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1. Publisher Correction

Author

M. N. A. Beurskens, Uwe Hergenhahn, M. Borchardt, H. M. Smith, K. J. Brunner, Kian Rahbarnia, D. Zhang, Ulrich Neuner, J. Baldzuhn, E. Pasch, J. Svensson, Sehyun Kwak, Tamara Andreeva, G. Fuchert, E. R. Scott, S. A. Bozhenkov, Felix Warmer, O. P. Ford, M. Hirsch, H. P. Laqua, Jonathan Schilling, R. Kleiber, U. Höfel, Thomas Sunn Pedersen, R. C. Wolf, Ye. O. Kazakov, H. Thomsen, Michael Drevlak, Torsten Stange, Andrea Pavone, Yuriy Turkin, Andreas Langenberg, M. Krychowiak, A. Alonso, J. Geiger, H. Damm, N. A. Pablant, Per Helander, C. D. Beidler, Science and Technology of Nuclear Fusion, and Turbulence in Fusion Plasmas

Subjects
Nuclear physics, Physics, Multidisciplinary, Wendelstein 7-X, Publisher Correction, Energy transport
Abstract

In the original version of this Article, in the fifth paragraph of the section titled “Qneo for W7-X discharge 20180918.045,” errors appeared in reference to the configurations shown in the curves of Fig. 3a and associated Fig. 3b−e panels. In the sentence originally reading “This comparison is provided in Fig. 3a for the configurations (Fig. 3b) W7-X standard, (Fig. 3c) W7-X high-mirror, (Fig. 3d) LHD R0 = 3.6 m, and (Fig. 3e) LHD R0 = 3.75 m....,” the references to Fig. 3b−e should instead have referred to the lettered curves “b,c,d,e” shown in the graph of Fig. 3a. The text has now been amended to read: “This comparison is provided in Fig. 3a for the configurations (b) W7-X standard, (c) W7-X high-mirror, (d) LHD R0 = 3.6 m, and (e) LHD R0 = 3.75 m….” Additionally, a member of the W7-X Team was incorrectly listed as “M. Sanchez”; their name has been corrected to “E. Sánchez.” The original Article has been corrected online.

Published
2021

2. First neutral beam experiments on Wendelstein 7-X

Author

Uwe Hergenhahn, Christian Brandt, P. Valson, Wendelstein X Team, E. Pasch, M. W. Jakubowski, P. Pölöskei, Nikolai B. Marushchenko, Aleix Puig Sitjes, Kian Rahbarnia, Kunihiro Ogawa, Manfred Thumm, L. Vano, Bernd Heinemann, Wolfgang Leonhardt, Dirk Hartmann, D. Mellein, Jonathan Schilling, Jörg Weggen, R. Riedl, Tamara Andreeva, Daniel Papenfuß, Adnan Ali, C. Slaby, Rouven Lang, R. Schroeder, Samuel Lazerson, R. Burhenn, Michael Drevlak, Torsten Stange, Birger Buttenschoゆ, A. Spanier, John Jelonnek, R. C. Wolf, R. Koenig, S. Wadle, T. Wegner, Martina Huber, G. M. Weir, H. Thomsen, Kai Jakob Brunner, Yu Gao, G. Fuchert, P. McNeely, E. R. Scott, R. Bussiahn, P. Traverso, N. Chaudhary, Holger Niemann, Stefan Illy, Theo Scherer, H. Damm, Christian Hopf, S. A. Bozhenkov, Gerd Gantenbein, O. P. Ford, Andreas Langenberg, M. N. A. Beurskens, Simppa Äkäslompolo, Ulrich Neuner, Yuriy Turkin, Naoki Tamura, Andrea Pavone, J. P. Knauer, Niek den Harder, Thorsten Kobarg, N. A. Pablant, U. Hoefel, N. Rust, Philipp Nelde, Department of Applied Physics, Aalto-yliopisto, Aalto University, and W7-X Team, Max Planck Institute for Plasma Physics, Max Planck Society

Subjects
Physics, Nuclear and High Energy Physics, Technology, Fast ions, Condensed Matter Physics, 01 natural sciences, Neutral beam, 010305 fluids & plasmas, law.invention, Nuclear physics, law, 0103 physical sciences, Energetic particles, Wendelstein 7-X, 010306 general physics, Fusion, ddc:600, Stellarator, Beam (structure)
Abstract

In the previous divertor campaign, the Wendelstein 7-X (W7-X) device injected 3.6 MW of neutral beam heating power allowing for the achievement of densities approaching 2 × 1020 m−3, and providing the first initial assessment of fast ion confinement in a drift optimized stellarator. The neutral beam injection (NBI) system on W7-X is comprised of two beam boxes with space for four radio frequency sources each. The 3.6 MW of heating reported in this work was achieved with two sources in the NI21 beam box. The effect of combined electron-cyclotron resonance heating (ECRH) and NBI was explored through a series of discharges varying both NBI and ECRH power. Discharges without ECRH saw a linear increase in the line-integrated plasma density, and strong peaking of the core density, over the discharge duration. The presence of 1 MW of ECRH power was found to be sufficient to control a continuous density rise during NBI operation. Simulations of fast ion wall loads were found to be consistent with experimental infrared camera images during operation. In general, NBI discharges were free from the presence of fast ion induced Alfvénic activity, consistent with low beam betas. These experiments provide data for future scenario development and initial assessment of fast-ion confinement in W7-X, a key topic of the project.

Published
2021

3. Stellarator-tokamak energy confinement comparison based on ASDEX Upgrade and Wendelstein 7-X hydrogen plasmas

Author

P. A. Schneider, U. Stroth, J. P. Knauer, G. Birkenmeier, F. Günzkofer, G. Fuchert, E. R. Scott, D. Zhang, P. Hacker, O. J. W. F. Kardaun, Mst Team, M. N. A. Beurskens, Kian Rahbarnia, Kai Jakob Brunner, and MST1 Team

Subjects
Physics, Nuclear and High Energy Physics, Tokamak, Hydrogen, chemistry.chemical_element, Plasma, Condensed Matter Physics, 01 natural sciences, 7. Clean energy, 010305 fluids & plasmas, law.invention, Nuclear physics, ASDEX Upgrade, chemistry, law, 0103 physical sciences, Wendelstein 7-X, 010306 general physics, Stellarator, Energy (signal processing)
Abstract

A confinement database with mainly electron-heated hydrogen plasmas from ASDEX Upgrade and Wendelstein 7-X was assembled. Stellarator confinement scaling expressions describe both standard discharges in the stellarator and L-mode plasmas in the tokamak similarly well and indicate a similar quality of energy confinement in both devices. While the energy confinement time in ASDEX Upgrade benefits from the smaller aspect ratio of the device, the transport coefficients in Wendelstein 7-X appear to be smaller possibly due to reduced average magnetic field curvature. A physics based confinement scaling is derived from a model that successfully describes transport in tokamaks. The dimensionally correct scaling has very similar parameter dependencies as the stellarator scalings and reproduces also the trends in the data from ITER L- and H-mode databases reasonably well. On the basis of this scaling, which represents the confinement times of the present data base, average tokamak L-mode and H-mode confinement is 7% lower and 76% higher, respectively.

Published
2021

4. Features of near and far scrape-off layer heat fluxes on the Wendelstein 7-X inboard limiters

Author

Fabio Pisano, Felix Warmer, L. Rudischhauser, Andreas Langenberg, S. A. Bozhenkov, M. W. Jakubowski, Florian Effenberg, B. Cannas, Torsten Stange, Kian Rahbarnia, G. A. Wurden, Holger Niemann, D. Carralero, and W7-X Team, Max Planck Institute for Plasma Physics, Max Planck Society

Subjects
Nuclear and High Energy Physics, Materials science, Condensed Matter Physics, 01 natural sciences, 010305 fluids & plasmas, Computational physics, law.invention, law, 0103 physical sciences, Limiter, Wendelstein 7-X, 010306 general physics, Layer (electronics), Stellarator
Published
2020

5. High-performance plasmas after pellet injections in Wendelstein 7-X

Author

N. A. Pablant, G. A. Wurden, H. P. Laqua, Andreas Langenberg, P. Xanthopoulos, A. von Stechow, H. M. Smith, Samuel Lazerson, Matthias Otte, Kian Rahbarnia, J. Baldzuhn, Olaf Grulke, Dmitry Moseev, G. Fuchert, D. Zhang, Andrea Pavone, Torsten Stange, H. Thomsen, R. C. Wolf, E. Pasch, E. R. Scott, J. P. Knauer, U. Höfel, J. H. E. Proll, J. Geiger, M. Krychowiak, M. N. A. Beurskens, Z. Huang, M. Hirsch, O. P. Ford, H. Damm, Yu. Turkin, J. A. Alcuson, S. Bozhenkov, Kai Jakob Brunner, Javier Alonso, Ye. O. Kazakov, Christian Brandt, Nikolai B. Marushchenko, Science and Technology of Nuclear Fusion, Turbulence in Fusion Plasmas, and W7-X Team, Max Planck Institute for Plasma Physics, Max Planck Society

