Electron beam relaxation in inhomogeneous plasmas

International audienceIn this work, we studied the effects of backgroundplasma density fluctuations on the relaxation of electronbeams. For the study, we assumed that the level of fluctuationswas so high that the majority of Langmuir waves generatedas a result of beam-plasma instability were trappedinside density depletions. The system can be considered as agood model for describing beam-plasma interactions in thesolar wind. Here we show that due to the effect of wave trapping,beam relaxation slows significantly. As a result, thelength of relaxation for the electron beam in such an inhomogeneousplasma is much longer than in a homogeneousplasma. Additionally, for sufficiently narrow beams, processof relaxation is accompanied by transformation of significantpart of the beam kinetic energy to energy of acceleratedparticles. They form the tail of the distribution and cancarry up to 50% of the initial beam energy flux