RT Journal Article
T1 Formation and termination of runaway beams during vertical displacement events in tokamak disruptions
A1 Martín Solís, José Ramón
A1 Mier Maza, Jose Angel
A1 Lehnen, M.
A1 Loarte, A.
AB A simple 0D model which mimics the plasma surrounded by the conducting structures (Kiramov and Breizman 2017 Phys. Plasmas 24 100702) and including self-consistently the vertical plasma motion and the generation of runaway electrons during the disruption is used for an assessment of the effect of vertical displacement events on the runaway current formation and termination. The total plasma current and runaway current at the time the plasma hits the wall is estimated and the effect of injecting impurities into the plasma is evaluated. In the case of ITER, with a highly conducting wall, although the total plasma current when the plasma touches the wall is the same for any number of injected impurities, however the fraction of the plasma current carried by runaway electrons can significantly decrease for large enough amounts of impurities. The plasma velocity is larger and the time when the plasma hits the wall shorter for lower runaway currents, which are obtained when larger amounts of impurities are injected. When the plasma reaches the wall, the scraping-off of the runaway beam occurs and the current is terminated. During this phase, the plasma vertical displacement velocity and electric field can substantially increase leading to the deposition of a noticeable amount of energy on the runaway electrons (∼hundreds of MJ). It is found that an early second impurity injection reduces somewhat the amount of energy deposited by the runaways. Also larger temperatures of the companion plasma during the scraping-off might be efficient in reducing the power fluxes due to the runaways onto the PFCs. The plasma reaches the qa = 2 limit before the runaway electron current is terminated and by that time the amount of energy deposited on the runaway electrons can be substantially lower than that expected until the beam is fully terminated. Negligible additional conversion of magnetic into runaway kinetic energy is predicted during the runaway deconfinement following the large magnetic fluctuations after qa = 2 is crossed for characteristic deconfinement times lower than 0.1 ms which is a characteristic timescale for ideal MHD instabilities to develop.
PB IOP Publishing Limited
SN 0029-5515
YR 2022
FD 2022-05-05
LK https://hdl.handle.net/10016/39467
UL https://hdl.handle.net/10016/39467
LA eng
NO The first author wishes to thank F.J. Artola for helpful suggestions. This work was done under support from Projects ENE2015-66444-R (MINECO/FEDER, UE) and PID2019-110734RB-I00 (AEI, Spain), from Comunidad de Madrid under the agreement with UC3M in the line of Excellence of University Professors (EPUC3M14) and has been carried out under the coordinated research programme of the Disruption and Runaway Theory and Simulation group of the ITER Scientist Fellow Network to which the first author belongs. ITER is the Nuclear Facility INB No. 174. This paper explores physics processes during the plasma operation of the tokamak when disruptions take place; nevertheless the nuclear operator is not constrained by the results of this paper. The views and opinions expressed herein do not necessarily reflect those of the ITER Organization.
DS e-Archivo
RD 27 jul. 2024