Subjects
Nuclear and High Energy Physics, Materials science, Hydrogen, Plasma parameters, Pellets, chemistry.chemical_element, 01 natural sciences, 7. Clean energy, 010305 fluids & plasmas, law.invention, stellarator, law, Physics::Plasma Physics, Phase (matter), 0103 physical sciences, Wendelstein 7-X, 010306 general physics, Plasma, Condensed Matter Physics, chemistry, Heat transfer, Atomic physics, improved confinement, pellet injection, heat transport, Stellarator
Abstract

A significant improvement of plasma parameters in the optimized stellarator W7-X is found after injections of frozen hydrogen pellets. The ion temperature in the post-pellet phase exceeds 3 keV with 5 MW of electron heating and the global energy confinement time surpasses the empirical ISS04-scaling. The plasma parameters realized in such experiments are significantly above those in comparable gas-fuelled discharges. In this paper, we present details of these pellet experiments and discuss the main plasma properties during the enhanced confinement phases. Local power balance is applied to show that the heat transport in post-pellet phases is close to the neoclassical level for the ion channel and is about a factor of two above that level for the combined losses. In comparable gas-fuelled discharges, the heat transport is by about ten times larger than the neoclassical level, and thus is largely anomalous. It is further observed that the improvement in the transport is related to the peaked density profiles that lead to a stabilization of the ion-scale turbulence.

Published
2020
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6. Experimental characterization of a quasi-coherent turbulent structure in the edge plasma in Wendelstein 7-X

Author

A. Krämer-Flecken, Olaf Grulke, T. Windisch, J. Geiger, Xiuwen Han, G. Fuchert, Kian Rahbarnia, M. Hirsch, S. C. Liu, and W7-X Team, Max Planck Institute for Plasma Physics, Max Planck Society

Subjects
Physics, Nuclear and High Energy Physics, Coherent turbulent structure, Plasma, Edge (geometry), Condensed Matter Physics, 01 natural sciences, 010305 fluids & plasmas, Characterization (materials science), Computational physics, Physics::Plasma Physics, 0103 physical sciences, Wendelstein 7-X, ddc:620, 010306 general physics
Abstract

A quasi-coherent mode (QCM) near the plasma edge is characterized experimentally by measuring the density fluctuation via a poloidal correlation reflectometer (PCR) in Wendelstein 7-X. This QCM frequency descends from 25 kHz near the separatrix to 10 kHz as the cutoff position penetrates toward the core. A similar mode structure is also observed in the spectra of electron cyclotron emission edge channels and Mirnov coil signals, which shows a clear correlation with respect to the PCR measurement. The mode evaluation yields a range for the poloidal mode number of , and for the normalized mode scale , which suggest a drift type instability. The QCM structure appears in the standard and narrow-mirror configurations (both with the rotational transform in the boundary), but is absent in the high- configuration (boundary ). The impact of plasma parameters on the QCM is discussed. It is observed that the QCM frequency and amplitude can be affected by the edge magnetic topology and plasma parameters. The shifts upward during the negative and non-stellarator-symmetric control coil current scans, which may be attributed to the effect of the shear, Er, and ne in the plasma edge region.

Published
2020
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7. Concept for the calibration of the Rogowski coil system of the Wendelstein 7-X stellarator

Author

Kian Rahbarnia, Christoph von Sehren, Thomas Klinger, M. Endler, H. Thomsen, and Ulrich Neuner

Subjects
Physics, business.industry, Mechanical Engineering, Plasma, Low frequency, 01 natural sciences, 010305 fluids & plasmas, law.invention, Optics, Nuclear magnetic resonance, Nuclear Energy and Engineering, law, 0103 physical sciences, Calibration, General Materials Science, Wendelstein 7-X, Current (fluid), 010306 general physics, business, Electrical conductor, Rogowski coil, Stellarator, Civil and Structural Engineering
Abstract

While the low frequency part of the response of the Rogowski coils mounted in the stellarator Wendelstein 7-X has been calculated, the high frequency part is planned to be calibrated by means of an actively applied current. In a staged approach different conductors have been designed to be mounted inside the plasma vessel and an AC current of 1 kA is foreseen to be driven through them at frequencies up to 1 kHz to simulate the plasma current.

Published
2017
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8. First Observation of a Stable Highly Dissipative Divertor Plasma Regime on the Wendelstein 7-X Stellarator

Author

F. Penzel, Carsten Killer, F. Reimold, Sehyun Kwak, D. Zhang, A. Alonso, B. Buttenschön, Thomas Sunn Pedersen, H. Damm, Thomas Klinger, Kenneth Hammond, Andrea Pavone, Yu Gao, Holger Niemann, Florian Effenberg, H. Thomsen, S. Brezinsek, E. Pasch, J. P. Knauer, R. Burhenn, R. Laube, Kian Rahbarnia, M. Hirsch, Y. Feng, U. Höfel, L. Giannone, N. A. Pablant, C. D. Beidler, M. Krychowiak, Kai Jakob Brunner, Victoria Winters, H. P. Laqua, G. Fuchert, J. Baldzuhn, Christoph Biedermann, F. Wagner, S. A. Bozhenkov, M. W. Jakubowski, J. Svensson, W-X Team, P. Drewelow, R. König, and W7-X Team, Max Planck Institute for Plasma Physics, Max Planck Society

Subjects
Materials science, Hydrogen, Divertor, Nuclear engineering, General Physics and Astronomy, chemistry.chemical_element, Plasma, Radiation, Dissipation, 01 natural sciences, 7. Clean energy, law.invention, chemistry, law, 0103 physical sciences, Thermography, Wendelstein 7-X, 010306 general physics, Stellarator
Abstract

For the first time, the optimized stellarator Wendelstein 7-X has operated with an island divertor. An operation regime in hydrogen was found in which the total plasma radiation approached the absorbed heating power without noticeable loss of stored energy. The divertor thermography recorded simultaneously a strong reduction of the heat load on all divertor targets, indicating almost complete power detachment. This operation regime was stably sustained over several energy confinement times until the preprogrammed end of the discharge. The plasma radiation is mainly due to oxygen and is located at the plasma edge. This plasma scenario is reproducible and robust at various heating powers, plasma densities, and gas fueling locations. These experimental results show that the island divertor concept actually works and displays good power dissipation potential, producing a promising exhaust concept for the stellarator reactor line.

Published
2019

9. First results from divertor operation in Wendelstein 7-X

Author

S. Brezinsek, Andreas Langenberg, Holger Niemann, J. Baldzuhn, Ralf König, N. A. Pablant, Yu Gao, Kian Rahbarnia, S. A. Bozhenkov, Thomas Sunn Pedersen, M. Krychowiak, Hans-Stephan Bosch, Yevgen O. Kazakov, G. Fuchert, M. W. Jakubowski, D. Zhang, and W7-X Team, Max Planck Institute for Plasma Physics, Max Planck Society

Subjects
Materials science, Hydrogen, Divertor, Nuclear engineering, Thermal power station, Plasma confinement, chemistry.chemical_element, Condensed Matter Physics, 7. Clean energy, 01 natural sciences, 010305 fluids & plasmas, law.invention, Nuclear Energy and Engineering, chemistry, law, Electrical equipment, 0103 physical sciences, Wendelstein 7-X, ddc:620, 010306 general physics, Stellarator, Helium
Abstract

Wendelstein 7-X is a highly optimized stellarator that went into operation in 2015. With a 30 cubic meter volume, a superconducting coil system operating at 2.5 T, and steady-state heating capability of eventually up to 10 MW, it was built to demonstrate the benefits of optimized stellarators at parameters approaching those of a fusion power plant. We report here on the first results with the test divertor installed, during the second operation phase, which was performed in the second half of 2017. Operation with a divertor, and the addition of several new fueling systems, allowed higher density operation in hydrogen as well as helium. The effects that higher density operation had on both divertor operation and global confinement will be described. In particular, at high densities detachment was observed, and the highest fusion triple product for a stellarator was achieved.

