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This paper aims at understanding the main processes responsible for the erosion/deposition pattern observed on the surface of the Toroidal Pumped Limiter of Tore Supra, using the 3D local impurity transport code ERO. The influence of the plasma impurity content, CX-flux and surface temperature on the global carbon balance and erosion/deposition pattern is discussed. Main results are (1) that considering medium-range transport of C ions is mandatory for reproducing the main characteristics of the global C balance and erosion/deposition pattern, (2) that impurities and CX-atoms increase the erosion by a factor ⩽2 (without changing the net/gross erosion ratio), and (3) that chemical erosion is governed by the re-erosion of deposits, which depends strongly on the surface temperature. [ABSTRACT FROM AUTHOR]

Abstract: In carbon dominated devices, the in vessel D inventory obtained from post-mortem analyses of plasma facing component samples is generally smaller by a factor of ∼4 than that estimated from gas balance measurements. However, for an accurate evaluation of the wall inventory, gas balance measurements must be done not only during discharges and conditioning procedures, but also in between discharges and during vents. From the analysis of the whole Tore Supra database for the 2002–2007 period, we show that long term outgassing during nights, weekends and vents is essential for evaluating the deuterium release. Taking these contributions into account reconciles the gas balance and post-mortem estimations of fuel retention. [Copyright &y& Elsevier]

Abstract: Disruptive plasma termination was proposed for controlling long-term fuel retention because the subsequent increase of the post-discharge outgassing could help in minimizing the fuel stored in the vessel after each discharge. The efficiency of this method is investigated by analyzing the Tore Supra database for the period 2004–2010 (450 disruptions). Results are shown for the plasma motion during the current quench and the heating of deposits at the Toroidal Pumped Limiter surface. Dependences of the outgassing with internal and magnetic energy contents, increment of the wall inventory and cumulated time between two disruptions are characterized. It is shown: (1) that the desorbed gas originates from D-rich deposits close to the plasma when those located in remote areas are weakly affected and (2) that the amount of released gas saturates with discharge duration and time delay between two disruptions, which limits the efficiency of the method for long discharge operation. However, due to the larger volume/surface ratio, the efficiency of the method is expected to increase with the size of the device. [Copyright &y& Elsevier]

Abstract: Fuel retention inside plasma facing components will be a crucial issue not only in fusion reactors of the future, but also in ITER. The estimation of the fraction of the fuel which remains trapped inside the vessel is quite a difficult task. Particle balance analysis provides information for the whole vacuum chamber as a function of time and can be use to monitor the tritium in-vessel retention in real-time. On Tore Supra with a careful choice and position of pressure sensors, proper calibration procedures, the accuracy of the balance is around 10%. Particle balance analysis have been performed on many long pulse discharges and deuterium in-vessel retention has been found to be a constant around 5×1020 D/s after several minutes of plasma. The evolution of the retention rate with plasma parameters indicates that deuterium bulk implantation and diffusion could dominate codeposition with carbon atoms. Particle balance is a powerful tool that should be implemented in ITER. [Copyright &y& Elsevier]

During the DITS (Deuterium Inventory in Tore Supra) project, inner vessel walls of Tore Supra tokamak have been loaded with deuterium during a specific plasma experiment based on long pulse operation. Then, and in order to determine where the deuterium used as a plasma fuel was lost in the plasma facing components, the Tore Supra limiter had been dismounted and post mortem analysis had been performed on samples coming from different places corresponding to erosion or deposited area. In this the thermo-desorption spectrometry (TDS) studies are presented. All the TDS spectra present independently to their origin the same behaviour e.g. 5 desorption bands at 560 K, 820 K, 1050 K, 1238 K and 1375 K. These bands correspond to different trapping processes in carbon material which are identified with the help of laboratories experiments. Finally, the spectra are fitted by a rate equation model in which one of the main parameter which is the exponential pre-factor is experimentally evaluated (2.7·10 15 s −1 ). This gives the possibility to unambiguously determine the trapping energies for the 5 trapping processes: 1.8 eV, 2.8 eV 3.6 eV, 4.2 eV and 4.7 eV. The model uses a dispersion in energy around these values due to the complex structure of Carbon Fibre Composite. [ABSTRACT FROM AUTHOR]

Abstract: A dedicated study on fuel retention has been launched in Tore Supra, which includes a D wall-loading campaign and the dismantling of the main limiter (Deuterium Inventory in Tore Supra, DITS project). This paper presents new results from a second post-mortem analysis campaign on 40 tiles with special emphasis on the D retention in the gaps. SIMS analysis reveals that only 1/3 of the thickness of deposits in the plasma shadowed zones are due to the DITS wall-loading campaign. As pre-DITS deposits contain less D than DITS deposits, the contribution of DITS to the D inventory is about 30–50%. The new estimate for the total amount of D retained in the Tore Supra limiter is 1.7×1024 atoms, close to the previous estimate, with the gap surfaces contributing about 33%. NRA measurements show a stepped decrease of D along the gap with strong asymmetries between different gap orientations. [Copyright &y& Elsevier]

Abstract: Real time monitoring of edge plasma impurity content is used in a radiofrequency heated plasma scenario, to operate the tokamak safely by preventing any large increase in the impurity source, and to asses the global machine conditions after wall conditioning procedures. By means of high resolution Vacuum Ultraviolet spectroscopy, the main intrinsic impurity line brightnesses (C IV,O IV,Fe XV and Cu XIX) are routinely monitored and stored in a database along with basic plasma parameters (plasma current, electron density, injected power). The radiated power and the effective charge are also included for data consistency analysis. This paper describes the impurity monitoring technique implemented on Tore Supra (TS) and presents the main results concerning the evolution of the plasma edge impurity content for two scenarios performed on TS: high power scenario and long pulse duration scenario. [Copyright &y& Elsevier]

Abstract: This paper presents a model of gas injection treating coherently matter deposition and thermal effects on the plasma. It is demonstrated from an analytical model that an injection can trigger thermal bifurcations toward radiative or recombinant regimes. 1D simulations were performed to study the radial dynamics. They indicate that the injection can create a cold detached region in the outer plasma. The ionization front is located at the transition between this zone and the hot plasma, characterized by a radiative layer and strong temperature gradients. In spite of a better neutral penetration, strong sources are needed for efficient core fuelling and extrapolations for ITER remain pessimistic. Moreover a thermal instability linked to the bifurcation is evidenced for strong particle sources. However, a 1D parallel model shows that the perturbation linked to the injection can remain localized along the parallel direction, thus favoring neutrals penetration, but this effect strongly depends on the perpendicular–parallel transport interplay. [Copyright &y& Elsevier]

Abstract: In Tore Supra long pulses, particle balance gives evidence that a constant fraction of the injected gas (typically 50%) is retained in the wall for the duration of the shot, showing no sign of wall saturation after more than 6min of discharge. During the discharge, the retention rate first decreases (phase 1), then remains constant throughout the pulse (phase 2). Phase 1 could be interpreted as implantation of particles combined with a constant codeposition rate, while phase 2 could correspond to codeposition alone, once the implanted surfaces are saturated with deuterium. This paper presents a possible contribution of charge exchange neutrals to the implantation process, based on modelling results with the Eirene neutral transport code. A complex pattern of particle implantation is evidenced, with saturation time constants ranging from less than one to several hundreds seconds, compatible with the experimental behaviour during phase 1. [Copyright &y& Elsevier]

Abstract: A new pellet injector, able to inject continuously hydrogen or deuterium pellets, was installed on Tore Supra in 2003 and preliminary experiments aiming to fuel long discharges were performed. In combination with Lower Hybrid (LH) Current Drive, pure pellet fuelled discharges lasting up to 2min were achieved. The LH power was switched off just before each pellet injection (LH notching) to maintain a relatively deep pellet penetration by reducing the energy of the super-thermal electrons driven by the LH wave. A comparison, based on a particle balance study, between two comparable pellet fuelled and gas fuelled discharges has been done. In the two cases, the volume average density is the same and the analysis shows that the particle source, the pumped flux and the wall retention are similar and appear to be independent of the fuelling method for the low plasma current and density conditions considered (I p =0.6MA, 〈n e〉=1.5×1019 m−3). [Copyright &y& Elsevier]

Abstract: A diagnostic based on confocal microscopy was developed at CEA Cadarache in order to measure erosion on large plasma facing components during shutdown in situ in Tore Supra. This paper describes the diagnostic and presents results obtained on Beryllium and Carbon Fibre Composite (CFC) materials. Erosion in the range of 800μm was found on one sector of the Toroidal Pumped Limiter (TPL) which provides, by integration to the full limiter a net carbon erosion of about 900g over the period 2002–2007. [Copyright &y& Elsevier]

Abstract: This paper reports on the observation on the tokamak Tore Supra of a very high density, highly radiating edge regime featuring a high recycling divertor. This regime is stable over several energy confinement times, without any additional external control. It is achieved through strong deuterium gas puffing, in an ICRH heated plasma scenario. When the electron density reaches ∼1.1 times the Greenwald density, a bifurcation occurs, leading to strong edge asymmetries: electron density, enhanced edge radiated power localized close to the limiter surface, and a consistent reduction of the conducted power to the limiter. A Greenwald fraction up to ∼1.4 is then achieved, without any loss of confinement, and with low plasma core contamination. [Copyright &y& Elsevier]