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The ICRH antenna for the stellarator Wendelstein 7-X (W7-X) foreseen for heating, fast particle production, plasma start-up and wall conditioning in W7-X, is designed to handle powers up to 1.5MW in pulses lasting a maximum of 10 seconds for the frequency range 25-38 MHz. Construction and testing of the ICRH antenna took place at the Institute for Energy and Climate Research/Plasmaphysics (IEK-4) and the Central Institute for Engineering, Electronics and Analytics (ZEA-1) of the Research Centre Jülich, in an intense collaboration with the Laboratory for Plasma Physics of the Royal Military Academy in Brussels (LPP-ERM/KMS). Following the successful construction and testing phase, the ICRH antenna has been installed in W7-X and is currently in its commissioning phase. The purpose of this paper is to provide an overview of the design, construction, and installation process of the antenna, as well as the plans for experiments with the ICRH system in the upcoming months. [ABSTRACT FROM AUTHOR]

The possibility of increasing the coupling of ICRH power to plasmas on TEXTOR by gas injection was investigated, for a given voltage applied at the input of an antenna pair. The antenna pair was operated in the conjugated T mode, D(H) heating was used. Modeling of the antenna by transmission line theory shows that load resilience is maintained in a broad range of independent resistance variation for each strap. It is found that the absolute value of the reflection coefficient can be maintained below 0.2 for typical values of resistance measured in plasma shots (2-10 Ω/m) in good matching conditions. During gas injection, the loading resistance showed a clear increase with increasing line average electron density measured close to the plasma edge. Evidence of fast wave eigenmodes was also found, as characteristic resonant behavior of loading resistance and antenna self-inductance, due to poor absorption in the plasma caused by high H minority concentration. [ABSTRACT FROM AUTHOR]

In this paper the edge diagnostic equipment at the TEXTOR tokamak is described and its importance for detailed transport studies in the helical ergodic divertor imposed by the dynamic ergodic divertor (DED) is demonstrated. The helical ergodic divertor topology is controlled by adapting the perturbation field base mode number, the perturbation field strength and the plasma equilibrium. As unique feature the DED perturbation field can be rotated with frequencies of up to 10kHz. The impact of the helical divertor field structure and the fast rotation of the external perturbation field on local transport properties is analyzed here on selected examples from the various edge diagnostics with high time and/or high spatial resolution. [ABSTRACT FROM AUTHOR]

The dynamic ergodic divertor (DED) in TEXTOR is designed to provide a perturbed volume in the plasma edge in order to control heat and particle exhaust. The stochastic boundary layer is generated in the outermost region of the plasma, which can be divided into ergodic and laminar regions. The topology of the magnetic field is substantial for the transport properties and plasma parameters. It is expected that the formation of the proper laminar zone allows decoupling the plasma edge from the core. Due to enhancement of the radial electron heat transport in the ergodic region the electron temperature in the plasma boundary is reduced. Therefore one needs to find the proper ratio of the ergodic and laminar zone, which gives optimal performance of the divertor. The structure of the perturbed volume strongly depends on the safety factor profile and the plasma pressure. At the higher level of ergodization (i.e. at higher plasma current and lower beta poloidal) the laminar zone is dominant, while at the lower level of ergodization the ergodic region is more important. The topology of the perturbed volume is modeled with the ATLAS-code and basing on the results of modeling the experiments are performed and compared to the calculated structures. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]