Impurity Transport in Tokamaks with Toroidal Rotation and Non-ideal 3D Perturbations – Plasma Strand Project
Supervisors: Alessandro Geraldini and Jon Graves (University of York).
Predicting and controlling the flow of heavy impurities in a tokamak is essential, as heavy impurities accumulating in the core will cool down the plasma by radiation. Toroidal plasma rotation and three-dimensional (3D) perturbations to the magnetic equilibrium affect the impurity flows, but an understanding of their combined effect is still incomplete [1]. A key player in determining the impurity flows is the radial electric field, whose value is constrained by the “ambipolarity” condition of vanishing net radial current. The radial electric field is thus determined by main-ion and electron transport, depends on the magnetic geometry, and strongly influences impurity dynamics.
VENUS-LEVIS [2] (recently upgraded to VENUS-GPU) is a Monte Carlo code which follows particles (markers) of the full particle distribution function (full-f) to compute the “neoclassical” main-ion and impurity flows in a wide range of scenarios. Neoclassical transport is the result of collisions causing jumps between neighbouring confined collisionless orbits. Although only ideal magnetic configurations (i.e. nested magnetic surfaces) have been studied so far, the approach used in VENUS-LEVIS lends itself to study transport in non-ideal magnetic configurations (i.e. including the presence of magnetic islands). However, the radial particle fluxes computed from VENUS-LEVIS are generally far too noisy to allow for a solution of the ambipolar electric field, restricting impurity flux prediction to cases where the radial electric field can be obtained analytically.
The aim of this PhD project is to develop a delta-f version of VENUS-LEVIS that evolves only the deviation of the distribution function from a Maxwellian. A delta-f scheme greatly reduces statistical noise and will enable an accurate computation of the radial particle fluxes, and thus of the ambipolar radial electric field, in arbitrary magnetic geometries, including those with 3D perturbations and magnetic islands. Its radial electric field output could be used to calculate the heavy impurity transport in tokamak plasmas with rotation and non-ideal 3D magnetic perturbations. This project combines advanced numerical method development, high-performance computing, and neoclassical transport physics relevant to next-generation fusion devices.
[1] E. Lascas Neto, J. P. Graves et al. “Heavy impurity transport in tokamaks subject to plasma rotation, NTV and the influence of saturated ideal MHD perturbations.” Plasma Phys. Control. Fusion 64, 014002 (2022)
[2] D. Pfefferlé et al. “VENUS-LEVIS and its spline-Fourier interpolation of 3D toroidal magnetic field representation for guiding-centre and full-orbit simulations of charged energetic particles.” Computer Physics Communications 185, 3127 (2014).
The project will be mainly based in York, but there is the opportunity for travel to conferences and collaborations with other groups, in particular to EPFL.
During the first six months of the PhD students will typically travel to undertake taught modules at all of the Fusion CDT partner universities.
This project is offered by University of York. For more information please contact: Jonathan Graves (j.graves@york.ac.uk).
This project may be compatible with part time study, please contact the project supervisors if you are interested in exploring this.
For details on how to apply, please visit: Apply
Image above: From E. Lascas Neto, J. P. Graves et al 2022 Plasma Phys. Control. Fusion 64 014002