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One metric for comparing confinement properties of different magnetic fusionenergy configurations is the linear critical gradient of drift wave modes. Thecritical gradient scale length determines the ratio of the core to pedestaltemperature when a plasma is limited to marginal stability in the plasma core.The gyrokinetic turbulence code GS2 was used to calculate critical temperaturegradients for the linear, collisionless ion temperature gradient (ITG) mode inthe National Compact Stellarator Experiment (NCSX) and a prototypical shapedtokamak, based on the profiles of a JET H-mode shot and the stronger shaping ofARIES-AT. While a concern was that the narrow cross section of NCSX at sometoroidal locations would result in steep gradients that drive instabilitiesmore easily, it is found that other stabilizing effects of the stellaratorconfiguration offset this so that the normalized critical gradients for NCSXare competitive with or even better than for the tokamak. For the adiabatic ITGmode, NCSX and the tokamak had similar critical gradients, though beyondmarginal stability, NCSX had larger growth rates. However, for the kinetic ITGmode, NCSX had a higher critical gradient and lower growth rates until a/L_T isapproximately 1.5 times a/L_{T,crit}, when it surpassed the tokamak's. Adiscussion of the results presented with respect to a/L_T vs. R/L_T isincluded.

Comparing linear ion-temperature-gradient-driven mode stability of the National Compact Stellarator Experiment and a shaped tokamak