Beam focusing and plasma channel formation in the PASOTRON HPM source

Elmira S. Ponti; Dan M. Goebel; Robert L. Poeschel

doi:10.1117/12.255422

28 October 1996 Beam focusing and plasma channel formation in the PASOTRON HPM source

Elmira S. Ponti, Dan M. Goebel, Robert L. Poeschel

Proceedings Volume 2843, Intense Microwave Pulses IV; (1996) https://doi.org/10.1117/12.255422
Event: SPIE's 1996 International Symposium on Optical Science, Engineering, and Instrumentation, 1996, Denver, CO, United States

Abstract

In the PASOTRON high power microwave source, electron beam focusing is achieved using a plasma channel (usually helium or xenon, ionized by beam impact) to neutralize the radial space charge forces within the beam so that the beam's own J X B forces will produce self focusing of the beam according to the Bennett effect. In order to take maximum advantage of this effect, the physics of the formation of the plasma channel and the resulting beam focusing has been studied and a simple computer model of this process is evolving based on the experimental results. A diagnostic tube was fabricated with a removable slow-wave structure to investigate the beam dynamics during the pulse. Two rows of probes extending down the length of the tube at 90 degree(s) to each other are used to monitor the radial profile of the beam as it propagates as a function of time and axial distance, and a biased beam collector measures the total current arriving at the end of the tube. The dynamics of the plasma channel formation and the plasma density over time were then determined from these measurements and compared to the model. A small axial magnetic field (< 250 Gauss) was also applied to assist the focusing mechanism with excellent results. The optimal range of background gas pressures and solenoid magnetic field as a function of beam current and voltage, as well as the dynamics of the beam focusing and plasma channel formation, will be presented.

Citation Download Citation

Elmira S. Ponti, Dan M. Goebel, and Robert L. Poeschel "Beam focusing and plasma channel formation in the PASOTRON HPM source", Proc. SPIE 2843, Intense Microwave Pulses IV, (28 October 1996); https://doi.org/10.1117/12.255422

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