The role of isotope mass on neutral fueling and density pedestal structure in the DIII-D tokamak

• Published in: Nuclear fusion 2024-01
• Main Authors: Chaban, Ryan A., Mordijck, Saskia, Rosenthal, Aaron Michael, Bortolon, Alessandro, Hughes, Jerry W., Knölker, M., Laggner, Florian M., Osborne, Tom H., Schmitz, Lothar, Thome, Kathreen E., Wilks, Theresa M.
• Format: Article
• Language: English
• ISSN: 0029-5515; 1741-4326

Abstract Experimental measurements on DIII-D of hydrogen neutral penetration lengths (λ n 0 ) on the high field side are longer by a factor of √2 than for deuterium consistent with the thermal velocity ratio for neutrals at the same temperature (v th H / v th H = √2). This ratio is constant for both low and high pedestal electron density. At low pedestal density (n e ∽4 × 10 19 m -3 ), the neutral penetration length is greater than the density pedestal width for both isotopes, and the additional 41% increase of neutral penetration in hydrogen widens the pedestal by the same amount. As the density pedestal height increases (n e ∽6 × 10 19 m -3 ), the neutral penetration lengths drop below the density pedestal widths for both isotopes, and the increased penetration of hydrogen has no increased effect on the pedestal width compared to deuterium. Extrapolating to future reactor-relevant high electron density pedestals, the isotope-mass increase on neutral fueling on the high field side in hydrogen will be negligible (0.2-0.4cm) in comparison to estimates of the width of the density pedestal (6-8.5 cm). Extrapolating to other isotopes compared to deuterium, while hydrogen is an increase of 41% \ (√2 \sim 1.41), moving from deuterium to tritium the neutral penetration will decrease 19% (√(2/3) \sim 0.81) implying the isotope mass effect on neutral fueling in the pedestal will be negligible in a D-T reactor.