Study of high frequency field effect electron emission

A cavity was developed in order to investigate field emission in a radio frequency (RF) regime. Field emitted current from a removable sample is directly collected by a probe. A correlation was made between RF field emission and surface defects such as scratches and dust particles. Consequently, experiments on intentionally dust contaminated niobium samples were performed. Microscopic surface analysis revealed: 1/ important thermal effects, 2/ geometrical changes of the emitting sites (iron particles stand up and pile up) that led to revisit the protrusion model, 3/ RF field emission from alumina. On the other hand, measurements of the contact thermal resistance between particles and the substrate seem to point out ion bombardment (micro-plasma) as a possible cause of the global particle melting observed. An efficient surface treatment is highly required if one wishes to raise up threshold field at which field emission starts. RF pulse processing is a promising one, as it provides a damage free surface under certain conditions. Finally, first comparisons on continuous and RF field emission seem to show that the basic mechanism is unchanged for the two field emission regimes. (author)