The effect of increasing toroidal magnetic field in the Globus-M spherical tokamak

• Published in: Nuclear fusion 2018-12, Vol.58 (12), p.126029
• Main Authors: Bakharev, N.N., Bulanin, V.V., Chernyshev, F.V., Gusev, V.K., Khromov, N.A., Kiselev, E.O., Kurskiev, G.S., Melnik, A.D., Minaev, V.B., Mironov, M.I., Miroshnikov, I.V., Patrov, M.I., Petrov, A.V., Petrov, Yu.V., Sakharov, N.V., Shchegolev, P.B., Sladkomedova, A.D., Solokha, V.V., Telnova, A.Yu, Tokarev, V.A., Tolstyakov, S.Yu, Yashin, A.Yu
• Format: Article
• Language: English
• Subjects: Alfven eigenmode; energy confinement; Globus-M; neutron rate; radiation losses; spherical tokamak; toroidal magnetic field increase
• ISSN: 0029-5515; 1741-4326
• DOI: 10.1088/1741-4326/aae60d

In the final Globus-M experimental campaign Btor and Ip were raised by 25% up to 0.5 T and 250 kA, respectively, expanding available range of experimental parameters. In these experiments an overall improvement in plasma performance was observed, plasma total stored energy and neutron rate increased significantly. The energy confinement time dependence on Btor and ne was close to linear. L-H transition threshold was 5-10 times higher than threshold predicted by the scaling. Despite the small plasma-wall distance, the level of radiation losses in the main plasma volume was relatively small and decreased as Btor rised. An increase in Btor and Ip led to a decrease in the sawtooth-induced losses. While a rise in the plasma current led to a decrease of fast ion losses per TAE burst at the same amplitude; frequency of bursts and their amplitude increased. Doppler backscattering, applied to study TAE localization for the first time, revealed that TAE fluctuations are localized in the region of normalized minor radii ρ  =  0.5-0.75. A new movable 9-pin head probe provided data, necessary for power decay length scaling investigation. Significant power decay length contraction, stronger than predicted by Eich's scaling, was observed.