Detailed experimental studies of ion heat transport have been carried out in JET exploiting the upgrade of Active Charge Exchange Spectroscopy and the availability of multi-frequency ICRH with 3 He minority. The determination of ion threshold and stiffness offers unique opportunities for validation of the well-established theory of Ion Temperature Gradient driven modes. Ion stiffness is observed to decrease strongly in presence of toroidal rotation when the magnetic shear is sufficiently low. This effect is dominant with respect to the well-known w ExB threshold up-shift and plays a major role in enhancing core confinement in Hybrid regimes and Ion Internal Transport Barriers. The effects of T e /T i and s/q on ion threshold are found rather weak in the domain explored. Quasi-linear fluid/gyro-fluid and linear/non-linear gyro-kinetic simu lations have been carried out. Whilst threshold predictions show good match with experimental observations, some significant discrepancies are found on the stiffness behaviour.

Effect of Ti-Al cathode composition on plasma generation and plasma transport in direct current vacuum arc Estimation of electron temperature and density of the decay plasma in a laser-assisted discharge plasma extreme ultraviolet source by using a modified Stark broadening method A magnetized hydrogen plasma beam was generated with a cascaded arc, expanding in a vacuum vessel at an axial magnetic field of up to 1.6 T. Its characteristics were measured at a distance of 4 cm from the nozzle: up to a 2 cm beam diameter, 7.5ϫ 10 20 m −3 electron density, ϳ2 eV electron and ion temperatures, and 3.5 km/ s axial plasma velocity. This gives a 2.6ϫ 10 24 H + m −2 s −1 peak ion flux density, which is unprecedented in linear plasma generators. The high efficiency of the source is obtained by the combined action of the magnetic field and an optimized nozzle geometry. This is interpreted as a cross-field return current that leads to power dissipation in the beam just outside the source.

Several parametric scans have been performed to study momentum transport on JET. A neutral beam injection modulation technique has been applied to separate the diffusive and convective momentum transport terms. The magnitude of the inward momentum pinch depends strongly on the inverse density gradient length, with an experimental scaling for the pinch number being -Rv pinch/χϕ = 1.2R/L n + 1.4. There is no dependence of the pinch number on collisionality, whereas the pinch seems to depend weakly on q-profile, the pinch number decreasing with increasing q. The Prandtl number was not found to depend either on R/L n, collisionality or on q. The gyro-kinetic simulations show qualitatively similar dependence of the pinch number on R/L n, but the dependence is weaker in the simulations. Gyro-kinetic simulations do not find any clear parametric dependence in the Prandtl number, in agreement with experiments, but the experimental values are larger than the simulated ones, in particular in L-mode plasmas. The extrapolation of these results to ITER illustrates that at large enough R/L n > 2 the pinch number becomes large enough (>3–4) to make the rotation profile peaked, provided that the edge rotation is non-zero. And this rotation peaking can be achieved with small or even with no core torque source. The absolute value of the core rotation is still very challenging to predict partly due to the lack of the present knowledge of the rotation at the plasma edge, partly due to insufficient understanding of 3D effects like braking and partly due to the uncertainties in the extrapolation of the present momentum transport results to a larger device.

The core charge-exchange diagnostic at the Joint European Torus (JET) provides measurements of the impurity ion temperature T(i), toroidal velocity V(phi), and impurity ion densities n(imp), across the whole minor radius. A contribution to the uncertainty of the measured quantities is the error resulting from the multi-Gaussian fit and photon statistics, usually quoted for each measured data. Absolute intensity calibration and especially alignment of the viewing directions can introduce an important systematic error. The technique adopted at JET to reduce this systematic contribution to the error is presented in this paper. The error in T(i), V(phi), and n(imp) is then discussed depending on their use.