Published
2019
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10. Tuning of the rotational transform in Wendelstein 7-X

Author

Yu Gao, Tamara Andreeva, Christoph Biedermann, L. Rudischhauser, Kenneth Hammond, M. Endler, Kian Rahbarnia, Fabio Pisano, R. König, Aleix Puig Sitjes, G. Satheeswaran, Samuel Lazerson, Monica Spolaore, P. Drewelow, Tamás Szepesi, Adnan Ali, S. Klose, Carsten Killer, G. A. Wurden, G. Kocsis, Kai Jakob Brunner, Ulrich Neuner, U. Wenzel, M. W. Jakubowski, Dirk Nicolai, Barbara Cannas, Holger Niemann, J. Geiger, J. P. Knauer, Boyd Blackwell, Olaf Grulke, G. Schlisio, Matthias Mulsow, S. A. Bozhenkov, H. Thomsen, Jonathan Schilling, Matthias Otte, and W7-X Team, Max Planck Institute for Plasma Physics, Max Planck Society

Subjects
Physics, Nuclear and High Energy Physics, Thesaurus (information retrieval), superconducting coils, Nuclear engineering, Divertor, islands, error fields, magnetic field, Condensed Matter Physics, 01 natural sciences, 010305 fluids & plasmas, law.invention, Magnetic field, stellarator, law, 0103 physical sciences, divertor, Wendelstein 7-X, 010306 general physics, Superconducting Coils, Stellarator
Abstract

The control of rotational transform in Wendelstein 7-X (W7-X) is key to both the island divertor operation and safety of plasma facing components. The island divenor concept in W7-X relies on an edge flux surface with rotational transform of t = 1 resonating with an intrinsic n/m = 5/5 resonance to form a five lobed island chain. This island chain intersects with divertor plates to give rise to the island divertor. Changes in the relative position of the rational surface and the divertor plates can result in changes in divenor performance, thus the control of the rotational transform is essential to operation of the W7-X device. During the first divertor campaign electromagnetic loads resulted in elastic deformations of the shaped modular stellarator coils. Such deformations made these coils more planar, reducing the vacuum rotational transform, subsequently shifting the t = 1 resonance outward. Unintended plasma wall interactions provided the first clear evidence of this effect during plasma operation. Flux surface measurements were utilized to estimate the correct level of current in the planar coils for correction of t, and found to be around similar to-100 A. Scans the planar coil current for iota correction were performed during plasma operation. These measurements suggest planar coil currents between -250 and similar to 0 A would place the strike lines at the designed distance from the pumping gaps. Divertor Langmuir and upstream probe measurements confirm these estimates along with measurements of divertor neutral gas pressure.

Published
2019
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11. Effects of toroidal plasma current on divertor power depositions on Wendelstein 7-X

Author

M. Zanini, D. Zhang, Yunfeng Liang, Tamara Andreeva, Kian Rahbarnia, Holger Niemann, J. Geiger, Yu Gao, S. A. Bozhenkov, Aleix Puig Sitjes, Torsten Stange, Matthias Otte, P. Drewelow, Samuel Lazerson, M. Rack, Adnan Ali, Heinrich P. Laqua, M. W. Jakubowski, Kenneth Hammond, M. Endler, Ulrich Neuner, Fabio Pisano, Barbara Cannas, A. Knieps, Tamás Szepesi, S. Marsen, H. Thomsen, Carsten Killer, Y. Feng, Jonathan Schilling, Yasuhiro Suzuki, and W7-X Team, Max Planck Institute for Plasma Physics, Max Planck Society

Subjects
Nuclear and High Energy Physics, Toroid, Materials science, Divertor, Condensed Matter Physics, 01 natural sciences, 010305 fluids & plasmas, Magnetic field, Power (physics), Heat flux, Physics::Plasma Physics, 0103 physical sciences, Wendelstein 7-X, Electric current, Atomic physics, ddc:620, 010306 general physics, Deposition (law)
Abstract

The paper presents experimental observations and simulations for the effects of toroidal plasma current on divertor power depositions on W7-X. With increasing toroidal current accompanying changes in the island geometry result in a sweep of the strike line and a redistribution of the heat flux footprints. Good agreement between experiments, which partly used electron cyclotron current drive to generate an additional toroidal current contribution, and modelling using field line tracing in vacuum magnetic fields including an ad-hoc toroidal current on the magnetic axis is found for both standard and low-iota magnetic configurations.

Published
2019
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12. Pellet fueling experiments in Wendelstein 7-X

Author

Kian Rahbarnia, Ye. O. Kazakov, N. A. Pablant, Tamás Szepesi, M. N. A. Beurskens, G. Kocsis, F. Köchl, Thomas Sunn Pedersen, C. D. Beidler, Yuriy Turkin, A. von Stechow, G. A. Wurden, H. Damm, J. Baldzuhn, Kieran J. McCarthy, Peter Lang, Bernhard Ploeckl, S. A. Bozhenkov, M. Dibon, D. Zhang, J. Geiger, Andreas Langenberg, Victoria Winters, U. Höfel, H. P. Laqua, E. Pasch, Olaf Grulke, F. Wagner, Thomas Klinger, J. P. Knauer, G. Fuchert, E. R. Scott, P. Kornejew, Kai Jakob Brunner, Torsten Stange, N. Panadero, Wendelstein X Team, G. Schlisio, Christoph Biedermann, and W7-X Team, Max Planck Institute for Plasma Physics, Max Planck Society

Subjects
Physics, Nuclear Energy and Engineering, Nuclear engineering, 0103 physical sciences, Pellet, Wendelstein 7-X, 010306 general physics, Condensed Matter Physics, 7. Clean energy, 01 natural sciences, 010305 fluids & plasmas
Abstract

During the two most recent experimental campaigns in the advanced stellarator Wendelstein 7-X (W7-X) (Klinger et al 2017 Plasma Phys. Control. Fusion 59 014018; Bosch et al 2017 Nucl. Fusion 57 116015; Wolf et al 2017 Nucl. Fusion 57 102020; Pedersen et al 2017 Phys. Plasmas 24 0555030) hydrogen ice pellet injection was performed for the first time. In order to investigate the potential of pellet fueling in W7-X and to study the particle deposition in a large stellarator, a blower-gun system was installed with 40 pellets capability. The experience gained with this system will be used for the specification of a future steady-state pellet injector system. One important motivation for a pellet injector (Dibon 2014 Master-Thesis Technical University Munich, Max-Planck Institut IPP) on W7-X is the mitigation of hollow density profiles expected in case of predominant neoclassical transport. For long-pulse operation of up to 30 min, only electron cyclotron resonance heating is available on W7-X. Hence, pellet injection will be the only source for deep particle fueling. Deep particle fueling by pellets in tokamaks is supported by a grad-B drift, if the pellets are injected from the magnetic high-field-side. This approach was tested in W7-X, as well. The injection of series of pellets was also tested. Here, deep fueling is supported for later pellets in the series by the plasma cooling following the initial pellets in the same series. As in earlier experiments in the heliotron LHD (Takeiri et al 2017 Nucl. Fusion 57 102023), deep and rapid fueling could be achieved successfully in W7-X.

Published
2019

13. Validation of the BEAMS3D neutral beam deposition model on Wendelstein 7-X

Author

Tamara Andreeva, M. N. A. Beurskens, P. Valson, Simppa Äkäslompolo, G. Fuchert, Ulrich Neuner, E. R. Scott, Adnan Ali, Dirk Hartmann, Carolin Nuehrenberg, N. A. Pablant, J. P. Knauer, E. Pasch, Kian Rahbarnia, M. Hirsch, P. Pölöskei, R. C. Wolf, U. Hoefel, N. Chaudhary, Andrea Pavone, M. W. Jakubowski, Nikolai B. Marushchenko, Mike Machielsen, N. Rust, Philipp Nelde, Yuriy Turkin, Jonathan Schilling, Holger Niemann, P. Traverso, Samuel Lazerson, S. A. Bozhenkov, O. P. Ford, Uwe Hergenhahn, A. Spanier, Andreas Langenberg, H. Thomsen, L. Vano, Christian Brandt, G. M. Weir, Aleix Puig Sitjes, Tristan W. C. Neelis, David Pfefferlé, R. Koenig, Yu Gao, Jonathan Graves, Kai Jakob Brunner, P. McNeely, H. Damm, Torsten Stange, Max-Planck-Institut für Plasmaphysik, Department of Applied Physics, Swiss Federal Institute of Technology Lausanne, Eindhoven University of Technology, University of Western Australia, United States Department of Energy, Auburn University, University of Wisconsin-Madison, Aalto-yliopisto, Aalto University, and W7-X Team, Max Planck Institute for Plasma Physics, Max Planck Society

Subjects
Nuclear and High Energy Physics, neutral beam, Cyclotron, Plasma confinement, 01 natural sciences, 010305 fluids & plasmas, law.invention, stellarator, beams3d, law, 0103 physical sciences, Deposition (phase transition), fast ions, 010306 general physics, Stellarator, Plasma density, validation, Physics, magnetic confinement, Magnetic confinement fusion, simulation, Condensed Matter Physics, BEAMS3D, magnetic confnement, Wendelstein 7-X, Atomic physics, Beam (structure)
Abstract

openaire: EC/H2020/633053/EU//EUROfusion The neutral beam deposition model in the BEAMS3D code is validated against neutral beam attenuation data from Wendelstein 7-X (W7-X). A set of experimental discharges where the neutral beam injection system of W7-X was utilized were reconstructed. These discharges scanned the magnetic configurations and plasma densities of W7-X. The equilibrium reconstructions were performed using STELLOPT which calculates three-dimensional self-consistent ideal magnetohydrodynamic equilibria and kinetic profiles. These reconstructions leveraged new capabilities to incorporate electron cyclotron emission and X-ray imaging diagnostics in the STELLOPT code. The reconstructed equilibria and profiles served as inputs for BEAMS3D calculations of neutral beam deposition in W7-X. It is found that if reconstructed kinetic profiles are utilized, good agreement between measured and simulated beam attenuation is found. As deposition models provide initial conditions for fast-ion slowing down calculations, this work provides a first steptowards validating our ability to predict fast ion confinement in stellarators.

