Radiation potential of a point antenna immersed in drifting cold or hot (hydrodynamical) plasma

Abstract

Drift effects on forced oscillations generated by an oscillating antenna are analysed in two cases: 1.(i) For the first we consider a Water Bag model with temperature T ≥ 0 (with a special treatment for T=0). A non usual normalisation of the distances based on a parameter p equal to the thermal velocity divided by the drift one allows us to treat cold plasma in the W.B. formalism. A mixed analytical and numerical method is used. The numerical part is shown to be quite necessary to obtain results outside the perpendicular and parallel directions to the drift. Radiation diagrams at different distances from the antenna give the behaviour of the potential. The existence of a radiation cone of Cherenkov toe is pointed: outside a cone centered on the drift direction with angle α given by α = Arcsin √3ϱ, the potential is strictly independent of the temperature. On the other hand, the bulk of thermal effects are concentrated in an inner cone of smaller angle given by Bohm and Gross relation. Between these two cones, precursors effects appear.2.(ii) In the second case for which the normalisation of the distances is made classically in term of Debye length, we take a Maxwellian plasma represented by Multi Water Bag (M.W.B.) model with 60 bags. The integration is performed by the same analytico-numerical method. We discuss the topology of the poles, and the problems introduced by the choice of the model are pointed out. The difficulties lessen with increasing drift velocity. Radiation diagrams for low drift velocity (VD = 0.35 VT) and ω = 1.2 ωp are given at various distances from the source.