Impact of the background toroidal rotation on particle and heat turbulent transport in tokamak plasmas

Camenen, Y.; Peeters, A. G.; Angioni, C.; Casson, F. J.; Hornsby, W. A.; Snodin, A. P.; Strintzi, D.

doi:10.1063/1.3057356

Cited by 88 publications

(141 citation statements)

References 25 publications

(25 reference statements)

Supporting

Mentioning

136

Contrasting

Order By: Relevance

“…Also, the effect of rotation, which is one of the mechanisms that causes poloidal asymmetry, has not been taken into account. Fluid and gyrokinetic modeling of rotation induced contributions to the transport fluxes, 19,20 have shown that in the ITG-dominated case, the centrifugal force leads to higher inward convection for impurities ͑increasing with impurity mass͒. This agrees with the predictions of the present work, since the strength of the asymmetry increases with Z, and accumulation at the outboard side should lead to an increased inward flux.…”

Section: -3supporting

confidence: 82%

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

Fülöp

Moradi

2011

Physics of Plasmas

View full text Add to dashboard Cite

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...

show abstract

Section: -3supporting

confidence: 82%

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

Fülöp

Moradi

2011

Physics of Plasmas

View full text Add to dashboard Cite

show abstract

“…The term containing U ef f is the only O(ρ 0 * ) term in equation (8). The O(ρ * ) and higher terms have been assembled in the right-hand-side: by definition, γ is such that…”

Section: Physical Meaning Of the Velocity Determined By The Cctd Methodsmentioning

confidence: 99%

“…However, both theoretical and experimental works of the past two decades [2][3][4][5][6][7][8][9][10][11][12][13][14][15] suggest that sheared E × B flows can moderate such anomalous transport and hence improve the performance of magnetically confined fusion plasmas.…”

Section: Introductionmentioning

confidence: 99%

Measurement and physical interpretation of the mean motion of turbulent density patterns detected by the beam emission spectroscopy system on the mega amp spherical tokamak

Ghim¹,

Field²,

Dunai³

et al. 2012

Plasma Phys. Control. Fusion

106

View full text Add to dashboard Cite

Abstract. The mean motion of turbulent patterns detected by a two-dimensional (2D) beam emission spectroscopy (BES) diagnostic on the Mega Amp Spherical Tokamak (MAST) is determined using a cross-correlation time delay (CCTD) method. Statistical reliability of the method is studied by means of synthetic data analysis. The experimental measurements on MAST indicate that the apparent mean poloidal motion of the turbulent density patterns in the lab frame arises because the longest correlation direction of the patterns (parallel to the local background magnetic fields) is not parallel to the direction of the fastest mean plasma flows (usually toroidal when strong neutral beam injection is present). The experimental measurements are consistent with the mean motion of plasma being toroidal. The sum of all other contributions (mean poloidal plasma flow, phase velocity of the density patterns in the plasma frame, non-linear effects, etc.) to the apparent mean poloidal velocity of the density patterns is found to be negligible. These results hold in all investigated L-mode, H-mode and internal transport barrier (ITB) discharges. The one exception is a high-poloidal-beta (the ratio of the plasma pressure to the poloidal magnetic field energy density) discharge, where a large magnetic island exists. In this case BES detects very little motion. This effect is currently theoretically unexplained.

show abstract

“…In this paper, particular interest is given to impurity (more specifically on roto-diffusion [17]) and momentum transport as they both rely on parallel symmetry breaking [12,17,18]. To this end the neoclassical first order distribution function is needed for impurities as well as for the main ions.…”

Section: A Analytical First Order Neoclassical Distribution Functionmentioning

confidence: 99%

“…The impact of the neoclassical equilibrium on turbulent momentum transport has been explored in details in [12][13][14][15][16] and found to be significant compared to other sources of momentum flux [16] such as the Coriolis drift and the flux surface up-down asymmetry. Turbulent momentum and impurity transport being not completely disconnected, in particular with respect to the role of symmetry breaking mechanisms [17,18], these results motivated a study of the impact of the neoclassical equilibrium distribution function on turbulent impurity transport. To this end, two approaches are adopted: the derivation of a fluid model including this correction and numerical simulations using the coupled codes NEO [19,20] and GKW [22].…”

Section: Introductionmentioning

confidence: 99%

Impact of the neoclassical distribution function on turbulent impurity and momentum fluxes: fluid model and gyrokinetic simulations

Manas¹,

Hornsby²,

Angioni³

et al. 2017

Plasma Phys. Control. Fusion

View full text Add to dashboard Cite

The impact of the neoclassical background on turbulent impurity transport is investigated by means of gyrokinetic simulations supported by fluid equations. The latter are derived, using a Laguerre polynomials expansion of the first order neoclassical distribution function, and analytical expressions of the turbulent momentum flux and impurity transport coefficients are assessed. Comparisons of gyrokinetic simulations including this neoclassical background (coupling between the codes GKW and NEO) and the fluid model are used to identify the main mechanisms behind the modification of the turbulent transport channels and benchmark the numerical implementation. These mechanisms include a modification of the parallel dynamics of the main ions and direct contributions stemming from the asymmetry in the parallel velocity space of the neoclassical distribution function. The latter which is found dominant for turbulent impurity transport, increases with increasing collisionality, R/LT i , R/Ln, impurity mass, safety factor and aspect ratio. These contributions to momentum and impurity fluxes are also found to depend on the directions of the toroidal magnetic field and plasma current.

show abstract

Impact of the background toroidal rotation on particle and heat turbulent transport in tokamak plasmas

Cited by 88 publications

References 25 publications

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

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

Measurement and physical interpretation of the mean motion of turbulent density patterns detected by the beam emission spectroscopy system on the mega amp spherical tokamak

Impact of the neoclassical distribution function on turbulent impurity and momentum fluxes: fluid model and gyrokinetic simulations

Contact Info

Product

Resources

About