Electron cyclotron emission and absorption for a two-dimensional momentum distribution

Analytic expressions for the electron cyclotron emissivity of a two-dimensional (2-D) momentum distribution, i.e. for a δ(μ) distribution in the cosine of the pitch angle μ, are obtained for both low and high frequencies. For the high-frequency range for which the Carlini approximation to the Bessel function is used, the 2-D emissivity of the perpendicular extraordinary mode is a factor (2/√π)(ω/ωc)1/2 (>1) larger than the corresponding emissivity averaged with respect to an isotropic pitch angle distribution, such a result being consistent with a Gaussian shape in μ of width (ωc/ω)1/2. The emission coefficient, i.e. the emissivity integrated over the energy distribution, and the absorption coefficient are evaluated for the case of a 2-D relativistic Maxwellian. In particular, for frequencies such that χ≡(9/2)(ω/ωc)(T/mc2)>>1, the 2-D absorption coefficient is a factor χ1/6 larger than the corresponding 3-D result. (author) 4 refs