Measurement and Instability Analysis of Three-Dimensional Anisotropic Electron Distribution Functions

A velocity analyzer with high angular resolution ($\frac{d\Omega }{4\pi }={10}^{-4\mathrm{}}$) has been used to measure the electron distribution function $f(v, \theta , \phi )$ in a neutral sheet of a large laboratory plasma. Contours of $f\left(\mathrm{v}\right)=\mathrm{const}$ form surfaces in velocity space. As $f\left(\mathrm{v}\right)$ decreases, anisotropic tails form detached surfaces which send filaments out toward the main body. The highly anisotropic structures occur at the Doppler-shifted phase velocity of observed whistler-wave turbulence. Instability analysis of $f\left(\mathrm{v}\right)$ is consistent with the observed whistler- and Langmuir-wave turbulence.