The polarization of the directed ECRH power has to be matched to the plasma boundary with respect to the magnetic field at the density gradient region close to the last closed flux surface (LCFS). This is achieved by means of grooved mirrors, which provide the required polarization and which are part of the matching optics unit (MOU) of the gyrotrons. The RF radiation from the gyrotrons has to pass typically 16 mirrors in a complex three-dimensional arrangement in order to reach the plasma. The paper discusses the modeling of the ECRH transmission in order to find the required polarizer adjustment for each possible injection angle and plasma wave type (O- or X-mode). This includes the calculation of the polarization state on the plasma boundary, the back-propagation through the transmission line up to the MOU and finally the calculation of the corresponding angles of both polarizers.

The W7-X start-up scheduled for 2015 demands a lot of integrated tests at all auxiliaries as well as the ECRH installation in order to ensure a reliable interaction. Up to 10 gyrotrons have to be controlled as well as 10 different wave guides and two additional remote steering launchers apart from the 10 ordinary front steering launchers. The ECRH remote control system has to be connected to the central W7-X control system in a reliable and easily maintainable way. The main challenges and developed solutions will be discussed.

The construction of the 140 GHz, 1 MW CW gyrotrons for the 10 MW ECRH system of the stellarator W7-X at IPP Greifswald is ongoing. While acceptance testing of the gyrotrons is progressing, reliable output parameters and stable production have been achieved. This report summarizes the actual status and some topical results. Focus is put on the final construction and latest parameters measured at factory-acceptance tests and site-acceptance tests. Parallel to the design optimization a new spectral measurement method has been developed, which allows time-dependent broadband spectral measurements with μs resolution for ms range pulses. Results of measurements done with W7-X gyrotrons are shown.

Electron cyclotron resonance heating (ECRH) is the main heating system for W7-X. A 10-MW ECRH plant with continuous wave (cw) capability is under construction to support the W7-X operation, which aims at demonstrating the steady-state capability of stellarators at reactor-relevant plasma parameters. The ECRH system consists of ten radio-frequency (rf) modules with I MW power each at 140 GHz. The rf beams of the individual gyrotrons are transmitted in common to the W7-X torus via open multibeam mirror lines. The losses of individual components of the transmission system were measured with both low- and high-power methods. Integrated full-power, cw measurements of the long-distance transmission losses are reported and compared to theoretical design estimates.

Abs tract: Electron cyclotron heating (ECH) has proven to be one of the most attractive heating schemes for stellarators, as it provides net current free plasma start up and heating. Both, the stellarator Wendelstein 7-X (W7-X), which is under construction at IPP-Greifswald, Germany, and the ITER tokamak, which will be built at Cadarache, France, will be equipped with a strong EC-heating and current drive system. Both systems are comparable in frequency and have CW (continuous wave) capability (0.14 THz, 10 MW for W7-X and 0.17 THz, 24 MW for ITER). The commissioning of the ECH plant for W7-X is well underway, the status of the project and first integrated full power test results from two modules are reported and may provide valuable input for the ITER plant. The 10 gyrotrons at W7-X will be arranged in two sub-groups symmetrically to a central beam duct in the ECH hall. The RF-wave of each subgroup will be combined and transmitted by a purely optical multibeam wave guide transmission line (copper mirrors) from the gyrotrons to the plasma torus. The combination of the 5 gyrotron beams to two beam lines each with a power of 5 MW reduces the complexity of the system considerably. The single-beam as well as the multi-beam waveguide mirrors and the polarizers have been already manufactured. Cold tests of a full size uncooled prototype line delivered an efficiency exceeding 90%. The mm-wave power will be launched to the plasma through ten synthetic-diamond barrier windows and in-vessel quasi-optical plug-in launchers allowing each 1 MW RF-beam to be steered independently. The polarization as well as the poloidal and toroidal launch angle will be adjusted individually to provide optimum conditions for different heating and current drive scenarios. The first series gyrotrons were tested and yielded a total output power of 0.98 MW, with an efficiency of 31% (without a single-stage depressed collector) in short-pulse operation and of 0.92 MW in pulses of 1800 s (efficiency of almost 45% at a depression voltage of 29 kV). The Gaussian mode output power was 0.90 MW and the power measured in a calorimetric load after a 25-m-long quasi-optical transmission line (seven mirrors) was 0.87 MW.

Electron Cyclotron Resonance Heating (ECRH) is the main heating method for the Wendelstein 7-X stellarator (W7-X) which is presently under construction at IPP Greifswald. The mission of W7-X is to demonstrate the inherent steady state capability of stellarators at reactor relevant plasma parameters. A modular 10 MW ECRH-plant at 140 GHz with 1 MW CW-capability power for each module is also under construction to support the scientific objectives. The commissioning of the ECRH-plant is well under way; three gyrotrons are operational. The strict modular design allows to operate each gyrotron separately and independent from all others. The ECRH-plant consists of many devices such as gyrotrons and high voltage power supplies, superconductive magnets, collector sweep coils, gyrotron cooling systems with many water circuits and last but not least the quasi-optical transmission line for microwaves with remote controlled mirrors and further water cooled circuits. All these devices are essential for a CW operation. A steady state ECRH has specific requirements on the stellarator machine itself, on the microwave sources, transmission elements and in particular on the central control system. The quasi steady state operation (up to 30 min) asks for real time microwave power adjustment during the different segments of one stellarator discharge. Therefore, the ECRH-plant must operate with a maximum reliability and availability. A capable central control system is an important condition to achieve this goal. The central control system for the 10 MW ECRH-plant at W7-X comprises three main parts. In detail these are the voltage and current regulation of each gyrotron, the interlock system to prevent the gyrotrons from damages and the remote control system based on a hierarchy set of PLCs and computers. The architecture of this central control system is presented.

