The general kinetic theory of slow-wave electron cyclotron maser (ECM)
interaction is presented. Using the Vlasov-Maxwell equations the pert
urbation inflicted on the electron distribution function by the action
of slow hybrid waves is obtained. A general expression for the power
transfer between an electron beam of any equilibrium distribution func
tion and the hybrid fields is derived, which can reveal all the intera
ctions that potentially can occur in the system. The effect of the ele
ctron guiding-centre drift and the development of a dipole beam curren
t is also considered. To illustrate the physics of the interaction, th
e theory is applied to the case of a filamentary cold electron beam wi
th exclusively axial initial electron momentum placed on the axis of t
he system, and expressions for the starting beam current and the frequ
ency pulling due to the beam presence are derived for the case of the
slow-wave ECM mechanism. Numerical examples are presented showing that
an electron beam with an accelerating voltage of the order of 200 kV
to 500 kV can excite oscillations in the cavity in HE(11) mode with st
arting currents of 10A to 50 A.