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Overview of Recent JET Results and Future Perspectives

ABSTRACT. Two complementary improvements to the ELM tolerance of the existing A2 antennas on JET are being assessed. The use of external conjugate-T matching of straps of adjacent antenna arrays could reduce the VSWR levels at RF amplifier output during fast load perturbations. The scheme under consideration uses coaxial line-stretchers (trombones) for tuning the conjugate-T to low resistive impedance (3-6Ohm) with subsequent stub/trombone circuit impedance transformation to 30Ohms. Another technique is to modify the RF plant protection system logic to reduce the high VSWR trip duration to an absolute minimum corresponding to a typical ELM response (~1-2ms) without compromising the plant safety. Both projects are presently being tested and could increase the average power delivered by RF plant into ELMy plasmas at JET

Overview of JET Results

ABSTRACT JET's new Microwave Access system requires a configurable interface to share the transmission lines between the various reflectometric instruments. A confocal quasi optical system made of modular blocks was designed and built for operation in the 60-160GHz range, allowing full configuration and polarization flexibility. This paper deals with the design and test of the instrument

Predictive Analysis of q-profile Influence on Transport in JET and AUG Hybrid Scenarios Predictive analysis of q-profile influence on transport in JET and AUG hybrid scenarios2

Abstract. Hybrid scenarios in present machines are characterized by improved confinement compared to the IPB98(y,2) empirical scaling law expectations. This work concentrates on isolating the impact of increased s/q at outer radii (where s is the magnetic shear) on core confinement in low-triangularity JET and ASDEX Upgrade (AUG) experiments. This is carried out by predictive heat and particle transport modelling using the integrated modelling code CRONOS coupled to the GLF23 turbulent transport model. For both machines, discharge pairs were analyzed displaying similar pedestal confinement yet significant differences in core confinement. From these comparisons, it is found that s/q shaping at outer radii may be responsible for up to ∼ 50% of the relative core confinement improvement observed in these specific discharges. This relative improvement is independent of the degree of rotational shear turbulence suppression assumed in the GLF23 model. However, employing the full GLF23 rotational shear model leads to an overprediction of the ion temperatures in all discharges analyzed. Additional mechanisms for core confinement improvement are discussed and estimated. Further linear threshold analysis with QuaLiKiz is carried out on both pairs of discharges. This work aims to validate recent predictions of the ITER hybrid scenario also employing CRONOS/GLF23, where a high level of confinement and resultant fusion power sensitivity to the s/q profile was found

Overview of Recent JET Results and Future Perspectives

ABSTRACT A number of codes are in use at JET to model the edge plasma. The range of edge codes is described as is the range of physics issues being explored by these codes. The balance between focussed modelling (that looking at particular physics effects) and integrated modelling (attempting to combine codes or encapsulate the physics from some codes into other codes) is examined

Overview of Recent JET Results and Future Perspectives

ABSTRACT The effect of ELMs on the JET far SOL plasma parameters has been investigated using a multi-probe system. Radial velocities up to 1 km/s have been observed in the far SOL implying that the ELMs arrival time to the plasma wall can be comparable to, or even smaller than, the characteristic time of transport to the divertor. It has been observed that the effective radial transport is higher for the large amplitude ELMs so that the fraction of the ELM energy reaching the main chamber wall increases with the ELM size. In spite of the large particle flux measured in the far SOL plasma during type I ELMs, the energy carried by electrons to the main chamber PFCs is very small (≤ 5% of the ELM losses)

Overview of Recent JET Results and Future Perspectives

ABSTRACT. Gamma-ray spectra from nuclear reactions between fusion-born alpha (α) particles and Be impurities were measured for the first time in deuterium plasmas in the Joint European Torus. The time dependence of the measured spectra allowed the determination of the density evolution of fast α particles. Correlation between the decay time of the γ-ray emission and the plasma parameters in different plasma scenarios was established. Results of the measurements are consistent with classical slowing down of the a particles in discharges with high plasma currents (I p ≥ 2.0 MeV) and monotonic q-profiles. In low plasma current discharges and in the discharges with large on-axis current holes (and, hence, extreme central magnetic shear reversal) the γ-ray emission decay times are shorter than the classical slowing down times, indicating an α-particle confinement degradation in such discharges in line with theoretical predictions. The obtained data provides essential information for studying α-particle confinement and for assessing the potential of the diagnostic technique in the perspective of ITER