A novel table-top stellarator experiment at UW-Madison - parameters and design

A new table-top stellarator experiment has been designed for UW Madison using one helical coil and one planar coil to produce a five-period symmetric magnetic field structure with quasi-poloidal symmetry in the core. The effective major and minor radii of the plasma are 19 cm and 1.8 cm, respectively, translating to an aspect ratio of 10.7. The torsatron coil design employed here minimizes Lorentz forces on the coil enabling the coil supports to be 3D printed from plastic. Considering currents of up to 10 kA, a core magnetic field of 0.08 T can be achieved with a maximum linear force density of only 5 N/cm on the coils. VMEC equilibrium reconstructions show that the two coils generate a rotational transform of up to 0.12 with an effective magnetic ripple of 0.1 which will provide reasonably good neoclassical confinement. First estimates of the performance of the new experiment using the ISS04 scaling and 200 W of absorbed 2.45 GHz ECRH suggest that core electron temperatures of about 40 eV can be reached which translates to a normalized electron gyro-radius of about 0.01.