Published
2020
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14. Soft x-ray tomography measurements in the Wendelstein 7-X stellarator

Author

R Gutzmann, M. N. A. Beurskens, H. Damm, M Schülke, T. Broszat, Ulrich Neuner, Ph Nelde, Jonathan Schilling, G. Fuchert, E. R. Scott, Tamara Andreeva, T. Schröder, J. P. Knauer, K. Gallowski, J Recknagel, M. Marquardt, Kian Rahbarnia, A. Card, H. P. Laqua, S. A. Bozhenkov, Kai Jakob Brunner, H. Thomsen, R. Laube, T. Sieber, Christian Brandt, E. Pasch, C Cordes, and W7-X Team, Max Planck Institute for Plasma Physics, Max Planck Society

Subjects
Soft x ray, Materials science, business.industry, Resolution (electron density), X-ray, Soft X-radiation, Condensed Matter Physics, 01 natural sciences, Electronic equipment, 010305 fluids & plasmas, law.invention, Optics, Nuclear Energy and Engineering, law, 0103 physical sciences, Tomography, Wendelstein 7-X, 010306 general physics, business, Stellarator
Abstract

The soft x-ray tomography diagnostic in the stellarator Wendelstein 7-X consists of twenty pinhole cameras, up–down symmetrically arranged in a poloidal, triangular cross-section of the plasma vessel. The x-ray emissivity is measured with 16 bit amplitude resolution at 2 MHz sampling rate along 360 lines-of-sight by silicon photodiode arrays. In the recent operation campaign data acquisition (DAQ) has been working reliable for the conducted plasma pulse lengths

Published
2020
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15. Design, capabilities, and first results of the new laser blow-off system on Wendelstein 7-X

Author

Th. Wegner, Kian Rahbarnia, G. Offermanns, F. Kunkel, H. Thomsen, R. Burhenn, N. A. Pablant, K. P. Hollfeld, Ulrich Neuner, Wendelstein X Team, Jonathan Schilling, Olaf Grulke, G. Kocsis, Carsten Killer, Tamás Szepesi, Dirk Nicolai, B. Schweer, G. Satheeswaran, O. Marchuk, T. Krings, Philipp Drews, Andreas Langenberg, B. Buttenschön, Gábor Cseh, Christoph Biedermann, T. Schröder, Benedikt Geiger, and W7-X Team, Max Planck Institute for Plasma Physics, Max Planck Society

Subjects
010302 applied physics, Materials science, business.industry, Plasma parameters, Laser, 01 natural sciences, Spectral line, 010305 fluids & plasmas, law.invention, Optics, law, Ionization, Extreme ultraviolet, 0103 physical sciences, Plasma diagnostics, Wendelstein 7-X, business, Instrumentation, Stellarator
Abstract

We present a detailed overview and first results of the new laser blow-off system on the stellarator Wendelstein 7-X. The system allows impurity transport studies by the repetitive and controlled injection of different tracer ions into the plasma edge. A Nd:YAG laser is used to ablate a thin metal film, coated on a glass plate, with a repetition rate of up to 20 Hz. A remote-controlled adjustable optical system allows the variation of the laser spot diameter and enables the spot positioning to non-ablated areas on the target between laser pulses. During first experiments, clear spectral lines from higher ionization stages of the tracer ions have been observed in the X-ray to the extreme ultraviolet spectral range. The temporal behavior of the measured emission allows the estimate of transport properties, e.g., impurity transport times in the order of 100 ms. Although the strong injection of impurities is well detectable, the global plasma parameters are barely changed.

Published
2018

16. Diamagnetic energy measurement during the first operational phase at the Wendelstein 7-X stellarator

Author

G. Fuchert, Tamara Andreeva, Wendelstein X Team, H. Thomsen, Torsten Bluhm, Bernardo B. Carvalho, A. Werner, Kian Rahbarnia, Dag Hathiramani, J. Geiger, Jonathan Schilling, Ulrich Neuner, M. Endler, Manfred Zilker, and W7-X Team, Max Planck Institute for Plasma Physics, Max Planck Society

Subjects
Physics, Nuclear and High Energy Physics, Thomson scattering, Phase (waves), Condensed Matter Physics, Kinetic energy, 01 natural sciences, Electromagnetic radiation, 010305 fluids & plasmas, Magnetic field, law.invention, Nuclear physics, law, 0103 physical sciences, Diamagnetism, Wendelstein 7-X, 010306 general physics, Stellarator
Published
2018
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17. Global energy confinement in the initial limiter configuration of Wendelstein 7-X

Author

Andreas Langenberg, N. A. Pablant, M. Beurskens, Kian Rahbarnia, G. Fuchert, J. Svensson, Tamara Andreeva, J. P. Knauer, E. Pasch, A. Alonso, H. Trimino Mora, D. Zhang, T. Sunn Pedersen, G. A. Wurden, M. Hirsch, S. A. Bozhenkov, U. Höfel, Torsten Stange, Yuriy Turkin, C. D. Beidler, H. P. Laqua, R. C. Wolf, Wendelstein X Team, Holger Niemann, J. Geiger, Andreas Dinklage, and W7-X Team, Max Planck Institute for Plasma Physics, Max Planck Society

Subjects
Physics, Nuclear and High Energy Physics, Global energy, Nuclear engineering, Divertor, Plasma, Condensed Matter Physics, 7. Clean energy, 01 natural sciences, 010305 fluids & plasmas, 0103 physical sciences, Limiter, Radiative transfer, Wendelstein 7-X, 010306 general physics, Scaling, Energy (signal processing)
Abstract

Global confinement properties of the limiter plasmas of the first operational campaign of W7-X are investigated with special focus on the energy confinement and possible operational limits. The energy confinement time was found to be close to expectations from the empirical ISS04 scaling for stellarators. Absolute values up to 160 ms were achieved. This can be considered as a great success for the initial operation of the device. However, a clear degradation of the performance was observed when radiative losses became significant, which was typically the case at low heating power. While a significant improvement of the plasma purity is expected during divertor operation, the presented results underline the importance of the impurity dynamics for the development of high-performance steady-state scenarios in W7-X. Furthermore, comparisons of the global performance properties with neoclassical transport modeling are presented. These studies are not yet fully conclusive, which could indicate that anomalous transport may have played an essential role in the low-density OP1.1 plasmas.

Published
2018
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18. Engineering design for the magnetic diagnostics of Wendelstein 7-X

Author

T. Windisch, M. Y. Ye, T. Sieber, A. Dudek, Ulrich Neuner, V. Bykov, Kian Rahbarnia, X.B. Peng, A. Werner, Joris Fellinger, Stefan Thiel, K. Rummel, A. Vorköper, J. Geiger, K. Höchel, K. Grosser, F. Dobmeier, Martin Köppen, M. Endler, D. A. Hartmann, Dag Hathiramani, Olaf Grulke, B. Brucker, A. Carls, R. Laube, and A. Cardella

Subjects
Physics, Cryostat, business.industry, Mechanical Engineering, Cyclotron resonance, Plasma, Electron cyclotron resonance, law.invention, Nuclear magnetic resonance, Optics, Nuclear Energy and Engineering, law, General Materials Science, Electric current, Wendelstein 7-X, business, Stellarator, Rogowski coil, Civil and Structural Engineering
Abstract

The magnetic diagnostics foreseen for the Wendelstein 7-X (W7-X) stellarator are diamagnetic loops to measure the plasma energy, Rogowski coils to measure the toroidal plasma current, saddle coils to measure the Pfirsch–Schluter currents, segmented Rogowski coils (poloidal magnetic field probes) to add information on the distribution of the plasma current density, and Mirnov coils to observe magnetohydrodynamic modes. All these magnetic field sensors were designed as classical pick-up coils, after the time integration of induced signals for 1/2 hour had been successfully demonstrated. The long-pulse operation planned for W7-X causes nevertheless significant challenges to the design of these diagnostics, in particular for the components located inside the plasma vessel, which may be exposed to high levels of microwave (electron cyclotron resonance) stray radiation and thermal radiation. This article focuses on the tests and modelling performed during the development of the magnetic diagnostics and on the design solutions adopted to meet the conflicting requirements. All pick-up coils foreseen for the initial operation phase of W7-X and their signal cable sections inside the plasma vessel and the cryostat are now installed, and their electronics and data acquisition are under preparation.

Published
2015
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19. Advanced electron cyclotron heating and current drive experiments on the stellarator Wendelstein 7-X

Author

U. Höfel, Dmitry Moseev, E. Pasch, Andreas Langenberg, Kai Jakob Brunner, Toru Ii Tsujimura, J. P. Knauer, M. Hirsch, R. Brakel, F. Gellert, R. C. Wolf, Yuriy Turkin, S. Marsen, S. A. Bozhenkov, M. N. A. Beurskens, Novomir Pablant, Dirk Hartmann, Alvaro Cappa, Torsten Stange, Nikolai B. Marushchenko, Tom Wauters, V. Erckmann, Gerd Gantenbein, W. Kasparek, H. Braune, Humberto Trimino Mora, Hans-Stephan Bosch, G. Fuchert, Heinrich P. Laqua, Olaf Grulke, Kian Rahbarnia, Andreas Dinklage, and W7-X Team, Max Planck Institute for Plasma Physics, Max Planck Society

Subjects
Physics, Technology, Plasma parameters, Divertor, QC1-999, Cyclotron, 7. Clean energy, 01 natural sciences, Electron cyclotron resonance, 010305 fluids & plasmas, law.invention, law, 0103 physical sciences, Limiter, Electron temperature, Atomic physics, Wendelstein 7-X, 010306 general physics, ddc:600, Stellarator
Abstract

During the first operational phase (OP 1.1) of Wendelstein 7-X (W7-X) electron cyclotron resonance heating (ECRH) was the exclusive heating method and provided plasma start-up, wall conditioning, heating and current drive. Six gyrotrons were commissioned for OP1.1 and used in parallel for plasma operation with a power of up to 4.3 MW. During standard X2-heating the spatially localized power deposition with high power density allowed controlling the radial profiles of the electron temperature and the rotational transform. Even though W7-X was not fully equipped with first wall tiles and operated with a graphite limiter instead of a divertor, electron densities of n e > 3·1019 m-3 could be achieved at electron temperatures of several keV and ion temperatures above 2 keV. These plasma parameters allowed the first demonstration of a multipath O2-heating scenario, which is envisaged for safe operation near the X-cutoff-density of 1.2·1020 m-3 after full commissioning of the ECRH system in the next operation phase OP1.2.

Published
2017
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20. The effects of magnetic topology on the scrape-off layer turbulence transport in the first divertor plasma operation of Wendelstein 7-X using a new combined probe

Author

S. Xu, Malte Henkel, J. Q. Cai, Olaf Grulke, Xiang Gao, Yu Gao, A. Knieps, A. Krämer-Flecken, S. C. Liu, P. Drews, U. Hoefel, Olaf Neubauer, Wendelstein X Team, J. Geiger, A. Charl, Kenneth Hammond, M. Hirsch, E. Pasch, Yunfeng Liang, Dirk Nicolai, Kian Rahbarnia, Yan Li, R. König, Carsten Killer, B. Schweer, Ning Yan, G. Satheeswaran, D. Höschen, Huiqian Wang, J. Cosfeld, N. Sandri, Guosheng Xu, S. Sereda, E. H. Wang, M. Rack, Xiuwen Han, G. Fuchert, and W7-X Team, Max Planck Institute for Plasma Physics, Max Planck Society

Subjects
Physics, Nuclear and High Energy Physics, Turbulence, Divertor, Topology (electrical circuits), Plasma, Condensed Matter Physics, 01 natural sciences, 010305 fluids & plasmas, Computational physics, 0103 physical sciences, Wendelstein 7-X, 010306 general physics, Layer (electronics)
Published
2019
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21. Overview of diagnostic performance and results for the first operation phase in Wendelstein 7-X (invited)

Author

Oliver Schmitz, E. Pasch, S. A. Bozhenkov, O. P. Ford, Ireneusz Książek, J. Svensson, Robert Wolf, M. Endler, R. Burhenn, G. M. Weir, Dirk Naujoks, Florian Effenberg, L. Ryć, M. N. A. Beurskens, Olaf Grulke, T. Sunn Pedersen, G. A. Wurden, S. Marsen, Ulrich Neuner, S. Jablonski, S. C. Liu, T. Fornal, J. Baldzuhn, B. Schweer, Yunfeng Liang, Thomas Klinger, T. Schröder, B. Wiegel, Monika Kubkowska, D. A. Hartmann, Boyd Blackwell, J. P. Knauer, H. Thomsen, A. Dzikowicka, A. O. Marchuk, M. W. Jakubowski, G. Fuchert, H.-J. Hartfuß, Dag Hathiramani, Gábor Cseh, U. Wenzel, A. Adnan, Helmut Schuhmacher, N. A. Pablant, A. Alonso, B. Standley, Philipp Drews, J. Kaczmarczyk, Matthias Otte, T. Kremeyer, Christoph Biedermann, T. Szabolics, P. Kornejew, Hayato Tsuchiya, V. Erckmann, A. Werner, M. Krychowiak, S. Schmuck, N. Krawczyk, Laurie Stephey, D. Zhang, Hans-Stephan Bosch, J. W. Oosterbeek, V. Moncada, J.-M. Travere, B. Buttenschön, H. Neilson, T. Estrada, A. Cappa, A. Krämer-Flecken, Andreas Langenberg, U. Höfel, H. P. Laqua, Samuel Lazerson, T. Bräuer, M. Hirsch, Torsten Stange, R. König, Olaf Neubauer, Wendelstein X Team, B. B. Carvalho, S. Zoletnik, Holger Niemann, Andreas Zimbal, J. Geiger, T. Barbui, A. Lorenz, Andreas Dinklage, Heinke Frerichs, Wolfgang Biel, J. H. Harris, Martin Laux, Wolf-Dieter Schneider, Tamara Andreeva, A. Czarnecka, T. Windisch, S. Klose, H. Trimino Mora, Fabio Pisano, R. Brakel, Tamás Szepesi, G. Kocsis, Kian Rahbarnia, Science and Technology of Nuclear Fusion, and W7-X Team, Max Planck Institute for Plasma Physics, Max Planck Society

Subjects
Physics, business.industry, Plasma parameters, Instrumentation, Plasma, 01 natural sciences, Radiation zone, 010305 fluids & plasmas, law.invention, Optics, law, 0103 physical sciences, Limiter, ddc:530, Plasma diagnostics, Wendelstein 7-X, 010306 general physics, business, Stellarator
Abstract

Wendelstein 7-X, a superconducting optimized stellarator built in Greifswald/Germany, started its first plasmas with the last closed flux surface (LCFS) defined by 5 uncooled graphite limiters in December 2015. At the end of the 10 weeks long experimental campaign (OP1.1) more than 20 independent diagnostic systems were in operation, allowing detailed studies of many interesting plasma phenomena. For example, fast neutral gas manometers supported by video cameras (including one fast-frame camera with frame rates of tens of kHz) as well as visible cameras with different interference filters, with field of views covering all ten half-modules of the stellarator, discovered a MARFE-like radiation zone on the inboard side of machine module 4. This structure is presumably triggered by an inadvertent plasma-wall interaction in module 4 resulting in a high impurity influx that terminates some discharges by radiation cooling. The main plasma parameters achieved in OP1.1 exceeded predicted values in discharges of a length reaching 6 s. Although OP1.1 is characterized by short pulses, many of the diagnostics are already designed for quasi-steady state operation of 30 min discharges heated at 10 MW of ECRH. An overview of diagnostic performance for OP1.1 is given, including some highlights from the physics campaigns.

