Modeling separatrix splitting and magnetic footprints in TCABR

• Grant number: 23/15063-0
• Support Opportunities: Scholarships in Brazil - Doctorate (Direct)
• Start date: February 01, 2024
• End date: July 31, 2027
• Field of knowledge: Physical Sciences and Mathematics - Physics - Physics of Fluids, Plasma Physics and Electrical Discharge
• Principal Investigator: Gustavo Paganini Canal
• Grantee: José Roberto Fernandes Junior
• 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 also 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. When field lines from inside the perturbed plasma volume connect to the targets through intersections of the magnetic lobes with the target plates, structures termed magnetic footprints appear on the targets. Footprints consist of several stripes that are periodic in the toroidal direction, with the number of stripesbeing related to the toroidal mode number of the perturbation, e.g. an n = 3 perturbation creates three stripes on the targets. However, when several modes are present, the actual number of stripes can vary. The shape of the footprints, therefore, depends strongly on the amplitude of the magnetic lobes and harmonic content of the perturbation. Most of the exhausted heat and particles are deposited in the 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. Manifolds act as the boundary of the footprints and they determine the footprints position and shape. This project aims to calculate the magnetic footprints and the separatrix splitting caused by a new set of non-axisymmetric ELM control coils that are being designed for the TCABR tokamak. This new set of coils is composed of six toroidal arrays: three arrays (54 coils) located in the low field side and three arrays (54 coils) located in the high field side. Each of these arrays is composed of 18 coils equally spaced in the toroidal direction, leading to a total of 108 coils. This unique set of coils will allow to apply magnetic perturbations with toroidal mode numbers up to n = 9 and to produce magnetic footprints and separatrix splittings never observed in other tokamaks around the world.