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Hans-stephan Bosch - One of the best experts on this subject based on the ideXlab platform.
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Backside Protection for Wendelstein 7-X In-Vessel Components
IEEE Transactions on Plasma Science, 2020Co-Authors: Victor Bykov, Andre John, Lutz Wegener, Hans-stephan BoschAbstract: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/m2 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.
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performance of wendelstein 7 x stellarator plasmas during the first divertor Operation Phase
Physics of Plasmas, 2019Co-Authors: R C Wolf, Hans-stephan Bosch, S Bozhenkov, J. Baldzuhn, C. Biedermann, C. D. Beidler, Alejandro Alonso, S Akaslompolo, M Beurskens, R BrakelAbstract:Wendelstein 7-X is the first comprehensively optimized stellarator aiming at good confinement with plasma parameters relevant to a future stellarator power plant. Plasma Operation started in 2015 using a limiter configuration. After installing an uncooled magnetic island divertor, extending the energy limit from 4 to 80 MJ, Operation continued in 2017. For this Phase, the electron cyclotron resonance heating (ECRH) capability was extended to 7 MW, and hydrogen pellet injection was implemented. The enhancements resulted in the highest triple product (6.5 × 1019 keV m−3 s) achieved in a stellarator until now. Plasma conditions [Te(0) ≈ Ti(0) ≈ 3.8 keV, τE > 200 ms] already were in the stellarator reactor-relevant ion-root plasma transport regime. Stable Operation above the 2nd harmonic ECRH X-mode cutoff was demonstrated, which is instrumental for achieving high plasma densities in Wendelstein 7-X. Further important developments include the confirmation of low intrinsic error fields, the observation of current-drive induced instabilities, and first fast ion heating and confinement experiments. The efficacy of the magnetic island divertor was instrumental in achieving high performance in Wendelstein 7-X. Symmetrization of the heat loads between the ten divertor modules could be achieved by external resonant magnetic fields. Full divertor power detachment facilitated the extension of high power plasmas significantly beyond the energy limit of 80 MJ.Wendelstein 7-X is the first comprehensively optimized stellarator aiming at good confinement with plasma parameters relevant to a future stellarator power plant. Plasma Operation started in 2015 using a limiter configuration. After installing an uncooled magnetic island divertor, extending the energy limit from 4 to 80 MJ, Operation continued in 2017. For this Phase, the electron cyclotron resonance heating (ECRH) capability was extended to 7 MW, and hydrogen pellet injection was implemented. The enhancements resulted in the highest triple product (6.5 × 1019 keV m−3 s) achieved in a stellarator until now. Plasma conditions [Te(0) ≈ Ti(0) ≈ 3.8 keV, τE > 200 ms] already were in the stellarator reactor-relevant ion-root plasma transport regime. Stable Operation above the 2nd harmonic ECRH X-mode cutoff was demonstrated, which is instrumental for achieving high plasma densities in Wendelstein 7-X. Further important developments include the confirmation of low intrinsic error fields, the observation of curr...
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engineering challenges in w7 x lessons learned and status for the second Operation Phase
IEEE Transactions on Plasma Science, 2018Co-Authors: Hans-stephan Bosch, A Holtz, H P Laqua, T Andreeva, R Brakel, T Brauer, D Hartmann, T Klinger, M Nagel, D NaujoksAbstract:In 2015, the optimized stellarator Wendelstein 7-X stellarator (W7-X) started with Operation. The main objective of W7-X is the demonstration of the integrated reactor potential of the optimized stellarator line. An important element of this mission is the achievement of high heating power and high confinement in the steady-state Operation. The approach to this mission is the following three steps. First, plasmas were produced in a limiter configuration [Operation Phase (OP 1.1)], then a test divertor unit is being installed (temporary divertor unit) for the next campaign, OP 1.2, before the full steady-state capability will be achieved implementing active cooling of all in-vessel components and a steady-state high heat-flux divertor. In December 2015, the first helium plasma was generated using electron cyclotron resonance heating (ECRH), in February 2016, the working gas was switched to hydrogen. The first OP (OP 1.1) was successfully finished in March 2016. At the end of OP 1.1, the discharge duration was close to 6 s, the limit for the integrated heating power was increased to 4 MJ and electron temperatures of ~10 keV were achieved. Due to the low densities in the range of 1019 cm−3 and the pure electron heating by ECRH, the ion temperatures reached only 2 keV. At present, W7-X is undergoing the next completion Phase, including the installation of the test divertor unit, the installation of the carbon tiles on the inner plasma vessel wall, an upgrade of existing diagnostics, and the installation of new diagnostics. This paper discusses the first Operational Phase, lessons learned and implemented, and the status before the start of the second OP (OP 1.2).
