Improved plasma performance in tokamaks with negative magnetic shear

Kessel, C.; Manickam, J.; Rewoldt, G.; Tang, W. M.

doi:10.1103/physrevlett.72.1212

Cited by 378 publications

(264 citation statements)

References 11 publications

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“…The NCSRS regime combines high confinement, potentially high beta limits with wall stabilization, high bootstrap fraction with well-aligned bootstrap current (Turnbull 1995, Kessel 1994. With increased emphasis around the world in progress toward steady-state high performance scenarios, for example in the TPX design studies (Goldston 1994, Davidson 1993, and the DIII-D advanced tokamak program (Simonen 1992, Taylor 1994; there has been renewed interest in the NCS regime.…”

Section: Negative Central Magnetic Shear (Ncs/lis/optimized Shear)mentioning

confidence: 99%

Physics of advanced tokamaks

Taylor¹

1997

Plasma Phys. Control. Fusion

208

153

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Significant reductions in the size and cost of a fusion power plant core can be realized if simultaneous improvements in the energy replacement time, τ E , and the plasma pressure or beta, β T = 2 µ 0 P /B 2 can be achieved in steady-state conditions with high selfdriven, bootstrap current fraction. Significant recent progress has been made in experimentally achieving these high performance regimes and in developing a theoretical understanding of the underlying physics. Three operational scenarios have demonstrated potential for steadystate high performance, the radiative improved mode, the high internal inductance or high i scenario, and the negative central magnetic shear, NCS (or reversed shear) scenario. In a large number of tokamaks, reduced ion thermal transport to near neoclassical values, and reduced particle transport have been observed in the region of negative or very low magnetic shear: the transport reduction is consistent with stabilization of microturbulence by sheared E × B flow. There is strong temporal and spatial correlation between the increased sheared E × B flow, the reduction in the measured turbulence, and the reduction in transport. The DIII-D tokamak, the JET tokamak and the JT-60U tokamak have all observed significant increases in plasma performance in the NCS operational regime. Strong plasma shaping and broad pressure profiles, provided by the H-mode edge, allow high beta operation, consistent with theoretical predictions; and normalized beta values up to β T /(I /aB) ≡ β N ∼ 4.5% m T MA −1 simultaneously with confinement enhancement over L-mode scaling, H = τ/τ ITER-89P ∼ 4, have been achieved in the DIII-D tokamak. In the JT-60U tokamak, deuterium discharges with negative central magnetic shear have reached equivalent breakeven conditions, Q DT (equiv) = 1.

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Section: Negative Central Magnetic Shear (Ncs/lis/optimized Shear)mentioning

confidence: 99%

Physics of advanced tokamaks

Taylor¹

1997

Plasma Phys. Control. Fusion

208

153

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“…Recent predictions of highly improved tokamak performance in the presence of negative (or reversed) magnetic shear [2,3] have generated great interest in understanding the beta limits of such equilibria. Moreover, recent experimental observations of greatly reduced transport in plasmas with negative central shear provide strong motivation to further explore techniques by which such equilibria may be established and maintained for time scales beyond the characteristic current diffusion time (or L/R time) [4,5].…”

Section: Introductionmentioning

confidence: 99%

Negative magnetic shear modes of operation in the Alcator C-Mod tokamak near the beta limit

Bonoli

Porkoláb

Ramos

et al. 1997

Plasma Phys. Control. Fusion

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The stability properties of non-inductively driven, reversed shear type current profiles that may be achieved for Alcator C-Mod tokamak-like parameters (aspect ratio R/a=3) are examined. It is found that without a conducting wall, the best stability results (ON up to 3.7) are achieved for highly triangular plasmas (b = 0.7) at qmin=2.2, for relatively broad pressure profiles (p(0)/pavg = 2.8) and large values of rmin/a(= 0.75). For elliptical or circular cross-section plasmas with little triangularity, the stability limits are significantly lower (QNmax=2.2).Finally, more peaked pressure profiles (p(0)/payg = 4.5) have lower beta limits than broader profiles.1

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“…[4,22,23] also relevant to the equilibria discussed here is that intermediate-n (3 B/n B/10) kink modes often determine the minimum wall separation distance provided that k is not too large. This is shown in Fig.…”

Section: Kink Stability Of Ballooning Marginal Equilibriamentioning

confidence: 99%

“…To estimate the value of a , such that Q max,0 does not exceed 10 MW/m 2 , we solve for a using Eq. (22). For the inboard divertors, this gives a 0/17.…”

Section: Dissipating Power By Divertor Shapingmentioning

confidence: 99%

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Physics basis for a spherical torus power plant

Jardin

Kessel

Ménard

et al. 2003

Fusion Engineering and Design

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The spherical torus, or low-aspect-ratio tokamak, is considered as the basis for a fusion power plant. A special class of wall-stabilized high-b high-bootstrap fraction low-aspect-ratio tokamak equilibrium are analyzed with respect to MHD stability, bootstrap current and external current drive, poloidal field system requirements, power and particle exhaust and plasma operating regime. Overall systems optimization leads to a choice of aspect ratio A0/1.6, plasma elongation k 0/3.4, and triangularity d0/0.64. The design value for the plasma toroidal b is 50%, corresponding to b N 0/7.4, (based on the toroidal b , not the total b ) which is 10% below the ideal stability limit. The bootstrap fraction of 99% greatly alleviates the current drive requirements, with tangential neutral beam injection mainly for profile control and rotation drive. The design is such that 45% of the thermal power is radiated in the plasma by Bremstrahlung and trace Krypton, with Neon in the scrapeoff layer radiating the remainder. The scarcity of spherical torus experimental data caused the design to be based largely on theoretical predictions, some of which may turn out to be overly optimistic. This highlights the need for a strong experimental research program in this area. #

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Improved plasma performance in tokamaks with negative magnetic shear

Cited by 378 publications

References 11 publications

Physics of advanced tokamaks

Physics of advanced tokamaks

Negative magnetic shear modes of operation in the Alcator C-Mod tokamak near the beta limit

Physics basis for a spherical torus power plant

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