Diagnostics of magnetic antenna fields for low frequency whistlers in r-t and /spl omega/-k space

Summary form only given. In a large uniform laboratory plasma the magnetic field B/sub (r,t)/ of a shielded magnetic loop antenna (5 cm diam.) has been measured in both near and far zones. The antenna is driven with a single short current pulse which excites a whistler wave packet. With a movable magnetic probe and repeated pulses the vector field B/sub x/, B/sub z/ vs. x, y, z is mapped at 10,000 spatial positions with high time resolution. In the space-time domain the evolution of a dispersive wave packet from the antenna near-zone fields is observed. The wave packet consists of nested cones propagating with wave normals highly oblique to B/sub o/ but energy flow at a small angle to B/sub o/. In order to analyze the wave packet in terms of eigenmodes, the field B/sub (r,t)/ has been Fourier-transformed in time and 3-D space, B/sub (/spl omega/,k)/. At a selected frequency, the finite-size antenna launches a spectrum of k-vectors which, for an antenna dipole moment along B/sub o/, is highly axisymmetric. In the k/sub /spl perp - k/sub 1/ plane the wave energy is spread out along the refractive index curve of whistlers with the largest wave energy oblique to B/sub o/.