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Challenges for the Wendelstein 7-X Magnet Systems During the Next Operation Phase
IEEE Transactions on Plasma Science, 2018Co-Authors: Thomas Rummel, Konrad Risse, Michael Nagel, Thomas Mönnich, Frank Füllenbach, Hans-stephan BoschAbstract:During the first Operation Phase OP1.1 of Wendelstein 7-X, the magnet systems were not operated up to its maximum capabilities. During the next Operation Phase OP1.2, a big step in the direction to a full current Operation will be taken. The superconducting magnet system consists of the two different coil types: the nonplanar coils (NPCs) and the planar coils (PLCs). With respect to OP1.1, the NPC current in OP1.2 will be increased slightly, but will be doubled in the PLC. Also a reversal of the current direction in the PLC will be required. Tests during and after OP1.1 showed that it might be advantageous to reduce the electrical stress during fast discharges. Therefore, the magnet protection system was optimized. In order to avoid the risk of a quench, the magnet system is being operated with a certain temperature margin with respect to the critical temperature of the superconductor. The safety Operation system will be updated to secure automatic observation and reaction. The five trim coils are normal conducting coils mounted at the outer surface of the cryostat. They were operated during OP1.1 up to 2/3 of the maximum current. Therefore, full current Operation needs to be tested for the first time. For OP1.2, also measures were studied and installed to minimize the cross-link between the trim coils and the superconducting main field coils.
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Transition From Construction to Operation Phase of the Wendelstein 7-X Stellarator
IEEE Transactions on Plasma Science, 2014Co-Authors: Hans-stephan Bosch, Michael Nagel, Rudolf Brakel, Maurizio Gasparotto, Heinz Grote, Dirk A. Hartmann, René Herrmann, Dirk Naujoks, Matthias Otte, Konrad RisseAbstract:Assembly of the superconducting stellarator Wendelstein 7-X is well advanced, and commissioning of the device is being prepared. A first draft of the commissioning tasks has been developed and will be discussed in this paper.
Luisa F Cabeza - One of the best experts on this subject based on the ideXlab platform.
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comparative life cycle assessment of thermal energy storage systems for solar power plants
Renewable Energy, 2012Co-Authors: Alvaro De Gracia, Dieter Boer, Luisa F CabezaAbstract:The present work compares the environmental impact of three different thermal energy storage (TES) systems for solar power plants. A Life Cycle Assessment (LCA) for these systems is developed: sensible heat storage both in solid (high temperature concrete) and liquid (molten salts) thermal storage media, and latent heat storage which uses Phase change material (PCM). The aim of this paper is to analyze if the energy savings related to the stored energy of the different systems are enough to balance the environmental impact produced during the manufacturing and Operation Phase of each storage system. Some hypothetical scenarios are studied using LCA methodology to point out the differences between each TES system.
R Brakel - One of the best experts on this subject based on the ideXlab platform.