Published
2016
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22. The set of diagnostics for the first operation campaign of the Wendelstein 7-X stellarator

Author

S. Jablonski, H. P. Laqua, S. Klose, S. A. Bozhenkov, H. Thomsen, Andreas Langenberg, Olaf Grulke, V. Moncada, Helmut Schuhmacher, Ralf König, Torsten Stange, T. Estrada, P. Kornejew, Matthias Otte, G. A. Wurden, Wolf-Dieter Schneider, B. Buttenschön, A. Werner, E. Pasch, L. Ryć, Yunfeng Liang, Tamás Szepesi, A. Czarnecka, M. Hirsch, Ulrich Neuner, Wolfgang Biel, M. Krychowiak, Olaf Neubauer, S. Zoletnik, Oliver Schmitz, B. B. Carvalho, M. W. Jakubowski, J. Baldzuhn, T. Kremeyer, Hans-Stephan Bosch, A. Zimbal, T. Windisch, Gábor Cseh, J. Geiger, B. Wiegel, Robert Wolf, M. Endler, R. Burhenn, A. Lorenz, Thomas Sunn Pedersen, Christoph Biedermann, J. Kaczmarczyk, A. O. Marchuk, Martin Laux, U. Wenzel, N. A. Pablant, G. Kocsis, T. Bräuer, B. Schweer, Monika Kubkowska, V. Erckmann, Kian Rahbarnia, J. W. Oosterbeek, D. Zhang, J.-M. Travere, Thomas Klinger, Dag Hathiramani, D. A. Hartmann, A. Krämer-Flecken, Science and Technology of Nuclear Fusion, and W7-X Team, Max Planck Institute for Plasma Physics, Max Planck Society

Subjects
Physics, Heating power, business.industry, Plasma parameters, Nuclear engineering, Nuclear instruments and methods for hot plasma diagnostics, Electrical engineering, 01 natural sciences, 010305 fluids & plasmas, law.invention, Plasma diagnostics - interferometry, spectroscopy and imaging, law, 0103 physical sciences, Plasma diagnostics - interferometry, spectroscopy and imaging, Limiter, Plasma diagnostics, Plasma diagnostics - probes, Wendelstein 7-X, 010306 general physics, business, Instrumentation, Mathematical Physics, Stellarator
Abstract

Wendelstein 7-X (W7-X) is a large optimized stellarator (B=2.5T, V=30m3) aiming at demonstrating the reactor relevance of the optimized stellarators. In 2015 W7-X will begin its first operation phase (OP1.1) with five inertially cooled inboard limiters made of graphite. Assuming the heat loads can be spread out evenly between the limiters, 1 second discharges at 2 MW of ECRH heating power could be run in OP1.1. The expected plasma parameters will be sufficient to demonstrate the readiness of the installed diagnostics and even to run a first physics program. The diagnostics available for this first operation phase, including some special limiter diagnostics, and their capabilities are being presented. A shorter version of this contribution is due to be published in PoS at: 1st EPS conference on Plasma Diagnostics

Published
2015

23. Performance and properties of the first plasmas of Wendelstein 7-X

Author

T. Windisch, H. Maaßberg, Tom Wauters, S. Marsen, Matt Landreman, Olaf Grulke, Kian Rahbarnia, José Luis Velasco, A. Alonso, S. A. Bozhenkov, Peter Traverso, M. Hirsch, G. Kocsis, H. Thomsen, Andreas Langenberg, G. M. Weir, H. P. Laqua, J. Geiger, J. P. Knauer, E. Pasch, Tamás Szepesi, Andreas Dinklage, Samuel Lazerson, Matthias Otte, Thomas Klinger, R. Burhenn, Torsten Stange, N. A. Pablant, A. Krämer-Flecken, G. Fuchert, and W7-X Team, Max Planck Institute for Plasma Physics, Max Planck Society

Subjects
Physics, Nuclear engineering, Plasma, Condensed Matter Physics, 7. Clean energy, 01 natural sciences, Electron cyclotron resonance, 010305 fluids & plasmas, law.invention, Power (physics), Nuclear Energy and Engineering, law, Magnet, 0103 physical sciences, Limiter, ddc:530, Atomic physics, Wendelstein 7-X, 010306 general physics, Scaling, Stellarator
Abstract

The optimized, superconducting stellarator Wendelstein 7-X went into operation and delivered first measurement data after 15 years of construction and one year commissioning. Errors in the magnet assembly were confirmend to be small. Plasma operation was started with 5 MW electron cyclotron resonance heating (ECRH) power and five inboard limiters. Core plasma values of ${{T}_{\text{e}}}>8$ keV, ${{T}_{\text{i}}}>2$ keV at line-integrated densities $n\approx 3\centerdot {{10}^{19}}~{{\text{m}}^{-2}}$ were achieved, exceeding the original expectations by about a factor of two. Indications for a core-electron-root were found. The energy confinement times are in line with the international stellarator scaling, despite unfavourable wall conditions, i.e. large areas of metal surfaces and particle sources from the limiter close to the plasma volume. Well controlled shorter hydrogen discharges at higher power (4 MW ECRH power for 1 s) and longer discharges at lower power (0.7 MW ECRH power for 6 s) could be routinely established after proper wall conditioning. The fairly large set of diagnostic systems running in the end of the 10 weeks operation campaign provided first insights into expected and unexpected physics of optimized stellarators.

Published
2016
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24. Wall conditioning in fusion devices with superconducting coils

Author

Vladimir E. Moiseenko, Torsten Stange, G. Fuchert, J. P. Knauer, A.I. Lyssoivan, S. Sereda, L. Vano, H. P. Laqua, R. Brakel, EUROfusion Mst Team, D. Ricci, S. Brezinsek, Heinz Grote, Jet Contributors, J. Buermans, V. Rohde, O. P. Ford, Antti Hakola, D. Borodin, O. Volzke, Kian Rahbarnia, T. Loarer, Stefano Coda, Dmitry Moseev, Kai Jakob Brunner, J. Ongena, Francisco L. Tabarés, D. Douai, Jt Team, Tcv Team, A. Goriaev, E. Wang, Tom Wauters, E. Joffrin, Andreas Dinklage, S. Romanelli, ASDEX Upgrade Team, Max Planck Institute for Plasma Physics, Max Planck Society, TCV Team, EUROfusion MST1 Team, W7-X Team, Max Planck Institute for Plasma Physics, Max Planck Society, JT-60A Team, and JET Contributors

Subjects
Materials science, Tokamak, EFFICIENCY, Nuclear engineering, STELLARATOR, Cyclotron, PLASMAS, CODE, tritium recovery, JT-60SA, 01 natural sciences, MAGNETIC-FIELDS, 010305 fluids & plasmas, law.invention, stellarator, law, ITER, 0103 physical sciences, 010306 general physics, OPTIMIZATION, w7-x, rf conditioning, Glow discharge, magnetic-fields, iter, Divertor, RF conditioning, Plasma, wall conditioning, wendelstein 7-x, Condensed Matter Physics, plasmas, Magnetic flux, W7-X, BORON, jt-60sa, Nuclear Energy and Engineering, Physics and Astronomy, WENDELSTEIN 7-X, efficiency, code, ddc:620, Wendelstein 7-X, boron, optimization, Stellarator
Abstract

Wall conditioning is essential in tokamak and stellarator research to achieve plasma performance and reproducibility. This paper presents an overview of recent conditioning results, both from experiments in present devices and modelling, in view of devices with superconducting coils, with focus on W7-X, JT-60SA and ITER. In these devices, the coils stay energised throughout an experimental day or week which demands for new conditioning techniques that work in presence of the nominal field, in addition to the proven conditioning methods such as baking, glow discharge conditioning (GDC) and low-Z wall coating through GDC-plasma, which do not work under such condition. The discussed techniques are RF conditioning without plasma current, both in the ion cyclotron and electron cyclotron range of frequencies, and diverted conditioning plasmas with nested magnetic flux surfaces. Similarities and differences between tokamaks and stellarators are highlighted. Finally a conditional tritium recovery strategy for ITER is proposed based on Ion Cyclotron Wall Conditioning and L-mode plasma results from JET, equipped with an ITER-like wall (beryllium main chamber wall and tungsten divertor).

