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A vacuum vessel which is the first confinement barrier of Tokamak fusion reactor should have numerous in-vessel components. Since those components are to be exposed to the plasma under ultrahigh vacuum condition and should be maintained during Tokamak operation, a threaded connection of vacuum vessel and in-vessel components is necessary. The threaded connection of stainless steel with the components causes difficulties during assembly or disassembly due to the large friction coefficient of stainless steel. To resolve this issue, anti-seize coating that does not affect the mechanical property, thermal stability, and outgassing rate of the threaded insert needs to be developed. In this study, adhesion, porosity, outgassing, and friction wear tests for a cyanide copper electrodeposited surface on 316 L austenitic stainless steel test coupons were performed to validate the high level of confidence in the performance of a cyanide copper electrodeposited threaded insert. The validation tests results showed that cyanide copper electrodeposition for anti-seizing could be applied to the 316 L stainless steel threaded insert in the vacuum vessel and in-vessel components of the Tokamak fusion reactor. [ABSTRACT FROM AUTHOR]

The results of a study of the chemical composition, vacuum and thermal properties of boron carbide ceramics, which is planned to be used in ITER diagnostic ports, are presented. The measured boron carbide content in sintered and hot pressed ceramics is 99,0÷99,7%, they do not contain unauthorized impurities, which in accordance to ITER requirements. The outgassing rate of sintered and hot pressed boron carbide produced by Virial Ltd meets the requirements of the ITER Vacuum Handbook. Sintered ceramic is cheaper than hot pressed, and it is produced in large volumes, which it would be preferable for use in ITER ports, but with its massive use may create a significant gas load on the vacuum system that requires accurate analysis and outgassing tests on all candidated ceramics. [ABSTRACT FROM AUTHOR]

Remote maintenance in fusion machines such as JET (Joint European Torus) and ITER (International Thermonuclear Experimental Reactor) relies on sliding interfaces such as bolted joints. Experience in JET, where removal torques much higher than installation values with uncoated bolts is commonplace, led to the installation of experimental bolted assemblies in 2015: the first of its kind in JET. These assemblies included some 660B stainless steel ITER Blanket-specific bolts with a solid sputtered coating of MoS 2 as part of an ITER-funded project known as CHEF (Coating and Humidity Experiments on Fasteners). CHEF also includes two ex-vessel activities. The first is a characterisation of the coating fundamental properties including outgassing, friction, wear and sensitivity to humidity: on flat sample discs. The second is the measurement of the coating performance on bolted assemblies subjected to a sequence of tests: initial tightening cycles, thermal vacuum exposure, environmental exposure (high humidity and high temperature), repeated thermal vacuum exposure, and final tightening cycles. This sequence approximates to a possible operation cycle of ITER bolted joints which receive an accidental humidity exposure during operation. [ABSTRACT FROM AUTHOR]

Highlights • Antenna performance is described with coefficients of transmission and dissipation. • Effect of RF conditioning on the antenna performance is quantitatively analyzed. • Outgassing rate per dissipated power decreases by the RF conditioning. • A new figure-of-merit is defined to evaluate degree of the RF conditioning. • Antenna performance is almost doubled in well-conditioned stage. Abstract RF conditioning is conducted to improve coupling and current drive performance of the comb-line antenna which is to excite fast wave in lower hybrid resonance frequency range in Versatile Experiment Spherical Torus (VEST). It has been observed that considerable outgassing, power dissipation and high reflection take place while diminishing transmitted power with poor reproducibility without the RF conditioning process which cleanses antenna surface by RF surface heating. Outgassing source during the RF conditioning is identified mainly as water vapor. A new dimensionless figure-of-merit to evaluate degree of the RF conditioning is defined with dissipated power and outgassing rate by analyzing experimentally observed RF conditioning data. Optimum performance of the antenna with low figure-of-merit (5 × 10−9) is achieved after conditioning for 3 days a week (∼40 shots) at less than 10 kW of input power. Coefficients of transmission, reflection, and dissipation reach to about 80%, 2%, and 18%, respectively indicating almost doubled antenna performance. Introduced new figure-of-merit provides a quantitative basis for antenna conditioning in order to improve antenna performance. [ABSTRACT FROM AUTHOR]

