Relaxation of a highly concentrated electron beam in a plasma

The electron energy distribution is determined to be anisotropic in a low-temperature plasma, when it is far from equilibrium. This leads to a kinetic instability of the highly concentrated beam in rarefied and dense plasmas over a wide range of the Knudsen parameter. The experimental criterion of threshold is true over a wide range of the Knudsen parameter. The beam isotropisation in plasma oscillations is shown to be realised simultaneously with the energy relaxation.