High fusion power experiments using DT mixtures in ELM-free H mode and optimized shear regimes in JET are reported. A fusion power of 16.1 MW has been produced in an ELM-free H mode at 4.2 MA/3.6 T. The transient value of the fusion amplification factor was 0.95±0.17, consistent with the high value of nDT(0)τEdiaTi(0) = 8.7 × 1020±20% m-3 s keV, and was maintained for about half an energy confinement time until excessive edge pressure gradients resulted in discharge termination by MHD instabilities. The ratio of DD to DT fusion powers (from separate but otherwise similar discharges) showed the expected factor of 210, validating DD projections of DT performance for similar pressure profiles and good plasma mixture control, which was achieved by loading the vessel walls with the appropriate DT mix. Magnetic fluctuation spectra showed no evidence of Alfvénic instabilities driven by alpha particles, in agreement with theoretical model calculations. Alpha particle heating has been unambiguously observed, its effect being separated successfully from possible isotope effects on energy confinement by varying the tritium concentration in otherwise similar discharges. The scan showed that there was no, or at most a very weak, isotope effect on the energy confinement time. The highest electron temperature was clearly correlated with the maximum alpha particle heating power and the optimum DT mixture; the maximum increase was 1.3±0.23 keV with 1.3 MW of alpha particle heating power, consistent with classical expectations for alpha particle confinement and heating. In the optimized shear regime, clear internal transport barriers were established for the first time in DT, with a power similar to that required in DD. The ion thermal conductivity in the plasma core approached neoclassical levels. Real time power control maintained the plasma core close to limits set by pressure gradient driven MHD instabilities, allowing 8.2 MW of DT fusion power with nDT(0)τEdiaTi(0) ≈ 1021 m-3 s keV, even though full optimization was not possible within the imposed neutron budget. In addition, quasi-steady-state discharges with simultaneous internal and edge transport barriers have been produced with high confinement and a fusion power of up to 7 MW; these double barrier discharges show a great potential for steady state operation. © 1999, Euratom

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At the onset of neutral beam injection (NBI) in JET, the toroidal angular momentum is observed to rise rapidly in the outer regions of the plasma. The toroidal angular momentum in the plasma centre, where the fast ions are injected into passing orbits, and the thermal energy are found to rise on the slowing down time-scale of the fast ions. This behaviour can be explained by a model that incorporates three mechanisms for momentum transfer of fast ions to the bulk: (a) quasi-instantaneous, or first orbit, transfer which results mainly from particles that are injected into trapped orbits, (b) collisional transfer of momentum from passing ions during their slowing down process, (c) enhancement of the total angular momentum of the rotating plasma once the particles have thermalized. The model for the torque is applied to the study of toroidal angular momentum confinement in transient hot ion H mode plasmas in JET. In contrast to steady state conditions, such as L mode and ELMy H mode, where the toroidal angular momentum confinement time τL is approximately equal to the thermal energy confinement time τE, τL is found to be about a factor of 2 smaller than τE in the transient part of the ELM-free phase of the discharge.

Abstract. The charge transfer reaction of neutral deuterium beams with impurities enables one of the principle quantitative diagnostic measurements of the hot core fusion plasma; that is, charge exchange spectroscopy. The complementary measurement of beam emission spectroscopy has been fruitful in motional Stark wavelength shift and fluctuation studies, but less so in using absolute measured intensities. In the last two years we have achieved substantial improvement in the quantitative analysis and agreement between the observed and modelled beam emission at the JET Joint Undertaking. This has depended on improved spectral fitting of the overlayed D α motional Stark multiplet, self-consistent beam emission and impurity charge exchange modelling and analysis, and revision of the data entering the modelling of the beam emission process. The paper outlines the present JET beam emission diagnostic system and the collisional radiative modelling of deuterium beam stopping and emission. The nature and organization of the effective derived data directly used in experimental interpretation at JET are described and some results of spectral analysis of deuterium beam emission given. The practical implementation of the methods described here is part of the ADAS Project.

An analytical procedure is presented which enables a fast estimate of collisionenergy-dependent cross-section effects on thermal charge exchange specba. The model is based both on experimental evidence and numerical simulations showing that the observed charge exchange (CX) spectra are essentially Gaussian in their shape. The collision-energydependent emission rcde leads effectively to a lineshift (appmnt velocity), usually to a reduction in linewidth (appmnt temperature), and to a change in the effective emission k t e averaged over the entire thermal velocity disuibution function. It is demonshated that the cross-section effect can be tresed analytically introducing an approximated emission rate factor which retains the characteristics of a Maxwellian velocity distribution function using an exponential expression with only i i n w and quadratic velocity terms in its exponent.An algebraic deconvolution procedure is described, which enables the reconstruction of vue temperature, velocity and intensities from measured CX s p e m . Examples taken from a recent E T expenmental campaign are used to illustrate the cross-section effects on low-Z impunty CX spectra for B comprehensive variety of neutnl beams (deuterium. tritium or helium), target densities, temperatures and toroidal rotation speeds. An overview is given of representative conection factors established for high-power, high-temperature plasmas, as well as for plasmas with combined neuval beam and radiofrequency heating, and for the case of locked modes.