Electrostatic waves near the lower hybrid frequency

The propagation of slow electrostatic waves across a magnetic field ${\overrightarrow{\mathrm{B}}}_0$ ($\frac{k_{\parallel }^2}{k_{\perp }^2}\lesssim \frac{m_e}{m_i}$) near the lower hybrid frequency ($\omega \gtrsim {\omega }_{\mathrm{LH}}$) has been investigated experimentally in a large uniform magnetoplasma. The dispersion is in good agreement with the fluid description; warm-plasma effects appear near $k_{\perp }{r}_{\mathrm{ci}}\simeq 2\pi$. Propagation of wave packets reveals the dispersive and backward wave nature of the modes ($v_g>0\mathrm{}$, $v_{\mathrm{ph}}<0\mathrm{}$, $v_g\ll \left|v_{\mathrm{ph}}\right|$), the different directions of phase and group velocity ($\frac{\omega }{\overrightarrow{\mathrm{k}}}\sim \perp \frac{\partial \omega }{\partial \overrightarrow{\mathrm{k}}}\sim \parallel {\overrightarrow{\mathrm{B}}}_0$) and the cone structure of the antenna radiation pattern.