Whistlers in thermally generated ducts with enhanced plasma density: Excitation and propagation

A study is made of the excitation and guided propagation of whistler waves along magnetic-field-aligned cylindrical ducts with enhanced plasma density. The ducts have been created in the large plasma device as a result of the thermal-diffusion-driven redistribution of plasma due to electron heating in the quasistatic held of a current loop having a radius commensurate with the electron heat-conduction length in the radial direction. The whistler waves are excited by a comparatively small magnetic loop antenna immersed in the duct. Detailed measurements of the excited field and the density distribution are reported. It is concluded that thermally generated ducts observed in the experiments can guide whistler-mode waves launched from the magnetic antenna. With the use of the full wave formulation, the total source-excited field is calculated and compared with the experimental data. Excellent agreement is found between the measured and calculated wave patterns. The results are relevant to both the basic properties of whistlers and to applications such as transmitting systems using artificial near-antenna ducts in space plasmas.