MHD modeling of shattered pellet injection in JET

Abstract

Nonlinear 3D MHD simulations of shattered-pellet injection (SPI) in JET show prototypical SPI-
driven disruptions using the M3D-C1 and NIMROD extended-MHD codes. Initially, radiation-driven
thermal quenches are accelerated by MHD activity as the pellet crosses rational surfaces, leading to a
radiation spike, global stochasticization of the magnetic field, and a complete thermal quench. Eventually,
current quenches, preceded by a current spike are seen as the Ohmic heating becomes equal to the
radiative cooling. The results are qualitatively similar for both a single monolithic pellet, pencil-beam
model, and a realistic shatter to represent the SPI plume. A scan in viscosity from 500-2000 m2/s for
MHD simulations finds that reducing viscosity increases MHD activity and decreases thermal quench time
1slightly. A realistic cloud of fragments modeling shows that mixed-D-Ne pellet travels deeper into the
plasma core before the thermal quench. At the slow pellet speeds, the pellet is found to be moving slowly
enough inward that even the 5% neon in the mixed pellet is enough to effectively radiate the thermal
energy available. Radiation toroidal peaking is predicted to be at levels consistent with experimental
observations and reduced as the pellet travels deeper into the plasma. These simulations lay the ground
work for more-sophisticated validative and predictive modeling of SPI in JET using both M3D-C1 and
NIMROD

3D radiated power analysis of JET SPI discharges using the Emis3D forward modeling tool

“…These simulated radiation structures produce a spectrum consistent with coronal equilibrium and the dominant power is not in visiblefrequencies. SPI simulations from DIII-D using NIMROD also show similar helical structures [30].…”

Plasmoid drift and first wall heat deposition during ITER H-mode dual-SPIs in JOREK simulations

“…Resolving these two competing factors is part of our future plan. Last, our choice of viscosities might impact the TQ duration, as is demonstrated in [10]. The current values we chose are the minimum value we could use without rampant numerical instabilities.…”

“…There have been intensive studies, both experimentally [2][3][4][5][6] and numerically [7][8][9][10], on both the total radiated energy and the radiation power density within the plasma volume after SPIs. It has been found in general that an apparent toroidal asymmetry in the radiation power density exists for the single SPI cases, especially in the early injection phase.…”

Interpretative 3D MHD modelling of deuterium SPI into a JET H-mode plasma

“…SPI systems have been installed on various tokamaks around the world such as AUG [3], DIII-D [4][5][6], HL-2A [7], KSTAR [8], JET [2,9,10] and J-TEXT [11]. 3D non-linear MHD codes such as JOREK, M3D-C1 and NIMROD have been applied to predict the thermal quench (TQ) and current quench (CQ) dynamics during SPI [12][13][14][15][16][17][18][19][20], with the knowledge gained from studies on massive gas injection (MGI) [21-25, and references therein]. In addition, experiments and interpretative modelling have been performed for a dispersive shell pellet injection technique [26,27].…”