Proof-of-principle measurements using the 300 GHz collective scattering diagnostic

Experiments designed to provide a proof-of-principle measurement with the WVU 300 GHz collective scattering diagnostic continue. The collective scattering system, capable of measuring wave-numbers ranging from 62 to 89 cm$^{-1}$, is operated in conjunction with a new electrostatic double probe (with a measureable wave-number range up to $\sim $50 cm$^{-1})$. To directly excite finite $k_{\bot }$ electrostatic waves propagating perpendicular to the magnetic field that can be detected with this diagnostic, an internal antenna designed to launch electrostatic ion-cyclotron waves has been built and installed in HELIX. For the magnetic field strength of HELIX, the wave dispersion of such waves is essentially that of an ion-acoustic wave. Wave number measurements for naturally occurring and externally driven waves, using both the scattering system and electrostatic double probe, are presented.