Articles you may be interested inDesign of an X-mode fast-scanning reflectometry for edge density profile measurement on HT-7 tokamak Rev. Sci. Instrum. 74, 1522 (2003; 10.1063/1.1527253 Ultrashort pulse reflectometry for electron density profile measurements Rev. Sci. Instrum. 70, 1038 (1999); 10.1063/1.1149530Broadband reflectometry for the density profile and fluctuation measurements in the JT60 tokamak (abstract) Rev. Sci.The use of an ordinary mode refiectometer has already proved to be a good means for determining the density profile of a plasma, but the fact that this mode reflects where its frequency equals the local plasma frequency restricts its use to the region of the density gradient. The extraordinary mode refiectometry investigated here permits the observation of the scrape-off layer as well as the near-axis region and in certain conditions also the high magnetic field side of the density profile. It is also shown that this mode requires a range of frequency sweep for measuring a given density profile smaller than the ordinary mode. On the Petula-B tokamak, the density profile has been measured in 200 ps, its evolution when applying the lower hybrid current drive could be also followed. Since the measurement is particularly sensitive near the reflection point of the wave, it could be used to determine precisely the position of magnetic islands and the fluctuation amplitudes. In addition, the access and place occupied in the vacuum chamber being very small, this diagnostic should be compatible with reactor conditions. 539

To support the design of ITER ion-cyclotron range of frequency heating system and to mitigate risks of operation in ITER, CEA has initiated an ambitious Research & Development program accompanied by experiments on Tore Supra or test bed facility together with a significant modeling effort. The paper summarizes the recent results in the following area:• Comprehensive characterization of a new Faraday screen concept tested on Tore Supra antenna. RF sheath rectification is now better understood: a new model has been developed and applied to ITER. • Full wave modeling of ITER ICRH heating and current drive scenarios with EVE code. With 20MW of power, a current of ±400kA could be driven on axis in the DT scenario. • First operation of CW test bed facility, TITAN, designed for ITER ICRH components testing and could host up to a quarter of an ITER antenna. • R&D of high permittivity materials to improve load of test facilities to mimic ITER plasma conditions.

Tore Supra routinely addresses the physics and technology of very long duration plasma discharges, thus bringing precious information on critical issues of long pulse operation of ITER. A new ITER relevant LHCD launcher has allowed coupling to the plasma a power level of 2.7 MW for 78 s, corresponding to a power density close to the design value foreseen for an ITER LHCD system. In accordance with the expectations, long distance (10 cm) power coupling has been obtained. Successive stationary states of the plasma current profile have been controlled in real time featuring i) control of sawteeth with varying plasma parameters, ii) obtaining and sustaining a "hot core" plasma regime, iii) recovery from a voluntarily triggered deleterious MHD regime. The SOL parameters and power deposition have been documented during L-mode ramp-up phase, a crucial point for ITER before the X-point formation. Disruption mitigation studies have been conducted with massive gas injection, evidencing the difference between He and Ar and the possible role of the q=2 surface in limiting the gas penetration. ICRF assisted wall conditioning in the presence of magnetic field has been investigated, culminating in the demonstration that this conditioning scheme allows to recover normal operation after disruptions. Effect of the magnetic field ripple on the intrinsic plasma rotation has been studied, showing the competition between turbulent transport processes and ripple toroidal friction. During dedicated dimensionless experiments, the effect of varying the collisionality on turbulence wavenumber spectra has been documented, giving new insight into the turbulence mechanism. Turbulence measurements have also allowed quantitatively comparing experimental results to predictions by 5D gyrokinetic codes: numerical results simultaneously match the magnitude of effective heat diffusivity, rms values of density fluctuations, and wave-number spectra. A clear correlation between electron temperature gradient and impurity transport in the very core of the plasma has been observed, strongly suggesting the existence of a threshold above which transport is dominated by turbulent electron modes. Dynamics of edge turbulent fluctuations has been studied by correlating data from fast imaging cameras and Langmuir probes, yielding a coherent picture of transport processes involved in the SOL.

The main results of the Tore Supra experimental programme in the years 2007-2008 are reported. They document significant progress achieved in the domain of steady-state tokamak research, as well as in more general issues relevant for ITER and for fusion physics research. Three areas are covered: ITER relevant technology developments and tests in a real machine environment, tokamak operational issues for high power and long pulses, and fusion plasma physics. Results presented in this paper include: test and validation of a new, load-resilient concept of ICRH antenna and of an inspection robot operated under ultra-high vacuum and high temperature conditions; an extensive experimental campaign (5 h of plasma) aiming at deuterium inventory and carbon migration studies; real-time control of sawteeth by ECCD in the presence of fast ion tails; ECRHassisted plasma startup studies; dimensionless  scalings of transport and turbulence; transport experiments using active pertubation methods; resistive and fast-particle driven MHD studies. The potential role of Tore Supra in the worldwide fusion programme before the start of ITER operation is also discussed.