ICRH on JET high performance plasmas

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Abstract
ICRH on JET is used for a wide range of experiments: confinement and H-mode threshold scaling experiments, combined heating experiments at high plasma current and heating in high performance plasmas which will be presented here. Experiments of combined NBI and ICRH in ELM-free Hot Ion H-modes have been carried out in the JET MKII campaign in 3.8 MA/3.4 T plasmas with up to 9.5 MW of ICRH power together with 16 MW of NBI using minority hydrogen resonance. ICRH results in increased core electron temperature, increased core ion temperature and increased stored energy up to a record of 14.5 MJ. Various schemes have been used including polychromatic mode of operation. Data analysis suggests that a substantial part of the ICRH power is coupled to deuterons at the second harmonic resonance. This is the dominant heating mechanism in new experiments with shear optimisation where the power is injected during the current ramp-up phase of the discharge. Very peaked ion pressure profiles are achieved, up to 3.5 bar and central ion temperatures ranging from 25 to 32 keV are obtained, 5 to 10 keV higher in combined heating than with NBI only. The highest neutron yield has been achieved with π/2 phasing and good coupling is obtained during the L-mode phase. Absolute fusion yield records in DD operation on JET (5.6 10 6 neutrons/s ) have now been established with combined NBI and ICRH, the latter increasing the neutron yield by about 30 to 40%.

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