INVESTIGATION OF LANGMUIR TURBULENCE EXCITED BY A RELATIVISTIC ELECTRON-BEAM IN A MAGNETIC-FIELD

The Thomson scattering technique has been employed for the observation of turbulent waves excited by a relativistic electron beam. The frequ ency and k-spectra of the Langmuir waves are measured both in the exci ted and damped regions. The waves interact directly with the beam elec trons inside a narrow section of k-space amid the region occupied by t he non-resonant waves, which concentrate near k - omega(pe)/c. Both re sonant and non-resonant waves hold equal (to within an order of magnit ude) amounts of energy. Incoherent scattering of the second harmonic o f a Nd:glass laser is used to measure the time history of the electron distribution function including the super thermal tails. The typical beam and plasma parameters are as follows: (n(e) - 10(15) cm(-3), n(b) /n(e) - 10(-4), B = 1-4 T, t(b) = 100-200 ns). The peculiarity of thes e experiments is the presence of a strong magnetic field (omega(Be)c/o mega(pe)V(Te) much greater than 1, but omega(pe) much greater than ome ga(Be)) which, together with plasma non-isothermality (T-e much greate r than T-i), sets conditions typical for laboratory and space plasmas. At present, the processes under these conditions have not been adequa tely investigated, either experimentally or theoretically, especially for our case of developed Langmuir turbulence, when the spatial and te mporal scales far exceed those for a single caviton. This work is cent red on the study of developed Langmuir turbulence in a magnetized plas ma. (C) 1996 Elsevier Science Ltd.