Experimental Observation of Drift Instabilities in a Collisionless Plasma

Pressure-gradient---driven drift waves have been identified in a collisionless (${n}_{0}={10}^{10}$ ${\mathrm{cm}}^{\ensuremath{-}3}$, ${T}_{e}=10$ eV), 5.4-m-long, hydrogen plasma. Measurements show large but finite parallel wavelengths and short transverse wavelengths as predicted by the theory. For these wavelengths, computations give the maximum linear theoretical growth rate.