Whistler wave propagation and interplay between electron inertia and Larmor radius effects

The influence of finite Larmor radius effects in the propagation of whistler waves is investigated experimentally in the laboratory plasma. The waves are excited using a loop antenna of diameter less than electron skin depth, the natural scale length in this regime. In an earlier experiment, it was shown that such waves assume an elongated shape with perpendicular dimensions of the order of skin depth. In the present work, we show that the wave propagation is significantly modified when external guiding magnetic field is decreased. The wave spread in the perpendicular direction in spite of starting of as an elongated whistler due to electron inertia effects. In the near region, antenna field becomes dominant even forming null points, however physical processes take shape and wave is still guided. However, the feeble magnetic field in the region away from the antenna is unable to guide the wave any further and wave packet spreads. In spite of large current pulse, the wave remains linear probably because the physical processes are confined within a short distance of skin depth where antenna field dominates. The observed results are attributed to the interplay between electron inertia and finite Larmor radius effects and are explained in terms of a modified physical model.