Hybrid meshing techniques for full-orbit particle-in-cells simulation of full scrape-off layers including plasma-surface interaction and Monte Carlo collision effects

Huq, Md Fazlul

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https://hdl.handle.net/2142/129691 Copy

Description

Title

Hybrid meshing techniques for full-orbit particle-in-cells simulation of full scrape-off layers including plasma-surface interaction and Monte Carlo collision effects

Author(s)

Huq, Md Fazlul

Issue Date

2025-04-30

Director of Research (if dissertation) or Advisor (if thesis)

Curreli, Davide

Doctoral Committee Chair(s)

Curreli, Davide

Committee Member(s)

• Kozlowski, Tomasz
• Sankaran, Ramanathan
• Sahni, Onkar

Department of Study

Nuclear, Plasma, & Rad Engr

Discipline

Nuclear, Plasma, Radiolgc Engr

Degree Granting Institution

University of Illinois Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• Hybrid Meshing Technique
• Particle-in-Cells
• Scrape-Off Layer
• Plasma-Surface Interaction
• Monte Carlo Collision

Abstract

Some of the most significant challenges that fusion research is dealing with today are directly related to how the plasma behaves in the Near and Far Scrape-off Layer (SOL) regions, and their interaction with the Plasma Facing Components (PFC). The best first-principle approach to model the plasma behavior in the SOL is to perform full-orbit kinetic simulations of the SOL by solving the multi-species electrostatic Boltzmann equation using a Particle-in-Cell numerical approach. However, the computational requirements of these types of simulations pose substantial challenges, particularly in terms of time and resources needed. Even with hybrid parallel Particle-in Cell (PIC) codes, such as hPIC2, trying to simulate the entire poloidal cross-section of the SOL of a tokamak soon becomes impractical due to the multiscale and complex nature of the plasma and to the requirement of uniform meshes typical of PIC approaches. In this work, we explore how to reduce the computational demands of full-scale tokamak PIC simulations by relaxing the mesh requirements. We propose and analyze an anisotropic structured-unstructured mesh, hereon referred as “hybrid mesh”, specifically tailored for full-scale PIC simulations of the SOL of a tokamak. An important feature of our meshing methodology is that it allows to resolve the plasma sheath spatially forming at the plasma-material interface, a feature not tackled in previous approaches. In the near SOL region, where large density and temperature gradients and large fluxes are present, we used an anisotropic, multi-block, boundary-layer-refined, structured mesh. This structured mesh ensures to capture steeper gradients in this region. For the far SOL region, which experiences weaker ionization and gradients and has a more complex geometry, we used an unstructured mesh. This unstructured mesh is well-suited to accommodate the complex geometry of the far SOL region. A highly resolved mesh is employed in the high potential gradient sheath region at the vicinity of the first wall throughout the device. This ensures proper refinement in this critical region, capturing the sharp electric potential gradient normally occurring within the sheath. This new mesh reduces the number of degrees of freedom significantly, thus enabling sheath-resolved full-orbit PIC simulations of the entire SOL. We tested our hybrid mesh algorithm by successfully running a full-orbit hPIC2 simulation of the full Scrape-Off Layer of the WEST tokamak. The simulation includes a dynamic wall model via coupling to the RustBCA code across the full extension of the first wall of the device. The tungsten sputtered because of ion irradiation enters the SOL plasma and is further ionized into multi-step ionization (ZW = 0, +1, +2, ..., +18 included). The simulation produces distributions of W impurity charge in the near-wall layer of the SOL, along with a prediction of the gross erosion fluxes over the full extension of the tokamak wall. Our model allows estimating from first principles, at a reasonable computational cost, which wall regions are eroded the most by plasma exposure.

Graduation Semester

2025-05

Type of Resource

Thesis

Handle URL

https://hdl.handle.net/2142/129691

Copyright and License Information

Copyright 2025 Md Fazlul Huq

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