Propagation of a cloud of hot electrons in the regime of fast relaxation

The propagation of a cloud of hot electrons and generation of Langmuir waves are investigated using numerical simulation of the quasilinear equations and analytical gas-dynamic theory. The validity of the gas-dynamic theory is investigated and the accuracy of Ryutov and Sagdeev’s gas-dynamic equations is explored. It is found that inclusion of spontaneous emission terms in the gas-dynamic equations is necessary for self-consistency of analytical solutions. Results of numerical simulations show that the electron distribution function relaxes to a plateau state and excites Langmuir waves. Evolution of the upper boundary and the height of the plateau are investigated and it is found at a given time and location there are three different regions in the electron beam distribution which correspond to unrelaxed, partially relaxed, and completely relaxed states. In the completely relaxed region there is a good agreement between the results of numerical simulation and the predictions of gas-dynamic theory. As the ...