ORCID ID

https://orcid.org/0000-0002-4359-094X

Date Awarded

2022

Document Type

Dissertation

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Physics

Advisor

Saskia Mordijck

Committee Member

Michael Kordosky

Committee Member

George Vahala

Committee Member

Jerry W Hughes

Committee Member

Ian Abel

Abstract

Understanding edge neutral dynamics in high-field tokamaks has strong consequencesfor both fueling and plasma profile predictions. We validate the ability of SOLPS-ITER, a 2D fluid plasma/kinetic Monte Carlo neutral code, to accurately model the upstream neutral density profiles of L-mode, I-mode, and H-mode discharges in the Alcator CMod tokamak, for which Lyman-alpha emission measurements were available. We achieve simulated Lyman-alpha emission and neutral density profiles that are within one standard deviation of empirically inferred profiles for all three discharges, via iterative tuning of the perpendicular transport coefficient profiles alone, providing confidence in the conclusion that while further physics (drifts, impurities, etc.) may be important in certain cases, the baseline SOLPS neutral model sufficiently simulates neutral distributions in the upstream edge region. We then use SOLPS to show that electron density pedestal structure is mostly unaffected by increased edge fueling when approaching fusion-relevant opaqueness conditions. Simulation results also suggest that upstream fueling dominates over X-point fueling, an important consideration for future fusion devices operating in high density, high neutral opacity regimes. In order to assess the relative role of fueling versus transport at the plasma edge, an experimental basis is formed from a set of similar high density (ne,PED 2x1020 m-3) EDA H-mode discharges from Alcator C-Mod. Gas puffs of varying magnitude are applied to these discharges to probe the response of the pedestal to increased edge fueling. Analysis of the simulated neutral e-folding length around the plasma reveals that in high opacity conditions, neutrals tend to become trapped in the PFR, confirming our assertion that edge fueling mainly occurs through the upstream midplane.

DOI

https://dx.doi.org/10.21220/s2-p7cc-5p08

Rights

© The Author

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