Toroidal modeling of resistive wall mode stability and control in HL-2M tokamak

Xia, Guoliang; Liu, Yueqiang; Ham, Christopher; Wang, Shuo; Li, Li; Zheng, Guoyao; Li, J.X.; Zhang, N.; Bai, Xue; Dong, Guangsheng

doi:10.1088/1741-4326/aaf02c

Cited by 6 publications

(12 citation statements)

References 46 publications

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“…Figure 1 shows the radial profiles for some key equilibrium quantities. Normalizations for the plasma pressure, current density and toroidal rotation frequency follow that from [42]. The STEP design continues to evolve, and the case studied here represents a particular snapshot during the design process.…”

Section: Equilibrium Specification and Results With Fluid Modelmentioning

confidence: 96%

Control of resistive wall modes in the spherical tokamak

et al. 2023

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In this work, the MARS-F/K codes (Liu Y Q et al 2000 Phys. Plasmas 7 3681 & Liu Y Q et al 2008 Phys. Plasmas 15 112503) are utilized to model the passive and active control of the n=1 (n is the toroidal mode number) resistive wall mode (RWM) in a spherical tokamak (aspect ratio A=1.66). It is found that passive stabilization of the RWM gives a relatively small increase in normalized beta above the no-wall limit, relying on toroidal plasma flow and drift kinetic resonance damping from both thermal and energetic particles. Results of active control show that with the flux-to-voltage control scheme, which is the basic choice, a proportional controller alone does not yield complete stabilization of the mode. Adding a modest derivative action, and assuming an ideal situation without any noise in the closed-loop, the RWM can be fully stabilized with the axial plasma flow at 5% of the Alfven speed. In the presence of sensor signal noise, success rates exceeding 90% are achieved, and generally increase with the proportional feedback gain. On the other hand, the required control coil voltage also increases with feedback gain and with the sensor signal noise.

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Section: Equilibrium Specification and Results With Fluid Modelmentioning

confidence: 96%

Control of resistive wall modes in the spherical tokamak

et al. 2023

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“…Here, β is the plasma pressure normalized by the toroidal magnetic pressure, a = 0.59 m the plasma minor radius, B 0 = 2.2 T the vacuum toroidal magnetic field at the major radius of 1.78 m, and I p = 2 MA the plasma current. Note that the target equilibrium chosen in [44] has 10% higher plasma pressure than Basic geometry of the RWM control on HL-2M: the plasma boundary shape (red solid line) for a 2 MA double-null equilibrium from the high performance scenario, the shape of the conducting vacuum vessel with double-wall structure (blue solid and dashed lines), the locations of the active (black dots) and sensor (red dot) coils. The poloidal angle of the center of the active coils is |θc| = 29.9 • , with the poloidal coverage of ∆θ = 21.8 • .…”

Section: Numerical Resultsmentioning

confidence: 99%

“…Previous studies have shown that combination of passive stabilization and active control provides an effective way to suppress the RWM [42][43][44]. In particular, reference [44] investigated the combined effects of toroidal plasma flow, drift kinetic effects from thermal particles, and magnetic feedback on the RWM stability in an HL-2M plasma. Drift kinetic stabilization is ignored in this work, by two reasons.…”

Section: Introductionmentioning

confidence: 99%

“…First, this work aims at a conservative estimate of the control power requirements for HL-2M. Since the kinetic contribution provides additional stabilization to the RWM in HL-2M [44], we obtain the worst-scenario results, in terms of the control requirements, by neglecting kinetic effects. Secondly, drift kinetic stabilization of the RWM sensitively depends on the assumed plasma toroidal rotation frequency, with the latter being difficult to be accurately predicted for HL-2M.…”

Section: Introductionmentioning

confidence: 99%

“…• Initial value simulation of the close-loop system with or without assuming toroidal equilibrium flow of the plasma, allowing quantification of the control voltage and current requirements for the RWM feedback on HL-2M. This is different from the eigenvalue approach taken in the previous work [44].…”

Section: Introductionmentioning

confidence: 99%

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Modeling active control of resistive wall mode with power saturation and sensor noise on HL-2M

Wang¹,

Liu²,

Xia³

et al. 2021

Plasma Phys. Control. Fusion

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The resistive wall mode (RWM) control on the HL-2M tokamak is simulated with the MARS-F code (Liu et al 2000 Phys. Plasmas 7 3681), aiming at quantifying control current and voltage requirements when more realistic issues are taken into account, i.e. the control power saturation and the sensor signal noise. The fluid model predicts a narrow stability region for the n = 1 RWM without magnetic feedback, in the 2D parameter space of the plasma pressure versus the toroidal flow speed. Magnetic feedback can fully stabilize the RWM on HL-2M. Without considering the voltage limitation and the sensor signal noise, it is found that plasma flow helps active control of the mode, by reducing the required critical feedback gain for both flux-to-current and flux-to-voltage control schemes. In the absence of the sensor signal noise, the lowest control voltage saturation level, below which the RWM control is lost, is found to roughly satisfy a linear relation to the plasma flow frequency, indicating that subsonic plasma flow is effective in relaxing the control power requirement for the RWM feedback stabilization. The presence of the sensor signal noise substantially modifies the feedback results. A statistical study finds that the sensor signal noise, with the standard deviation of 0.1 G on HL-2M, roughly doubles the required control voltage for successful mode control. The synergistic stabilization effect due to plasma flow is somewhat weakened by the presence of the sensor signal noise. At a given rotation, the tolerable voltage limit generally increases with increasing feedback gain due to the sensor signal noise.

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Active control of resistive wall mode via modification of external tearing index

et al. 2021

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Modification of the external tearing index, Δext′, by magnetic feedback is analytically investigated for the purpose of controlling the resistive plasma resistive wall mode (RP-RWM). The matching method is pursued by deriving expressions for the close-loop Δext′ and by linking it to the counterpart from the inner layer. Various feedback coil configurations are found to generally reduce Δext′ and stabilize the RWM, with either proportional or derivative control. Feedback modification of Δext′ is found to be generally independent of the inner layer resistive interchange index DR, confirming that feedback action primarily modifies the solution in the outer ideal region for the RP-RWM. Exception occurs when either the inner layer favorable curvature effect becomes sufficiently large or the feedback action is sufficiently strong to introduce a rotating RP-RWM in the static plasma, leading to complex-valued close-loop Δext′. The perturbed magnetic energy dissipation in the outer region, associated with the eddy current in the resistive wall, is identified as the key physics reason for feedback induced complex Δext′. Similar results are also obtained for active control of the external kink instability, whose open-loop growth rate is significantly reduced by inclusion of the plasma resistivity. Within the single poloidal harmonic approximation, which is most suitable for the matching approach, external active coils combined with poloidal sensors are often found to be more efficient for feedback stabilization of the mode at large proportional gain values. This counter-intuitive result is explained as the lack of (non-resonant) poloidal harmonics for proper description of the feedback coil geometry.

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Toroidal modeling of resistive wall mode stability and control in HL-2M tokamak

Cited by 6 publications

References 46 publications

Control of resistive wall modes in the spherical tokamak

Control of resistive wall modes in the spherical tokamak

Modeling active control of resistive wall mode with power saturation and sensor noise on HL-2M

Active control of resistive wall mode via modification of external tearing index

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