Comparison of detachment in Ohmic plasmas with positive and negative triangularity
In recent years, negative triangularity (NT) has emerged as a potential high-confinement L-mode reactor solution. In this work, detachment is investigated using core density ramps in lower single null Ohmic L-mode plasmas across a wide range of upper, lower, and average triangularity (the mean of upper and lower triangularity: delta) in the TCV tokamak. It is universally found that detachment is more difficult to access for NT shaping. The outer divertor leg of discharges with delta approximate to - 0.3 could not be cooled to below 5 eV through core density ramps alone. The behavior of the upstream plasma and geometrical divertor effects (e.g. a reduced connection length with negative lower triangularity) do not fully explain the challenges in detaching NT plasmas. Langmuir probe measurements of the target heat flux widths (lambda q ) were constant to within 30% across an upper triangularity scan, while the spreading factor S was lower by up to 50% for NT, indicating a generally lower integral scrape-off layer width, lambda int. The line-averaged core density was typically higher for NT discharges for a given fuelling rate, possibly linked to higher particle confinement in NT. Conversely, the divertor neutral pressure and integrated particle fluxes to the targets were typically lower for the same line-averaged density, indicating that NT configurations may be closer to the sheath-limited regime than their PT counterparts, which may explain why NT is more challenging to detach.
WOS:001206067300001
2024-06-01
66
6
065005
REVIEWED
EPFL
Funder | Grant Number |
Euratom Research and Training Programmehttp://dx.doi.org/10.13039/100018708 | 101052200 |
European Union via the Euratom Research and Training Programme | |
Swiss State Secretariat for Education, Research and Innovation (SERI) | |
European Commission or SERI | |
Swiss National Science Foundation | DE-SC0010529 |
US Department of Energy | |