PERIODS OF ENHANCED TRANSPORT DURING H-MODE IN PBX-M

In PBX-M, periods of enhanced transport are often observed in high beta(pol) H-mode discharges. They can reduce the energy confinement time by a factor of two. Their duration is typically between 2 to 20 ms. They are followed by periods of normal transport of a similar duration. These periods of enhanced transport consist of a series of turbulent m=even MHD events, starting several cm inside the plasma edge. They propagate into the confinement region in 600 mus, causing a progressive erosion of the profile. Each m=even event can also cause an energy loss of 1% or less, mainly from the confinement region. These m=even events are reminiscent of grassy ELMs.