LNF:Fuelling and Impurity Control Studies in the stellarators TJ-II and W7-X using Cryogenic Pellets and Tracer-Encapsulated Solid Pellets (TESPEL): Difference between revisions

1. A pellet-induced enhanced confinement regime (or PiEC) has been identified in NBI-heated discharges made in TJ-II after the injection of a single cryogenic fuel pellet into the plasma core [1]. In addition to the expected increase in core electron density, the plasma diamagnetic energy content, as determined using a diamagnetic loop, is seen to rise by up to 40%, with respect to reference discharges without pellet injection. Furthermore, the energy confinement time is significantly enhanced when compared to predictions obtained using the 2004 International Stellarator Scaling law, ISS04. Indeed, the operational regimes of other stellarator devices, such as LHD and W7-X, can be similarly extended to performance well beyond those obtainable with gas puffing alone.

2. Additional studies, performed with multiple pellet injections, have extended the TJ-II operational regime well beyond limits previously achieved in this device using NBI heating and gas puff. In order to achieve best results, the plasma target electron density should to be in the range 1x10^1919 to 2.5x10^19 m^-3 and time separations between pellets should be close to energy confinement times, around 10 ms.