other operational limits such as the pressure [1,2] and density limits [3]. Triangularity and elongation have a strong influence on the core stability, e.g.…”

Section: Introductionmentioning

confidence: 99%

Electron heat transport in shaped TCV L-mode plasmas

Camenen

Pochelon

Bottino

et al. 2005

Plasma Phys. Control. Fusion

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Electron heat transport experiments are performed in L-mode discharges at various plasma triangularities, using radially localized electron cyclotron heating to vary independently both the electron temperature T e and the normalized electron temperature gradient R/L T e over a large range. Local gyrofluid (GLF23) and global collisionless gyro-kinetic (LORB5) linear simulations show that, in the present experiments, trapped electron mode (TEM) is the most unstable mode. Experimentally, the electron heat diffusivity χ e is shown to decrease with increasing collisionality, and no dependence of χ e on R/L T e is observed at high R/L T e values. These two observations are consistent with the predictions of TEM simulations, which supports the fact that TEM plays a crucial role in electron heat transport. In addition, over the broad range of positive and negative triangularities investigated, the electron heat diffusivity is observed to decrease with decreasing plasma triangularity, leading to a strong increase of plasma confinement at negative triangularity.

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“…However there are limits to the density, pressure and current which a plasma can withstand and above which MHD instabilities occur, destroying the desired configuration. The influence of plasma shape on MHD stability was theoretically studied in [2,3] and has been experimentally observed in the TCV, DIII-D and JET tokamaks in various scenarios [3][4][5][6].…”

Section: Introduction and Overview Of Tcv Experimentsmentioning

confidence: 99%

The effect of plasma triangularity on turbulent transport: modeling TCV experiments by linear and non-linear gyrokinetic simulations

Marinoni¹,

Brunner²,

Camenen³

et al. 2009

Plasma Phys. Control. Fusion

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The effect of plasma shape on confinement has been experimentally explored in the TCV tokamak revealing that the core electron heat transport is significantly reduced by a negative triangularity configuration, which could indicate a (partial) stabilization of the microinstabilities at play in a conventional positive triangularity configuration.This work is a theoretical investigation of the effect exerted by triangularity on plasma turbulence. In particular, it compares the TCV experimental results with non-linear local gyrokinetic simulations performed on the basis of actual MHD equilibrium reconstructions.In both the linear and non-linear phases, negative triangularity is found to have a stabilizing influence on ion-scale instabilities, specifically on the so-called trapped electron mode (TEM) which is the dominant instability in the conditions of the TCV experiments considered; more specifically, the variation of the heat flux with triangularity calculated by the non-linear simulations is in fair agreement with the experimental results.The resulting stabilization is a result of a rather complex modification of the toroidal precessional drift of trapped particles exerted by negative triangularity.

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Experimental and Theoretical Stability Limits of Highly Elongated Tokamak Plasmas

Cited by 37 publications

References 24 publications

Unified Ideal Stability Limits for Advanced Tokamak and Spherical Torus Plasmas

Unified Ideal Stability Limits for Advanced Tokamak and Spherical Torus Plasmas

Electron heat transport in shaped TCV L-mode plasmas

The effect of plasma triangularity on turbulent transport: modeling TCV experiments by linear and non-linear gyrokinetic simulations

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