Comment on 'High current oversized electron beam formation for high-power microwave research'

摘要

The research presented in the paper describes a new approach to the generation of high power microwave radiation using a high current low density electron beam. The high current electron beam obtained has been transported along a 2 m long coaxial channel immersed in a uniform guide and undulating magnetic field. A coaxial geometry with a large average diameter was used to increase the volume of the interaction region and hence reduce the surface electric fields below the threshold for field emission and breakdown. The researchers' approach, like the work of Friedman, Davis et al., Friedman et al., Nation and Read, and Nation, studies microwave generation from a beam in an annular enclosure. In the previous works the mechanisms limiting the transport of high current electron beams inside such a coaxial interaction space were demonstrated. However, the very high current density of the electron beams used to drive these high power microwave sources meant that the delivery of the power, efficiency, and the pulse length was challenging. These very high current density devices were susceptible to beam instabilities and coherence issues and are well documented in experiments conducted in the US and in Russia. The authors' paper uses a beam of lower current density to produce a long pulse which can be transported through a long (2 m) interaction region without beam loss and beam disruption due to instabilities.