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performance of wendelstein 7 x stellarator plasmas during the first divertor Operation Phase
Physics of Plasmas, 2019Co-Authors: R C Wolf, Hans-stephan Bosch, S Bozhenkov, J. Baldzuhn, C. Biedermann, C. D. Beidler, Alejandro Alonso, S Akaslompolo, M Beurskens, R BrakelAbstract:Wendelstein 7-X is the first comprehensively optimized stellarator aiming at good confinement with plasma parameters relevant to a future stellarator power plant. Plasma Operation started in 2015 using a limiter configuration. After installing an uncooled magnetic island divertor, extending the energy limit from 4 to 80 MJ, Operation continued in 2017. For this Phase, the electron cyclotron resonance heating (ECRH) capability was extended to 7 MW, and hydrogen pellet injection was implemented. The enhancements resulted in the highest triple product (6.5 × 1019 keV m−3 s) achieved in a stellarator until now. Plasma conditions [Te(0) ≈ Ti(0) ≈ 3.8 keV, τE > 200 ms] already were in the stellarator reactor-relevant ion-root plasma transport regime. Stable Operation above the 2nd harmonic ECRH X-mode cutoff was demonstrated, which is instrumental for achieving high plasma densities in Wendelstein 7-X. Further important developments include the confirmation of low intrinsic error fields, the observation of current-drive induced instabilities, and first fast ion heating and confinement experiments. The efficacy of the magnetic island divertor was instrumental in achieving high performance in Wendelstein 7-X. Symmetrization of the heat loads between the ten divertor modules could be achieved by external resonant magnetic fields. Full divertor power detachment facilitated the extension of high power plasmas significantly beyond the energy limit of 80 MJ.Wendelstein 7-X is the first comprehensively optimized stellarator aiming at good confinement with plasma parameters relevant to a future stellarator power plant. Plasma Operation started in 2015 using a limiter configuration. After installing an uncooled magnetic island divertor, extending the energy limit from 4 to 80 MJ, Operation continued in 2017. For this Phase, the electron cyclotron resonance heating (ECRH) capability was extended to 7 MW, and hydrogen pellet injection was implemented. The enhancements resulted in the highest triple product (6.5 × 1019 keV m−3 s) achieved in a stellarator until now. Plasma conditions [Te(0) ≈ Ti(0) ≈ 3.8 keV, τE > 200 ms] already were in the stellarator reactor-relevant ion-root plasma transport regime. Stable Operation above the 2nd harmonic ECRH X-mode cutoff was demonstrated, which is instrumental for achieving high plasma densities in Wendelstein 7-X. Further important developments include the confirmation of low intrinsic error fields, the observation of curr...
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engineering challenges in w7 x lessons learned and status for the second Operation Phase
IEEE Transactions on Plasma Science, 2018Co-Authors: Hans-stephan Bosch, A Holtz, H P Laqua, T Andreeva, R Brakel, T Brauer, D Hartmann, T Klinger, M Nagel, D NaujoksAbstract:In 2015, the optimized stellarator Wendelstein 7-X stellarator (W7-X) started with Operation. The main objective of W7-X is the demonstration of the integrated reactor potential of the optimized stellarator line. An important element of this mission is the achievement of high heating power and high confinement in the steady-state Operation. The approach to this mission is the following three steps. First, plasmas were produced in a limiter configuration [Operation Phase (OP 1.1)], then a test divertor unit is being installed (temporary divertor unit) for the next campaign, OP 1.2, before the full steady-state capability will be achieved implementing active cooling of all in-vessel components and a steady-state high heat-flux divertor. In December 2015, the first helium plasma was generated using electron cyclotron resonance heating (ECRH), in February 2016, the working gas was switched to hydrogen. The first OP (OP 1.1) was successfully finished in March 2016. At the end of OP 1.1, the discharge duration was close to 6 s, the limit for the integrated heating power was increased to 4 MJ and electron temperatures of ~10 keV were achieved. Due to the low densities in the range of 1019 cm−3 and the pure electron heating by ECRH, the ion temperatures reached only 2 keV. At present, W7-X is undergoing the next completion Phase, including the installation of the test divertor unit, the installation of the carbon tiles on the inner plasma vessel wall, an upgrade of existing diagnostics, and the installation of new diagnostics. This paper discusses the first Operational Phase, lessons learned and implemented, and the status before the start of the second OP (OP 1.2).
R C Wolf - One of the best experts on this subject based on the ideXlab platform.
