Internal transport barriers in tokamak plasmas*

Wolf, R. C.

doi:10.1088/0741-3335/45/1/201

Cited by 330 publications

(327 citation statements)

References 369 publications

(547 reference statements)

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“…Realization of advanced tokamak operation in ITER and future reactors requires operating a plasma in an enhanced confinement regime, likely characterized by the existence of core transport barriers. [1][2][3] Necessarily this is rekindling interest in internal transport barrier (ITB) dynamics and/or the improvement of ion thermal confinement at zero or low external torque, because of the limited capability of driving the necessary torque in a reactor by neutral beam injection (NBI). Most of the ion ITBs in current experiments have been observed when sufficiently large external momentum is delivered by NBI.…”

Section: Role Of External Torque In the Formation Of Ion Thermal Intementioning

confidence: 99%

Role of external torque in the formation of ion thermal internal transport barriers

2012

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We present an analytic study of the impact of external torque on the formation of ion internal transport barriers (ITBs). A simple analytic relation representing the effect of low external torque on transport bifurcations is derived based on a two field transport model of pressure and toroidal momentum density. It is found that the application of an external torque can either facilitate or hamper bifurcation in heat flux driven plasmas depending on its sign relative to the direction of intrinsic torque. The ratio between radially integrated momentum (i.e., external torque) density to power input is shown to be a key macroscopic control parameter governing the characteristics of bifurcation.

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Section: Role Of External Torque In the Formation Of Ion Thermal Intementioning

confidence: 99%

Role of external torque in the formation of ion thermal internal transport barriers

2012

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“…This is not only because of the impact on plasma confinement due to turbulence suppression by sheared flows [44,45], which give rise to internal transport barriers (ITB), but also due to the impact of flow on MHD stability [46,47]. Plasmas in NBI heated spherical tokamaks show a fast toroidal rotation with thermal Mach numbers measured on MAST of up to M th = v φ /v th 0.8 [48].…”

Section: Momentum Confinementmentioning

confidence: 99%

Overview of physics results from MAST

Raman¹,

Ahn²,

Allain³

et al. 2011

Nucl. Fusion

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Several improvements to the MAST plant and diagnostics have facilitated new studies advancing the physics basis for ITER and DEMO, as well as for future spherical tokamaks. Using the increased heating capabilities P NBI ≤ 3.8 MW H-mode at I p = 1.2 MA was accessed showing that the energy confinement on MAST scales more weakly with I p and more strongly with B t than in the ITER IPB98(y,2) scaling. Measurements of the fuel retention of shallow pellets extrapolate to an ITER particle throughput of 70% of its original design value. The anomalous momentum diffusion, χ φ , is linked to the ion diffusion, χ i , with a Prandtl number close to P φ ≈ χ φ /χ i ≈ 1, although χ i approaches neoclassical values. New high spatially resolved measurements of the edge radial electric field, E r , show that the position of steepest gradients in electron pressure and E r are coincident, but their magnitudes are not linked. The T e pedestal width on MAST scales with the β pol rather than ρ pol . The ELM frequency for type-IV ELMs, new in MAST, was almost doubled using n = 2 resonant magnetic perturbations from a set of 4 external coils (n = 1, 2). A new internal 12 coil set (n ≤ 3) has been commissioned. The filaments in the inter-ELM and L-mode phase are different from ELM filaments, and the characteristics in L-mode agree well with turbulence calculations. A variety of fast particle driven instabilities were studied from 10 kHz saturated fishbone like activity up to 3.8 MHz compressional Alfvén eigenmodes (CAE). The damping rate of ellipticityinduced AE was measured to be 4% using the new internal coils as antennae. Fast particle instabilities also affect the off-axis NBI current drive and lead to fast ion diffusion of the order of 0.5 m 2 /s and reduce the driven current fraction from 40% to 30%. EBW current drive start-up is demonstrated for the first time in a spherical tokamak generating plasma currents up to 55 kA. Many of these studies contributed to the physics basis of a planned upgrade to MAST. Introduction: MAST [1]is one of the two leading tight aspect ratio (A = ε −1 = R/a = 0.85 m/0.65 m ∼ 1.3, I p ≤ 1.5 MA) tokamaks in the world. The hot T ≤ 3 keV, dense n e = (0.1 − 1) × 10 20 m −3 and highly shaped (δ ≤ 0.5, 1.6 ≤ κ ≤ 2.5) plasmas are accessed at moderate toroidal field B t (R = 0.7 m) ≤ 0.62 T and show many similarities to conventional aspect ratio tokamaks. Detailed physics studies using the extensive array of state of the art diagnostics and access to different physics regimes help to consolidate the physics basis for ITER and DEMO [2,3], and explore the viability of future devices based on the spherical tokamak (ST) concept such as a component test facility (CTF) [4] or an advanced power plant [5]. The challenge for today's experiments is to find an integrated scenario that extrapolates to these future devices, in particular to develop plasmas with reduced power load on plasma facing components, notably from edge localised modes (ELM), but high confinement facilitated by internal or edge transport ba...

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“…On the other hand, the former is useful for easy identification of an ITB. A normalized temperature gradient R/L T is often used for ITB definition when ITBs are compared between different devices, where R and L T are the major radius of the plasma and the scale length of temperature gradient, respectively [7]. This definition is based on the so-called "critical gradient scale length model" of transport [8].…”

Section: Introductionmentioning

confidence: 99%

Parameter Regime of Ion Internal Transport Barrier Formation in the Large Helical Device

Nagaoka

Takeiri

Ida

et al. 2010

Plasma and Fusion Research

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Improvement of ion heat transport was observed in the core plasma heated by neutral beam injection (NBI) in the Large Helical Device (LHD). A peaked ion temperature profile with a steep gradient (an ion internal transport barrier, ion ITB) formed in the plasma. To investigate the formation conditions of the ion ITB, a simple definition of ITB based on the reversal of the temperature gradient between the core and the edge is proposed. An ion ITB formed in the low-collisionality regime of 1/ν with low density and high ion heating power in the LHD.

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Internal transport barriers in tokamak plasmas*

Cited by 330 publications

References 369 publications

Role of external torque in the formation of ion thermal internal transport barriers

Role of external torque in the formation of ion thermal internal transport barriers

Overview of physics results from MAST

Parameter Regime of Ion Internal Transport Barrier Formation in the Large Helical Device

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