Diamond as a support material for TWT helices

This paper presents a status report on the development of methods for using diamond supports for helix slow-wave structures in TWT's. The motivation for using diamonds in this fashion is the need for higher average output power octave bandwidth coverage in the higher frequency regions. The limit of average output power for octave bandwidth helix TWT's is determined by the thermal conduction from the helix to the outer shell, and has always been directly related to the helix support material. Progress was made by replacing glass with alumina, and alumina with beryllia and boron nitride. Natural diamond is an excellent dielectric and has a thermal conductivity over three times better than copper and ten times better than beryllia. The use of diamond dielectric helix supports, therefore, provides the next logical step to increase the output power of helix TWT's. In recent years, the necessary technology has been developed to metalize and braze diamonds for use in diamond-supported helix structures.