Traveling wave tube devices

A traveling wave tube device comprising a traveling wave tube including a source of an electron beam, an electron beam collector, a helical delay line disposed between said source of electron beam and said electron beam collector, a pumped envelope surrounding the elements described above, means disposed between said pumped envelope and said helical delay line for supporting the same, a carbonaceous coating applied on said pumped envelope and an electroconductive coating applied on said carbonaceous coating for preventing peeling off thereof;

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• a periodic permanent magnet assembly which includes means for a microwave power input and output to and from said traveling wave tube, a plurality of annular permanent magnets and a plurality of pole pieces, said permanent magnets and pole pieces being alternately disposed between the microwave power input and output means, each of said pole pieces having an inner diameter that is smaller than that of the permanent magnets and larger than that of said pumped envelope, adjacent pole pieces and one of the permanent magnets interposed therebetween defining an annular recess, and a plurality troidal metal spring rings contained in each annular recess and in contact with said electroconductive coating and said permanent magnets.