Mike Kryjak

University of York

About:

Mike Kryjak obtained his Master's degree in Mechanical Engineering in 2015 and embarked on a career in combustion CFD modelling for power generation. As a CFD engineer, he was technical lead in several large scale, international simulation-driven emission reduction and combustion optimisation projects in coal, gas, oil, biomass and refuse-derived fuels. He achieved chartered status in 2020 but shortly after changed course to pursue his life-long dream of working in nuclear fusion, joining the Fusion CDT programme at the University of York where he is now a PhD researcher specialising in tokamak plasma edge simulation.

Mike is one of the developers of the 1D/2D and 3D turbulence edge plasma code Hermes-3 as well as DLS-Extended, a simple 1D model to estimate the impact of divertor magnetic configuration on detachment. His main research interests are the development of advanced fluid neutral models, studying the response of the detachment front to transients as well as the impact of atomic reactions and kinetic effects on scrape-off layer physics.

He is currently based at the UK Atomic Energy Authority where he works in close collaboration with the STEP and MAST-U exhaust teams, while also working with Tokamak Energy to benchmark several edge codes on the ST40 spherical tokamak.

Abstract:
Using the DLS-Extended model to optimise STEP divertor magnetic configuration for detachment performance

The divertor heat exhaust problem is a key challenge on the way to commercial fusion in reactor-class tokamaks. One way to mitigate the divertor heat loads is through detachment, a power loss driven process leading to plasma recombining near the target and forming a protective cloud of neutral gas which then acts as a sink of plasma energy, density and momentum. STEP (Spherical Tokamak for Energy Production) is the United Kingdom’s proposed reactor-class project whose exhaust solution currently depends on achieving detachment driven through impurity radiation. The plasma edge features highly complex physics and detachment performance is most often studied in high fidelity 2D codes such as SOLPS-ITER. However, such codes have high computational cost and divertor design programs can be significantly accelerated by the use of simpler models capable of rapid scoping studies to inform both equilibrium design as well as higher fidelity simulations. The DLS (Detachment Location Sensitivity) model [1,2,3] is a 1D analytical code allowing the prediction of the location where most of the energy has been dissipated (the detachment front) for a given upstream density, impurity fraction and power input as well as the detachment threshold, window and sensitivity [1] for a given magnetic configuration. The DLS approach is similar to a Lengyel model [4] with a dynamic target position representing the detachment front. It assumes all heat transfer is occurring through electron conduction, pressure being constant and fixed-fraction impurity radiation across a negligibly wide front representing the sole mode of energy loss in the system. While these are significant simplifications, DLS has been compared to SOLPS-ITER in nitrogen seeded slab geometry and was found to have reasonable performance with results that were conservative with respect to SOLPS [2].In the present work the DLS is extended, relaxing the assumption of a thin radiation region and allowing the domain to extend past the X-point up until the midplane. This makes the model more applicable for reactor-relevant impurities such as argon and neon which can radiate over a large temperature range. The impact of the DLS-Extended improvements on the predictions of detachment threshold, window and sensitivity is assessed for the current STEP divertor design as well as for a range of alternative magnetic configurations. The model is then used to suggest an optimised inner and outer divertor design.

References:
[1] Lipschultz B., Parra F.I. and Hutchinson I.H. 2016 Sensitivity of detachment extent to magnetic configuration and external parameters Nucl. Fusion 56 056007
[2] Cowley C. et al 2022 Optimizing detachment control using the magnetic configuration of divertors Nucl. Fusion 62 086046
[3] Myatra O. et al 2016 Sensitivity of detachment extent to magnetic configuration and external parameters Nucl. Fusion 63 096018
[4] Lengyel L. 1981 Analysis of radiating plasma boundary layers Tech. Rep.This work was in part performed under the auspices of the U.S. DoE by LLNL under Contract DE-AC52-07NA27344.This project was funded by EPSRC CDT in the Science and Technology of Fusion Energy, Grants EP/L01663X/1, EP/S022430/1