Transport of impure plasma with arbitrary toroidal rotation

Wong, S. K.

doi:10.1063/1.866333

Cited by 41 publications

(51 citation statements)

References 15 publications

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“…Often it is assumed, sometimes incorrectly, that transport along the magnetic field is strong enough to make the density and temperature of all species flux-functions to first order in d ¼ q=L, the ion gyroradius normalized the radial scale length, which is ( 1 over most of the plasma volume. But, as has been pointed out by several authors, [1][2][3][4][5][6][7][8][9][10] it is possible to sustain gradients in impurity pressure along the field, even while retaining the nominal flux-surface symmetry of the main-ion and electron species. Recent theoretical work suggests that such poloidal variations of high-Z impurity density can have a large impact on their turbulence-driven, flux-surface averaged radial transport, 11,12 increasing the importance of a fully validated theory for n z ðhÞ.…”

Section: Introductionmentioning

confidence: 96%

Parallel transport studies of high-Z impurities in the core of Alcator C-Mod plasmas

et al. 2013

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Measurements of poloidal variation, ñz/⟨nz⟩, in high-Z impurity density have been made using photodiode arrays sensitive to vacuum ultraviolet and soft x-ray emission in Alcator C-Mod plasmas. In/out asymmetries in the range of −0.2<nz,cos/⟨nz⟩<0.3 are observed for r/a<0.8, and accumulation on both the high-field side, nz,cos<0, and low-field side, nz,cos>0, of a flux surface is found to be well described by a combination of centrifugal, poloidal electric field, and ion-impurity friction effects. Up/down asymmetries, −0.05<nz,sin/⟨nz⟩<0.10, are observed over 0.5<r/a<0.9 with nz,sin>0 corresponding to accumulation opposite the ion ∇B drift direction. Measurements of the up/down asymmetry of molybdenum are found to disagree with predictions from recent neoclassical theory in the trace limit, nzZ2/ni≪1. Non-trace levels of impurities are expected to modify the main-ion poloidal flow and thus change friction-driven impurity density asymmetries and impurity poloidal rotation, vθ,z. Artificially modifying main-ion flow in parallel transport simulations is shown to impact both ñz/⟨nz⟩ and vθ,z, but simultaneous agreement between measured and predicted up/down and in/out asymmetry as well as impurity poloidal rotation is not possible for these C-Mod data. This link between poloidal flow and poloidal impurity density variation outlines a more stringent test for parallel neoclassical transport theory than has previously been performed. Measurement and computational techniques specific to the study of poloidal impurity asymmetry physics are discussed as well.

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Section: Introductionmentioning

confidence: 96%

Parallel transport studies of high-Z impurities in the core of Alcator C-Mod plasmas

et al. 2013

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“…• A reduction of the overall magnitude of the neoclassical transport, in particular, by a reduction of the usual low field side (LFS) localization of the W density produced by centrifugal (CF) effects, 7,8 which is known to produce an enhancement of the neoclassical transport. [9][10][11][12][13] This can be obtained by a reduction of the plasma toroidal rotation, or by the impact of auxiliary heating systems. In particular, ion cyclotron resonance heating (ICRH) produces a temperature anisotropy of the resonant minority species, which consequently develops a poloidally asymmetric density distribution and impacts the poloidal asymmetry of the background electrostatic potential, as well as the asymmetry of the W density.…”

Section: Introductionmentioning

confidence: 99%

The impact of poloidal asymmetries on tungsten transport in the core of JET H-mode plasmas

et al. 2015

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Recent progress in the understanding and prediction of the tungsten behaviour in the core of JET H-mode plasmas with ITER-like wall is presented. Particular emphasis is given to the impact of poloidal asymmetries of the impurity density. In particular, it is shown that the predicted reduction of temperature screening induced by the presence of low field side localization of the tungsten density produced by the centrifugal force is consistent with the observed tungsten behaviour in a JET discharge in H-mode baseline scenario. This provides first evidence of the role of poloidal asymmetries in reducing the strength of temperature screening. The main differences between plasma parameters in JET baseline and hybrid scenario discharges which affect the impact of poloidally asymmetric density on the tungsten radial transport are identified. This allows the conditions by which tungsten accumulation can be avoided to be more precisely defined.

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“…Central radio frequency (RF) heating has been identified as a reliable method to limit the central concentration of heavy impurities [1][2][3][4][5][6][7][8][9]. Since the behaviour and the profile shapes of heavy impurities are determined by both turbulent [10][11][12][13][14][15][16][17][18][19][20][21][22][23] and neoclassical transport [25][26][27][28][29][30], and are also affected by the presence of magneto-hydrodynamic (MHD) instabilities [6,[31][32][33][34][35], the physics behind the reduction of the central peaking of the W density produced by central RF heating can be expected to involve a certain level of complexity, in which multiple effects are combined. Central RF heating not only modifies the temperature, density and rotation profiles of the main plasma, but can also directly modify the impurity transport.…”

Section: Introductionmentioning

confidence: 99%

A comparison of the impact of central ECRH and central ICRH on the tungsten behaviour in ASDEX Upgrade H-mode plasmas

et al. 2017

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A comparison of the impact of additional central electron cyclotron resonance heating (ECRH) and ion cyclotron resonance heating (ICRH) on the behaviour of the tungsten (W) density in the core of H-mode plasmas heated with neutral beam injection (NBI) is performed in ASDEX Upgrade. Both localized and broad profiles of the power density of the ECRH have been obtained, where broad profiles reproduce the profile shape of the ICRH power density, which is applied with a hydrogen minority heating scheme. In contrast to ECRH, which produces direct electron heating only, ICRH eventually heats both electrons and ions in almost equal fractions. It is found that both additional RF heating systems reduce the peaking of the W density profile with increasing central RF heating power. Approximately the same values of W density peaking are obtained when the same values of electron heating are produced by the two RF heating systems, which implies that less total heating power is required with ECRH than with ICRH to reduce the W density peaking. A related modelling activity shows that an important ingredient to explain the experimentally observed trend is the variation of the turbulent W diffusion as a function of the electron to ion heat flux ratio. Additional effects are connected with the more favorable W neoclassical transport convection in the presence of ICRH, produced by the combination of stronger central ion temperature gradients and the impact of the H minority on the W poloidal density asymmetry.

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Transport of impure plasma with arbitrary toroidal rotation

Cited by 41 publications

References 15 publications

Parallel transport studies of high-Z impurities in the core of Alcator C-Mod plasmas

Parallel transport studies of high-Z impurities in the core of Alcator C-Mod plasmas

The impact of poloidal asymmetries on tungsten transport in the core of JET H-mode plasmas

A comparison of the impact of central ECRH and central ICRH on the tungsten behaviour in ASDEX Upgrade H-mode plasmas

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