Design of an apparatus for optical and VUV spectroscopy of explosive emission processes

This study focuses on the design of an experimental apparatus for optical and vacuum ultraviolet (VUV) spectroscopy of explosive emission processes at the cathode in a high power vacuum sealed tube. The system consists of a high power pulsed Nd:YAG laser with a highly tunable optical parametric oscillator (OPO, 200 to 2600 nm), a 300 kV, 80 J Marx Generator, and a triode-geometry vircator that is 6 inches in diameter and 11 inches in length. It has been observed that the explosive emission occurring at the cathode forms a plasma front propagating across the A-K gap negatively affecting the impedance of the gap thus shortening pulse length and spoiling the desired consistent low vacuum within the sealed tube. The scope of this project is to probe the plasma formed between the A-K gap to determine the species emitted off the cathode. The timing integration of each sub-system is very critical as the window for measurement is approximately 200 ns. A compact, fiber optically coupled, battery-operated, low jitter (500 ps), fast risetime (20 ns) pulse trigger generator has been designed and incorporated as the trigger source in a trigatron triggering scheme for the Marx generator. Preliminary jitter measurements of 20 to 30 ns have been seen on the fully erected Marx Generator. The intent of this paper is to discuss the details of the various sub-systems and the timing between them, enabling optical / VUV spectroscopic measurements of the explosive emission process.