Finite ion gyroradius effects in exciting low frequency electrostatic waves in a {\it Q}-machine

Low-frequency ($\sim 3~f_{ci}$) electrostatic waves appear in a magnetized, cylindrical barium plasma in a double-ended {\it Q}-machine. Coaxial plasmas with different potential were formed, yielding a strong (up to $25~V/cm$), narrow ($HWHM \sim \rho_{i}/2$) radial electric field at the cylindrical interface. We evaluate the plausibility of three free energy sources. (1) Cross-field electron current (2) ${E \times B}$-drift shear, and (3) ion-temperature anisotropy. We characterize the dependence of the wave frequency and wave-vector on the magnetic field strength and neutral pressure. We eliminate drift, cyclotron, and ion-acoustic mechanisms and are left with shear-modified ion acoustic, velocity space, and Farley-Buneman instability mechanisms.