Abstract: A traveling wave tube having a helix continuously supported within a dielectric barrel provides efficient operation at high power levels. The wire forming the helix has a greater width along its inner surface adjacent the interaction space of the traveling wave tube than along its outer surface which is continuously secured to the dielectric barrel. The wire confines the electromagnetic field to an area adjacent the interaction space for low dielectric loading thereby assuring a good coupling impedance into and out of the traveling wave tube and a wide bandwidth. Improved thermal conductivity for heat from the helix is provided as a result of the helix being continuously supported and in contact with the dielectric barrel. The tube is low in cost, which makes it attractive for expendable use.