Progress in the 10-MW 140-GHz ECH System for the Stellarator W7-X

• Published in: IEEE transactions on plasma science Vol. 36; no. 2; pp. 341 - 355
• Main Authors: Thumm, M., Brand, P., Braune, H., Dammertz, G., Erckmann, V., Gantenbein, G., Illy, S., Kasparek, W., Laqua, H.P., Lechte, C., Leonhardt, W., Michel, G., Neffe, G., Piosczyk, B., Schmid, M., Weissgerber, M.
• Format: Journal Article Conference Proceeding
• Language: English
• Published: New York, NY IEEE 01.04.2008; Institute of Electrical and Electronics Engineers; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Beams (radiation); Current drive; helicity injection; Cyclotrons; Electron cyclotron heating (ECH); Electrons; Exact sciences and technology; Gyrotrons; Heating; high-power continuous-wave (CW) gyrotron; Inductors; Launches; Magnetic confinement and equilibrium; Nuclear physics; Nuclear reactors; Particle accelerators; Physics; Physics of gases, plasmas and electric discharges; Physics of plasmas and electric discharges; Plasma; Plasma heating by microwaves; ecr, lh, collisional heating; Plasma production and heating; Plasmas; Power plants; quasi-optical transmission; Radio frequencies; Radio frequency; stellarator; Stellarators; Stellarators, torsatrons, heliacs, bumpy tori, and other toroidal confinement devices; Structural beams; Subgroups; Testing; Tokamaks; Cadarache France; Greifswald Germany; quasi-optical transmission; high-power continuous-wave (CW) gyrotron; Electron cyclotron heating (ECH); stellarator; Polarization; ITER tokamak; Diamonds; Microwave amplifiers; Microwave generation; Microwave generator; Transmission lines; Cadarache; Magnetic confinement; Microwave devices; Confined plasma; ECR heating; Microwave resonator; Plasma heating; Electron cyclotron-resonance; Current drive; Plasma confinement; Microwave technology; High power; Gyrotrons; Waveguides; Microwave oscillators; Microwave emission; Wendelstein-7 stellarator
• ISSN: 0093-3813; 1939-9375
• DOI: 10.1109/TPS.2008.917950

During the last years, electron cyclotron heating (ECH) was proven to be one of the most attractive heating schemes for stellarators because it provides net-current-free plasma startup and heating. Both the stellarator Wendelstein 7-X (W7-X), which is under construction at the Max-Planck-Institut fu umlr Plasmaphysik, Greifswald, Germany, and the International Thermonuclear Experimental Reactor (ITER) tokamak, which will be built in Cadarache, France, will be equipped with a strong ECH and current-drive system. Both systems are comparable in frequency and have continuous-wave capability (140 GHz, 10 MW for W7-X and 170 GHz, 24 MW for ITER). The commissioning of the ECH plant for W7-X is well underway; the status of the project and the first integrated full-power test results from two modules are reported and may provide valuable input for the ITER plant. The ten gyrotrons at W7-X will be arranged in two subgroups 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-waveguide (MBWG) transmission line from the gyrotrons to the torus. The combination of five 1 MW gyrotron beams to one beam line with a power of 5 MW reduces the complexity of the system considerably. The single- and MBWG mirrors and the polarizers have been manufactured. Cold tests of a full-size uncooled prototype line delivered an efficiency exceeding 90%. The microwave power will be launched to the plasma through ten chemical-vapor-deposited-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 angles, will be adjusted individually to provide optimum conditions for different heating and current-drive scenarios.