Patent ID: 9455112
Filing Date: 2016-09-27
CPC Classification: G03F,H01J

Claim Text:
1. A cathode arrangement comprising: a thermionic cathode comprising an emission portion provided with an emission surface for emitting electrons, and a reservoir for holding a material, wherein the material, when heated, releases work function lowering particles that diffuse towards the emission portion and emanate at the emission surface at a first evaporation rate; a focusing electrode comprising a focusing surface for focusing the electrons emitted from the emission surface of the cathode; and an adjustable heat source configured for keeping the focusing surface at a temperature at which accumulation of work function lowering particles on the focusing surface is prevented wherein the thermionic cathode further comprises a cathode body housing the emission portion and the reservoir, the adjustable heat source is configured for heating the cathode body, the focusing electrode further comprises a heat trapping surface facing at least a portion of the cathode body and arranged for receiving heat radiation emitted by the cathode body during use, wherein the heat trapping surface is in thermal communication with the focusing surface, wherein the contact between the cathode body and the focusing electrode is limited by radial spacers defining a radial interspacing between the heat trapping surface and an outer surface of the cathode body, and/or by spacing structures provided between a non-emission surface surrounding the emission surface and an inner electrode surface of the focusing electrode facing the emission portion, for providing a spacing between the focusing electrode and the emission portion.