Stellarators: the once and future thing

Some ideas go out of fashion, only to come back in when their execution is feasible. One of those ideas is the stellarator, a fusion energy device that resembles the more symmetric tokamak and offers some unique advantages-along with some unique design problems. Like the tokamak, a stellarator is a ring of plasma confined within magnetic coils. Unlike a tokamak-where the ring looks like an inflated inner tube and the magnetic field varies in only two dimensions-the stellarator has plasma with kinks in it and a magnetic field that varies in three dimensions One of the partners involved with the computational side of the major stellarator projects is the University of Texas in Austin's Fusion Research Center. The Center originally had its own project, but when the decision was made to build the NCSX and Oak Ridge machines, the group's emphasis changed. However, some of the computational tools it developed are now in use by the national projects. One of these is a genetic algorithm that optimizes the shape of the external coils for the desired plasma configuration. In this iterative process, the genetic algorithm can scope around in parameter space very quickly. Another code, NESVD, helps calculate the coil shapes and the maximum magnetic field strength for a given plasma concentration.