2-DIMENSIONAL CHERENKOV EMISSION ARRAY FOR STUDIES OF RELATIVISTIC ELECTRON DYNAMICS IN A LASER-PLASMA

In laser-produced plasmas there are several effects which will scatter a longitudinally probing relativistic electron beam. In vacuum, the l aser itself will ponderomotively defocus the electron beam, while in p lasma the ponderomotive force can dig an ion channel which would focus the electron beam. In the cases of plasma wave excitation via the bea t-wave or wake-field mechanisms, the thermalization of the electron di stribution function can lead to large scale magnetic fields via the We ibel instability. One way of studying such phenomena is to time resolv e the transverse current distribution of the electron beam after it ex its the plasma. A wire mesh has insufficient time resolution for this purpose, so we instead use a mesh of optical fibers. When the electron beam strikes the fiber mesh, Cherenkov radiation is generated within whichever fibers have current running across them. The Cherenkov radia tion from all the fibers can then be analyzed on a streak camera. This allows the reconstruction of j(x,y,t) where j is the current density. We have successfully implemented this technique in the study of beat- excited laser plasmas. (C) 1997 American Institute of Physics.