A Novel Technique for Probing the Transverse Interactions Between an Electron Beam and a Plasma*

In laser-plasma interaction experiments there are a variety of effects which will scatter or deflect a probing electron beam. For example, a longitudinally probing electron beam is defocused by the ponderomotive force of a laser, but in a plasma the laser can set up fields which actually confine the electron beam. In the cases of plasma wave excitation via the beatwave or wakefield mechanisms, the thermalization of the electron distribution function can lead to large scale magnetic fields via the Weibel instability. A novel Cherenkov probe has been built and tested which measures the transverse current distribution of an electron beam with at least 50 ps time resolution. A solenoid lens is used to map angular deflections within the interaction region into x-y space at the location of the Cherenkov probe. This allows the cases mentioned above to be experimentally studied. I