Mitigation of cavitation effects by means of gas bubbles on a surface

Cavitation turned out to be a severe problem for the pulsed spallation neutron sources which are currently under construction in the US and in Japan. Target windows are eroded quickly and are still far from meeting their preferred lifetime requirements. A simple idea is proposed how to protect the window surface: with a sufficient number of tiny bubbles of some non-condensable gas sitting at the surface. The suggested procedure aims at protecting almost any surface prone to cavitation attack by ensuring a sufficient density of gas bubbles of suitable composition and size residing right at the surface to be protected and its close vicinity. The amount of gas can be controlled accurately to yield an advantageous volume fraction of gas in the liquid in the relevant volume. In order to concentrate gas at an exposed surface it is proposed to structure it in a suitable way to agglomerate, trap and retain gas bubbles there. A fraction of the bubbles is allowed to escape to the volume of the liquid exerting well established beneficial effects there. Lost gas can best be replenished through feeding ducts inside the wall structure. In the following a short outline of proposed implementations and expected effects is given.