Installation of the Multi-Point Thomson Scattering System for the Pegasus-III Experiment

The Pegasus-III experiment uses a multi-point Thomson scattering system to observe the electron temperature and density evolution of non-solenoidal startup plasmas. Following upgrades to the entire Pegasus experiment, the Thomson system has been re-installed and calibrated. The installation saw a realignment of the laser head, alignment of the laser beam path, and new light gates to monitor its hard drive fast optical shutter system. The calibration process utilized backlit fibers to align the system’s fiber cables, Hg and Kr lights to map out the spectrometer’s wavelength response, and a Rayleigh scattering process to determine the necessary geometric values for the electron density calculations. One goal for the system will be to further investigate coaxial helicity injection (CHI) plasmas. CHI is a form of non-solenoidal startup using current driven on open field lines connecting two coaxial, electrically isolated divertor plates to create the plasma. CHI modeling indicates that the electron temperature plays a key role in plasma current evolution and closed flux current generated. Thus, Thomson scattering measurements are critical to investigating CHI dynamics and expanding the current models.