Three-dimensional codes to design stellarators

Equilibrium, stability, and transport in stellarators can be studied theoretically by running large computer codes. Some of the codes have excellent resolution, and experimental data have been used to validate the results of numerical calculations. An analysis has been made of recent measurements from the Large Helical Device experiment in Japan to see how they compare with the theory [A. Komori, H. Yamada, O. Kaneko et al., Plasma Phys. Control. Fusion 42, 1165 (2000)]. Observations of confinement time at low collisionality like that in a reactor agree well with estimates using a quasineutrality algorithm to determine the electric potential. A nonlinear magnetohydrodynamic calculation of stability for various pressure profiles gives predictions of the beta limit that are consistent with the observations. Correlation of the theory with measurements justifies using the codes as a tool to design quasisymmetric configurations for a modular stellarator experiment promising better performance at reactor conditions.