Optical plasma diagnostics in high intensity electron beam diodes

Summary form only given. This paper is an overview of the optical plasma diagnostics fielded on the RITS-6 accelerator at Sandia National Laboratories for the investigation of plasmas created in high intensity electron beam diodes. Sandia National Laboratories is actively researching pulsed-electron beam diodes for use as flash x-ray radiographic sources. Typical parameters are 150 kA at 7 MeV for a 70 ns pulse (45 ns radiation pulse). The on-target current densities can reach in excess of 1.5 MA/cm², which rapidly form plasmas on the surface that range in densities from 10¹²-10¹⁸ cm³. These plasmas move out into the A-K vacuum gap at velocities of up to 10 cm/μsec during the pulse, affecting the overall impedance behavior of the diode. In an effort to better understand these plasmas, several optical diagnostics are employed, including: gated and streaked imaging and spectroscopy. Examples will be given of both, as well as methods used to analyze the data, including: detailed, time-dependent, collisional-radiative (CR) and radiation transport modeling of spectral lines and continua. These methods will be shown for two different types of e-beam diodes, the self-magnetic pinch (SMP) and the negative polarity rod pinch (NPRP). Several detailed results have been obtained including: spatially-resolved measurements of the early and late-time plasma compositions, their densities as a function of time, and their motion both axially and radially across the vacuum gap. These are the first comprehensive spectroscopic measurements of plasmas in these types of e-beam diodes being used to advance our understanding of the dominant processes occurring within the diodes. Finally, an overview of spectroscopic techniques required to measure local magnetic and electric fields will be given.