Partial experimental checking of theoretical predictions on time dependent electrical conductivity of the secondary plasma created in atmosphere by a high power electron beam

The key role played by secondary plasma electrical conductivity in stability of a high power electron beam propagating in gaseous atmosphere,is well-known. For a long time, in theoretical models, this parameter has been considered as a given space and time constant or, at best, as a time constant possessing a radial dependence: σ(r). Recent calculations have shown the very important stabilizing effect of the rapid time variation of σ, as the secondary plasma is progressively created, cooled or heated. The theoretical and numerical model PEGASE gives access to σ(r,z,t). It is a 2D, axisymmetric, multifluid (e, N⁺2, N⁺, N, N*,‥) model based on macroscopic equations of continuity -including a detailed air chemistry-, motion and energy, closed by the full set of Maxwell equations. A partial experimental check has been performed at the C.E.A.-D.A.M. Valduc Research Center, on the EUPHROSYNE facility, with a 1.7 MeV, 40 kA, 2.5 cm diameter, 75 ns electron beam, propagating in nitrogen at a variable pressure. The measured net current has been compared to predictions of a circuit model including the time dependent electrical resistance of the secondary plasma column. The agreement is highly satisfactory.