Survival and in-vessel redistribution of beryllium droplets after ITER disruptions

Abstract

The motion and temperature evolution of beryllium droplets produced by first wall surface melting after ITER major disruptions and vertical displacement events mitigated during the current quench are simulated by the MIGRAINe dust dynamics code. These simulations employ an updated physical model which addresses droplet-plasma interaction in ITER-relevant regimes characterized by magnetized electron collection and thin-sheath ion collection, as well as electron emission processes induced by electron and high-Z ion impacts. The disruption scenarios have been implemented from DINA simulations of the time-evolving plasma parameters, while the droplet injection points are set to the first-wall locations expected to receive the highest thermal quench heat flux according to field line tracing studies. The droplet size, speed and ejection angle are varied within the range of currently available experimental and theoretical constraints, and the final quantities of interest are obtained by weighting single-trajectory output with different size and speed distributions. Detailed estimates of droplet solidification into dust grains and their subsequent deposition in the vessel are obtained. For representative distributions of the droplet injection parameters, the results indicate that at most a few percents of the beryllium mass initially injected is converted into solid dust, while the remaining mass either vaporizes or forms liquid splashes on the wall. Simulated in-vessel spatial distributions are also provided for the surviving dust, with the aim of providing guidance for planned dust diagnostic, retrieval and clean-up systems on ITER.

Simulations of liquid metal flows over plasma-facing component edges and application to beryllium melt events in JET

“…The spreading dynamics of hot droplets impinging on cold surfaces in fusionrelevant conditions will also be explored separately using dedicated calculations. This will not only facilitate the link between numerical results and post-mortem observations of splashing traces, but also open the way for more accurate descriptions of mechanical impacts in dust and droplet transport codes [31].…”

On the Klimontovich description of complex (dusty) plasmas

“…It is worth pointing out that electron-induced electron emission (secondary electron emission, electron backscattering, electron reflection) and ion-induced electron emission (potential and kinetic) can be adequately described with the aid of particle incident energy and incident angle dependent yields together with electron exit energy and angular distributions. [51][52][53][54] In addition, photoelectric emission, thermionic emission, and field electron emission can also be adequately described with the aid of emitted electron flux formulas together with electron exit energy and angular distributions. [55][56][57] Thus, in principle, electron emission processes could be incorporated in the Klimontovich description without dropping the mesoscopic variables and without sacrificing the classical description.…”

Analytical expressions for thermophysical properties of solid and liquid beryllium relevant for fusion applications

“…The summary table is self-containing, in the sense that the interested code developer can directly copy the empirical expressions of one's interest without being pre-occupied with details (only the primary reference has been provided). It is worth mentioning that the macroscopic melt layer motion code MEMOS-U [16,17,18] and the dust transport code MIGRAINe [24,25,125] have already been updated following the present recommendations.…”