Investigation of plasma formation and propagation in relativistic electron beam diodes

Summary form only given: A series of experiments were conducted at Sandia National Laboratories on the RITS-6 accelerator configured in the low impedance mode (7.5 MV, 180 kA) to investigate electrode plasma formation and propagation in relativistic electron beam diodes used for flash x-ray radiography. In particular the Self- Magnetic Pinch diode (SMP), which employed a hollow metal cathode positioned ~12 mm from a thin aluminum foil anode, in-front of a high atomic number bremsstrahlung x-ray converter, was studied. Anode and cathode plasmas composed of surface contaminants and metals with densities of up to 10¹⁷ cm^-3 are formed and expand across the gap with velocities of 10´s of cm/microsecond. It is believed that the dynamics and interactions of these plasmas are responsible for the observed impedance behavior of the diode. Visible and ultraviolet spectroscopy is used to spatially and temporally measure individual plasma species. Plasma densities and temperatures are determined using collisional-radiative models. Diagnostics include gated, intensified CCD camera imaging and gated/streaked spectroscopy using high resolution 1 meter Czerny-Turner monochromators. Recent results are presented.