Free surface stability of liquid metal plasma facing components

Abstract

An outstanding concern raised over the implementation of liquid metal plasma facing components in fusion reactors is the potential for ejection of liquid metal into the fusion plasma. The influences of Rayleigh–Taylor-like and Kelvin–Helmholtz-like instabilities were experimentally observed and quantified on the thermoelectric-driven liquid-metal plasma-facing structures (TELS) chamber at the University of Illinois at Urbana–Champaign. To probe the stability boundary, plasma currents and velocities were first characterized with a flush probe array. Subsequent observations of lithium ejection under exposure in the TELS chamber exhibited a departure from previous theory based on linear perturbation analysis. The stability boundary is mapped experimentally over the range of plasma impulses of which TELS is capable to deliver, and a new theory based on a modified set of the shallow water equations is presented which accurately predicts the stability of the lithium surface under plasma exposure.

Laser-impact-induced splashing: an analysis of the splash crown evolution after Nd:YAG ns-pulse laser impact on a liquid tin pool

“…We further note that 'impactor-free' liquid metal splashing such as in the current case is also a critical concern in fusion reactors of the tokamak type. Millisecond transients in the fusion plasma can deliver significant heat loads and pressure [24] to advanced liquid metal heat shields [25,26] which may subsequently splash, potentially disrupting the plasma reactor. Preventive measures can be taken, such as the use of porous structure in which the liquid is constrained by capillary forces.…”

Flow of a thin liquid-metal film in a toroidal magnetic field

“…The flow of a liquid metal in the presence of a strong applied magnetic field is described by magnetohydrodynamics (MHD), which couples Maxwell's equations of electromagnetism with the Navier-Stokes equations of hydrodynamics. MHD modelling is ubiquitous in astrophysics for describing plasma, and has also been used widely to model liquid metals in areas such as metallurgy (Davidson 1999(Davidson , 2001, crystal growth processes (Langlois & Lee 1983), pumps and power systems (Kantrowitz et al 1962;Weier et al 2007), as well as for use within a tokamak, the vessel used to magnetically confine a plasma (Fiflis et al 2016). This latter scenario is the focus of the present study.…”

“…The anticipated difficulties in maintaining a specified stable liquid metal thickness and velocity Morley et al 2002) have led many fusion projects to pursue a capillary-porous system (Golubchikov et al 1996;Evtikhin et al 1997). However, experimental evidence suggests that MHD flow along a solid substrate is still a viable candidate (Fiflis et al 2016).…”

Simulated dynamics of a plasma-sheath-liquid interface*

“…One intriguing development is to coat the plasma-facing walls with liquid lithium which enables self-replenishment of any eroded material [6][7][8]. The production of liquid droplets is observed from both accidentally-melted and intentionally-molten metal surfaces [9,10].Maintaining the stability of the plasma-liquid interface remains a crucial challenge in these new technologies and, accordingly, has received widespread attention: Kelvin-Helmholtz [11], Rayleigh-Taylor [12] and Rayleigh-Plateau [13] instabilities, as well as droplet ejection from liquid splashing [14] or the bursting of surface bubbles [15], have all been identified as potential causes of surface disruption and droplet ejection. However all of these studies have neglected the fundamental role of the plasma sheath at the plasma-liquid interface.…”

“…Maintaining the stability of the plasma-liquid interface remains a crucial challenge in these new technologies and, accordingly, has received widespread attention: Kelvin-Helmholtz [11], Rayleigh-Taylor [12] and Rayleigh-Plateau [13] instabilities, as well as droplet ejection from liquid splashing [14] or the bursting of surface bubbles [15], have all been identified as potential causes of surface disruption and droplet ejection. However all of these studies have neglected the fundamental role of the plasma sheath at the plasma-liquid interface.…”