Development of an innovative set of ELM control coils for the TCABR tokamak

Abstract

The high confinement mode is seen as the most promising operational regime for obtaining economically attractive fusion power plants based on the tokamak concept. A particular feature of plasmas operated in this regime is the presence of instabilities known as edge localized modes (ELMs), which can cause unacceptably high transient heat fluxes onto material wall - the divertor plates. The erosion caused by these energy bursts can reduce significantly the lifetime of plasma-facing components thus driving the need for ELM control in large devices. Experiments world wide have demonstrated that externally applied, relatively small, non-axisymmetric, resonant magnetic perturbations (RMPs) can be used to suppress ELMs and, for this reason, ELM control coils were added to the ITER baseline design. However, numerical modeling of such plasmas subject to RMP fields reveals that present RMP physics models are still not capable of providing quantitative results. The lack of a reliable physics model of the impact of RMP fields on tokamak plasmas is a fundamental issue when trying to predict the response of ITER plasmas to these fields. To improve the reliability of numerical codes, experiments carefully designed to validate RMP physics models are being carried out in existing tokamaks. This research proposal aims at designing, constructing and testing of a unique and innovative set of RMP coils for TCABR that allows for carrying out detailed experimental validation of RMP physics models over a wide range of plasma scenarios, RMP coil geometries and perturbed magnetic field spectra. This new set of RMP coils has the capability of applying static or rotating (up to 10 kHz) RMP fields with dominant toroidal harmonics as high as n = 9 from both the low field side and the high field side, which was never achieved in any existing tokamak. However, to mitigate risks of damaging the TCABR vacuum vessel, it was decided that it is safer first to develop all the national know-how in a 72 degrees replica of the original TCABR vacuum vessel that is available at the Plasma Physics Laboratory of the Institute of Physics of the University of São Paulo. This replica will, therefore, serve as a workbench in which all the different technological solutions can be safely tested without risking the original TCABR vacuum vessel. Therefore, the goal of this project is to develop and test the critical technologies so that the full implementation of the TCABR upgrade can be planned on solid basis. (AU)