Design and Implementation of a Photodiode Array 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 investigate the correlation between argon's ionization and the RT instability, we have built a monochromator coupled to a 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 a gradual decline in Ar-II lines 427-429 nm from around 23 𝜇s to 40 𝜇s, during which the RT instability typically occurs. We will similarly study how the intensities of Ar-III spectral lines 348 and 350 nm vary with time and ultimately track a range of both Ar-II and Ar-III wavelengths. The spectral lines will reveal changes in ion temperature, signifying 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.