Abstract Details
Abstracts
Author: Jason Hamilton
Requested Type: Consider for Invited
Submitted: 2025-02-21 15:14:18
Co-authors: L. Chacon, X. Tang
Contact Info:
Los Alamos National Laboratory
Theoretical Division
Los Alamos, NM 87545
US
Abstract Text:
A major disruption in a tokamak is a sudden termination of the plasma
discharge, which involves the removal of the plasma thermal energy and
the magnetic energy associated with the plasma current. A normal
disruption has two distinct phases: a short thermal quench (TQ) phase
to rid of the plasma thermal energy and a relatively longer current
quench (CQ) phase to dissipate the plasma current. For a tokamak
reactor like ITER, the TQ is projected to bring down Te from 10-20 keV
tens of eV over a time period of around a millisecond (ms). The CQ
can be much longer but the desired range, for limiting the
electromagnetic force-loading in the blankets and vacuum vessel, is
around tens of ms for ITER. The conventional approach for TQ
mitigation is through a high-Z impurity injection that radiates away
the plasma thermal energy before it reaches the wall. The downside is
a robust Ohmic-to-runaway current conversion due to the radiatively
clamped low post-TQ Te. An alterative approach is to deploy a low-Z
(either D or H) injection that aims to slow down the TQ, and ideally
aligns it with the CQ. This approach has been investigated here via 3D
MHD simulations using the PIXIE3D code. By boosting the hydrogen
density, a fusion-grade plasma is dilutionally cooled at approximately
the original pressure. Energy loss to the wall is controlled by a Bohm
outflow condition at the boundary where the magnetic field in-
tercepts a thin plasma sheath at the wall, in addition to
Bremsstrahlung bulk losses. Robust MHD instabilities proceed as
usual, while the collisionality of the plasma has been greatly
increased and parallel transport is now in the Braginskii regime. The
main conclusion of this study is that the decreased transport loss
along open field lines due to a sufficient low-Z injection slows down
the thermal quench rate to the order of 20 ms, aligned with the
current quench timescale for a 15 MA ITER plasma.
Characterization: 1.0
Comments: