This paper reports the successful installation of the JET ITER-like Wall and the realisation of its technical objectives. It also presents an overview of the planned experimental programme which has been optimised to exploit the new wall and other JET enhancement in 2011/12. IntroductionThe ITER reference materials [pitts] have been tested in isolation in tokamaks, plasma simulators, ion beams and high heat flux test beds. However, an integrated test demonstrating both acceptable tritium retention, predicted to be one to two orders of magnitude lower than for a carbon wall [roth], and an ability to operate a large high power tokamak within the limits set by these materials has not yet been carried out. The ITER-like Wall now installed in JET by remote handling comprises solid beryllium limiters and a combination of bulk W and Wcoated CFC divertor tiles.Work is also well advanced in defining the 2011/12 JET experimental programme and setting up the teams. A phased approach will be adopted which maximises the scientific output early in the programme on the basic materials and fuel retention questions whilst minimising the risk associated with operation in an all metal machine. However, re-establishing H-modes at similar power levels to those with the carbon walls is a priority for establishing a reference database. The JET upgrades also include an increase in neutral beam heating power, up to 35MW for 20s [ciric], this has led to a requirement that the most critical first wall Be and W components are monitored in real time by an appropriate imaging protection system [Alves, Jouve, Stephen]. In the main chamber, an array of thermocouples has been fitted to unambiguously monitor the bulk temperature of critical tiles. Before this upgrade, only a divertor system was available which proved essential for interpretation of IR data [Eich] and this will be even more the case with an all metal wall due to reflection and uncertain emissivity. Safe expansion of operating space will also be a priority. Experiments will have to be carefully managed if they have the potential to jeopardise interpretation of the long term samples which are planned to be removed in a 2012 intervention. Here the concern is that

In this paper, a new burn-through model is introduced in detail, and the quantative validation of the simulation results against JET data is presented for the first time. In order to calculate the particle confinement time, a dynamic effective connection length model including an eddy current effect is used assuming ambipolar transonic transport and Bohm diffusion model for parallel and perpendicular particle losses, respectively. Plasma-Surface Interaction (PSI) effect is treated with an impurity sputtering yield and an exponential decay model of the deuterium recycling coefficient. The rate and power coefficients in the Atomic Data and Analysis Structure (ADAS) package are adopted to solve energy and particle balance. The neutral screening effects are taken into account according to particle species, and the sophisticated energy and particle balances are presented. The new burn-through simulation shows good agreement against carbon wall JET data. This indicates that the burn-through simulation can be applied to investigate the key aspect of physics in plasma burn-through and to perform a predictive simulation for ITER start-up.

The pedestal profile measurements in high triangularity JET plasmas show that with low fuelling the pedestal width decreases during the ELM cycle and with high fuelling it stays constant. In the low fuelling case the pedestal pressure gradient keeps increasing until the ELM crash and in the high fuelling case it initially increases then saturates during the ELM cycle.Stability analysis reveals that both JET plasmas become unstable to finite-n ideal MHD peeling-ballooning modes at the end of the ELM cycle. During the ELM cycle, n = ∞ ideal MHD ballooning modes and kinetic

The formation of magnetic islands with mode numbers (m>1,n=1) apparently triggered by sawtooth crashes has for a long time been a concern in JET discharges with auxiliary heating as it affects the peak performance, in terms of stored energy or of neutron yield (in DT experiments). The phenomenological association of the sawtooth crash with the onset of resistive modes is becoming particularly relevant in the context of Neoclassical Tearing Modes (NTM) theory that requires the formation of a "seed" island above a critical value. Relying on observations and on a critique of the assumed role of the collapse phase of the (1,1) instability we propose as physical mechanism of destabilisation of the metastable NTM a forced reconnection process due to electro-dynamic mode-mode coupling. For specific frequency matching conditions a bifurcation pattern appears in the ∆(W) plot. Modeling of a JET discharge shows that for perfectly frequency matching conditions the triggering of the (m=3, n=2) NTM could be due to either two-mode toroidal coupling or threemode non-linear coupling. The observed mode frequencies are consistent with the non-linear coupling. 1-Introduction In several experiments performed at JET, the peak performance, in terms of neutron yield and plasma stored energy, has been observed to deteriorate in coincidence with the onset of fast

