Bulk ion heating with ICRH in JET DT plasmas

Reactor relevant ICRH scenarios have been assessed during DT experiments on the JET tokamak using H mode divertor discharges with ITER-like shapes and safety factors. Deuterium minority heating in tritium plasmas was demonstr ated for the first time. For 9% deuterium, an ICRH power of 6 MW gave 1.66 MW of fusion power from reactions between suprathermal deutrons and thermal tritons. The Q value of the steady state discharge reached 0.22 for the le ngth of the RF flat-top (2.7 s), corresponding to three plasma energy repla cement times. The Doppler broadened neutron spectrum showed a deuteron ener gy of 125 keV, which was optimum for fusion and close to the critical energ y. Thus, strong bulk ion heating was obtained at the same time as high fusi on efficiency. Deuterium fractions around 20% produced the strongest ion he ating together with a strong reduction of the suprathermal deuteron tail. T he ELMs had low amplitude and high frequency and each ELM transported less plasma energy content than the 1% required by ITER. The energy confinement time, on the ITERH97-P scale, was 0.90, which is sufficient for ignition in ITER. He-3 minority heating, in approximately 50:50 DT plasmas with up to 10% He-3, also demonstrated strong bulk ion heating. Central ion temperatur es up to 13 keV were achieved, together with central electron temperatures up to 12 keV. The normalized H mode confinement time was 0.95. Second harmo nic tritium heating produced energetic tritons above the critical energy. T his scheme heats the electrons in JET, unlike in ITER where the lower power density will allow mainly ion heating. The inverted scenario of tritium mi nority ICRH in a deuterium plasma was demonstrated as a successful heating method producing both suprathermal neutrons and bulk ion heating. Theoretic al calculations of the DT reactivity mostly give excellent agreement with t he measured reaction rates.