ORCID ID

https://orcid.org/0000-0002-4315-4822

Date Awarded

2024

Document Type

Dissertation

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Physics

Advisor

Saskia Mordijck

Committee Member

Patricia Vahle

Committee Member

Justin R Stevens

Committee Member

Florian M Laggner

Committee Member

Calvin Lowe

Abstract

The H-mode plasma edge is a region of steep gradients in density and temperature known as the “pedestal” which greatly increases energy confinement. The complex links between neutral-plasma interactions and both diffusive and convective transport in the pedestal must be understood to model, predict, and achieve the high performance required for a fusion power plant. This dissertation explores the effects of different hydrogenic isotope neutral particles and plasma transport from the edge pedestal region into the Scrape-Off Layer. Current experiments typically use deuterium (H with amu=2 or D), however future fusion power plants may startup with hydrogen (H), and eventually burn a mixture of deuterium and tritium (H with amu=3 or T). As isotope mass increases, energy confinement also increases in direct contradiction to the predicted scaling from diffusive theory, a phenomenon known as the “isotope effect”. Using a database of H and D pedestals on the DIII-D tokamak, we show indications that both species pedestals are in electron-dominant turbulence regimes, where increased outwards convection for hydrogen contributes to lower electron density pedestals consistent with gyrokinetic theory. However, this is complicated by indications of fueling differences between the isotopes. To isolate the effect of fueling, we conducted an experiment on DIII-D to match electron density (ne) and temperature (Te) profiles between hydrogen and deuterium, where neutral particle ionization profiles were measured with the newly available Lyman-α LLAMA diagnostic. On the High Field Side (HFS), neutral penetration lengths (λn0 ) across the pedestal are 40% longer for hydrogen compared to deuterium, consistent with the thermal velocity ratio between the isotopes (v_{H_{th}}/v_{D_{th}} = √2), while measurements on the Low Field Side (LFS) suggest a transport effect. The influence of neutral penetration on electron density pedestal width (∆ne) diminishes with increasing opaqueness (η ≡ ∆ne /λn0 ), shown by low opaqueness pedestals (η ∼ 0.9) in hydrogen being ∼ 40% wider than their deuterium counterparts. Higher opaqueness η ∼ 2 more effectively shields the pedestal from neutrals, as indicated by hydrogen and deuterium having nearly identical ∆ne . Moving across the separatrix into the Scrape-Off Layer, we conducted a diagnostic validation exercise using the ELZAR analysis method with stereoscopic fast cameras on MAST to detect field-aligned turbulent transport events known as “filaments”. Comparisons between the cameras show similar data in individual frames, inversion maps, and statistical distributions of located blobs. The two most important parameters for the framework connecting the statistics to SOL steady-state profiles are the lognormal distributions for filament radial position and major axis width which are within error between the cameras. The remaining distributions are unimportant to the statistical framework and we systematically attribute their differences to the experiment setup.

DOI

https://dx.doi.org/10.21220/s2-jmvv-s544

Rights

© The Author

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