Successful physical experiment campaigns have been performed on the most advanced modular stellarator Wendelstein 7-X (W7-X) during the second operation phase (OP1.2). The completion phase (CP2) lasting until 2021 is devoted to the installation of cryo-vacuum pumps (CVPs), new diagnostics, and actively cooled in-vessel components instead of the inertially cooled ones used in OP1.2. This update allows us to move forward to achieve the steady state operation during the next operation phase (OP2). Several first wall components which are exposed to heat flux in the range from 250 to 500 kW/m 2 are covered by graphite tiles facing the plasma. Due to construction constraints, the backside area of the graphite tiles is not fully covered by the actively cooled CuCrZr heat sinks. This results in the presence of high-temperature graphite rims, which become an additional heat radiation source for the components behind the first wall. This article presents stepwise development of backside protections (BSPs) to mitigate the problem mentioned above. The process is supported by: 1) the study of BSP shielding performances through thermal analysis taking into account plasma radiation and electron-cyclotron resonance heating (ECRH) loads; 2) BSP sizing restricted by electromagnetic forces during main coil/plasma current decay; and 3) mechanical analysis to confirm the structural fixation of BSP. In addition, several analysis iterations for CVP have been repeated to minimize BSP cost by identification of first wall components with minor heat radiation to the CVP and marginal influence on its cooling system capacity.
A. Bortolon 1 , E. Gilson 1 , R. Lunsford 1 , R. Maingi 1 , A. Nagy 1 , C. Chrobak 2 , A. Hyatt 2 , T. Wilks 3 , M. Fenstermacher 4 , T. Rognlien 4 , C. Samuell 4 , M. Umansky 4 , J. Boedo 5 , I. Bykov 5 , D. Rudakov 5 , R. Smirnov 5 , M. Shafer 6 , D. Curreli 7 , J. Drobny 7 , D. Donovan 8 , J. Duran 8 , J. Ren 8 , A. Drenik 9 , R. Dux 9 , A. Herrmann 9 , A. Kallenbach 9 , R. McDermott 9 , R. Neu 9 , V. Rohde 9 , E. Wolfrum 9 and the DIII-D and ASDEX-Upgrade teams
The final design process of the ITER EC upper launcher (UL) was carried out between 2011 and 2018 under a Grant agreement between the European Domestic Agency F4E and a consortium of European associations, namely KIT (D), SPC (CH), DIFFER (NL), IPP (D), CNR (I), and IPF (D). The final design is scheduled for 2019. The final design review (FDR) will be split into several review processes for dedicated sub-components. One of these sub-components is the structural system of the EC launcher. This article presents a brief overview on the final design status of the ITER EC UL structure of spring 2018, including the history of development since 2004. It highlights the most challenging design issues and debates demanding project management steps. The lesson learned in the technical development of the design will be discussed, in view of the design work for future fusion devices.
The superconducting stellarator Wendelstein 7-X has completed the first three experimental phases, the first one with a limiter only and two phases with an inertially cooled carbon divertor configuration. The main mission of the latter two phases (the last one with two scraper elements) was to pave the way for the planned steady-state operation with high-power plasmas and a steady-state divertor. Presently, the device is being completed by installing a high-heat-flux (HHF) divertor and the corresponding water-cooling and ten cryo pumps in the divertor chambers. After this completion phase of W7-X, the device is ready for long-pulse divertor operation with heating power beyond 10 MW.
Diagnostic pressure gauges (DPGs) shall provide measurements of the neutral gas pressure in various locations of the International Thermonuclear Experimental Reactor (ITER) vacuum vessel. This parameter is essential for the basic control of ITER operation as well as for input to physics models of the plasma boundary. The hot cathode (filament) is the component of the DPG sensor that is exposed to most demanding loads. In order to reach the required electron emission from the filament, it has to be heated to high temperatures by a direct current. As a result, thermal stresses appear, and in the presence of a magnetic field, additional mechanical stresses caused by Lorentz forces arises. On the one hand, due to a large number of pulses foreseen in ITER, this load will be cyclic, which may result in filament failure caused by fatigue. On the other hand, the longest pulses in ITER are expected to be in the order of 30 min, and thus, filaments could fail due to creep. In order to verify that the filament of the DPG sensor can withstand fatigue and creep dedicated experiments have been conducted. Results of these tests are discussed in this article.
