MODELING OF ALMOST DIMENSIONALLY SIMILAR DISCHARGES

For dimensionally similar tokamak discharges, all relevant dimensionless parameters are the same, except for the gyroradius relative to the system size. Such discharges can be simply scaled to ignition, provided the scaling with respect to the relative gyroradius-rho* can be determined. This letter argues that owing to imperfection in achieving the dimensional similarity conditions, recent DIII-D experiments with similar heating profiles showing Bohm-like gross confinement scaling can be modelled equally well with Bohm-like (chi is-proportional-to c(s)rho) or gyroBohm-like (chi is-proportional-to c(s)rho-rho*) local diffusion models having marginality to a critical temperature gradient.