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performance of wendelstein 7 x stellarator plasmas during the first divertor Operation Phase
Physics of Plasmas, 2019Co-Authors: R C Wolf, Hans-stephan Bosch, S Bozhenkov, J. Baldzuhn, C. Biedermann, C. D. Beidler, Alejandro Alonso, S Akaslompolo, M Beurskens, R BrakelAbstract:Wendelstein 7-X is the first comprehensively optimized stellarator aiming at good confinement with plasma parameters relevant to a future stellarator power plant. Plasma Operation started in 2015 using a limiter configuration. After installing an uncooled magnetic island divertor, extending the energy limit from 4 to 80 MJ, Operation continued in 2017. For this Phase, the electron cyclotron resonance heating (ECRH) capability was extended to 7 MW, and hydrogen pellet injection was implemented. The enhancements resulted in the highest triple product (6.5 × 1019 keV m−3 s) achieved in a stellarator until now. Plasma conditions [Te(0) ≈ Ti(0) ≈ 3.8 keV, τE > 200 ms] already were in the stellarator reactor-relevant ion-root plasma transport regime. Stable Operation above the 2nd harmonic ECRH X-mode cutoff was demonstrated, which is instrumental for achieving high plasma densities in Wendelstein 7-X. Further important developments include the confirmation of low intrinsic error fields, the observation of current-drive induced instabilities, and first fast ion heating and confinement experiments. The efficacy of the magnetic island divertor was instrumental in achieving high performance in Wendelstein 7-X. Symmetrization of the heat loads between the ten divertor modules could be achieved by external resonant magnetic fields. Full divertor power detachment facilitated the extension of high power plasmas significantly beyond the energy limit of 80 MJ.Wendelstein 7-X is the first comprehensively optimized stellarator aiming at good confinement with plasma parameters relevant to a future stellarator power plant. Plasma Operation started in 2015 using a limiter configuration. After installing an uncooled magnetic island divertor, extending the energy limit from 4 to 80 MJ, Operation continued in 2017. For this Phase, the electron cyclotron resonance heating (ECRH) capability was extended to 7 MW, and hydrogen pellet injection was implemented. The enhancements resulted in the highest triple product (6.5 × 1019 keV m−3 s) achieved in a stellarator until now. Plasma conditions [Te(0) ≈ Ti(0) ≈ 3.8 keV, τE > 200 ms] already were in the stellarator reactor-relevant ion-root plasma transport regime. Stable Operation above the 2nd harmonic ECRH X-mode cutoff was demonstrated, which is instrumental for achieving high plasma densities in Wendelstein 7-X. Further important developments include the confirmation of low intrinsic error fields, the observation of curr...
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key results from the first plasma Operation Phase and outlook for future performance in wendelstein 7 x
Physics of Plasmas, 2017Co-Authors: T S Pedersen, G Fuchert, J Geiger, A Dinklage, Yu Turkin, R C Wolf, S Bozhenkov, H S Bosch, K Rahbarnia, H ThomsenAbstract:The first physics Operation Phase on the stellarator experiment Wendelstein 7-X was successfully completed in March 2016 after about 10 weeks of Operation. Experiments in this Phase were conducted with five graphite limiters as the primary plasma-facing components. Overall, the results were beyond the expectations published shortly before the start of Operation [Sunn Pedersen et al., Nucl. Fusion 55, 126001 (2015)] both with respect to parameters reached and with respect to physics themes addressed. We report here on some of the most important plasma experiments that were conducted. The importance of electric fields on global confinement will be discussed, and the obtained results will be compared and contrasted with results from other devices, quantified in terms of the fusion triple product. Expected values for the triple product in future Operation Phases will also be described and put into a broader fusion perspective.
S Bozhenkov - One of the best experts on this subject based on the ideXlab platform.