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25. Major results from the first plasma campaign of the Wendelstein 7-X stellarator

Author

H. Maaßberg, M. Grahl, V. Moncada, Marek Scholz, Naoki Tamura, H. Neilson, R. Koziol, M. Krychowiak, A. Lücke, T. Estrada, R. Munk, M. Marushchenko, K. Toi, Heinrich P. Laqua, S. Paqay, Olaf Grulke, K. Baumann, A. Czermak, Ivan Calvo, Yasuhiro Suzuki, P.J. Heitzenroeder, H. Hölbe, G. Offermanns, Gintautas Dundulis, U. Stridde, H. Hunger, S. Valet, P. Denner, N. Krawczyk, O. Mishchenko, Andrey Samartsev, Mantas Povilaitis, Andrea Pavone, H. Schumacher, P. Aleynikov, H. P. Laqua, U. Wenzel, M. Sibilia, J. Ongena, Kian Rahbarnia, A. Galkowski, T.A. Scherer, C. Slaby, J. Nührenberg, H.-J. Roscher, Martin Köppen, L.-G. Böttger, A. Czarnecka, R. Krampitz, M. Zilker, T. Kremeyer, J. Wendorf, V. Bykov, A. Goriaev, Josef Preinhaelter, A. Alonso, Peter Titus, G. Czymek, Andreas Langenberg, Matteo Zuin, A. Gogoleva, F. Musielok, A. Zeitler, Andreas Schlaich, P. Xanthopoulos, Victoria Winters, M. Losert, D. A. Hartmann, Roberto Guglielmo Citarella, L. Pacios Rodriguez, Boyd Blackwell, E. Blanco, Hans-Stephan Bosch, R. König, R. Stadler, J. Mittelstaedt, Ch. Linsmeier, U. Höfel, N. Panadero Alvarez, E. Pasch, Francesco Cordella, M. Knaup, Fabian Wilde, M. C. Zarnstorff, B. Mendelevitch, Toru Ii Tsujimura, T. Szabolics, Hayato Tsuchiya, J.C. Schmitt, Tadas Kaliatka, Sadayoshi Murakami, Samuel Lazerson, W. Spiess, J. M. García Regaña, P. Junghans, María Sánchez, A. Grosman, I. Yamada, K. P. Hollfeld, K. Aleynikova, Gábor Náfrádi, T. Krings, Daniel Papenfuß, José Luis Velasco, P. Drewelow, N. A. Pablant, S. Renard, Alessandro Zocco, F. Wagner, D. Böckenhoff, S. Ryosuke, Michael Kramer, A. Vorkörper, M. Turnyanskiy, R. Riedl, W. Figacz, H. Trimino Mora, A. da Silva, D. Gradic, M. Keunecke, A. Pieper, M. Houry, S. Pingel, K. H. Schlüter, J. Loizu Cisquella, L. Carraro, S. Schmuck, M. Banduch, Sehyun Kwak, T. Ilkei, X. Huang, Stefan Illy, N. Fahrenkamp, I. Vakulchyk, G. Kocsis, Ph. Mertens, T. Morizaki, K. Czerski, F. V. Chernyshev, Bernd Heinemann, L. Lewerentz, B.J. Peterson, Francisco Castejón, Olaf Neubauer, D. Zhang, Torsten Bluhm, F. Köchl, C.P. von Thun, Michael Cole, Fabio Pisano, R. Brakel, Peter Traverso, G. Orozco, Wolf-Dieter Schneider, A. A. Ivanov, S. Sipliä, V. Szabó, D. Pilopp, A. Cappa, G. Anda, H. Braune, A. Krämer-Flecken, R. Sakamoto, A. Charl, Hiroshi Kasahara, Massimiliano Romé, J.-H. Feist, Mark Cianciosa, M. Führer, G. Schlisio, Taina Kurki-Suonio, F. Purps, H. Esteban, A. H. Reiman, J. Krom, C. D. Beidler, D. Loesser, H. M. Smith, Nengchao Wang, Axel Könies, Oliver Schmitz, T. Bräuer, M. Hirsch, Gabriel G. Plunk, Felix Warmer, R. Karalevicius, Riccardo Nocentini, J.L. Terry, John Jelonnek, Arnold Lumsdaine, L. Ryć, M. N. A. Beurskens, H. Jenzsch, Z. Sulek, Donald A. Spong, A. Khilchenko, P. Marek, R. Schroeder, T. Schröder, B. Standley, Manfred Thumm, B. Brünner, T. Fornal, Benedikt Geiger, H. Frerichs, R. Kleiber, T. Funaba, Andreas Meier, S. Degenkolbe, P. Rong, Dag Hathiramani, Matthias F. Schneider, Simppa Äkäslompolo, M. R. Stoneking, A. Dudek, Jiawu Zhu, X. Han, T. Windisch, Y. Wei, Detlev Reiter, J. Tretter, N. Rust, J. P. Kallmeyer, J. Baldzuhn, P. Bolgert, Dirk Timmermann, Shinsuke Satake, Luis Vela Vela, Yu. Turkin, Z. Szökefalvi-Nagy, Sigitas Rimkevicius, Naoki Kenmochi, Ulrich Neuner, M. Garcia-Munoz, V. Perseo, Matthias Otte, A. Puig Sitjes, Tamás Szepesi, A. da Molin, Alexis Terra, C. Guerard, J.M. Hernández Sánchez, A. Rodatos, J. Assmann, D. Höschen, Albert Mollén, A. Hölting, Tom Wauters, Adnan Ali, Ewa Pawelec, W. Kasparek, Ryo Yasuhara, D. Kinna, P. Sinha, B. Wiegel, Horacio Fernandes, M. E. Puiatti, S. Récsei, E. Ascasíbar, J.-M. Travere, C. Hidalgo, Joris Fellinger, H. Schmitz, Suguru Masuzaki, Katsumi Ida, G. Pelka, Jim-Felix Lobsien, S. Wolf, Jörg Schacht, J. Koshurinov, Han Zhang, P. Kornejew, J M Fontdecaba, T. Ngo, E. Wang, B. Hein, Gerd Gantenbein, Michael Drevlak, M. Vervier, J. W. Oosterbeek, H. Röhlinger, J. P. Knauer, B. Schweer, Jakub Urban, David Maurer, I. Ksiazek, David Gates, S. C. Liu, S. Massidda, F. Remppel, A.H. Wright, G. Satheeswaran, Monika Kubkowska, K. Rummel, Kai Jakob Brunner, Torsten Stange, J. Riemann, Thomas Klinger, S. Obermayer, H. Brand, Christine Hennig, A. Werner, N. Gierse, S. A. Henneberg, R. Vilbrandt, J. Wolowski, T. Sunn Pedersen, M. Dostal, G. A. Wurden, I. Abramovic, Carsten Lechte, R. Lang, S. A. Bozhenkov, G. Ehrke, K. J. McCarthy, Egidijus Urbonavicius, M. Schröder, S. Jablonski, Martina Huber, M. Nagel, Yunfeng Liang, O. P. Ford, Barbara Cannas, T. Mizuuchi, Anatoly Panin, Jan Skodzik, V. V. Lutsenko, R. Koslowski, R. Laube, Jonathan T. Green, B. Unterberg, Jeremy Lore, Laurie Stephey, J. H. E. Proll, M. Czerwinski, Venanzio Giannella, Jörg Weggen, S. Marsen, Clifford M Surko, Grzegorz Gawlik, B. Roth, D. Birus, Ch. Brandt, M. Mardenfeld, K. Riße, Y. Feng, Alexandra M. Freund, M. Vergote, S. Wadle, H. Thomsen, Wilfried Behr, A. Runov, L. Wegener, Burkhard Plaum, J. Svensson, Dmitry Moseev, Łukasz Ciupiński, G. M. Weir, E. Winkler, W. Pan, E. Erckmann, D. Mellein, B. Shanahan, Th. Kobarg, Marek Barlak, John Howard, Günter Dammertz, M. Endler, D.P. Dhard, N. Vianello, L. V. Lubyako, R. Burhenn, J. Thomas, N. Panadero, M. Gruca, T. Mönnich, J. Majano-Brown, Wolfgang Biel, S. Tulipán, J. H. Harris, C. Nührenberg, A. Carls, H. Viebke, Walter H. Fietz, L. Haiduk, S. Brezinsek, Heinz Grote, S. Langish, V. Huber, Jacek Jagielski, David Ennis, P. Kraszewsk, J. Kacmarczyk, Kunihiro Ogawa, U. Kamionka, O. Bertuch, F. Durodié, B. Missal, A. de la Peña, Robertas Alzbutas, Anett Spring, Yu Gao, Matt Landreman, Dirk Naujoks, Florian Effenberg, P. McNeely, Ya. I. Kolesnichenko, B. Gonçalves, B. van Millingen, M. Blatzheim, X. Peng, F. Harberts, M. W. Jakubowski, F. Köster, Gábor Cseh, Ph. Drews, Christoph Biedermann, G. Claps, L. Rudischhauser, Bernardo B. Carvalho, M. Yokoyama, Seung Gyou Baek, Felix Schauer, V. Borsuk, Th. Rummel, J. Boscary, Fumimichi Sano, J. R. Danielson, M. Rack, G. Fuchert, H.-J. Hartfuß, W. Leonhardt, Georg Kühner, D. R. Mikkelsen, M. Borchardt, A. Benndorf, P. Scholz, R. C. Wolf, I.V. Shikhovtsev, Holger Niemann, Andreas Zimbal, J. Geiger, T. Barbui, M. Lennartz, A. Lorenz, Andreas Dinklage, G. Krzesiński, J. Zajac, B. Israeli, R. Schrittwieser, M.J. Cole, S. Zoletnik, O. Marchuk, Per Helander, B. Buttenschön, P. van Eeten, Tamara Andreeva, Hiroshi Yamada, Universidad de Sevilla. Departamento de Física Atómica, Molecular y Nuclear, Max-Planck-Institut fur Plasmaphysik Teilinstitut Greifswald, Wendelsteinstr. 1, 17491 Greifswald, Germany, Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas (CIEMAT), KFKI Research Institute for Particle and Nuclear Physics (KFKI-RMKI), Forschungszentrum Julich GmbH, Institut fur Energie- und Klimaforschung---Plasmaphysik, Partner of the Trilateral Euregio Cluster (TEC), Wilhelm-Johnen-Strase, 52428 Julich, Germany, University of Maryland, Princeton, Laboratory for Plasma Physics of the Ecole Royale Militaire/Koninklijke Militaire School (LPP-ERM/KMS), Avenue de la Renaissance 30, 1000 Bruxelles, Belgien, Los Alamos National Laboratory (LANL), Institute of Physics, Massachusetts Institute of Technology, Cambridge, University of Wisconsin-Madison, National Centre for Nuclear Research (NCBJ), Institut für Experimentelle Kernphysik, Universität Karlsruhe (IEKP), Geoscience Australia, Max Planck Institut für Plasma Physik and Excellence Cluster, Eindhoven University of Technology, Università degli Studi di Cagliari = University of Cagliari (UniCa), Consorzio Interuniversitario per la Fisica Spaziale (CIFS), Instituto Superior Técnico, Universidade de Lisboa (IST), A.F. Ioffe Physical-Technical Institute, Russian Academy of Sciences [Moscow] (RAS), Computer Science and Mathematics Division, Oak Ridge National Laboratory, Università di Milano, Warsaw University of Technology, ENEA-Frascati, IPPLM Institute of Plasma Physics and Laser Microfusion, 23 Hery Str., 01-497 Warsaw, Poland, Institute of Nuclear Physics PAN, University of Szczecin, 70-453, aleja Papieza Jana Pawla II 22A, Szczecin, Poland, Milano, University of California [San Diego] (UC San Diego), University of California (UC), International Center for Climate and Global Change Research and School of Forestry and Wildlife Sciences, Auburn University, Brandenburg University of Technology Cottbus-Senftenberg, Universitatsplatz 1, 01968 Senftenberg, Germany, National Institute for Fusion Science (NIFS), 322-6 Oroshicho, Toki, Gifu Prefecture 509-5202, Japan, Universidad Carlos III de Madrid (UC3M), Commissariat à l'énergie atomique et aux énergies alternatives (CEA), EURATOM/UKAEA Fusion Association, Culham Science Centre, Abingdon, Budker Institute of Nuclear Physics (BINP), 11, akademika Lavrentieva prospect, Novosibirsk, 630090, Russian Federation, Institut für Raumfahrtsysteme, Universität Stuttgart (IRS), Fraunhofer-Institut fur Schicht- und Oberflachentechnik IST, Bienroder Weg 54 E, 38108 Braunschweig, Germany, Institut für Weltraumforschung, Österreichische Akademie der Wissenschaften (IWF), Kiev Institute for Nuclear Research, A.M. Obukhov Institute of Atmospheric Physics, Russian Academy of Sciences (IAP), Institut für Optik und Atomare Physik, Technische Universität Berlin, University of Opole, plac Kopernika 11a, 45-001 Opole, Poland, School of Electrical Engineering, Aalto University, Physikalisch-Technische Bundesanstalt (PTB), Kyoto University, Institute of Plasma Physics, Chinese Academy of Sciences, 350 Shushanhu Rd., Hefei, Anhui 230031, People's Republic of China, Institute of Plasma Physics of the Czech Academy of Science, Za Slovankou 1782/3, 182 00 Prague 8---Liben, Czechia, Istituto di Fisica del Plasma, Consiglio Nazionale delle Ricerche (IFP-CNR), Fraunhofer-Institut fur Werkzeugmaschinen und Umformtechnik IWU, Reichenhainer Strase 88, 09126 Chemnitz, Germany, Universität Rostock, Wayne State University, Consiglio Nazionale delle Ricerche, Piazzale Aldo Moro, 7, 00185 Roma, Italy, Max Planck Institute for Plasma Physics, CIEMAT, Wigner Research Centre for Physics, Jülich Research Centre, University of Maryland, College Park, Princeton University, Royal Military Academy, Los Alamos National Laboratory, Lithuanian Energy Institute, Massachusetts Institute of Technology, Narodowe Centrum Badań Jadrowych, Karlsruhe Institute of Technology, Australian National University, University of Cagliari, National Research Council of Italy, Instituto Superior Tecnico Lisboa, Ioffe Institute, Oak Ridge National Laboratory, University of Salerno, Agenzia nazionale per le nuove tecnologie, l'energia e lo sviluppo economico sostenibile, Soltan Institute for Nuclear Studies, The Henryk Niewodniczanski Institute of Nuclear Physics of the Polish Academy of Sciences, University of Szczecin, University of Milan - Bicocca, University of California San Diego, Auburn University, Brandenburg University of Technology, National Institute for Fusion Science, Universidad Carlos III de Madrid, CEA, Culham Centre for Fusion Energy, RAS - Budker Institute of Nuclear Physics, University of Stuttgart, Fraunhofer Institute for Surface Engineering and Thin Films, Austrian Academy of Sciences, NASU - Institute of Nuclear Research, RAS - Institute of Applied Physics, Technical University of Berlin, University of Opole, Department of Applied Physics, Physikalisch-Technische Bundesanstalt, CAS - Institute of Plasma Physics, Czech Academy of Sciences, Istituto di Fisica Del Plasma Piero Caldirola, Fraunhofer Institute for Machine Tools and Forming Technology, University of Rostock, Lawrence University, Aalto-yliopisto, Aalto University, Science and Technology of Nuclear Fusion, Turbulence in Fusion Plasmas, Claps, G., and Cordella, F

