Isotope dependence of transport in ST40 hot ion mode plasmas

Journal Article · Wed Aug 09 00:00:00 EDT 2023 · Plasma Physics and Controlled Fusion

DOI:https://doi.org/10.1088/1361-6587/ace849· OSTI ID:1996980

Kaye, S. M. ^[1]; Sertoli, M. ^[2]; Buxton, P. ^[2]; Dnestrovskii, A. ^[2]; McNamara, S. ^[2]; Romanelli, M. ^[2]; Thomas, P. ^[2]

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1. Princeton Plasma Physics Laboratory (PPPL), Princeton, NJ (United States); Princeton Univ., NJ (United States)
2. Tokamak Energy Ltd (United Kingdom)

The ST40 compact, high-field spherical tokamak, operating at 2.1 T and with 1.8 MW of neutral beam heating, achieved central carbon impurity ion temperatures in excess of 10 keV, surpassing their business milestone of 100 M °C (8.6 keV). The high temperature discharges were in the hot ion mode, with $$T_i \gg T_e$$, and they were achieved in both hydrogen and deuterium plasmas with deuterium neutral beam injection. In order to achieve the high temperature scenarios, careful wall conditioning and scenario optimization was carried out in $$H^0 \rightarrow H^+$$, $$D^0 \rightarrow H^+$$, and finally in $$D^0 \rightarrow D^+$$ plasmas. The TRANSP transport code was employed to study the dependence of confinement and transport on isotopic mass, and the conditions that led to the high measured central ion temperatures in the $$D^0 \rightarrow H^+$$ and $$D^0 \rightarrow D^+$$ plasmas. The kinetic profiles input into TRANSP were inferred from line-of-sight and limited radial measurements as well as consistency with a number of other experimental constraints. The TRANSP results first showed that the main species central ion temperature was only 0.5–1 keV lower than the measured carbon impurity temperature, and thus in the high performance plasmas also surpassed the 100 M °C level. TRANSP also showed that while the electron thermal conduction loss was dominant, reductions in central ion transport, and an effective decoupling of the ions from the electrons, led to an increase in central ion temperatures with increasing plasma mass. In fact, the associated confinement times exhibited a strong dependence on the isotopic mass of the thermal plasma. These preliminary results are foundations for dedicated experiments with full kinetic profile measurements on ST40 in the next run campaign.

• Research Organization: Princeton Plasma Physics Laboratory (PPPL), Princeton, NJ (United States)
• Sponsoring Organization: USDOE Office of Science (SC)
• Grant/Contract Number: AC02-09CH11466
• OSTI ID: 1996980
• Report Number(s): CRADA NFE-19-07769
• Journal Information: Plasma Physics and Controlled Fusion, Journal Name: Plasma Physics and Controlled Fusion Journal Issue: 9 Vol. 65; ISSN 0741-3335
• Publisher: IOP Science
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
ST40
isotope dependence
spherical tokamak
transport and confinement