Improved Particle Confinement Mode in the H-1 Heliac Plasma

The first experimental observation of the sudden transition to the improved particle confinement mode in the H-1 heliac is reported and shows a clear dependence on magnetic configuration. In a low-temperature plasma a transition to improved confinement followed by a twofold increase in the electron density is observed when the magnetic field exceeds a critical value B_cr. At B≈B_cr the transition occurs spontaneously (within 1 ms). This B_cr strongly decreases with increasing rotational transform. The improvement in confinement correlates with the suppression of the fluctuations and fluctuation-induced particle flux and with the increase in the radial electric field.