Velvet cathodes are a popular emitter choice for high current electron beams and are utilized at several high dose radiography facilities, such as the Dual Axis Radiographic Hydrodynamic Test facility. Electron emission from a velvet surface has been studied for nearly 40 years and is shown to be a result of surface flashover. These cathodes produce stable, high current pulses on timescales less than 0.3μs. After this time frame is exceeded, cathode performance is altered and becomes increasingly unreliable. A test stand has been developed to investigate the emission characteristics of a variety of cathodes with pulse lengths up to 2.2μs.In this thesis, we evaluate the temporal evolution of velvet cathodes over pulse durations ranging from 0.3 - 1.5μs and explore the dependence on diode geometry. Charge accumulation on the velvet surface results in excess electron emission that presents as intense transients or arcs in the measured current. Additionally, the expansion of the hydrogen plasma formedon the face of the cathode causes a decrease in the gap distance between the cathode and anode shrouds. The combination of these effects makes velvet an unreliable emitter choice for long pulse applications. For future radiographic facilities, cathode candidates should produce stable current pulses up to 3μs with current densities on the order of 100A/cm^2.A critical element for diagnosing the quality of a particle source is measuring the extracted current density. Popular methods utilize invasive diagnostic screens. Electron beams produced on the cathode test stand are non-relativistic, where β = 0.5 - 0.75, and the resulting current density measurements are strongly affected by electron scatter and Cherenkov limits. Various measurement methods are evaluated including X-ray scintillation and Cherenkov emission. The limits for each measurement method and optimal measurement range are discussed for each technique and are confirmed with Monte Carlo modeling.
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