Demonstrating improved confinement of energetic ions is one of the key goals of the Wendelstein 7-X (W7-X) stellarator. In the past campaigns, measuring confined fast ions has proven to be challenging. Future deuterium campaigns would open up the option of using fusion-produced neutrons to indirectly observe confined fast ions. There are two neutron populations: 2.45 MeV neutrons from thermonuclear and beam-target fusion, and 14.1 MeV neutrons from DT reactions between tritium fusion products and bulk deuterium. The 14.1 MeV neutron signal can be measured using a scintillating fiber neutron detector, whereas the overall neutron rate is monitored by common radiation safety detectors, for instance fission chambers. The fusion rates are dependent on the slowing-down distribution of the deuterium and tritium ions, which in turn depend on the magnetic configuration via fast ion orbits. In this work, we investigate the effect of magnetic configuration on neutron production rates in W7-X. The neutral beam injection, beam and triton slowing-down distributions, and the fusion reactivity are simulated with the ASCOT suite of codes. The results indicate that the magnetic configuration has only a small effect on the production of 2.45 MeV neutrons from DD fusion and, particularly, on the 14.1 MeV neutron production rates. Despite triton losses of up to 50 %, the amount of 14.1 MeV neutrons produced might be sufficient for a time-resolved detection using a scintillating fiber detector, although only in high-performance discharges.

After completing the main construction phase of Wendelstein 7-X (W7-X) and successfully commissioning the device, first plasma operation started at the end of 2015. Integral commissioning of plasma start-up and operation using electron cyclotron resonance heating (ECRH) and an extensive set of plasma diagnostics have been completed, allowing initial physics studies during the first operational campaign. Both in helium and hydrogen, plasma breakdown was easily achieved. Gaining experience with plasma vessel conditioning, discharge lengths could be extended gradually. Eventually, discharges lasted up to 6 s, reaching an injected energy of 4 MJ, which is twice the limit originally agreed for the limiter configuration employed during the first operational campaign. At power levels of 4 MW central electron densities reached 3  ×  1019 m−3, central electron temperatures reached values of 7 keV and ion temperatures reached just above 2 keV. Important physics studies during this first operational phase include a first assessment of power balance and energy confinement, ECRH power deposition experiments, 2nd harmonic O-mode ECRH using multi-pass absorption, and current drive experiments using electron cyclotron current drive. As in many plasma discharges the electron temperature exceeds the ion temperature significantly, these plasmas are governed by core electron root confinement showing a strong positive electric field in the plasma centre.

The next step in the Wendelstein stellarator line is the large superconducting device Wendelstein 7-X, currently under construction in Greifswald, Germany. Steady-state operation is an intrinsic feature of stellarators, and one key element of the Wendelstein 7-X mission is to demonstrate steady-state operation under plasma conditions relevant for a fusion power plant. Steady-state operation of a fusion device, on the one hand, requires the implementation of special technologies, giving rise to technical challenges during the design, fabrication and assembly of such a device. On the other hand, also the physics development of steady-state operation at high plasma performance poses a challenge and careful preparation. The electron cyclotron resonance heating system, diagnostics, experiment control and data acquisition are prepared for plasma operation lasting 30 min. This requires many new technological approaches for plasma heating and diagnostics as well as new concepts for experiment control and data acquisition.

For stellarators, which need no or only small amounts of current drive, electron-cyclotron-resonance heating (ECRH) is a promising heating method even for the envisaged application in a fusion power plant. Wendelstein 7-X (W7-X) is equipped with a steady-state capable ECRH system, operating at 140 GHz, which corresponds to the 2nd cyclotron harmonic of the electrons at a magnetic field of 2.5 T. Ten gyrotrons are operational and already delivered 7 MW to W7-X plasmas. Combined with pellet injection, the highest triple product (0.68×10 20 keV m −3 s), observed up to now in stellarators,

For the fabrication of carbon fibre reinforced composites used in aerospace industry, microwave curing technologies are more effective than traditional thermal curing technologies. However, the manufacturer's recommended cure cycles used in traditional autoclave curing are directly adopted into current microwave curing technologies without thorough validation. Here, a new cyclic heating and cooling methodology for microwave curing process control of composite is proposed by analyzing mechanisms of heat conduction, stress generation and curing kinetics. The results of the experiment carried out show significant reductions in residual strain, warpage, total curing time and energy consumption, compared with both traditional thermal curing and current microwave curing technologies. The mechanical properties of samples cured by the new process are compared with the autoclave cured ones.