The status and recent achievements of the electron cyclotron heating system at the stellarator W7-X in Greifswald, Germany are discussed. Three prototype gyrotrons and one from a series of 7 are operable now, one additional is under test. The transmission system is ready up to the stellarator hall; part of it has passed high-power tests (900 kW, 30 min). The test of the multi-beam waveguide is in preparation. At present, optics in front of the stellarator, the antennas, as well as in-vessel components are constructed.

This paper reports the results of the high-power tests of a remote-steering-launcher mock-up at 140 GHz, which were performed at the electron cyclotron resonance heating installation for the future stellarator Wendelstein 7-X (W7-X) at Max-Planck-Institut fur Plasmaphysik, Greifswald. The mock-up test system consists of a 6.62-m-long square corrugated waveguide with a steerable optic at the entrance and various diagnostics at the exit of the waveguide. A straight launcher and a version with two integrated miter bends were investigated.The ohmic loss of the waveguide was measured via the temperature increase of the waveguide wall and was used to calibrate the calculated angular dependence of the total ohmic losses of the waveguide. Short-pulse radiation pattern measurements with thermographic recording show high beam quality and confirm the steering range of -12...12 deg. The version with two miter bends produces similar results but with an increased level of side lobes.Although the tests were performed under atmospheric pressure, no arcing was observed in the straight waveguide. In the version with the miter bends. however, arcing limited the power and pulse length.

The stellarator W7-X, which is currently under construction at IPP Greifswald, Germany, will be equipped with a 10 MW ECRH system working at 140 GHz in CW regime. The microwave power will be generated by 10 gyrotrons delivering I MW each and will be transmitted from the gyrotron hall to the W7-X stellarator ports via a fully optical system.The status of the construction of the transmission lines and the design of the launchers is reported. Low-power tests of a prototype system at IPF Stuttgart are reviewed. Now, the first two gyrotrons are operating at IPP Greifswald, and high-power long-pulse tests have started. Measurements on transmission performance, behaviour of the water-cooled mirrors under thermal and microwave loads as well as alignment issues, characteristics of directional couplers, calorimetric loads, and other diagnostics are discussed. (c) 2005 Elsevier B.V. All rights reserved.

This paper reports the results of the high-power test of a remote steering launcher mock-up at 140 GHz, which were performed at the ECRH installation for the future stellarator W7-X at IPP Greifswald. The mock-up test system consists of a 6.62 m long corrugated square waveguide with a steerable optic at the entrance and various diagnostics at the exit of the waveguide. A straight and a dog-leg version of the launcher were investigated.

The ECRH system of the stellarator W7-X, which is currently under construction, plays a dominant role for continuous plasma heating and current drive during the operation of the machine. The ECRH system will provide a power of 10 MW in continuous wave at 140 GHz. The RF power is generated by 10 gyrotrons which are placed 25-40 m away from the W7-X torus in a special building, the transmission of the power is performed by an optical system which includes in total about 160 reflecting mirrors.

B. Plaum*, V. Erckmann, G. Gantenbein*, W. Kasparek*, K. Schworer*, H. Braune, M. Grunert*, F. Hollmann, L. Jonitz, H.P. Laqua, G. Michel, F. Noke, F. Purps, A. Bruschi, S. Cirant, F. Gandini, A.G.A. Verhoeven, ECRH groups at IPP Greifswald , FZK Karlsruhe and IPF Stuttgart*, Max-Planck-Institut fur Plasmaphysik (IPP), EURATOM-Association, D-17491 Greifswald, Germany Institut fur Plasmaforschung, Universitat Stuttgart, Pfaffenwaldring 31, D-70569 Stuttgart, Germany Istituto di Fisica del Plasma, EURATOM-ENEA-CNR Ass., via R Cozzi 53, 20125 Milano, Italy FOM Institute for Plasma Physics Rijnhuizen, Ass. EURATOM-FOM, Nieuwegein, The Netherlands Forschungszentrum Karlsruhe, Association EURATOM-FZK, IHM, D-76021 Karlsruhe, Germany

For the fusion plasma experiment Wendelstein 7-X, which is built up at the Max-Planck-Institut fur Plasmaphysik (IPP) at Greifswald, a CW millimetre wave heating system is under construction. Initial high-power tests using a prototype gyrotron are reported and results on transmission performance as well as the behaviour of water-cooled mirrors and diagnostic components are discussed.