Making Observations Of Liquid Metal Wall Oscillations

Nuclear fusion is quite a way off becoming viable although progress is being made with larger and larger fusion reactors being created all the time. So far the largest reactor that is being built at the moment, ITER,  will have an exhaust power of about 150 megaWatt. When a proper fusion power plant is created it would have an exhaust power of about 800 megaWatt. A divertor is a component of a fusion reactor which uses a magnetic field to define a plasma boundary. The divertor can be controlled to manage and shape the plasma into a D-shape plasma (a more elongated ovular form). In this state, the heavy ions, which are the main component of the “exhaust” of the fusion, are flung out and separated with greater ease. Unfortunately the current limit of divertors are 10 megaWatt per metre squared and it doesn’t seem this limit is set to increase. Radiative cooling has to be employed in future reactors if they can’t provide the exhaust space for the current divertor ability.

Even if they can, a divertor can’t be forced to work at maximum efficiency of it’s expulsion target or the reactor’s armour will have to be replaced far too often for the process to be viable. The hope is to use a liquid material for the plasma facing components (those parts of the reactor exposed to the plasma) which has the advantage of not degrading as material displaced by plasma impacting at not a perfect normal will be reversed. The other main advantage is that if that all liquids are surrounded by their vapour. This vapour can act as a shield from damage. If the exhaust heat increases, the vaporisation will increase and an automatic increase in shielding will occur.

This study showed that a vapour cloud formed off tin (Sn). The distance this cloud extended from the tins surface oscillated over time correlating with the temperature. An oscillating thickness of vapour shield means that an equilibrium has to arise between plasma and the liquid surface. The results showed that liquid metal divertor targets, probably made of tin and lithium, could certainly be feasible despite the slightly more complicated dynamics.

Paper link: Oscillatory vapour shielding of liquid metal walls in nuclear fusion devices

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