A first look at resistive MHD stability differences between NSTX and NSTX-U high beta discharges*

Comparison is made of the onset, growth rate and saturation of m/n $=$ 2/1 tearing modes in NSTX and NSTX-U high beta discharges. NSTX-U has stronger toroidal field, higher electron temperature (thus longer resistive diffusion time) and a larger aspect ratio (due to the expansion of the center stack). Experimental identification of the mode helicity, radial location, and width is accomplished by synergistically combining information from soft x-ray emission, Thomson scattering ($T_{e} $ profile), Charge Exchange Recombination ($T_{i} $ profile) and Mirnov diagnostics. Fitting the generalized Rutherford equation to the time-evolution of the island width allows evaluation of the different drive and stabilizing terms. Linear stability calculations have also been performed with M3D-C1.~ The possibility of a reduction in the stabilizing interchange effect due to curvature at somewhat larger aspect ratio in NSTX-U is one focus of the analysis.