Improved Confinement with Reversed Magnetic Shear in TFTR

Levinton, F. M.; Zarnstorff, M. C.; Batha, S. H.; Bell, M.G.; Bell, R. E.; Budny, R.; Bush, C. E.; Chang, Z.; Fredrickson, E. D.; Janos, A.; Manickam, J.; Ramsey, A. T.; Sabbagh, S. A.; Schmidt, G. L.; Synakowski, E.J.; Taylor, G.

doi:10.1103/physrevlett.75.4417

Cited by 695 publications

(517 citation statements)

References 25 publications

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“…A number of facilities have recently added the capability to accuratelv measure the internal a Drofile evolution. and this has made possible systematic study of the production a n i performance of NCY regimes (Rice' 1996a(Rice' , 1996b(Rice' , 1996cLevinton 1995;Fujita 1997aFujita , 1997b.…”

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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“…Therefore the slightly reduced set of equilibrium equations we will use in the following consists of Eqs. (2), (3), (4) for ions only, (5), (6), (7), (8), and (10). By expressing B θ in terms of the safety factor, q = rB θ /(R 0 B z ), with 2πR 0 associated with the length of the plasma column, and introducing the normalized radius ρ = r/r 0 with r 0 corresponding to the plasma surface, Eq.…”

Section: Two-fluid Cylindrical Equilibria With Reversed Magnetic Shearmentioning

confidence: 99%

“…(2)(3)(4)(5)(6)(7)(8) are advantageous in two respects: (i) the momentum equation includes the electric field and therefore the pressure gradient contribution to E can be calculated from this equation; this contribution is missing in the frame of MHD because E is calculated by Ohm's law, E + v × B = 0, and (ii) the current density J is related self-consistently to the fluid species velocities [Eq. (8)]. …”

Section: Two-fluid Cylindrical Equilibria With Reversed Magnetic Shearmentioning

confidence: 99%

“…Long quasi-steady or steady ITB states have been obtained in different tokamaks, e.g ASDEX Upgrate [1,2], JT-60U [3], Tore-Supra [4], and JET [5] where ITBs were maintained for up to 11 s. The ITBs usually are associated with reversed magnetic shear profiles [6], [7] and their main characteristics are steep pressure profiles in the barrier region [8] and radial electric fields associated with sheared flows [9,10]. The mechanism responsible for the formation of ITBs and the underlying physics is not completely understood.…”

Section: Introductionmentioning

confidence: 99%

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Two-fluid tokamak equilibria with reversed magnetic shear and sheared flow

Poulipoulis

Throumoulopoulos

Tasso³

2007

J. Plasma Phys.

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The aim of the present work is to investigate tokamak equilibria with reversed magnetic shear and sheared flow, which may play a role in the formation of internal transport barriers (ITBs), within the framework of two-fluid model. The study is based on exact self-consistent solutions in cylindrical geometry by means of which the impact of the magnetic shear, s, and the "toroidal" (axial) and "poloidal" (azimuthal) ion velocity components, v iz and v iθ , on the radial electric field, E r , its shear, |dE r /dr|, and the shear of the E × B velocity, ω E×B ≡ |d/dr(E × B/B 2 )|, is examined. For a wide parametric regime of experimental concern it turns out that the contributions of the v iz , v iθ and pressure gradient (∇P i ) terms to E r , |E ′ r | and ω E×B are of the same order of magnitude. The contribution of the ∇P i term is missing in the framework of magnetohydrodynamics (MHD) [G. Poulipoulis et al. Plasma Phys. Control. Fusion 46 (2004) 639]. The impact of s on ω E×B through the ∇P i term is stronger than that through the velocity terms; in particular for B z = constant, the contributions of the ∇P i and velocity terms to ω E×B at the point where dE r /dr = 0 are proportional to (1 − s)(2 − s) and (1 − s), respectively. The results indicate that, alike MHD, the magnetic shear and the sheared toroidal and poloidal velocities act synergetically in producing electric fields and therefore ω E×B profiles compatible with ones observed in discharges with ITBs; owing to the ∇P i term, however, the impact of s on E r , |E ′ r | and ω E×B is stronger than that in MHD.

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“…Another situation in which the presence of magnetic field chaos can help plasma confinement is the creation of a transport barrier to reduce particle escape in tokamaks. It has been recently observed that this may occur if there is a negative magnetic shear region within the plasma column [5,6]. Such a region is created by means of a non-peaked plasma current density, corresponding to a non-monotonic radial profile for the safety factor [7].…”

Section: Introductionmentioning

confidence: 99%

Non-twist field line mappings for tokamaks with reversed magnetic shear

Roberto¹,

Silva²,

Caldas³

et al. 2004

Braz. J. Phys.

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The structure of magnetic field lines in a tokamak with reversed magnetic shear is investigated by means of analytically derived area-preserving non-twist Poincaré maps. The basic configuration is the magnetic field produced by an ergodic limiter, superimposed to the tokamak equilibrium field in suitable coordinates. We consider the cases of one and two resonant modes, focusing on magnetic island dimerization and the formation of a transport barrier in the chaotic layer of field lines.

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Improved Confinement with Reversed Magnetic Shear in TFTR

Cited by 695 publications

References 25 publications

Physics of advanced tokamaks

Physics of advanced tokamaks

Two-fluid tokamak equilibria with reversed magnetic shear and sheared flow

Non-twist field line mappings for tokamaks with reversed magnetic shear

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