Influence of the radio frequency ponderomotive force on anomalous impurity transport in tokamaks

Nordman, Hans; Singh, Rameswar; Fülöp, Tünde; Eriksson, L.‐G.; Dümont, R.; Anderson, Johan; Kaw, P. K.; Strand, Pär; Tokar, M. Z.; Weiland, Jan

doi:10.1063/1.2908354

Cited by 24 publications

(24 citation statements)

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“…[13][14][15] The physical mechanism by which the change of the direction of the impurity convective flux occurs has not yet been clearly identified, in spite of the attempts that has been made. 3,4 When attempting to solve these issues, it is important to know when sophisticated theoretical models are needed and when it is reasonable to apply reduced models to interpret the results of experiments or numerical simulations.…”

Section: Introductionmentioning

confidence: 99%

“…1 It is therefore very important to understand the impurity transport so that accumulation in the core can be avoided. Models of impurity transport driven by microturbulence [2][3][4][5][6][7][8][9] and neoclassical processes [10][11][12] are now well developed, but there are still many open issues regarding the sign and magnitude of the impurity transport and its parametric dependencies. One example of this is the experimental observation that the direction of impurity flux depends on the auxiliary heating.…”

Section: Introductionmentioning

confidence: 99%

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Turbulent and neoclassical impurity transport in tokamak plasmas

Fülöp

Nordman

2009

Physics of Plasmas

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Impurity particle transport in tokamaks is studied using an electrostatic fluid model for main ion and impurity temperature gradient (ITG) mode and trapped electron (TE) mode turbulence in the collisionless limit and neoclassical theory. The impurity flux and impurity density peaking factor obtained from a self-consistent treatment of impurity transport are compared and contrasted with the results of the often used trace impurity approximation. Comparisons between trace and self-consistent turbulent impurity transport are performed for ITER-like profiles. It is shown that for small impurity concentrations the trace impurity limit is adequate if the plasma is dominated by ITG turbulence. However, in case of TE mode dominated plasmas the contribution from impurity modes may be significant, and therefore a self-consistent treatment may be needed.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Turbulent and neoclassical impurity transport in tokamak plasmas

Fülöp

Nordman

2009

Physics of Plasmas

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“…It further motivates impurity transport study by considering the effects of impurity profile on turbulence called non-trace impurity transport. 10-12, 30, 38, 46 No matter for non-trace or trace impurity transport, various physical interpretations regarding to the magnitude or the sign of the impurity transport as well as its parametric dependencies, such as Z, impurity mass number ( z A ) 11,14,18 and magnetic shear 30,32,47 have been widely studied.…”

Section: Introductionmentioning

confidence: 99%

“…The anomalous transport is attributed to the presence of drift wave-type turbulence. For turbulent impurity transport, the theoretical and simulation works [10][11][12][13][14][15][16][17][18][19][20][21] all hitherto existing mainly focused on ion temperature gradient mode (ITG) and trapped electron mode (TEM) turbulence.…”

Section: Introductionmentioning

confidence: 99%

Isotopic dependence of impurity transport driven by ion temperature gradient turbulence

2016

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Hydrogenic ion mass effects, namely the isotopic effects on impurity transport driven by ion temperature gradient (ITG) turbulence are investigated using gyrokinetic theory.For non-trace impurities, changing from hydrogen (H) to deuterium (D), and to tritium (T) plasmas, the outward flux for lower (higher) ionized impurities or for lighter (heavier) impurities is found to decrease (increase), although isotopic dependence of ITG linear growth rate is weak. This is mainly due to the decrease of outward (inward) convection, while the isotopic dependence of diffusion is relatively weak. In addition, the isotopic effects reduce (enhance) the impurity flux of fully ionized carbon (C 6+ ) for weaker (stronger) magnetic shear. In trace impurity limit, the isotopic effects are found to reduce the accumulation of high-Z tungsten (W). Moreover, the isotopic effects on the peaking factor (PF) of trace high-Z W get stronger with stronger magnetic shear.

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“…8,9 The physical mechanism by which the change of the direction of the impurity convective velocity occurs has not yet been clearly identified, in spite of the various efforts that have been made. [9][10][11] In this paper we suggest a mechanism that can give rise to a reduction of the impurity peaking, or even a sign change in the impurity convective flux, based on the asymmetry of the impurity density on the flux surface ͑which could be due to the presence of ICRH or other reasons͒. Since impurity transport is usually dominated by drift-wave turbulence, in this work we focus on the effect of the impurity poloidal asymmetry on impurity transport driven by microinstabilities.…”

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Effect of poloidal asymmetry on the impurity density profile in tokamak plasmas

Fülöp

Moradi

2011

Physics of Plasmas

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The effect of poloidal asymmetry of impurities on impurity transport driven by electrostatic turbulence in tokamak plasmas is analyzed. It is found that if the density of the impurity ions is poloidally asymmetric then the zero-flux impurity density gradient is significantly reduced and even a sign change in the impurity flux may occur if the asymmetry is sufficiently large. This effect is most effective in low shear plasmas with the impurity density peaking on the inboard side and may be a contributing factor to the observed outward convection of impurities in the presence of radio frequency heating. ͓doi:10.1063/1.3569841͔The presence of impurities in fusion plasmas has a significant effect on fusion performance. Accumulation of impurities in the core would have detrimental effect on fusion reactivity due to increased radiation losses and plasma dilution. On the other hand the presence of impurities at the edge can be beneficial, and seeded impurities are often used to create a radiative belt in order to reduce the heat loads on the walls. Therefore, it is of great value to understand the physics mechanisms governing the impurity transport, and to identify plasma conditions in which impurity accumulation in the core can be avoided.Experimental observations on several tokamaks show that the impurity distribution over the flux surface is often poloidally asymmetric. [1][2][3][4][5] The asymmetries are usually most pronounced for heavy impurities. In the plasma core, where the collisionality is low, in-out asymmetries can arise due to toroidal rotation or the presence of radio frequency ͑RF͒ heating. In the case of rotating plasmas, the poloidal asymmetry of the impurity ion distribution is due to the centrifugal force, which causes the impurities to accumulate on the outboard side of flux surfaces. 1,2 In the case of RF heated plasmas, the asymmetry is a result of the increase of the hydrogen-minority density on the outboard side. These particles tend to be trapped on the outside of the torus and the turning points of their orbits drift toward the resonance layer due to the heating. The poloidal asymmetry in the hydrogenminority density gives rise to an electric field that pushes the other ion species to the inboard side. In the case of highlycharged impurities, this effect is amplified by their large charge Z ͑Ref. 3͒. In the tokamak edge, where the plasma is sufficiently collisional, steep radial pressure or temperature gradients give rise to an in-out asymmetry. 6 Neoclassical theory also predicts an up-down asymmetry, which is caused by the ion-impurity friction. 7 Recent experiments have shown that auxiliary heating can influence the impurity convective flux. For example in JET, it has been observed that with ion cyclotron resonance heating ͑ICRH͒ the accumulation of high-Z impurities can be avoided. 8,9 The physical mechanism by which the change of the direction of the impurity convective velocity occurs has not yet been clearly identified, in spite of the various efforts that have been made. [9][10][11] I...

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Influence of the radio frequency ponderomotive force on anomalous impurity transport in tokamaks

Cited by 24 publications

References 14 publications

Turbulent and neoclassical impurity transport in tokamak plasmas

Turbulent and neoclassical impurity transport in tokamak plasmas

Isotopic dependence of impurity transport driven by ion temperature gradient turbulence

Effect of poloidal asymmetry on the impurity density profile in tokamak plasmas

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