Study of Intense Relativistic Electron Beam Modulation by Wakefield Effects

Abstract

Abstract : An experimental study has been undertaken in order to investigate plasma wakefield effects produced in intense electron beam propagation in a background plasma. A 2 MeV, 1 kA, electron beam is used for this experiment. A 50 cm diam., 3.6 m long drift tube is filled with a background gas, typically trimethylamine (TMA). This gas is ionized by electrons emitted from heated tungsten filaments which are biased at approximately -100 Volts. The resultant plasma density is fairly uniform and is adjustable in the range 10 to the 8th power to 5 x 10 to the 9th power per cubic cm. A higher density Ion Focused Regime (IFR) channel for electron beam propagation is generated by KrF-laser (248 nm) ionization of the background TMA gas. The intense electron beam propagating on an IFR channel in this background plasma experiences wakefield effects due to the natural oscillations of the background plasma which are excited by the beam current risetime. The Ez component of the induced field is responsible for producing beam current modulation near the background plasma frequency. The results scale with plasma density as expected and current modulation is nearly complete for a certain parameter range. This technique may be amenable to a high power microwave generation technique analogous to the relativistic klystron. Detailed experimental results of beam modulation will be presented.