• R&D work on HHLT facility for ITER large vacuum components is successful in China. • A satisfying result (lower than 2.69×10−10 Pa*m3/s) in the 1st HHLT on the shield block full-scale prototype. • H 2 O and H 2 outgassing is the major factor impacting the performance of HHLT facility at different temperatures. • The facilities' performance was improved by at least one order of magnitude after adopting outgassing-removal measures. • HHLT results of 50 shield blocks with the improved facilities are better and stable. China Domestic Agency (DA) will provide ITER with 220 shield blocks (SB) which are important, large, and actively water-cooled components in ITER vacuum vessel, their leakage rate shall not exceed 2.69 × 10 − 10 Pa · m 3 / s in hot helium leak tests (HHLT) at 250±20 °C. The HHLT work started with developing a HHLT facility and manufacturing a SB full-scale prototype (FSP). The result showed the FSP could satisfy ITER's requirement at 235 °C. H 2 outgassing from stainless steel surfaces is the main factor that impacts both the background leakage rate and sensitivity of the testing system in hot testing cases. Hydrogen-removal measures were taken to improve the facility performance, and a new facility was built. A better facility performance came out at 250 °C rather than 235 °C, the background leakage rate decreased by one order of magnitude while the system sensitivity increased by two orders of magnitude. The background is at 10−10 Pa.m3/s and 10−9 Pa.m3/s level at room temperature (RT) and 250 °C, respectively, while the system sensitivity is at 10−12 Pa.m3/s and 10−11 Pa.m3/s level at the two temperatures. With the two facilities, series HHLTs have been carried out on 50 SBs covering two types, with all results complying with ITER requirements. [ABSTRACT FROM AUTHOR]

In order to allow an efficient and economically attractive operation scenario of a pulsed fusion power plant, the length of the plasma pulses (burn phase) shall be maximized and the time in between the pulses (dwell phase) must be reduced to an absolute minimum. The time needed for evacuation of the vacuum vessel in the dwell phase to provide the necessary start vacuum for the next plasma discharge is mainly given by outgassing of helium and hydrogen isotopes that were adsorbed on or dissolved in the plasma facing materials in the previous plasma discharges. The paper shows that a reliable calculation of the pump-down time appears critical in view of the insufficient knowledge of the needed material properties whereas an empirical model of the outgassing term in the pump-down equation works better. This is validated by a comparison with existing pump-down data from ASDEX Upgrade with tungsten wall. Results of experiments on the mobile part of outgassing of tungsten surfaces are reported, which are evaluated to extract the decay factor in the empirical model of the outgassing rate. In conclusion, a window of expected minimum pump-down times is derived, which shows that the current DEMO target of approximately 20 min may be very difficult to meet. In view of the paucity of much of the data needed for a realistic assessment, a multidisciplinary R&D programme should be pursued. [ABSTRACT FROM AUTHOR]

Abstract: Preliminary results of a theoretical model which simulates the behaviour of hydrogen oxidation by a MnO2/Ag2O (10wt.%) metal oxide mixture at both ambient temperature and pressure are presented. Based on experimental results obtained at a range of intermediate and low initial hydrogen concentrations, this model allows one to perform calculations which aims at simulating the behaviour of this specific metal oxide mixture under real tritium degassing conditions. [Copyright &y& Elsevier]

Abstract: In most of applications involving both vacuum and high temperatures, outgassing of structural materials is a critical issue. For instance, this is the case of fusion test devices, where the gas released from the vessel walls contaminates the plasma. Four upper ports in the ITER vacuum vessel are reserved for Electron Cyclotron Heating and Current Drive (EC H&CD) Upper Launchers (UL), which have to provide plasma MHD stabilization by localized deposition of high power microwave beams. The structural material foreseen for the UL is the 316L(N)-IG stainless steel. It has to withstand temperatures in the range 120–150°C during normal operation and 240°C during the baking process. One of the preferred manufacturing routes for the UL is the Hot Isostatic Pressing (HIP) which is a very sophisticated method to manufacture structural components of complex geometry with good mechanical properties. The materials for use in the ITER vacuum systems have to comply with the outgassing limits given in the ITER vacuum handbook, but no outgassing data for HIPed stainless steel are available in literature, thus they must be obtained by experimental measurements. In this paper, measurements of partial outgassing rates are shown and discussed for stainless steel prototype samples AISI 316LN (on which the 316L(N)-IG is based) and AISI 317LMN, obtained by powder and solid HIPing method. A variant of the gas throughput method in vacuum systems was used for the measurements which were carried out over periods larger than 8h and at different temperatures. [Copyright &y& Elsevier]

