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 influence of axial and non-axial occlusal loads on the bone remodelling phenomena around oral implants in an animal experiment is simulated in a finite element analysis. The axial and non-axial loading conditions were introduced by inserting a bilaterally supported fixed partial prosthesis and a cantilever fixed partial prosthesis on two IMZ implants in the mandible of beagle dogs. Earlier quantitative and qualitative histological analyses revealed a statistically significant different remodelling response between both loading conditions. Two-dimensional and three-dimensional models are built to analyse and compare von Mises equivalent stress, maximum principal stress, maximum principal strain and strain energy density distributions, first around a free-standing implant and subsequently around the implants of the two prosthesis designs under the respective resultant in vivo loads. Strong correlations between the calculated stress distributions in the surrounding bone tissue and the remodelling phenomena in the comparative animal model are observed. It is concluded that the highest bone remodelling events coincide with the regions of highest equivalent stress and that the major remodelling differences between axial and non-axial loading are largely determined by the horizontal stress component of the engendered stresses.

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.

The paper reports on finite element (FE) method analyses aiming at the determination of the static load bearing capacity of critical components in the support structure of superconducting coils of Wendelstein 7-X (W7-X). These components are made of austenitic stainless steel that at 4 K is known to exhibit instable plastic flow -the so called serration effect, i.e. a scattering of the stress under increasing strain. This material behavior may significantly reduce the load bearing capacity of the components. The developed modeling approach uses a special procedure to simulate the serration effect in a conservative way. The expected reduction of the material properties due to the welding process is also taken into account. It is demonstrated that the models are capable to determine the limit loads for the critical components in a flexible and efficient way.Dear Sirs, Herewith, I submit our paper entitled " Limit analysis of W7-X critical magnet system components with consideration of material serration effect ". Kindly please consider its publication in the special issue of the Fusion Engineering and Design journal. The extended abstract of the paper has been positively evaluated by the organizer of SOFT 2010 conference and we were invited to submit full manuscript.With best regards, Łukasz Ciupiński The paper reports on finite element (FE) method analyses aiming at the determination of the static load bearing capacity of critical components in the support structure of superconducting coils of Wendelstein 7-X (W7-X). These components are made of austenitic stainless steel that at 4 K is known to exhibit instable plastic flow -the so-called serration effect, i.e. a scattering of the stress under increasing strain. This material behavior may significantly reduce the load bearing capacity of the components. The developed modeling approach uses a special procedure to simulate the serration effect in a conservative way. The expected reduction of the material properties due to the welding process is also taken into account. It is demonstrated that the models are capable to determine the limit loads for the critical components in a flexible and efficient way.

No abstract