Separatrix splitting and magnetic footprints in TCABR

• Grant number: 23/15651-9
• Support Opportunities: Scholarships in Brazil - Scientific Initiation
• Start date: February 01, 2024
• End date: December 31, 2024
• Field of knowledge: Physical Sciences and Mathematics - Physics - Physics of Fluids, Plasma Physics and Electrical Discharge
• Principal Investigator: Gustavo Paganini Canal
• Grantee: Júlia Rodriguez Richieri
• Host Institution: Instituto de Física (IF). Universidade de São Paulo (USP). São Paulo , SP, Brazil
• Associated research grant: 22/04857-2 - Development of an innovative set of ELM control coils for the TCABR tokamak, AP.JP

Abstract

In perfectly axisymmetric diverted plasmas, the equilibrium separatrix associated to an X-point is composed by a stable and an unstable manifold that perfectly overlay. When non-axisymmetric magnetic fields perturb such an axisymmetric configuration, the stable and unstable manifolds do not overlay anymore and complex topological structures, known as homoclinic tangles, arise from the intersection between these manifolds. This process is usually referred to as separatrix splitting. These manifolds oscillate and increase their excursions as they asymptotically approach an X-point, forming structures commonly named magnetic lobes, which act as the plasma boundary of this new perturbed equilibrium. When field lines from inside the perturbed plasma volume connect to the divertor plates through intersections of the magnetic lobes with the divertor plates, structures termed magnetic footprints appear on the plates. Magnetic footprints consist of several stripes that are periodic in the toroidal direction, with the number of stripes being related to the toroidal mode number, n, of the perturbation, e.g. an n = 3 perturbation creates 3 stripes on the plates. However, when several modes are present, the actual number of stripes can vary. The shape of the magnetic footprints, therefore, depends strongly on the amplitude of the magnetic lobes and harmonic content of the perturbation. Most of the exhausted heat and particles from the plasma are deposited in the magnetic footprints and, depending on the plasma conditions, damaging hot spots can appear over the divertor plates surface thus reducing the life time of these components. Controlling the intersection of magnetic lobes with divertor plates is essential to maintain the integrity of the plasma facing components as it controls the levels of heat and particle deposition on the divertor plates surface. The main goal of this work is to study the structure of the magnetic footprints expected to appear in the TCABR tokamak for the different plasma cenários envisaged. For that, the student will implement a numerical code to calculate the magnetic footprints and will use it to provide information about the presence of hot spots on the TCABR divertor plates.