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UKAEA-CCFE-PR(25)2712024
We detail here a semi-analytical model for the pellet rocket effect, which describes the acceleration of pellets in a fusion plasma due to asymmetries in the heat flux reaching the pellet surface and the corresponding ablation rate. This effect was shown in experiments to significantly modify the pellet trajectory, and projections for reactor sc…
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UKAEA-CCFE-PR(25)2702024
Pellets of frozen material travelling into a magnetically confined fusion plasma are accelerated by the so-called pellet rocket effect. The non-uniform plasma heats the pellet ablation cloud asymmetrically, producing pressure-driven, rocket-like propulsion of the pellet. We present a semi-analytical model of this process by perturbing a spherica…
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UKAEA-CCFE-PR(24)2092024
This study systematically explores the parameter space of disruption mitigation through shattered pellet injection in ITER with a focus on runaway electron dynamics, using the disruption modelling tool Dream. The physics fidelity is considerably increased compared to previous studies, by e.g., using realistic magnetic geometry, resistive wall confi…
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UKAEA-STEP-PR(25)282023
Generation of Runaway Electrons (REs) during plasma disruptions, and their impact on plasma facing components, is of great concern for ITER and future reactors based on the tokamak concept. Current STEP (Spherical Tokamak for Energy Production) concept design flat top operating point features a plasma current higher than 20 MA and thus any plasm…
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UKAEA-CCFE-PR(23)152023
Pellet injection is used for fuelling and controlling discharges in tokamaks, and it is foreseen in ITER. During pellet injection, a movement of the ablated material towards the low- field side (or outward major radius direction) occurs because of the inhomogeneity of the magnetic field. Due to the complexity of the theoretical models, computer…
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UKAEA-CCFE-PR(22)532022
An effective disruption mitigation system in a tokamak reactor should limit the exposure of the wall to localized heat losses and to the impact of high current runaway electron beams, and avoid excessive forces on the structure. We evaluate with respect to these aspects a two-stage deuterium-neon shattered pellet injection in an ITER-like plasma, u…
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UKAEA-CCFE-PR(22)352022
Understanding generation and mitigation of runaway electrons in disruptions is important for the safe operation of future tokamaks. In this paper we investigate runaway dynamics in reactor-scale spherical tokamaks. We study both the severity of runaway generation during unmitigated disruptions, as well as the effect that typical mitigation schem…
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UKAEA-CCFE-PR(20)1382020
The electron runaway phenomenon in plasmas depends sensitively on the momentum space dynamics. However, efficient simulation of the global evolution of systems involving runaway electrons typically requires a reduced fluid description. This is needed for example in the design of essential runaway mitigation methods for tokamaks. In this paper, we p…
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