Speaker
Ivan Zemtsov
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1086.pdf
Transport of Li and W impurities and their influence on discharge
parameters of the T-10 tokamak
I.A. Zemtsov, V.A. Krupin, M.R. Nurgaliev, L.A. Klyuchnikov, A.R. Nemets,
A.Yu. Dnestrovskij, G.M. Asadulin, A.A. Borschegovskij, V.A. Vershkov, S.A. Grashin,
T.B. Myalton, D.V. Sarychev, D.S. Sergeev, N.A. Solovyev, A.V. Sushkov, V.M. Trukhin
National Research Centre "Kurchatov Institute", Moscow, Russia
In 2016, a W-limiter made of ITER-grade WMP "POLEMA" tungsten and the moveable Li-
limiter has been installed on the T-10 tokamak [1]. The transport of Li and W impurities and
their influence on the parameters of T-10 OH and ECRH-discharges are studied in this paper.
Experiments in OH-discharges were performed with two positions of the Li-limiter: outside
and inside of the W-limiter radius. In the first case, short lifetime of Li1+ in scrape-off layer
is severely limiting lithium flux in the plasma that results in low concentration of Li nuclei in
the plasma center (nLi3+ < 0.3% of ne , which is insufficient to perform CXRS-measurements).
In the second case, the flow of lithium is significantly increased and high concentration of Li
nuclei in the plasma center is achieved (up to 26% of ne , according to CXRS-measurements).
Reliable data on nLi3+ made it possible to establish that the transport of lithium ions and nuclei
follows the same dependences as all impurities in T-10 plasma and can be described by the
transport model worked out for Ar, K, C, O, W impurities [2, 3]. The main influence of Li on
the parameters of OH discharges is a strong reduction of light impurities level. This leads to a
decrease of the effective charge Ze f f and opens the possibility for a strong peaking for both the
Ze f f (r) profile and the PW (r) radiation loss profile on W ions.
Study of the influx, transport, and radiation of W impurity in a plasma cord with a tungsten
limiter at high (Ze f f ≥ 4) and low (Ze f f ≈ 1) levels of light impurities is carried out. The follow-
ing recurring scenario is observed in the experiments: first, Ze f f (r) peaks, then W accumulates
at the plasma center, PW (r) peaks and suppresses the sawtooth oscillations (SO). Further the
peaking of PW (r) causes flattening and broadening of Te (r), which ends with the evolution of
the MHD mode m = 2 and the occurrence of a "small" disruption with the impurities removal
and loss of 30 ... 50% of the plasma stored energy. This scenario (W-cycle) can repeate many
times during the discharge, often resulting in a disruption. The conditions for development of
the W-cycle in T-10 plasma are determined in this work. It was found that off-axis ECRH leads
to the acceleration of the W-cycle due to the mitigation of SO suppression and the enhanced
accumulation and peaking of W. The on-axis ECRH prevents the development of W-cycle at
any stage due to the effective removal of tungsten from the plasma center [4].
References
[1] V.A. Vershkov et.al., Nuclear Fusion, Vol. 57 (10), 102017 (2017)
[2] V.A. Krupin et.al., 12th EPS Conference on Plasma Physics, Vol. 9F, 207-210 (1985)
[3] I.A. Zemtsov et.al., Problems of Atomic Science and Technology, Ser. Thermonuclear Fusion, Vol. 40, P. 29-35.
[4] V.A. Krupin et.al. Nuclear Fusion, Vol. 57 (6), 066041 (2017)
