Diffusion and Scattering of Test Particles in a Turbulent Plasma

A small-diameter, low-energy, test electron beam is injected along ${\overrightarrow{\mathrm{B}}}_0$ into a collisionless plasma in which current-driven ion sound turbulence can be generated. The scattering of the test particles across ${\overrightarrow{\mathrm{B}}}_0$ due to fluctuating fields ${\overrightarrow{\mathrm{E}}}_w\perp {\overrightarrow{\mathrm{B}}}_0$ gives a direct measure for the turbulent spatial diffusion coefficient $D_{e\perp }$. Investigation of the velocity-space diffusion shows strong pitch-angle scattering effects. No significant anomalous resistivity is observed.