Externally Launched Ion Bernstein Wave in the ACT-1 Toroidal Device

In a hydrogen plasma ($T_e=2.5\mathrm{}$ eV, $T_i=1.5\mathrm{}$ eV), excitation of ion Bernstein waves by an externally placed electrostatic antenna has been investigated for $\omega \simeq 2{\Omega }_i$. Mode transformation of the electron plasma wave at $\omega \simeq {\omega }_{\mathrm{pi}}$ without observable reflection was observed, followed by strong excitation of the ion Bernstein wave. Detailed measurements of $k_{\perp }(\omega ,k_{\parallel })$ and of the wave-packet trajectory show excellent agreement with theory.