Intense electron beam radius-tailoring experiment for propagation studies

We have generated a "radius-tailored" electron beam, a beam that is tapered with a larger head and a smaller tail, using a Fast rise-time magnetic Focusing Coil (FFC) around a vacuum drift tube placed downstream of the electron beam diode. The electron beam is injected during the rise time of the FFC magnetic field so that the beam head expands, while the beam body and tail are confined by the axial magnetic field of the FFC. The electron beam for this experiment is 1.7 MeV, 1 kA, and 13 ns flattop. Time-resolved beam radius measurements, from a scintillator viewed by a streak camera, indicate the beam radius as a function of time. Intense relativistic electron beams propagating through a gas exhibit the resistive hose instability. The growth rate of the hose instability can be reduced by "tailoring" the beam radius from a large head to a small tail. The next step of the experiment would be to study the propagation characteristics of the radius-tailored beam in neutral gas. This beam could be injected into a gas-filled drift tube to compare the propagation characteristics to those of an untailored beam. Diagnostics could include B probes to measure the beam centroid and an open-shutter camera.