Nonlinear magnetohydrodynamics of pulsed parallel current drive in reversed-field pinches

Reynolds, J. M.; Sovinec, C. R.; Prager, S. C.

doi:10.1063/1.2937770

Cited by 12 publications

(10 citation statements)

References 31 publications

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“…This study is an addition to the previous modelling of stabilization of core resonant (resonance surface is within the reversal surface) current-driven modes in RFP during PPCD [14,15] which explained their stabilization during the drive. The previous and present studies demonstrated stabilization of current-and pressure-driven modes during PPCD, thus explaining the significant improvement in plasma confinement.…”

Section: Introductionmentioning

confidence: 65%

Stabilization of ideal pressure gradient driven edge modes during pulsed parallel current drive in reversed field pinch

Svidzinski¹,

Li²

2010

Nucl. Fusion

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Significant improvement of plasma confinement in the Madison Symmetric Torus reversed field pinch (RFP) has been routinely achieved by applying an inductive electric field at the plasma boundary in the direction parallel to the equilibrium magnetic field at the plasma edge. An auxiliary edge current is driven by this electric field with the goal of replacing the dynamo-driven current and modifying the parallel current profile to reduce current-driven instabilities. This current-drive technique is called pulsed parallel current drive (PPCD) in RFP. During PPCD plasma fluctuations are reduced everywhere resulting in tokamak-like confinement parameters, while the edge density profile steepens significantly and plasma beta increases. A steep edge plasma pressure profile, a relatively high plasma beta and a strong unfavourable curvature of equilibrium magnetic field near the edge in RFP could excite pressure-driven fluid turbulence near the edge and worsen plasma confinement, opposite to the experimental observations. In this study stability analysis of edge pressure gradient driven ideal modes in standard-like and in PPCD-like plasma equilibria is performed. An ideal magnetohydrodynamic plasma model in cylindrical RFP equilibrium with a step function plasma pressure profile and a vacuum layer between the plasma boundary and the conducting shell is used. Standard-like and PPCD-like plasma equilibria in the model are defined by the direction of the surface current at the plasma–vacuum interface. The results show that while in standard-like equilibrium the edge pressure gradient driven modes are highly unstable in this model, the transition to PPCD-like equilibrium completely stabilizes these modes. The modes stabilization is primarily due to strengthening of magnetic shear at the location of the pressure gradient during the drive and due to the proximity of this location to the conducting wall. This stabilization mechanism is not specific to RFPs, making PPCD a general method of stabilization of the edge pressure gradient driven instabilities which could be applied in other magnetic confinement systems. Application of PPCD to stabilize the edge localized modes in tokamaks is proposed.

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Section: Introductionmentioning

confidence: 65%

Stabilization of ideal pressure gradient driven edge modes during pulsed parallel current drive in reversed field pinch

Svidzinski¹,

Li²

2010

Nucl. Fusion

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“…Good energy confinement in steady state RFP equilibrium will require a current drive profile aligned with the equilibrium current density, which can be tailored to stabilize the tearing fluctuations. This has been demonstrated transiently by PPCD [1].…”

Section: Introductionmentioning

confidence: 77%

Electron Bernstein Wave Studies in MST

Seltzman¹,

Anderson²,

Nonn³

et al. 2011

AIP Conference Proceedings

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The overdense plasma in an RFP prevents electromagnetic waves from propagating past the edge, however use of the electron Bernstein wave (EBW) has the potential to heat and drive current in the plasma. MHD simulations have demonstrated that resistive tearing mode stability is very sensitive to gradients in the edge current density profile allowing EBW to potentially be a stabilizing influence. A new MW level experiment is being commissioned on MST to evaluate the potential use of the EBW for current profile control on the RFP. The development of new equipment includes a 5.5GHz klystron driven by a novel switchmode power supply. A quartz window has been constructed and coupling with a cylindrical molybdenum wave guide antenna has been studied. Due to the steep edge density gradient in the RFP, it is possible to efficiently couple to the EBW with O or X mode launch. The EBW is strongly damped at the electron cyclotron resonance where it couples to the electron gyromotion and alters the electron distribution. Either Fisch-Boozer or Ohkawa current drive mechanisms can be activated to drive off axis current in the plasma. Preliminary experiments have been performed to verify high power coupling and understand heating via observed x-ray emission when compared to Fokker-Plank modeling in CQL3D.

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“…This type of analysis has been useful for studying nonlinear MHD dynamics in RFPs, (e.g., Refs. [37] and [38] ). Here, the power transfer analysis shows slow growth phase of n = 1 is driven by multiple nonlinear interactions.…”

Section: Discussionmentioning

confidence: 98%

Growing Neoclassical Tearing Modes Seeded via Transient-Induced-Multimode Interactions

Howell,

King,

Callen

et al. 2021

Preprint

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Nonlinear extended MHD simulations demonstrating seeding of neoclassical tearing modes (NTMs) via MHD-transient-induced multimode interactions are presented. Simulations of NTMs are enabled by two recent NIMROD code developments: the implementation of heuristic neoclassical stresses and the application of transient magnetic perturbations (MPs) at the boundary. NTMs are driven unstable by the inherently pressure driven kinetic bootstrap current, which arises due to collisional viscosity between passing and trapped electrons. These simulations use heuristic closures that model the neoclassical electron and ion stresses. NTM growth requires a seed island, which is generated by a transiently applied MP in simulations. The capability is demonstrated using kineticbased reconstructions with flow of a DIII-D ITER Baseline Scenario discharge [R.J. La Haye, et al., Proceedings IAEA FEC 2020]. The applied MP seeds a 2/1 NTM that grows in two phases: a slow growth phase followed by a faster robust growth phase like that observed experimentally. Additionally, an evolving sequence of higher order core modes are excited at first. Power transfer analysis shows that nonlinear interactions between the core modes and the 2/1 helps drive the initial slow growth. Once the induced 2/1 magnetic island reaches a critical width, the NTM transitions to faster robust growth which is well described by the nonlinear modified Rutherford equation. This work highlights the role of nonlinear mode coupling in seeding NTMs.

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Nonlinear magnetohydrodynamics of pulsed parallel current drive in reversed-field pinches

Cited by 12 publications

References 31 publications

Stabilization of ideal pressure gradient driven edge modes during pulsed parallel current drive in reversed field pinch

Stabilization of ideal pressure gradient driven edge modes during pulsed parallel current drive in reversed field pinch

Electron Bernstein Wave Studies in MST

Growing Neoclassical Tearing Modes Seeded via Transient-Induced-Multimode Interactions

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