Impurity behavior during sawtooth activity in tokamak plasmas

Nicolas, T; Lütjens, H.; Luciani, J. F.; Garbet, X.; Sabot, R.

doi:10.1063/1.4861859

Cited by 31 publications

(30 citation statements)

References 42 publications

(41 reference statements)

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“…This behaviour is consistent with the Kadomtsev reconnection model [23], [24] for different pre-crash impurity profiles [25]. In addition, the presence of 2D structures of impurity density during sawtooth crashes has been evidenced in the XTOR-2F simulations [26].…”

Section: Introductionsupporting

confidence: 87%

“…Time-steps are automatically adjusted for an optimum number of iterations for the Newton-Krylov method. The plasma dynamics such as sawtooth crashes, which occur during a very short time scale compared to the confinement time, can then be studied with an appropriate time resolution [32], [26]. The radial resolution is chosen such that the current sheet at the reconnection layer is accurately computed.…”

Section: Non-linear Mhd Model In the Xtor-2f Codementioning

confidence: 99%

“…Both are coupled self-consistently with the two-fluid set of equations describing the bulk plasma, which is an important improvement compared to the work in Ref. [26]. In Section 2, it is shown that the Pfirsch-Schlüter flux is recovered when using the appropriate fluid equations for impurity.…”

Section: Introductionmentioning

confidence: 99%

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Dynamics of heavy impurities in non-linear MHD simulations of sawtoothing tokamak plasmas

Ahn¹,

Garbet²,

Lütjens³

et al. 2016

Plasma Phys. Control. Fusion

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The effect of sawteeth on impurity dynamics is studied with the XTOR-2F code. Non-linear full 3D MHD simulations including appropriate fluid equations for heavy impurities show that the presence of regular sawtooth crashes affects the impurity behaviour. A spatial non-uniformity of 5% in post-crash impurity density profiles persists due to 2D structures of impurity density which appear during sawtooth crashes. They are shown to be mainly driven by the E × B velocity, and are responsible for the sudden impurity transport in the core plasmas.

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Section: Introductionsupporting

confidence: 87%

Section: Non-linear Mhd Model In the Xtor-2f Codementioning

confidence: 99%

See 1 more Smart Citation

Dynamics of heavy impurities in non-linear MHD simulations of sawtoothing tokamak plasmas

Ahn¹,

Garbet²,

Lütjens³

et al. 2016

Plasma Phys. Control. Fusion

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“…When the electrostatic potential and the ion density have a small poloidal asymmetry, the asymmetry of the impurity can still be determined analytically, but the steady state distribution has a remaining asymmetry. Numerical simulations are performed with the nonlinear MHD code XTOR [20] where neoclassical physics [21], as well as impurity dynamics [22,23] are implemented. The description of the model is given in section 3 and complemented in the Appendix B.…”

Section: Introductionmentioning

confidence: 99%

Natural poloidal asymmetry and neoclassical transport of impurities in tokamak plasmas

Maget

Frank

Nicolas

et al. 2019

Plasma Phys. Control. Fusion

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The neoclassical transport of impurities is investigated for a plasma without toroidal rotation nor anisotropic ion temperature. It is shown that a natural poloidal asymmetry of the impurity density exists in this case, and that it can be described with a simple analytical model. The poloidal asymmetry tends naturally to cancel as the impurity profile evolves towards its steady state, so that the main effect of the poloidal asymmetry is to slow down the impurity flux compared to its predicted value without poloidal asymmetry. The contribution of the asymmetries of the electrostatic potential and of the main ion density can be included in the analytical derivation, thus forming a self-consistent description of the neoclassical impurity flux together with its poloidal distribution. Numerical simulations with a non linear fluid code confirm the analytical findings, showing that the neoclassical transport of impurities is strongly modified by its natural poloidal distribution.

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“…Além de núcleos pesados, oriundos das paredes internas do dispositivo confinante, os próprios produtos da reação de fusão podem ser vistos como impurezas, pois na faixa de energias tipicamente disponíveis em um tokamak, eles não participam de novas reações. Diversos estudos mostram que existe uma relação entre as instabilidades e o transporte de impurezas [8,9,10]. Se por um lado a existência das instabilidades prejudicam o confinamento, por outro, elas são responsáveis por modificar o transporte de impurezas e neste sentido podem ser úteis no processo de limpeza do plasma.…”

Section: Introductionunclassified

Instabilidades MHD no Tokamak TCABR

Fernandes¹

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This work describes the study of magneto-hydro-dynamic instabilities (MHD) commonly observed in plasma discharges in tokamak TCABR (at Instituto de Física da USP). Two main diagnostics were employed to observe these instabilities: a poloidal set of 24 magnetic coils (Mirnov coils) placed near the plasma border and a detector of emissions in the Ultra Violet and soft X-ray range with 20 channels (SXR system) which improvement of the signal conditioning circuit was done as part of this work. These diagnostics were chosen because they provide complementary information, since the SXR system measures the central part of the plasma column, while the Mirnov coils detect the MHD instabilities in the outer part of the column. The information collected by these diagnoses was submitted to spectral analysis with temporal and spatial resolution, making it possible to determine the evolution of the spectral and spatial characteristics of the observed MHD instabilities. These analyzes revealed that during the initial stage of the plasma formation (when the plasma current is still increasing) magnetic islands with decreasing wave numbers, identified as edge kink modes, are detected in the Mirnov coils. After the plasma formation, when the equilibrium parameters are relatively flat (plateau), oscillations are detected in both Mirnov coils and SXR system, indicating the presence of MHD instability in the whole plasma column. In general, the fluctuations measured by the Mirnov coils have low amplitude corresponding to small magnetic islands, which were identified as tearing modes. On the other hand, the instabilities at the central region were identified as sawteeth oscillations that correspond to periodic relaxations in the internal region of the magnetic surface with safety factor q = 1 and that are accompanied by precursor oscillations which amplitude depends on the phase of the relaxation cycles. Due to this amplitude modulation, frequency satellite peaks appear in the spectrograms of the SXR signals. Furthermore, due to the fact that relaxation cycles are not sinusoidal, harmonics of the relaxation frequency also appear in the spectrograms. However, in many TCABR discharges, the intensity of the oscillations measured by the Mirnov coils increase significantly during the plateau, with affects the frequency of all MHD instabilities, even over the sawteeth in the central region of the column. In all cases, it was observed that during the plateau the frequency of the magnetic islands coincides with the frequency of the sawtooth precursors, although they are two different instabilities located in separated radial positions. This coincidence of frequencies allowed describing the frequency evolution of all measured oscillations by considering only two basic frequencies: the cycles of sawtooth relaxation and the magnetic islands.

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Impurity behavior during sawtooth activity in tokamak plasmas

Cited by 31 publications

References 42 publications

Dynamics of heavy impurities in non-linear MHD simulations of sawtoothing tokamak plasmas

Dynamics of heavy impurities in non-linear MHD simulations of sawtoothing tokamak plasmas

Natural poloidal asymmetry and neoclassical transport of impurities in tokamak plasmas

Instabilidades MHD no Tokamak TCABR

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