Advances in cold cathode physics and technology

We review recent progress in the physics and technology of cold cathode ele ctron emitters. The characteristics of emission from field emitter a,lays, photocathodes, and ferroelectrics are presented, together with a summary of the understanding of the physics involved. The paper concludes with a desc ription of L-band micropulse gun, based on secondary emission in an RF cavi ty. Emphasis is placed on cathode development for electron guns to drive mi crowave robes and RF accelerators.