Design and Implementation of a Photodiode Coupled Monochromator for Fast Spectrometry*

During the MHD-driven plasma jet experiment, spectrometric measurements have indicated a decrease in argon II and increase in argon III after the Rayleigh-Taylor (RT) instability, as captured by high-speed camera movies. To further investigate the correlation between argon's ionization and the RT instability, we have built a 1200 line/grating monochromator coupled to a 72-diode photodiode array that continuously captures a range of spectral features. Each diode returns a distinct voltage signal from which we can determine the relative emitted intensities of wavelengths down to 1 nanometer apart and deduce the ratio of Ar II to Ar III over the course of the jet's duration. Preliminary results have indicated that Ar II line 349 nm peaks before Ar III line 348 nm when the jet undergoes a kink instability, during which the RT instability typically occurs. We will ultimately build a PCB to extract signals from all 72 diodes and track a range of wavelengths containing both Ar II and Ar III lines, revealing whether energy flows into the ions and at what point during an instability. By comparing monochromator measurements with snapshots from a high-speed camera, we will better understand how plasma is energized over time.