No abstract

Motivated by the recent experimental observation that plasma stability can be improved by external magnetic perturbations, the general problem of plasma response to external magnetic perturbations is investigated. Different (vacuum, ideal and resistive) plasma response models are considered and compared. Plasma response, in experiments where stabilization was achieved, is obtained through computation using the MARS-F code, with a plasma model that includes both plasma resistivity and rotation. The resultant magnetic field line stochasticity is much reduced from that obtained formerly using the vacuum plasma model. This reduced stochasticity is more consistent with the favourable experimental observation of enhanced stability. Examples are given for the response of an ITER plasma to perturbations generated by the correction coils; and the response of a plasma to external coils (antenna) up to the Alfvén frequency.

Within the single fluid resistive magneto-hydrodynamic (MHD) model, systematic toroidal modelling efforts are devoted to investigate the plasma response induced screening of the applied external 3D magnetic field perturbations in the presence of sheared toroidal flow. One particular issue of interest is addressed, when the local flow speed approaches zero at the perturbation rational surface inside the plasma. Subtle screening physics, associated with the favourable averaged toroidal curvature effect (the GGJ effect [Glasser A H et al 1975 Phys. Fluids 7 875]), is found to play an essential role at slow flow near the rational surface by enhancing the screening at reduced flow. A strong cancellation effect between different terms of the Ohm's law is discovered, leading to different screening physics in the GGJ regime, as compared to that of the conventional screening of the typical resistive-inertial regime occurring at faster flow. These modelling results may be applicable to interpret certain mode locking experiments, as well as type-I edge localized mode suppression experiments, with resonant magnetic field perturbations being applied to tokamak plasmas at low input toroidal torque.

The extensive use of commodity polymer materials has led to the depletion of natural resources and caused the undesirable problem of plastic pollution. In this context, the design of novel polymeric structures with unique recyclability characteristics from renewable resources and the recycling of real-life plastic wastes are critical to address the problems associated with the increasing demand for plastics. Chemical degradation of wastes through polymerizationdepolymerization followed by re-polymerization has already emerged as a long-term strategy toward the attainment of completely sustainable cycles. Bisphenol-A-polycarbonates (BPA-PC) exhibit high thermal resistance, excellent mechanical properties, and high optical transparency, which make them suitable materials for commodity and engineering plastics. This review presents our vision for realizing a circular polymer economy for polycarbonate materials-from the chemical recycling of widely used BPA-PCs to the novel aliphatic polycarbonates from renewable resources.