Shattered pellet injection simulations with NIMROD

Abstract

Optimal strategies for disruption mitigation benefit from the understanding of details both spatially and temporally. Beyond the assessment of the efficacy of a particular proposed Disruption Mitigation System (DMS), ITER's longevity will require accounting of both mitigated and unmitigated disruptions. Accurate models and validated simulations that detail multiple ITER scenarios with mitigated and unmitigated disruptions are essential for accurate estimates of load damage. The primary candidate for ITER's DMS is Shattered Pellet Injection (SPI); its efficacy must be evaluated within the next several years. To perform critical time dependent 3-D nonlinear simulations, we have developed a particle based SPI model in the NIMROD code coupled to its modified single fluid equations with impurity and radiation [Izzo, Nucl. Fusion 46(5), 541 (2006)]. SPI validation simulations of the thermal quench and comparisons to DIII-D impurity scan experiments [Shiraki et al., Phys. Plasmas 23(6), 062516 (2016)] are presented. We also present an initial ITER Q = 10 pure neon SPI simulation and compare it with the DIII-D SPI simulations. NIMROD SPI simulations demonstrate that the ablating fragment drives strong parallel flows that transport the impurities and governs the thermal quench. Analysis of SPI simulations shows that the mixed deuterium/neon SPI results in a more benign thermal quench due to the enhanced transport caused by the additional deuterium. These results suggest that an optimal pellet mixture exists for the SPI system.

The JOREK non-linear extended MHD code and applications to large-scale instabilities and their control in magnetically confined fusion plasmas

“…This section summarizes work performed with JOREK on the TQ triggering mechanisms (section 6.2.1), the TQ dynamics and plasma current spike (section 6.2.2), the assimilation and mixing of injected material (section 6.2.3) and the radiation fraction and asymmetry (section 6.2.4). For work with other codes on these topics, see references [256][257][258][259][260][261] and references therein.…”

Physics of runaway electrons in tokamaks

“…This means ensuring sufficiently deep penetration of the fragments while avoiding that too many fragments cross the plasma and strike the opposite wall. NIMROD simulations for SPI in ITER show that the assimilation efficiency depends strongly on the initial fragment sizes [273]. Note that for late injection into an existing runaway beam, SPI is not expected to be more efficient than MGI (see Section X C).…”

First predictive simulations for deuterium shattered pellet injection in ASDEX Upgrade

“…To match these requirements, among other constraints, the current quench (CQ) time will have to stay between given upper and lower limits and the plasma density needs to increase by more than an order of magnitude across the whole plasma domain before intact flux surfaces begin to form again when runaway electrons are confined in the plasma. Besides NIMROD [5] and M3D-C1 [6], the JOREK code used for the present study is among the few extended non-linear MHD codes world-wide, which has the necessary ingredients for simulating all aspects of mitigated disruptions in realistic geometry. Previous studies for massive gas and shattered pellet injection [7][8][9][10][11][12] demonstrate some of the capabilities.…”