a1 Institute of General Physics of the USSR Academy of Sciences, Moscow, USSR
a2 Faculty of Physics, Sofia University, II26 Sofia, Bulgaria
A nonlinear relaxation is observed when an electron beam interacts with plasma in an external magnetic field. An acceleration of electrons to energies which are more than twice that of the initial beam energy is observed. The acceleration mechanism is connected with the modulation instability of the plasma waves which is excited when the beam relaxes.
(Received June 22 1987)