PURPOSE: To prevent charge storage by providing a support structure for supporting a slow wave structure with a dielectric material disposed on at least one structure support member including a support rod and an outer periphery of the support rod and different from the material of the support rod. CONSTITUTION: A slow wave delay line structure 12 consists of plural wiring parts of a conductive wire and supported in the vicinity of electron beams in an envelope body 14 by a support structure 3. There is a plural lengthwise non-conductive structure support member 34 disposed longitudinally parallel to a shaft 13 of a device. The structure support member 34 includes an inside support rod 34 of electric insulation and high thermal conductivity material. Thermal conductivity of a support rod 36 is increased to cool spiral wiring. The support rod 36 is boron nitride. The support rod 36 is covered with a film of a dielectric material on its outer face. On the outer face of the support rod 34, coating is applied with a film 39 of less than 1 micron that is thin in an electric material such as titania, magnesia, or berrylia. Thereby, rod charge is eliminated.
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