Feedback stabilization of RWM with in-vessel coils

Abstract

Active control of the resistive wall modes (RWMs) is analysed for the feedback system with internal correction coils (ICs). The analysis is performed using a single mode thin-wall model in the cylindrical approximation and proportional control. Three cases are considered: with radial field sensors, poloidal field sensors inside the vessel and poloidal sensors outside. It is shown that, within the model, the systems with such sensors and proportional feedback have similar characteristics. The feedback systems with internal and external correction coils are compared and advantages of the IC system are shown.

Intrinsic plasma rotation and Reynolds stress at the plasma edge in the HSX stellarator

“…Previous experiments have explored the role of Reynolds stress in plasmas with an approximate direction of symmetry. In the cylindrical plasma device CSDX, mean azimuthal flow has been measured which is sustained against viscosity by the Reynolds stress [12,13]. The azimuthal rotation calculated by balancing the Reynolds stress measured using Langmuir probes with the calculated ion-ion and ion-neutral viscosity was found to agree well with the rotation found by a time delay estimation technique using adjacent probe pins.…”

“…This method is similar to the one utilized in the linear device CSDX to calculate a rotation profile that matched the measured rotation in the azimuthal direction [12,13]. Calculating the viscosity in HSX is much more complicated than in a collisional linear device, however, and previous experiments have demonstrated that the experimental viscosity in HSX is several times larger than what is calculated by the analytic method used here [17].…”

“…Although it contains no cross-phase information, the scaling from equation (13) finds that the Reynolds stress drive is expected to scale approximately with the fluctuating potential squared. If adiabatic electrons are assumed so that Flip-1-4 and Mirror configurations are plotted in figure 15.…”

“…Combining these measurements with the simple estimate of the scaling from figure 15, the Reynolds stress drive would be expected to be about 4 times larger in the QHS case than in the Mirror configuration. Based on the scaling from equation (13) and the normalized fluctuations plotted in figure 15, the Reynolds stress may still be a large and important term in the momentum balance in these configurations, but it is generally smaller than it is in the QHS configuration. The Reynolds stress therefore does not appear to account for the increase in flows observed in the Mirror and Flip-1-4 configurations relative to QHS.…”

Local Gyrokinetic Vlasov Simulations with Realistic Tokamak MHD Equilibria

“…Although the above relations are consequence of general discussions, irrespective of the choice of (ρ, θ, ζ), one can construct more specific coordinate systems, which are useful for theoretical and/or numerical analyses. Following Pustovitov's method [25], the most important three fluxcoordinate systems, i.e., Hamada, Boozer, and axisymmetric (or natural) coordinates, are classified systematically.…”