Plasma Hollow Cathodes

Hollow cathode plasma discharges are a fundamental part of large variety of applications in industry, academia and space. From surface processing and coatings deposition to plasma-surface interactions research and electric propulsion, advances in hollow cathode modeling and performance are critically important to the progress and evolution of these and other technology areas. This paper describes perspectives on the progress has been made in recent years in the modeling and performance of hollow cathodes used in plasma discharges. While many of the developments have been driven by the demanding requirements of electric propulsion applications, the information provided applies to all thermionic hollow cathodes and their applications. In the paper we describe the status of 2-D global simulations of the hollow cathode plasmas, hollow cathode plume instabilities, the development of higher current cathodes and low current heaterless cathode technologies. Advances in the understanding and technology in these areas and some of the challenges that still need to be addressed and solved are discussed.This paper is an invited Perspective article.