Surface and bulk MHD instabilities due to insulator coating imperfections

Experiments were performed using copper electrodes inserted into the wall of a perfectly insulated duct to simulate insulator coating flaking or cracking. The results show that surface electric potential U and MHD pressure drop Δ P exhibit a non-monotonic behavior with increasing V 0 , while the magnetic field B 0 is held constant. Additional experiments were also performed keeping all external experimental conditions fixed while measuring the change of U , V 0 , B 0 , and Δ P with increasing time. It was found that while all external experimental conditions were kept constant, the system changed by itself and U , V 0 and Δ P exhibited a non-monotonic behavior with increasing time. The results seem contrary to the law of Δ P ∝ V 0 B 0 n , but are consistent with conservation of energy, which implies that the change is due to some inherent feature of the system, or possibly instabilities, which may occur due to insulator coating imperfections.