Radio-frequency wave interchange stability experiments below the ion cyclotron frequency

It has been demonstrated in the Phaedrus-B tandem mirror [Phys. Fluids 31, 714 (1988)] that radio-frequency (rf) waves applied below the ion cyclotron frequency (ω/Ωi ≊0.75) can stabilize a mirror plasma against the interchange instability. Results presented here demonstrate stabilization over a range of frequencies (0.65≤ω/Ωi≤0.8) with the mMHD =−1 instability stabilized and higher-order (‖mMHD‖≥2) low-amplitude modes present. Radial profiles of the rf magnetic fields at a number of axial locations as well as parallel wavenumber measurements indicate mrf =−1 slow shear Alfvén wave excitation over this frequency range. Measurements at frequencies below 0.75Ωi indicate attenuation of rf waves by gas baffles and a gas box.