Optical diagnostics for quantitative analyses of plasma parameters in high-energy electron-beam diodes

Plasmas are being investigated at Sandia National Laboratories (SNL) as part of an electron beam diode research program. The RITS-6 accelerator (4-8MeV, 100-200kA, 70ns) at SNL is being used to evaluate the Self-Magnetic Pinch (SMP) diode¹. This diode utilizes a small, hollowed, metal cathode and a planar high atomic number anode to produce a focused electron beam (<; 3mm) which generates a high energy Bremsstrahlung x-rays. During this process, electrode plasmas are formed that propagate into the A-K vacuum gap and affect the diode impedance, beam focal spot behavior, voltage, and x-ray spectrum. High speed camera and photodiode systems are used to measure these plasmas and determine their properties. The experiments described here make use of an intensified, 8-frame, CCD camera system and a fast (<;1ns) silicon PIN photodetector array. The 8-frame camera system collects eight separate 2D images of the plasmas in the vacuum gap region. Calibrations were performed to correlate the intensities measured with the camera to the actual photon flux within the diode, and from this information plasma densities were inferred. Similarly, the photodiode array measures lower intensity, time-resolved plasma light emission from the diode, and by careful calibrations, through different regions of the visible spectrum, absolute intensities were determined. The combination of these diagnostics allows for a comprehensive evaluation of the plasmas within the SMP diode. This work is being done in parallel with optical spectroscopy, which provides more detailed measurements of plasma parameters, including species ion and electron temperatures and densities. Recent results from RITS will be presented.