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performance of wendelstein 7 x stellarator plasmas during the first divertor Operation Phase
Physics of Plasmas, 2019Co-Authors: R C Wolf, Hans-stephan Bosch, S Bozhenkov, J. Baldzuhn, C. Biedermann, C. D. Beidler, Alejandro Alonso, S Akaslompolo, M Beurskens, R BrakelAbstract:Wendelstein 7-X is the first comprehensively optimized stellarator aiming at good confinement with plasma parameters relevant to a future stellarator power plant. Plasma Operation started in 2015 using a limiter configuration. After installing an uncooled magnetic island divertor, extending the energy limit from 4 to 80 MJ, Operation continued in 2017. For this Phase, the electron cyclotron resonance heating (ECRH) capability was extended to 7 MW, and hydrogen pellet injection was implemented. The enhancements resulted in the highest triple product (6.5 × 1019 keV m−3 s) achieved in a stellarator until now. Plasma conditions [Te(0) ≈ Ti(0) ≈ 3.8 keV, τE > 200 ms] already were in the stellarator reactor-relevant ion-root plasma transport regime. Stable Operation above the 2nd harmonic ECRH X-mode cutoff was demonstrated, which is instrumental for achieving high plasma densities in Wendelstein 7-X. Further important developments include the confirmation of low intrinsic error fields, the observation of current-drive induced instabilities, and first fast ion heating and confinement experiments. The efficacy of the magnetic island divertor was instrumental in achieving high performance in Wendelstein 7-X. Symmetrization of the heat loads between the ten divertor modules could be achieved by external resonant magnetic fields. Full divertor power detachment facilitated the extension of high power plasmas significantly beyond the energy limit of 80 MJ.Wendelstein 7-X is the first comprehensively optimized stellarator aiming at good confinement with plasma parameters relevant to a future stellarator power plant. Plasma Operation started in 2015 using a limiter configuration. After installing an uncooled magnetic island divertor, extending the energy limit from 4 to 80 MJ, Operation continued in 2017. For this Phase, the electron cyclotron resonance heating (ECRH) capability was extended to 7 MW, and hydrogen pellet injection was implemented. The enhancements resulted in the highest triple product (6.5 × 1019 keV m−3 s) achieved in a stellarator until now. Plasma conditions [Te(0) ≈ Ti(0) ≈ 3.8 keV, τE > 200 ms] already were in the stellarator reactor-relevant ion-root plasma transport regime. Stable Operation above the 2nd harmonic ECRH X-mode cutoff was demonstrated, which is instrumental for achieving high plasma densities in Wendelstein 7-X. Further important developments include the confirmation of low intrinsic error fields, the observation of curr...
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the thomson scattering diagnostic at wendelstein 7 x and its performance in the first Operation Phase
Journal of Instrumentation, 2017Co-Authors: S Bozhenkov, G Fuchert, M Beurskens, Dal A Molin, E Pasch, M R Stoneking, M Hirsch, U Hofel, J Knauer, J SvenssonAbstract:The optimized stellarator Wendelstein 7-X started Operation in December 2015 with a 10 week limiter campaign. Divertor experiments will begin in the second half of 2017. The W7-X Thomson scattering system is an essential diagnostic for electron density and temperature profiles. In this paper the Thomson scattering diagnostic is described in detail, including its design, calibration, data evaluation and first experimental results. Plans for further development are also presented. The W7-X Thomson system is a Nd:YAG setup with up to five lasers, two sets of light collection lenses viewing the entire plasma cross-section, fiber bundles and filter based polychromators. To reduce hardware costs, two or three scattering volumes are measured with a single polychromator. The relative spectral calibration is carried out with the aid of a broadband supercontinuum light source. The absolute calibration is performed by observing Raman scattering in nitrogen. The electron temperatures and densities are recovered by Bayesian modelling. In the first campaign, the diagnostic was equipped for 10 scattering volumes. It provided temperature profiles comparable to those measured using an electron cyclotron emission diagnostic and line integrated densities within 10% of those from a dispersion interferometer.
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key results from the first plasma Operation Phase and outlook for future performance in wendelstein 7 x
Physics of Plasmas, 2017Co-Authors: T S Pedersen, G Fuchert, J Geiger, A Dinklage, Yu Turkin, R C Wolf, S Bozhenkov, H S Bosch, K Rahbarnia, H ThomsenAbstract:The first physics Operation Phase on the stellarator experiment Wendelstein 7-X was successfully completed in March 2016 after about 10 weeks of Operation. Experiments in this Phase were conducted with five graphite limiters as the primary plasma-facing components. Overall, the results were beyond the expectations published shortly before the start of Operation [Sunn Pedersen et al., Nucl. Fusion 55, 126001 (2015)] both with respect to parameters reached and with respect to physics themes addressed. We report here on some of the most important plasma experiments that were conducted. The importance of electric fields on global confinement will be discussed, and the obtained results will be compared and contrasted with results from other devices, quantified in terms of the fusion triple product. Expected values for the triple product in future Operation Phases will also be described and put into a broader fusion perspective.