Enhancement of ion thermal anisotropy in helicon plasmas

Temperature anisotropies provide a source of free energy for instability growth in space and laboratory plasmas. The growth of electromagnetic ion temperature anisotropy driven instabilities is dependent on the anisotropy parameter T_⟘/T_|| and the local plasma β. These instabilities reduce the ion temperature anisotropy by inducing velocity-space diffusion, resulting in a limit on the ion temperature anisotropy that scales with plasma β. Here we report measurements of the ion temperature anisotropy in a helicon plasma source where the RF antenna responsible for plasma creation is amplitude modulated at the ion cyclotron frequency. The ion temperatures parallel and perpendicular to the magnetic field are measured with laser induced fluorescence in an argon plasma and the ion thermal anisotropy is characterized as a function of modulation frequency, modulation amplitude, and helicon source plasma parameters.