Disruption mitigation studies in DIII-D

Abstract

DISRUPTION MITIGATION STUDIES IN DIII-D Data on the discharge behavior, thermal loads, halo currents, and runaway electrons have been obtained in disruptions on the DIH-D tokamak [J.L. Luxon and L.G. Davis, Fusion Technology 8,2A 441 (198.31. These experiments have also evaluated techniques to mitigate the disruptions while minimizing runaway electron production. Experiments injecting cryogenic impurity "killer" pellets of neon and argon and massive amounts of helium gas have successfully reduced these disruption effects. The halo current generation, scaling, and mitigation are understood and are in good agreement with predictions of a semianalytic model. Results from "killer" pellet injection have been used to benchmark theoretical models of the pellet ablation and energy loss. Runaway electrons are often generated by the pellets and new runaway generation mechanisms, modifications of the standard Dreicer process, have been found to explain the runaways. Experiments with the massive helium gas puff have also effectively mitigated disruptions without the formation of runaway electrons that can occur with "killer" pellets.

Gas jet disruption mitigation studies on Alcator C-Mod and DIII-D

“…It has been found empirically that if a disrupting plasma is terminated quickly enough, halo currents in the divertor region are reduced [2]. Since the current quench time is determined by the L/R time of the post-thermal quench plasma, the current quench can be hastened if the resistivity is significantly increased, which is accomplished by decreasing the temperature of the post-thermal quench plasma and/or increasing Z eff .…”

Dynamics of the major disruption of a DIII-D plasma

“…For proposed next step experiments such as the International Thermonuclear Experimental Reactor, the stored energy will be approximately 100 times greater than present day devices 1 greatly increasing the potential damage of these events. Exacerbating the risk to the machine and increasing the engineering challenges, the disruption phenomena are often highly non-axisymmetric; 2 this results in localized deposition of the heat loads. Understanding the onset mechanisms and the nonlinear dynamics leading to the disruption is crucial for understanding ways to prevent or mitigate disruptions.…”

“…2 In major disruptions, the thermal energy is lost first in the thermal quench phase. The current density profile flattens, and the resultant change in the internal inductance causes the total plasma current to increase.…”

Desenvolvimento e utilização de um injetor de pastilhas de impurezas no estudo da mitigação de disrupções e atenuação de raios-X de altas energias

“…Com o objetivo de se obter o término controlado do plasma, uma série de estudos [28][29][30][31][32][33] tem sido desenvolvida utilizando a injeção de pastilhas para minimizar os efeitos deletérios de uma disrupção abrupta.…”

“…Dessa forma, uma parcela da energia do plasma é dissipada enquanto o processo de ablação da pastilha ocorre e o efeito danoso da disrupção fica, então, minimizado [24,32,33].…”