EVIDENCE AND CONCEPTS FOR NONLOCAL TRANSPORT

Until a few years ago, most transient transport studies observed prima rily diffusive plasma transport responses to fast, localized perturbat ions. Recently, several experiments have, in addition, observed 'non-l ocal' electron heat responses. Most remarkably, in 'cold-pulse' experi ments the abrupt edge cooling via radiative processes can induce both a diffusive cooling response moving in from the edge and, simultaneous ly, a rising electron temperature in the central core of tokamak plasm as-an opposite response even before the diffusive cooling from the edg e reaches the centre! These and other non-local electron heat transpor t conundra from recent experiments are reviewed. The models and physic al processes advanced to explain these puzzling phenomena are also dis cussed. The importance of resolving this transport enigma is emphasize d.