A laboratory quiescent plasma device for modeling velocity shear in space

Summary form only given. A continuing topic of interest among the space physics community is the acceleration of low-altitude ionospheric ions and the underlying mechanisms. One such mechanism, which has gained much attention in the past few years, is ion acceleration due to turbulence generated by a velocity-shear layer transverse to the local magnetic field, in particular, in situations where magnetic-field-aligned currents may be too small to destabilize current-driven electrostatic ion-cyclotron modes. These situations are modeled in a plasma produced by the WVU Q-machine. The plasma is a collisionless, low-temperature (T/sub i//spl ap/T/sub e/=0.2 eV), low-neutral-density alkali metal, typically sodium or barium, confined by a uniform magnetic field (B=0.5-3.0 kG). The shear layer is created by a segmented-disk electrode placed at the end of the plasma column opposite to the source; the voltage drop across any two groups of segments creates a radially localized electric field, and thus an inhomogeneous azimuthal E/spl times/B plasma drift. A variety of space-relevant parameters can be adjusted, such as the ratio of gyroradius to inhomogeneity scale length (/spl rho//sub i//L), ion-electron temperature ratio (T/sub i//T/sub e/), ratio of ions to neutrals (to model different altitudes), and ratio of ion densities in the case of multi-ion-species plasma studies.