Comparing Hydrogen and Deuterium Plasmas in DIII-D Using Gyrokinetic Simulation

Linear growth rate and dominant-mode-frequency spectra between dimensionally similar plasmas with differing isotope mass exhibit distinct features that suggest why confinement varies strongly with ion mass. Using the CGYRO code, we run linear simulations of DIII-D plasmas based on experimental profile data. First, we compare simulations based on data of two plasmas fueled by either deuterium or hydrogen, with nearly matched kinetic profiles with the same plasma current and toroidal field. Second, we compare the deuterium simulations using an artificial hydrogen ion mass. The deuterium case shows unstable modes that peak at normalized poloidal wavenumbers k_yρ_s between 0.6 and 0.8, while for hydrogen, growth rates also peak near 0.6, but are higher and vary more with respect to minor radius. We also investigate the effects of temperature gradient and density gradient to help identify the dominant mode at a given frequency and minor radius. Results indicate modes in the electron diamagnetic direction dominate in both deuterium and hydrogen. Initial nonlinear simulations of deuterium and artificial hydrogen plasmas are compared. We also examine the effects of carbon impurities, fast ions, and normalized gyroradius. Future work will examine aspect ratio, particularly that of NSTX-U.