Abstract
The linear response profiles for the 3D perturbed magnetic fields, currents, ion velocities, plasma density, pressures, and electric potential from low-n external resonant magnetic field perturbations (RMPs) are obtained from the collisional two-fluid M3D-C1 code [N. M. Ferraro and S. C. Jardin, J. Comput. Phys. 228, 7742 (2009)]. A newly developed post-processing RMPtran code computes the resulting quasilinear E×B and magnetic (J×B) radial transport flows with respect to the unperturbed flux surfaces in all channels. RMPtran simulations focus on ion (center of mass) particle and transient non-ambipolar current flows, as well as the toroidal angular momentum flow. The paper attempts to delineate the RMP transport mechanisms that might be responsible for the RMP density pump-out seen in DIII-D [M. A. Mahdavi and J. L. Luxon, Fusion Sci. Technol. 48, 2 (2005)]. Experimentally, the starting high toroidal rotation does not brake to a significantly lower rotation after the pump-out suggesting that convective and E×B transport mechanisms dominate. The direct J×B torque from the transient non-ambipolar radial current expected to accelerate plasma rotation is shown to cancel much of the Maxwell stress J×B torque expected to brake the plasma rotation. The dominant E×B Reynolds stress accelerates rotation at the top of the pedestal while braking rotation further down the pedestal.
Highlights
AND SUMMARYThis paper summarizes exploratory work on the theory and simulation of quasilinear transport from external resonant magnetic perturbations (RMPs)
A newly developed post-processing RMPtran code focuses on computation of the flux surface average (n 1⁄4 0) quasilinear radial transport of toroidal angular momentum (TAM), ion particle, and non-ambipolar current flows from the beating together of the single 6n linear response perturbations
The toroidally symmetric unperturbed flux surfaces, which define the co-ordinate system, by definition carry no radial current Jr0 1⁄4 0. (The dJ~ 1⁄4 r  dB linear perturbations contain no displacement current since @dE~=@t=4p 1⁄4 0 in the static linear perturbations, which are locked to the stationary RMP coil currents.) Combining the direct JÂB torque from the radial displacement current 1⁄2 with the JÂB torque normally associated with the Maxwell stress {} in Eq (3a), we find a significant non-ambipolar current torque cancelation
Summary
This paper summarizes exploratory work on the theory and simulation of quasilinear transport from external resonant magnetic perturbations (RMPs). A newly developed post-processing RMPtran code focuses on computation of the flux surface average (n 1⁄4 0) quasilinear radial transport of toroidal angular momentum (TAM), ion (center of mass) particle, and non-ambipolar current flows from the beating together of the single 6n linear response perturbations. The most vexing aspect of the RMPtran simulated quasilinear flows is how to interpret and account for the presumably fast relaxation of the radial nonambipolar magnetic-flutter currents, which like the RMPtran simulated torque density is found to switch between outward (at the island resonant surfaces, for example) and inward with multiple passes through zero over rather short (5%) radial scales Such flux surface average currents are displacement currents (@Er=@t 1⁄4 À4pJr) which must quickly vanish as the profiles are evolved by transport time stepping.
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