Application of a compound containing boron to the inner surface of a vacuum vessel to help reduce impurity radiation. In other words: before normal plasma operation starts an amorphous layer of Boron and Hydrogen is deposited within a glow discharge in diborane where the entire wall acts as the cathode towards which the ions are accelerated. These layers also have the beneficial property to getter oxygen – an impurity, present in all vacuum devices, which may lead to uncontrolled radiation.