Plasma Background Radiation Diagnostics for the CMFX

The Centrifugal Mirror Fusion Experiment (CMFX) seeks to investigate the stability and scalability of the centrifugal mirror concept to produce fusion energy, and diagnostics tools such as Thomson Scattering are needed to understand properties of the plasma. To reduce uncertainties in these diagnostics from background radiation from the plasma, we created a calibrated diagnostics tool to measure the spectrum of the plasma. Using an enclosed tube to limit outside noise, an iris of varying sizes is placed in front of a lens, focusing light through replaceable filters into a photodiode. Two devices were built for simultaneous use, each housing either a MTAPD-06-010 Avalanche photodiode or an FGA015 InGaAs photodiode which provide a wavelength responsivity between 400 -1100 nm and 800 -1700 nm, respectively. Implementation of exchangeable filters allows for easy insight into much narrower wavelength bands and avoids expected spikes in noise. The irises provide us with a controllable parameter of intensity and allow for a more precise localization of the probed plasma volume. Externally, one voltage source is used for each device, and an oscilloscope connected to a load resistor provides the background radiation signal of the plasma. Here we present details about the design, construction, and calibration measurements of the diagnostics tool.