Dispersion Measurements On the Irvine FRC in the Lower Hybrid Frequency Range

Measurements of the group velocity have been made on the Irvine Field Reversed Configuration (IFRC) by first exciting electromagnetic fields in the plasma with a folded-dipole antenna and then detecting the electric and magnetic fields with probes in the plasma. Key parameters for the plasma are $<$n$> \quad \sim $ 2 10$^{14}$ cm$^{-3}$, B$_{max}\sim $ 250 Gauss, lower hybrid frequency (slow wave) $\sim $ 10 MHz, launch frequency $\sim $ 30 MHz. Radial group velocities with values ranging from 5E8 cm/s to greater than 3E9 cm/s have been inferred from measurement of delay times between shots. This implies a radial group velocity index of refraction of up to 60. This agrees somewhat with the cold plasma dispersion relation, which predicts indices of refraction ranging from 30-300. Next steps include measurement of the group and phase velocities in both axial and radial dimensions.