How does such a system work with very hot matter, e.g. plasma in a fusion chamber? I assume some sort of medium (i.e. not vacuum) is needed to propagate the wa

How does such a system work with very hot matter, e.g. plasma in a fusion chamber? I assume some sort of medium (i.e. not vacuum) is needed to propagate the waves, and that at the temperatures necessary for fusion the medium would turn to plasma and the vibrating plates would melt. But I'd certainly like to be wrong.