Trapped particle confinement studies in l = 2 torsatrons for additional helical coils, radial electric field, and finite beta effect

Torsatrons are studied to improve the high energy trapped particle confinement with additional helical coils. The winding laws are selected in two ways. One is to realize 'sigma - optimization' by the additional helical coils, but this approach loses magnetic well region. The other selection is to produce or deepen the magnetic well by the additional helical coils. Helical coils are usable to this end. In this case the improvement of the trapped particle confinement depends on magnetic axis position. A radial electric field producing sheared rotational motion is also considered to improve the trapped particle confinement in a standard torsatron. By excluding cancellation between E x B and del(B) drift motion occurred for the parabolic potential profiles, all deeply trapped particles can be confined in the central region. Degradation of the trapped particle confinement by the Shafranov shift is mitigated by shifting the magnetic axis inside in the vacuum configuration.