Quasilinear perturbed equilibria of resistively unstable current carrying plasma

Di, Honggui; Zakharov, L.

doi:10.1017/s002237781500121x

Cited by 5 publications

(16 citation statements)

References 32 publications

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“…, driving the tearing instability [21]. Here, ψ s − , ψ s + and ψ s are the radial gradient of the perturbed magnetic flux at both sides of the resonant surface and the value of the perturbed flux at the resonant surface, respectively.…”

Section: Mhd Response Caused By the Spimentioning

confidence: 99%

3D non-linear MHD simulation of the MHD response and density increase as a result of shattered pellet injection

Nardon

Lehnen

et al. 2018

Nucl. Fusion

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The MHD response and the penetration of a deuterium shattered pellet into a JET plasma is investigated via the non-linear reduced MHD code JOREK with the neutral gas shielding (NGS) ablation model. The dominant MHD destabilizing mechanism by the injection is identified as the local helical cooling at each rational surface, as opposed to the global current profile contraction. Thus the injected fragments destabilize each rational surface as they pass through them. The injection penetration is found to be much better compared to MGI, with the convective transport caused by core MHD instabilities (e.g. 1/1 kink) contributing significantly to the core penetration. Moreover, the injection with realistic JET SPI system configurations is simulated in order to provide some insights into future operations, and the impact on the total assimilation and penetration depth of varying injection parameters such as the injection velocity or fineness of shattering is assessed. Further, the effect of changing the target equilibrium temperature or q profile on the assimilation and penetration is also investigated. Such analysis will form the basis of further investigation into a desirable configuration for the future SPI system in ITER.

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Section: Mhd Response Caused By the Spimentioning

confidence: 99%

3D non-linear MHD simulation of the MHD response and density increase as a result of shattered pellet injection

Nardon

Lehnen

et al. 2018

Nucl. Fusion

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“…For oblique modes, there is a logarithmic singularity in the derivative of the ideal solution since F /F is singular near the resonant surface 25,30 . However, the contribution of this logarithmic singularity to ψ is even in parity near the resonant surface, thus does not contribute to ∆ .…”

Section: A Effective Damping Caused By Linearly Stable Modesmentioning

confidence: 99%

“…The justification of using the linear growth rate to estimate effective damping may be formulated more precisely as follows. The effective island width w for a given Fourier component of the magnetic perturbation Bk (x, y, z) = B(0) k (x) exp (ik y y − ik z z) has the following dependence on mode numbers and the magnetic perturbation strength: 24,25 w…”

Section: A Effective Damping Caused By Linearly Stable Modesmentioning

confidence: 99%

Energy spectrum of tearing mode turbulence in sheared background field

Bhattacharjee

Huang

2018

Physics of Plasmas

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The energy spectrum of tearing mode turbulence in a sheared background magnetic field is studied in this work. We consider the scenario where the nonlinear interaction of overlapping large-scale modes excites a broad spectrum of small-scale modes, generating tearing mode turbulence. The spectrum of such turbulence is of interest since it is relevant to the small-scale back-reaction on the large-scale field. The turbulence we discuss here differs from traditional MHD turbulence mainly in two aspects. One is the existence of many linearly stable small-scale modes which cause an effective damping during energy cascade. The other is the scale-independent anisotropy induced by the large-scale modes tilting the sheared background field, as opposed to the scale-dependent anisotropy frequently encountered in traditional critically balanced turbulence theories. Due to these two differences, the energy spectrum deviates from a simple power law and takes the form of a power law multiplied by an exponential falloff. Numerical simulations are carried out using visco-resistive MHD equations to verify our theoretical predictions, and reasonable agreement is found between the numerical results and our model.

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“…While expensive 3D nonlinear MHD codes could be arranged to explore the aforementioned stability impact from profile modifications caused by either the DAS and the DMS, quasi-linear stability analysis using helical Grad-Shafranov equation [36] provides a more agile and cost-effective tool. In our simulation environment, which was run on a virtual machine on AMD R9 5900HX CPU, the typical convergence time ranges from 50 ms to 300 ms, depending on the strength of profile modification.…”

Section: Introductionmentioning

confidence: 99%

“…The advantage of this approach is its capability of avoiding the singularity in solutions close to the resonant surface, and accurately describing the impact of profile modification within the island on the stability criterion ∆ . [36] Considering a dominant finite sized island in a cylindrical analogue of the tokamak plasma with a toroidal effect multiplier 1 − m 2 /n 2 , [39] the 2D temperature and pressure profile modification with helical symmetry are described and their impact on the island stability is obtained through the calculation of ∆ up to the resonant surface. Several different combinations of the current density and pressure gradient modification are considered, and it is found that positive helical current perturbation on island O-point is always strongly stabilizing while the negative one does the opposite, consistent with previous analytical [40] and numerical results.…”

Section: Introductionmentioning

confidence: 99%

Stability impacts from the current and pressure profile modifications within finite sized island

Sun

2023

Chinese Phys. B

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The stability (or instability) of finite sized magnetic island could play a significant role in disruption avoidance or disruption mitigation dynamics. Especially, various current and pressure profile modifications, such as the current drive and heating caused by electron cyclotron wave, or the radiative cooling and current expulsion caused by the Shattered Pellet Injection could be applied within the island to modify its stability, thus change the ensuing dynamics. In this study, we calculate the mode structure modification caused by such profile changes within the island using the perturbed equilibrium approach, thus obtain the change of stability criterion ∆′ and assess the corresponding quasi-linear island stability. The positive helical current perturbation is found to always stabilize the island, while the negative one is found to do the opposite, in agreement with previous results. The pressure bump or hole within the island has a more complicated stability impact. In the small island regime, its contribution is monotonic, with pressure bump tends to stabilize the island while pressure hole destabilizes it. This effect is relatively weak, though, due to the cancellation of the pressure term’s odd parity contribution in the second derivatives of the mode structure. In the large island regime, such cancellation is broken due to the island asymmetry, and the pressure contribution to stability is manifested, which is non-monotonic. The stability analysis in this paper helps to more accurately clarify the expected island response in the presence of profile modifications caused by disruption avoidance or mitigation systems.

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Quasilinear perturbed equilibria of resistively unstable current carrying plasma

Cited by 5 publications

References 32 publications

3D non-linear MHD simulation of the MHD response and density increase as a result of shattered pellet injection

3D non-linear MHD simulation of the MHD response and density increase as a result of shattered pellet injection

Energy spectrum of tearing mode turbulence in sheared background field

Stability impacts from the current and pressure profile modifications within finite sized island

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