The super conducing stellarator Wendelstein 7-X (Bosch a al., 2017) started its first operational phase in October 2015 at the Max-Planck-Institute for Plasma Physics in Greifswald with the goal to verify that a stellarator magnetic confinement concept is a viable option for a fusion power plant, i.e. showing confinement comparable to tokamaks and running in steady state operation. Between 2015 and 2018 the first three experimental campaigns (operational phases) OP1.1, OP1.2a and OP1.2b of the W7-X stellarator have been successfully completed. Roughly 13 Months of operational time have been accumulated and have already shown the impressive capability and reliability of W7-X in achieving the physical and technical goals as set by the project. The working group Device Operation (DO) has implemented an organizational structure and workflow to ensure safe and reliable operation of the W7-X device. DO is responsible for planning and executing the commissioning and operation of the W7-X device. The operations plan is based on the physics planning which is a selection of individual physics proposals keeping in mind the technical limitations of W7-X. The operations plan is iterated between the lead physicists and device operation team (DOT). The "technischer Leiter vom Dienst" (TLvD or Engineer in Charge) plays a central role within the DOT in coordinating and supervising the technical operation of W7-X. To ensure safe and reliable operation of W7-X several procedures have been implemented and improved. This involves commissioning templates, checklists, procedures for e.g. plasma heating energy release, operation malfunction cards, logbooks, coordination meetings, duty-on-call and shift-planning. This paper will summarize the organizational aspects of W7-X technical operation as performed in the first three phases. It will also provide an outlook on the upcoming OP2 (actively cooled divertor) with the requirements for technical operation regarding commissioning and operation towards steady state plasma operation.
The Wendelstein 7-X experimental device has completed the third plasma operation campaign in November 2018. The running, two-year shut down phase is being used to install new diagnostics, new in-vessel-components (steady-state divertor and cryopumps), and their auxiliary supply systems. In particular, the installation of the ten cryopumps requires a substantial upgradation of the cryosystems. The work package comprises the installation of a 55-m long new transfer line from the cryoplant to the new valve box and the installation of ten transfer lines with lengths up to 15 m from the valve box to the ten cryovacuum pumps (CVPs) in the plasma vessel. The tasks have been split into two main contracts in industry. Both contracts are presently running, the production of the transfer lines and the valve box per September 2019 is in an advanced status. The aim is to complete the production in early 2020 and the installation work by the end of 2020. A second task regarding the cryosystems is the upgrade with respect to the foreseen long pulse operation of W7-X. Therefore, new storage tanks for helium gas and for liquid nitrogen are necessary. The helium gas storage has been installed at the end of 2018 whereas the liquid nitrogen storage tank is presently under design. This article gives an overview about individual upgrade tasks of the W7-X cryosystems, highlights the special design requirements, and reports the status of the contracts.
Heat load calculations have indicated the possible overloading of the ends of the water-cooled divertor facing the pumping gap beyond their technological limit. The intention of the scraper is the interception of some of the plasma fluxes both upstream and downstream before they reach the divertor surface. The scraper is divided into six modules of four plasma facing components (PFCs); each module has four PFCs hydraulically connected in series by two water boxes (inlet and outlet). A full-scale prototype of one module has been manufactured. Development activities have been carried out to connect the water boxes to the cooling pipes of the PFCs by tungsten inert gas internal orbital welding. This prototype was successfully tested in the GLADIS facility with 17 MW/m(2) for 500 cycles. The results of these activities have confirmed the possible technological basis for a fabrication of the water-cooled scraper.
An insertable probe head called high resolution probe (HRP) has been developed at Consorzio reversed field experiment in the framework of the EUROfusion S1 work program and in collaboration with IPP Greifswald, to study the electrostatic and electromagnetic features of turbulence in the edge region of Wendelstein 7-X using the multipurpose manipulator. This paper reports the design development of the HRP diagnostic head, from the choice of the sensors to the engineering design. The assumptions and evaluations supporting the main design choices, together with the R&D tests carried out to check the most critical parts, are described in detail.
