Tokamaks and Quasi-Axisymmetric Shaping

Since the pressure and current profiles are largely self- determined in a fusion plasma, plasma shaping is the primary design freedom. The importance of axisymmetric shaping to the feasibility of fusion in tokamaks is appreciated. Quasi- axisymmetric shaping gives additional degrees of design freedom that are associated with stellarators while retaining the well- confined particle trajectories associated with the axisymmetric tokamak. A factor of four extrapolation is expected to be required in the ratio of driven to bootstrap current between ITER and steady-state DEMO designs that are limited by axisymmetry. Quasi-axiymmetric shaping can not only ensure steady-state maintenance of the magnetic configuration but also address issues of MHD stability, robustness of plasma equilibria, density limit, and turbulent transport modification. Resources have been very limited for carrying out relevant design studies, but cases have been found that indicate the potential for addressing important physics issues that must be addressed between ITER and DEMO.