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 frequency and k-spectra of the Langmuir waves are measured both in the excited and damped regions. The waves interact directly with the beam electrons inside a narrow section of k-sppace amid the region occupied by the non-resonant waves, which concentrate near k ∼ ω_pe/c. Both resonant and non-resonant waves hold equal (to within an order of magnitude) amounts of energy. Incoherent scattering of the second harmonic of 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: (ne ∼ 10¹⁵ cm⁻³, n_b/n_e ∼ 10⁻⁴, B = 1–4 T, t_b = 100–200 ns). The peculiarity of these experiments is the presence of a strong magnetic field (ω_Bec/ω_pe V_Te ⪢ 1, but cope ⪢ ω_Be) which, together with plasma non-isothermality (T_e ⪢ T_i), sets conditions typical for laboratory and space plasmas. At present, the processes under these conditions have not been adequately investigated, either experimentally or theoretically, especially for our case of developed Langmuir turbulence, when the spatial and temporal scales far exceed those for a single caviton. This work is centred on the study of developed Langmuir turbulence in a magnetized plasma.