An electron-positron beam-plasma instability

Using a new technique to generate cold electron beams, an electron-beam pos itron-plasma experiment was performed in a previously unexplored range of e nergies. An electron beam, formed from a thermalized room-temperature elect ron plasma, is transmitted through a positron plasma stored in a quadrupole Penning trap geometry. The transit-time instability, which is excited by t he beam, was previously studied using a hot-cathode electron gun. The large beam energies produced by the cathode did not permit an investigation of t he instability in the interesting range of energies near its onset. Using a new 0.1 eV energy width electron beam, we have reinvestigated the system. The experimental data are compared with the results of a theoretical model, also described in this paper. The theory employs a linearized cold fluid a nd Vlasov approach to model the plasma and beam dynamics, respectively. The data and predictions are in good agreement over the broad range of energie s and beam currents studied. (C) 2001 American Institute of Physics.