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The TORE SUPRA lower hybrid current drive experiments (8 MWi3.7 GHz) use large phased waveguide arrays, four rows of 32 active waveguides and two passive waveguides for each of the two grills, to couple the waves to the plasma. These launchers are based on the 'multijunction' principle which allows them to be quite compact and is therefore attractive for the design of efficient multi-megawatt antennas in NETIITER. Extensive coupling measurements have been performed in order to study the radiofrequency (RF) characteristics of the plasma loaded antennas. Measurements of the plasma scattering coefficients of the antennas show good agreement with those obtained from the linear coupling theory (SWAN code). Global reflection coefficients of a few per cent have been measured in a large range of edge plasma densities (0.3 X 10" m-3 I neg I 1.4 X 10l8 m-3) or antenna positions (0.02-0.05 m from the plasma edge) and up to a maximum injected RF power density of 45 MWlm'. When the plasma is pushed against the inner wall of the chamber, the reflection coefficient is found to remain low up to distances of the order of 0.10 m. The coupling measurements allow us to deduce the 'experimental' power spectra radiated by the antennas when all their modules are fed simultaneously with variable phases. Thus, the multijunction launcher is assessed as a viable antenna for high power transmission with good coupling characteristics and spectrum control.

Conduction and low-frequency noise are analyzed in hydrogenated amorphous thin film transistors with small channel length. From current–voltage characteristics a set of conduction parameters is extracted pointing out parasitic resistances in series with the active channel. The low-frequency noise behavior is studied by means of the small equivalent circuit of the device. Intrinsic channel noise is separated from access resistance noise. Channel noise variations versus device biases agree with Hooge’s theory (carrier mobility fluctuations) but the noise levels are greater than in crystalline metal-oxide-semiconductor transistors. For high drain current 1/f noise in access series resistances prevails and becomes the main noise source. So, the results show the important part taken by these resistances in conduction and noise. Some comments for the design of thin film transistors are given.