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The design and the fabrication of a new Lower Hybrid (LH) actively cooled antenna based on the passive active concept is a part of the CIMES project (Components for the Injection of Mater and Energy in Steady-state). The major objectives of Tore-Supra program is to achieve 1000 s pulses with this LH launcher, by coupling routinely >3 MW of LH wave at 3.7 GHz to the plasma with a parallel index n{sub ||} = 1.7 {sup {+-}}{sup 0.2}. The launcher is on its way to achieve its validation tests--low power Radio Frequency (RF) measurements, vacuum and hydraulic leak tests--and will be installed and commissioned on plasma during the fall of 2009.

Combined operation of Lower Hybrid (LH) and Ion Cyclotron Resonance Frequency (ICRF) waves can result in a degradation of the LH wave coupling, as observed both in the Tore Supra and JET tokamaks. The reflection coefficient on the part of the LH launcher magnetically connected to the powered ICRF antenna increases, suggesting a local decrease in the electron density in the connecting flux tubes. This has been confirmed by Langmuir probe measurements on the LH launchers in the latest Tore Supra experiments. Moreover, recent experiments in JET indicate that the LH coupling degradation depends on the ICRF power and its launched k//‐spectrum. The 2D density distribution around the Tore Supra ICRF antennas has been modelled with the CELLS‐code, balancing parallel losses with diffusive transport and sheath induced E×B convection, obtained from RF field mapping using the ICANT‐code. The calculations are in qualitative agreement with the experimental observations, i.e. density depletion is obtained, localised mainly in the antenna shadow, and dependent on ICRF power and antenna spectrum.

In recent LHCD experiments in JET, a large effort has been placed on improving the coupling of Lower Hybrid waves in Optimised Shear plasmas, i.e. in conditions with internal transport barriers (ITB) or H-modes. Good coupling conditions have been obtained by using gas injection of CD4 near the LHCD launcher. This has resulted in a reflection coefficient as low as 5% during the ITB phase, at a plasma-launcher distance of 6 cm. Results from the coupling experiments have been compared with the SWAN coupling code, which has recently been extended to take into account the poloidal cut of the launcher mouth. The launcher mouth is composed of twelve rows of waveguides, all with different electrical lengths. By introducing the scattering matrices for all rows and calculating the resulting power splitting in the multijunctions, a more realistic model for the coupling has been obtained.

When the magnetic shear vanishes over a wide spatial region close to the q=2 surface, a strong MHD activity ascribed to a global tearing mode m/n=2/1 is observed, corresponding to a 15% reduction of the current drive efficiency, and a significant flattening of the HXR profile localized in the vicinity of the island. Calculations of the HXR bremsstrahlung and the LH current drive efficiency are reported based on Fokker-Planck calculations to assess the role played by the fastest electrons of the tail, and identify the fraction which is lost by the MHD perturbation.

To test on the Frascati Tokamak Upgrade (FTU) the concept of Passive Active Multijunction (PAM) proposed for Lower Hybrid Current Drive (LHCD) on ITER, studies and design have been made in collaboration between ENEA and CEA. The main properties of this launcher have been analyzed. A description of the antenna and the time schedule toward the experiment is given.

In order to increase the reliability of the launchers for LHCD on Tore Supra, to drive the main part of the plasma current for long pulses (1000 s), new antennae have been studied. Their front tip can be of 2 types: the first one using multijunctions, the second one using active-passive waveguide array to test this new concept for ITER. After a brief description of their design, results of the main studies and tests in order to realize them are given.

The ‘Quasi‐Optical Grill’ (QOG) has been proposed to increase the robustness and the simplicity of a Lower‐Hybrid Waves antenna for reactor application [1]. To compare the performance of a QOG antenna with that of conventional scheme, an experiment was envisaged in TORE‐SUPRA in cooperation with the ENEA. Encouraging modelling results [2] lead to conduct a pre‐design study [3]. The main results of this study are presented in this paper. In particular, an analysis of the practical system has shown a limitation of the injected power due to either the appearance of large electric fields in the resonant structure, or to an increased reflexion linked with departures from ideal conditions. This analysis is based on the results of the diffraction code [2] developed by the ENEA complemented by a simple ‘Fabry‐Perot’ model. A further optimization is thus needed and is being undertaken to assess the future of the concept.