Abstract-Experimental results using a step-frequency tunable D-band gyrotron are reported. The short-pulse (~3 ms) gyrotron is equipped with an elliptically brazed CVD diamond Brewster angle output window. It is designed for the operation in the frequency range from 111.6 GHz up to 165,7 GHz. Operating parameters for 10 different frequencies corresponding to an equal number of different cavity operating modes has been measured. A minimum output power of 830 kW and a peak output power of 1.3 MW have been realized. For all frequencies the parameters of the RF beam generated by the internal quasioptical converter, such as fundamental Gaussian contents and beam waist, are sufficiently good to allow an efficient coupling of the RF power out of the window. This is the first time a diamond Brewster angle window has been used in a high power gyrotron (~ 1 MW). Such a system offers the path to a simple and compact window solution for high power broadband applications using gyrotrons.

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Abstract-Europe is devoting significant joint efforts to develop and to manufacture MW-level gyrotrons for electron cyclotron heating and current drive of future plasma experiments. The two most important ones are the stellarator Wendelstein W7-X at Greifswald and the tokamak ITER at Cadarache. While the series production of the 140 GHz, 1 MW, CW gyrotrons for the 10 MW ECRH system of stellarator W7-X is proceeding, the European GYrotron Consortium (EGYC) is presently developing the EU-1 MW, 170 GHz, CW gyrotron for ITER. The initial design had already been initiated in 2007, as a risk mitigation measure during the development of the advanced ITER EU-2 MW coaxial-cavity gyrotron. The target of the ITER EU-1 MW conventional-cavity design is to benefit as much as possible from the experiences made during the development and series production of the W7-X gyrotron and of the experiences gained from the earlier EU-2 MW coaxial-cavity gyrotron design. Hence, the similarity of the construction will be made visible in the present article. During 2012, the scientific design of the ITER EU-1 MW gyrotron components has been finalized. In collaboration with the industrial partner Thales Electron Devices (TED), Vélizy, France, the industrial design of the technological parts of the gyrotron is being completed. A short-pulse prototype is under development to support the design of the CW prototype tube. The technological path towards the EU ITER-1MW gyrotron and the final design will be presented. . Both experiments are relying on electron cyclotron resonance heating (ECRH) as the main heating method for steady state operation, while in addition it is planned for ITER to apply electron cyclotron resonance technique for current drive (ECCD). ECRH & ECCD offer the compatibility to the various physics demands, such as controlled plasma start-up, steady state plasma control, and performance optimization by plasma profile shaping. It offers excellent coupling to the plasma, remote launching and very good localization of the absorbed power. Index Terms-PlasmaThe construction of the stellarator W7-X is almost completed and the device is approaching the commissioning phase [3]. W7-X operation will be supported by a 10 MW continuous wave ECRH system working at 140 GHz in 2 nd harmonic X-or O-mode. To date, the ECRH-system of W7-X is in stand-by with already 5 out of 10 gyrotrons operational. The series production of the W7-X 1 MW, CW gyrotrons [4,5] for the 10 MW ECRH system is proceeding.The European gyrotron development for ITER started with an advanced 170 GHz, 2 MW coaxial-cavity design. RF tests with an industrial CW prototype were done at the European test facility at EPFL-CRPP Lausanne in December 2011 [6]. The prototype did show an excellent voltage stand-off. It was directly possible to excite the nominal operating TE 34,19 -mode. The output RF-beam intensity was in good agreement with the expected one. Without further optimization, the RF output power reached the level of almost 2.1 MW in short-pulse (1 ms) operation with sin...