First Results from Recent JET Experiments in Hydrogen and Hydrogen Deuterium Plasmas
The hydrogen campaign completed at JET in 2016 has demonstrated isotope ratio control in JET ILW using gas puffing and pellets for fuelling, Neutral Beam Injection alone or in combination, with D/H spectroscopy as a diagnostic. The plasma properties such as confinement, L H threshold, density limit depend on the isotope composition. The L H transition power increases with the hydrogen concentration with a wide plateau in the range 0.2<nH/(nD+nH)<0.8. Energy confinement is significantly lower in hydrogen than in comparable deuterium ELMy H mode plasmas, suggesting an isotope mass scaling that is stronger than in IPB98(y,2) In L mode, the isotope dependence of confinement is weaker. The H mode density limit in hydrogen is up to 35% lower than in heuterium, whilst it is found to be higher in L mode. The lower ion mass leads to reduced tungsten sputtering in hydrogen plasmas. During the campaign, the nD/(nD+nH) ratio dropped to 1% in only a few discharges after the last deliberate introduction of deuterium, although it was seen to rise again to 2% with several seconds of exposure of the divertor tiles to 10MW of auxiliary heating. Several ICRH scenarios were also tested in hydrogen plasmas.