Development of powerful RF plasma sources for present and future NBI systems

This paper deals with the topic of RF plasma sources and their application in high-power neutral beam heating systems for nuclear fusion devices. RF sources represent an interesting alternative to the conventional arc discharge sources. Due to the absence of hot filaments they exhibit an inherent simplicity both in mechanical and electrical aspects and consequently offer advantages in terms of cost savings, gain in availability and reliability and reduced maintenance. This renders the RF plasma source attractive for any long pulse (> 10 sec) NBI system and in particular for the ITER NBI system. The latter, however, requires that the RF plasma source is also capable of delivering negative rather than positive hydrogen ions. In the first part of the paper the types, characteristics and operation experience of RF plasma sources for positive ions in operation are described. The second part is devoted to the development for ITER NBI: the basic requirements, physics and technology issues and the present status are discussed.