Magnetic plasma confinement research
The flexible heliac configuration allows the widest achievable variation of the three main parameters which control the shape of the plasma, and more importantly, its stability and confinement properties. Studies of plasma configuration involve computation of the predicted configuration from the magnet coils and their currents, experimental measurement of that shape, and investigation of its effect on equilibrium, confinement and stability. The three important shape parameters are magnetic well, related to curvature and indentation, rotational transform or twist (around the axis) per turn (along the axis), and shear, the rate of change of rotational transform with distance from the axis of the plasma.
PRL currently computes 'vacuum' configurations with the HELIAC and GOURDON supercomputer codes, and the interactive Bline code.
Experimental mapping of the vacuum magnetic surfaces is performed by electron beam tomography and fluorescent screen electron imaging. Recently, visible emission tomography has been demonstrated for use directly on plasma.
Confinement variation, in particular with rotational transform, is studied by computer-controlled fine scans of currents in the conductors. Stability is investigated chiefly by remote sensing of fluctuations by several arrays of magnetic field sensing coils during the current scans of configuration.