Abstract: Korea Superconducting Tokamak Advanced Research (KSTAR) is upgraded for its KSTAR 3rd campaign for new target mission to produce the D-shaped plasma with a target plasma current of 500kA and/or pulse length of 5s. New Plasma Facing Components (PFCs) are installed which leads to the increase of the surface area of the vessel by a factor of about 5. The vacuum conditioning such as the vessel baking has been performed in order to remove various kinds of impurities including H2O, carbon and oxygen for the plasma. The total outgassing rate in the KSTAR 1st campaign was measured as 1.5×10−4 mbarℓs−1 which is increased by a factor of 3 (6.49×10−4 mbarℓs−1) in the KSTAR 3rd campaign. Nevertheless, the outgassing rates per unit area have been decreased from 9.31×10−5 mbarℓm−2 s−1 to 1.22×10−5 mbarℓm−2 s−1 due to the upgrade of baking system and series of baking operation. [Copyright &y& Elsevier]

Abstract: On ITER the electrical connections to most in-vessel diagnostics, in particular the magnetic diagnostics, will require cables to be routed through the main vacuum vessel. The total in-vessel cabling requirement is predicted to be of order 80km. Due to the large quantity of cabling, the JET experience shows that the cabling has the potential to cause issues for the ITER vacuum and hence operability. Findings are presented from extensive tests to assess experimentally the outgassing of different types of mineral insulated cable, in damaged, undamaged and deliberately perforated conditions. Experience with using metal braided fibre insulated cable which has been used in-vessel on JET is given. Key points are concluded for the necessary manufacturing and installation techniques required for in-vessel cable to be used successfully on ITER. [Copyright &y& Elsevier]

Abstract: A mechanically attached divertor module with improved performance has been developed and partially installed in the large helical device (LHD). The advantage of the new design is to eliminate any metal bolts on the armor tile surface which leads to high Z impurity emission. The new module consists of a couple of armor tiles made of iso-graphite and a thin graphite sheet, which are tightened by two stainless steel (SS) or TZM bolts horizontally sandwiching a SS cooling pipe. The heat flows directly from the tile surface to the cooling pipe. The previous design used a copper heat sink has been used. Steady heat flux tests up to 1.2MW/m2 have been carried out for the new module without any trouble using a electron gun ACT while the allowable heat flux of the previous module was limited below 0.3MW/m2 due to deformation of the copper heat sink. The outgassing from the new module during heat flux tests up to 0.5MW/m2 is decreased to about one-third. Thermal fatigue test up to 115 cycles under a steady heat flux of 1MW/m2 for the new module has been performed without any troubles. Comparisons between the previous and new modules for the structure, thermal performance, and outgassing are made. [Copyright &y& Elsevier]

Non Evaporable Getter (NEG) technology has been studied as an alternative pumping solution in facilities for fusion research since the 80 s. The recent development of a new generation of Zr-V-Ti-Al (ZAO®) getter alloys with improved features makes NEG technology an attractive option in several fusion applications, including in particular, Neutral Beam Injectors (NBI). The main advantages of ZAO® NEG pumps are related to the high pumping speed for H 2 , the high capacity that results into a very promising availability, the ease of integration and the low power consumption. From the vacuum point of view, research fusion facilities are in the high vacuum pressure range (e.g. 1∙10−6 ÷1∙10-5 Pa background pressure) and may present leaks and significant outgassing from internal components. Specific activities have been devoted to test the NEG pump robustness, i.e. the ability to maintain adequate performances in conditions very far from UHV. In particular, the effects of carbon oxides and hydrocarbon adsorption have been investigated, as well as the outgassing from materials like polyimide or even fluorinated polymers as PTFE. The results show that the ZAO® getter material is intrinsically robust, able to perform repeated H 2 adsorption/desorption cycles with stable performances, and recover most of the original pumping speed even after significant exposure to hydrocarbons and fluorine species. These outcomes give promising indications for the future use of NEG solutions in real fusion facilities. [ABSTRACT FROM AUTHOR]