RESUMEN
Locally excited plasma waves are generated in a Coulomb crystal by "pushing" with radiation pressure on a rotating cloud of laser-cooled 9Be+ ions. The waves form a stationary wake that is directly imaged through the dependence of the ion fluorescence on Doppler shifts, and theoretical calculations in a slab geometry are shown to accurately reproduce these images. The technique demonstrates a new method of exciting and studying waves in cold ion clouds.
RESUMEN
Measurements of the viscosity in quiescent magnetized pure-electron plasmas are up to 10(8) times larger than predicted by classical collisional theory. This strong viscosity is due to long-range " E x B drift collisions" between electrons separated by up to a Debye length. Recent theories of long-range collisions show order-of-magnitude agreement with the measurements, but do not give the observed dependence on the plasma column length. A simple empirical scaling law fits the length and magnetic field dependence surprisingly well.