Whole-device modeling of HIDRA plasmas for experimental planning

The HIDRA stellarator at the University of Illinois at Urbana-Champaign is preparing for operations with flowing liquid lithium limiters inside the machine. The objective of these experiments is to test the operation of the limiters under steady-state conditions with a fusion-relevant plasma edge. In order to determine how to run the machine to achieve the desired experimental conditions (density, temperature, and fluxes to the limiters), it is beneficial to have a model to predict these plasma parameters under various operating conditions (external heating power, plasma radius, magnetic field strength, and rotational transform). The objective for this thesis is to develop a simple, whole-device model of HIDRA in order to predict the relationship between the control parameters and the plasma parameters. The model developed here is separated into two regions: (1) the magnetically confined core and (2) the unconfined Scrape-Off-Layer (SOL). The core is modeled using 1-dimensional (radial) particle and energy diffusion equations with a Bohm diffusivity. The primary innovation made here for the core analysis is a way to solve the diffusion equations without imposing a boundary condition at the edge of the confined region. The MHD pressure equilibrium profile for a screw-pinch configuration is used instead, where density and temperature solutions to the diffusion equations are evaluated by how well they meet the pressure constraints. By calculating the energy confinement time from the model, and comparing that to the Yamada scaling, it is found that the behavior produced by the core model is consistent with experimental results. The edge is modeled using a 1-dimensional (radial) particle balance, assuming a Simple SOL regime. Since there is little-to-no analytical theory for SOL plasmas with the type of axisymmetric limiter geometry used for HIDRA, the primary innovation made here is simply developing a way to model particle losses from the SOL in this asymmetric geometry. This is done by discretizing the plasma in the radial direction, calculating what proportion of the plasma will be swept out by the limiter in each radial layer, and tracking the cumulative loss of particles to the limiter as the plasma diffuses outward through the SOL. After developing the plasma core and edge models, they are tested with varying operating parameters. The primary finding is that maximizing the heat fluxes to the limiters can be achieved by decreasing the plasma radius, increasing the magnetic field, increasing the rotational transform, and decreasing the heating power. Lastly, we discuss some implications of discharging the central solenoid during stellarator operation. The plasma could easily be driven kink-unstable by operating this way, which could be used as a way to cause a plasma disruption and significantly increase heat fluxes to the limiters.

Name thesis:degree_name

M.S.

Level thesis:degree_level

Thesis

Discipline thesis:degree_discipline

Nuclear, Plasma, Radiolgc Engr

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2020

Author dc:creator

• Parsons, Matthew S.

Contributors dc:contributor

• Andruczyk, Daniel
• Curreli, Davide

• Stellarator
• Plasma Modeling

Statement dc:rights

• Copyright 2019 Matthew S. Parsons

Language dc:language

en

Handle dc:identifier

http://hdl.handle.net/2142/106368

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/106368