Metal impurity transport control in JET H-mode plasmas with central ion cyclotron radiofrequency power injection

Valisa, M.; Carraro, L.; Predebon, I.; Puiatti, M. E.; Angioni, C.; Coffey, I.; Giroud, C.; Taroni, L. Lauro; Alper, B.; Baruzzo, M.; daSilva, P. Belo; Buratti, P.; Garzotti, L.; Eester, D. Van; Lerche, E.; Mantica, P.; Naulin, V.; Tala, T.; Tsalas, M.; Contributors, Jet‐Efda

doi:10.1088/0029-5515/51/3/033002

Cited by 77 publications

(108 citation statements)

References 41 publications

(62 reference statements)

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“…10 The reduction of the zero-flux impurity gradient due to poloidal impurity asymmetries may be a contributing factor to the observed impurity flow reversal in the presence of RF-heating. According to recent observations from JET, 9 the higher the applied ion cyclotron resonance heating power the lower is the zero-flux impurity density gradient until it eventually changes sign and becomes negative. The reason for this may be that as the ICRH power is raised, the impurities are pushed to the inboard of flux surfaces.…”

Section: -3mentioning

confidence: 97%

“…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.…”

mentioning

confidence: 99%

“…These parameters are taken from a typical JET-shot with ICRH heating. 9 We assume that the impurities are present in trace quantities and do not affect the turbulence characteristics. The absolute value of the potential calculated by GYRO 13 is given in Fig.…”

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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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Section: -3mentioning

confidence: 97%

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confidence: 99%

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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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“…11 for the simulations of pulse 85080 just before (c) and after (d) the sawtooth crash at 12.04s. The code does not model the enhanced anomalous transport due to strong temperature gradients [27], nor does it include centrifugal effects on the massive toroidally rotating tungsten ions, which are clearly visible in the experimental data via the enhanced SXR signals on the outboard midplane at all times. The question still to be answered is whether experiments can be constructed that prevent both density accumulation during the sawtooth ramping phase, and control the sawteeth in order to avoid unwanted secondary MHD events like NTMs, which can also further increase impurity fluxes to the core.…”

Section: Sawtooth Control and Impurity Flushing During Higher Permentioning

confidence: 99%

Sawtooth control in JET with ITER relevant low field side resonance ion cyclotron resonance heating and ITER-like wall

Graves¹,

Lennholm²,

Chapman³

et al. 2014

Plasma Phys. Control. Fusion

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New experiments at JET with the ITER like wall show for the first time that ITER-relevant low field side resonance first harmonic ICRH with can be used to control sawteeth that have been initially lengthened by fast particles. In contrast to previous [J. P. Graves et al, Nature Communs 3, 624 (2012)] high field side resonance sawtooth control experiments undertaken at JET, it is found that the sawteeth of L-mode plasmas can be controlled with less accurate alignment between the resonance layer and the sawtooth inversion radius. This advantage, as well as the discovery that sawteeth can be shortened with various antenna phasings, including dipole, indicates that ICRH is a particularly effective and versatile tool that can be used in future fusion machines for controlling sawteeth. Without sawtooth control, NTMs and locked modes were triggered at very low normalised beta. High power H-mode experiments show the extent to which ICRH can be tuned to control sawteeth and NTMs while simultaneously providing effective electron heating with improved flushing of high Z core impurities. Dedicated ICRH simulations using SELFO, SCENIC and EVE, including wide drift orbit effects, explain why sawtooth control is effective with various antenna phasings, and show that the sawtooth control mechanism cannot be explained by enhancement of the magnetic shear. Hybrid kinetic-MHD stability calculations using MISHKA and HAGIS unravel the optimal sawtooth control regimes in these ITER relevant plasma conditions.

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“…ASDEX Upgrade [3] and more recently JET-ILW [4] experiments have shown that an efficient way of avoiding central impurity accumulation is to provide a localized heat source to the plasma centre, either by electron cyclotron (ECRH) or by ion cyclotron resonance heating (ICRH). The resulting peaked electron temperature profiles, flattened density profiles and enhanced fast ion pressure (ICRH only) have a direct impact on the transport of the high-Z impurities in the plasma core, both via neo-classical and via anomalous transport effects [5][6][7].…”

Section: Introductionmentioning

confidence: 99%

ICRH for core impurity mitigation in JET-ILW

2015

AIP Conference Proceedings

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Metal impurity transport control in JET H-mode plasmas with central ion cyclotron radiofrequency power injection

Cited by 77 publications

References 41 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

Sawtooth control in JET with ITER relevant low field side resonance ion cyclotron resonance heating and ITER-like wall

ICRH for core impurity mitigation in JET-ILW

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