Demonstrated simple sensor and actuator for feedback control of free-surface liquid metals

Fig. 1: Standstill Lorentz (j x B) force demonstration of actuator controlling liquid metal thickness between two electrodes.


Whether static or rapidly flowing, liquid metal coatings of fusion reactor walls will tend to bulge or deplete under the effect of various instabilities, and touch the plasma or expose the solid substrate as a result... unless something is done.

For this reason, a research program has started at Columbia to feedback-stabilize liquid metal flows. As an important step in this framework, Taha recently developed and tested a single local "sensor" of liquid metal thickness, and a simple local "actuator" capable of increasing or reducing the local thickness of the liquid metal at will.

The sensor is based on a simple measurement of the electrical conductance of the liquid metal. As expected, the conductance grows linearly with the metal thickness (Fig. 2), hence the conductance, apart from a factor, can be used as a proxy for thickness.

The actuator simply works by the Lorentz (j x B) force (Fig. 1). The liquid metal is already immersed in a magnetic field B, in a future reactor as well as in our lab test. By applying an electrical current of adequate direction and intensity, it is possible to "push" the liquid metal against the substrate and "pull" away from it, thus affecting its thickness between the electrodes.

The next step will be to "close the loop," and operate the actuator in feedback with the sensor measurements. Further to that, we will interface multiple sensors to multiple actuators.

Fig. 2: Experimental and analytical conductance versus liquid metal depth.
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