The three-dimensional plasma boundary displacements induced by applied non-axisymmetric magnetic perturbations have been measured in ASDEX Upgrade, DIII-D, JET, MAST and NSTX. The displacements arising from applied resonant magnetic perturbations (RMPs) are measured up to ±5% of the minor radius in present-day machines. Good agreement can be found between different experimental measurements and a range of models-be it vacuum field line tracing, ideal three-dimensional MHD equilibrium modelling, or nonlinear plasma amplification. The agreement of the various experimental measurements with the different predictions from these models is presented, and the regions of applicability of each discussed. The measured displacement of the outboard boundary from various machines is found to correlate approximately linearly with the applied resonant field predicted by vacuum modelling (though it should be emphasized that one should not infer that vacuum modelling accurately predicts the displacement inside the plasma). The RMP-induced displacements foreseen in ITER are expected to lie within the range of those predicted by the different models, meaning less than ±1.75% (±3.5 cm) of the minor radius in the H-mode baseline and less than ±2.5% (±5 cm) in a 9 MA plasma. Whilst a displacement of 7 cm peak-to-peak in the baseline scenario is marginally acceptable from both a plasma control and heat loading perspective, it is important that ITER adopts a plasma control system which can account for a three-dimensional boundary corrugation to avoid an n = 0 correction which would otherwise locally exacerbate the displacement caused by the applied fields.

Abstract. This paper presents the DYON simulations of the plasma burn-through phase at Joint European Torus (JET) with the ITER-like wall. The main purpose of the study is to validate the simulations with the ITER-like wall, made of beryllium. Without impurities, the burn-through process of a pure deuterium plasma is described using DYON simulations, and the criterion for deuterium burn-through is derived analytically. The plasma burn-through with impurities are simulated using wallsputtering models in the DYON code, which are modified for the ITER-like wall. The wall-sputtering models and the validation against JET data are presented. The impact of the assumed plasma parameters in DYON simulations are discussed by means of parameter scans. As a result, the operation space of prefill gas pressure and toroidal electric field for plasma burn-through in JET is compared to the Townsend avalanche criterion.Physics of plasma burn-through and DYON simulations for the JET ITER-like wall 2

A systematic study of the coupling of the Lower Hybrid (LH) power to JET plasmas has allowed us to overcome the problems of active current drive in the H-mode and ITB plasmas. As a result, LH power up to 4MW has been injected for longer than 8s in an ITB plasma. The LH coupling has been improved by fitting thepoloidal shapes of the plasma to that of the launcher, up to the degree allowed by the septum in the divertor, and by injecting deuterated methane (CD 4) from a pipe close to the LH antenna. Average values of the reflection coefficient as low as 4%, as in the previous Lmode operation are obtained. The reduced shape mismatch has strongly increased the poloidal uniformity of the plasma in front of the LH launcher and has permitted a balanced supply of the 3 grills. The major breakthrough, however, has been to puff CD 4 , which increases the density in front of the LH launcher at least by 1.5 times locally, raising it above the cutoff value. This technique does not affects the plasma performances nor contaminates the main plasma up to the maximum flow rate so far used, F CD4 >10 22 el./s. Now it is routinely applied in JET and has allowed us to modify the plasma current radial profile evolution during the ITB, producing very encouraging results. Even though CD 4 is not suitable for ITER for the large tritium retention, the possibility to control locally and safely the scrape off plasma density has been demonstrated.

ELMy H-mode experiments at JET in 2000/mid-2002 have focused on discharges with normalized parameters for plasma density, energy confinement and beta similar to those of the ITER Q DT = 10 reference regime (n/n GW ∼ 0.85, H 98(y,2) ∼ 1, β N ∼ 1.8). ELMy H-mode plasmas have been realized reaching or even exceeding those parameters in steady-state conditions (up to ∼5 s or 12τ E) in a reproducible way and only limited by the duration of the additional heating phase. These results have been obtained (a) in highly triangular plasmas, by increasing the average a Researcher at NFSR Belgium. b Partners in the Trilateral Euregio Cluster (TEC). c See annex in IAEA 2002 J. Pamela IAEA-CN94/OV-1/1.4.