Linear theory of a dielectric Cherenkov maser amplifier with a near-surface plasma layer

Summary form only given, as follows. The first results of experimental tests of the wide-bandwidth dielectric Cherenkov maser amplifier (DCMA) have been recently reported that revealed plasma presence in its interaction space. A near-surface plasma layer enriches the spectrum of the DCMA slow-wave structure modes which are capable of interacting with an electron beam. Previously, the features of the usual and hybrid waveguide and plasma modes in this system were discussed. The linear theory of the DCMA with a plasma layer has been developed. The dispersion relation has been derived for the model of infinitely thin, fully magnetized, monoenergetic electron beam propagating within a vacuum channel inside a hollow plasma layer adjoining a surface of hollow dielectric lining a circular waveguide. The case of axially symmetric TM modes was considered. The plasma was assumed to be uniform, collisionless, fully magnetized and cold, ion motion was neglected. In the case of dielectric constant equal to unity this configuration turns into the well-known plasma Cherenkov maser configuration; in the case of plasma absence it turns into the conventional DCMA configuration. The results of the numerical solution of the dispersion relation derived are presented for different parameters of the beam, plasma layer, and dielectric waveguide. Special attention is paid to the investigation of the beam coupling to hybrid modes: both hybrid waveguide and hybrid plasma modes. The possibility of achieving a superwide amplifier gain-bandwidth by means of the coupling between the hybrid plasma and waveguide modes through the electron beam is examined. The particular configuration of recent wide-bandwidth DCMA experiments is discussed as well.