April 15-17

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Abstracts

Author: Cesar F. Clauser
Requested Type: Poster
Submitted: 2019-02-22 08:50:02

Co-authors: S. C. Jardin, N. M. Ferraro

Contact Info:
Princeton Plasma Physics Laboratory
100 Stellarator Rd
Princeton, NJ   08543
United States

Abstract Text:
Vertical displacement events (VDEs) occur in elongated tokamaks when vertical stability control is lost due to a failure of the control system or other off-normal occurrences. These events cause large currents to flow in the vessel and other adjacent metallic structures, and the device must be designed to withstand the associated forces. In order to better understand the potential magnitude and distribution of these forces, we have used the M3DC1 code to simulate potential VDEs in ITER. This work builds on a recent VDE benchmark exercise between M3DC1, NIMROD and JOREK [1] which showed excellent agreement between the three codes for VDE simulations. In this present work, we started from a 15 MA ITER equilibrium and used actual values for the vessel resistivity and pre-quench temperatures. For a “hot VDE”, the plasma starts on the midplane and drifts upward, eventually making contact with the vessel, causing the outermost surfaces to be scraped off and the edge safety factor q_a to drop. When q_a=2, we initiate a thermal quench which takes the plasma temperature down from ~ 30 keV to tens of eV. In particular, we focused on the role of halo currents and their contribution to the total vertical force. We use first the 2D non-linear version of the code and vary the post-thermal quench thermal conductivity profile as well as the boundary temperature in order to generate a wide range of possible cases that could occur in the experiment. We have also studied “cold VDEs” where the thermal quench occurs on the midplane and the plasma subsequently drifts upward. For select cases, we have performed non-linear 3D simulations in which we switch from 2D to 3D when the configuration becomes unstable to non-axisymmetric modes. The 3D simulations produce a “sideway force” in the vessel primarily due to toroidal mode number n=1 instabilities.


[1] I. Krebs et al., “Axisymmetric simulations of vertical displacement events in tokamaks”, Nuclear Fusion (2019).

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