Plasma currents induced by resonant magnetic field perturbations in tokamaks

Abstract

The plasma response on externally applied resonant magnetic field perturbations is studied by means of numerical simulations. It is shown that dependent on collisionality and perturbation strength, plasma currents build up which can compensate the external field. These plasma currents are accompanied by out-of-phase currents and poloidal flows at the resonant surfaces. With an increasing perturbation field the screening of the externally applied field decreases and at a certain level, the vacuum field approximation holds for the total magnetic field.

Free energy minimization approach to penetration of resonant magnetic perturbations in tokamaks

“…͑22͒ and ͑23͒ are used for a comparison with results obtained by extended three-dimensional simulations with the ATTEMPT code similar to the ones described in Ref. 23. A comparison of the screening efficiency ␥ and the radial electric field as functions of the RMP field strength R for different plasma parameters p 2 at the respective resonant surface is shown in Figs.…”

“…The last separation is guided again by numerical results of extended drift-fluid simulations with the ATTEMPT code 23,24 proving that the nonprimed contributions are dominant in the respective spectra. Now the quantities , the flux-surface averaged radial electric field, and , the resonant piece of the total magnetic field, are considered as the basic degrees of freedom of the plasma state and minimization of the free energy W is carried out with respect to these parameters.…”

“…The latter is a result of a complex nonlinear interrelation of RMP field strength, plasma currents, and, in particular, plasma rotation. [18][19][20][21][22] In the recent numerical studies with the ATTEMPT code 23 it has been demonstrated that there is a bifurcationlike behavior of the screening of the RMP due to the electron dynamics governed by the interplay of the radial electric field and pressure gradient. These investigations were based on the solution of four-field drift-fluid equations, corresponding to the particle balance, quasineutrality condition, Ohm's law, and parallel ion momentum balance and describing the deviations of particle density n, electric potential , magnetic potential A, and parallel ion flow velocity u ʈ from equilibrium profiles, ‫ץ‬n ‫ץ‬t = − v E · ١͑n 0 + n͒ + 1 e ٌ ʈ J ʈ − n 0 ٌ ʈ u ʈ − n 0 K͑ ͒ …”

Resonant Pedestal Pressure Reduction Induced by a Thermal Transport Enhancement due to Stochastic Magnetic Boundary Layers in High Temperature Plasmas

“…However, these findings were obtained at high resonant field amplitudes in the order of 10 À3 relative to the confining toroidal field. Recent drift-fluid modeling of the plasma response on the external RMP field for typical TEXTOR cases [13] shows at similar high resonant field amplitudes vacuumlike penetration of the external field while at low amplitudes, a compensation of the external fields by internal response currents takes place. Also, for DIII-D H-mode plasmas with high rotation and low resis-PRL 103,…”

Rotation dependence of a phase delay between plasma edge electron density and temperature fields due to a fast rotating, resonant magnetic perturbation field

“…As resistivity increases, one expects a breakdown of this shielding currents and the opening of magnetic islands. 8,9 In this paper we study the rotation dependence of the impact of a fast rotating RMP field on the edge electron density n e ͑r , t͒ and temperature T e ͑r , t͒ fields in a highly resistive ͑Lunquist number S = R / A Ϸ 10 4 with A as Alfvén and R as resistive time͒ edge plasma. We show in this paper three first time observations, which in combination provide for low RMP field amplitudes ͑B r Ͻ 0.2 mT͒ evidence for a shielding of the external field even in the resistive edge of low confinement ͑L-mode͒ plasmas at TEXTOR.…”