The configuration flexibility provided to the TJ-II Heliac by the helical hard core permits a significant change in the stability properties of the plasma. In this numerical analysis of full three-dimensional equilibria it is found that, by exploiting the flexibility of the machine, the stability beta limit given by the Mercier criterion can be varied almost continuously over values of average beta from zero to more than 6%.
Optimized profiles for improved confinement and stability in the DIII-D tokamak