The influence of the rotating field and the driven current on confinement in the rotamak

A range of rotating field amplitudes, driven currents and filling pressures is explored in the ANSTO rotamak (vessel diameter 28 cm, Itor < 2.5 KA, Pr.f. < 60 kW, n-bare = 2-8 x 1012 cm-3, Te = 10-15 eV). The relationships between the externally controlled variables and their effect on the plasma parameters are investigated. Although the rotating field is responsible for creating and maintaining the rotamak configuration, its amplitude is seen to have little effect on many of the plasma parameters. The temperature and density, near the magnetic axis, and the particle confinement time are observed to scale mainly with the driven current, even though the same current can be achieved with a range of rotating field amplitudes and r.f. input powers. However, the details of the equilibrium magnetic field configuration do depend on the rotating field. This dependence is reflected by the r.f. power which is sensitive to the position of the separatrix in relation to the vessel wall. (author)