Neutral transport simulations using DEGAS2 for designing a gas puff imaging system on TCV

Harry Han


Tuesday, March 6, 2018



PSFC Student Seminars

Gas-Puff Imaging (GPI) measures the spatially-resolved fluctuations in the plasma edge and SOL by imaging emission from a local gas puff. We plan to design and install a GPI system on TCV in Switzerland by June 2018. Installing a GPI system on TCV will provide a way to measure the edge turbulence which can provide access to interesting physics, such as the neutral density shadowing effect in GPI, turbulence characteristics during L-H transitions, GAMs, density shoulder formation, and density limit. The key components are being made in PSFC and SPC. Given these components, in order to obtain a decent signal-to-noise ratio, we need to consider the following parameters: flow rate of gases, temperature of gases, nozzle type, and gas species. I have been studying this parameter space by using DEGAS 2 to optimize the diagnostic design. DEGAS 2 is a Monte-Carlo code which is capable of simulating neutral particle transport in plasmas. Running DEGAS 2 with different parameters gives the brightness and emission for each viewing chord. The results showed that the fiducial case with the given geometry gives a usable brightness at the LCFS. Moreover, using high temperature gas puff, D2 puff, and collimated puff will give more brightness inside the LCFS than the fiducial case.