In-situ experimental investigations of electron space-charge instabilities and noise mechanisms in a reentrant crossed-field amplifier via distributed-cathode emission and gated-beam injection

Summary form only given. Experimental investigations of the true physical conditions inside the crossed-field devices are of fundamental importance for the understanding of the operation of these devices and may lead to eventual improvement of the present tubes. At Northeastern University, tube research has taken up a combined approach of in situ plasma diagnostics and computer simulations using two frequency scaled CFAs as test vehicles. A collection of temporal and time-averaged diagnostic techniques have been developed through our research. Probe measurements as well as device performance of the linear CFA and the beam-injected, reentrant CFA have been directly compared with computer simulation results from MASK and NEAMP codes. We have recently incorporated in our reentrant CFA a secondary emission cathode for the purpose of gaining insight on improving the noise performance of both military and commercial devices. It has long been speculated and appears more so as a result of the improved diagnostic techniques, that the instabilities in the space charge cloud are the major source of noise in crossed-field devices. The average electron transit time is determined experimentally through a gated-electron injection scheme. Latest results are reported.