Subjects
Magnetic confinement, Nuclear and High Energy Physics, Technology and Engineering, Plasma heating, Cyclotron resonance, CONFINEMENT, 01 natural sciences, Electron cyclotron resonance, 010305 fluids & plasmas, law.invention, PHYSICS, Nuclear physics, stellarator, current drive, magnetic confinement, plasma heating, Condensed Matter Physics, law, 0103 physical sciences, ddc:530, 010306 general physics, tellarator, Stellarator, Physics, Magnetic confinement fusion, Plasma, 530 Physik, TRANSPORT, Current drive, Electron temperature, Plasma diagnostics, Atomic physics, Wendelstein 7-X, [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph]
Abstract

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. EURATOM 633053

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26. Impurity transport studies at Wendelstein 7-X by means of x-ray imaging spectrometer measurements

Author

Oleksandr Marchuk, T. Krings, G. Offermanns, R. C. Wolf, Andreas Langenberg, B. Schweer, G. Satheeswaran, J. A. Alonso, Benedikt Geiger, R. Burhenn, Felix Warmer, N. A. Pablant, Olaf Grulke, F. Kunkel, H. Thomsen, Ulrich Neuner, E. Pasch, Andreas Dinklage, K. P. Hollfeld, Jonathan Schilling, G. Fuchert, Th. Wegner, Kian Rahbarnia, K. J. Brunner, B. Buttenschön, M. Hirsch, S. A. Bozhenkov, J. P. Knauer, U. Höfel, Philipp Drews, Carsten Killer, Peter Traverso, and W7-X Team, Max Planck Institute for Plasma Physics, Max Planck Society

Subjects
Materials science, Imaging spectrometer, X-ray, Laser blow-off, Plasma, Condensed Matter Physics, 7. Clean energy, 01 natural sciences, 010305 fluids & plasmas, Impurity confinement, Plasma physics, Energy confinement, Nuclear Energy and Engineering, Impurity, 0103 physical sciences, Wendelstein 7-X, Atomic physics, 010306 general physics, Transport studies, Impurity transport
Abstract

This paper reports on the effect of on- and off-axis heating power deposition on the impurity confinement in purely electron cyclotron resonance heated He plasmas on the stellarator Wendelstein 7-X. Therefore, impurity transport times τ I have been determined after Fe impurity injections by laser ablations and monitoring the temporal impurity emissivities by the x-ray imaging spectrometer HR-XIS. A significant increase of τ I has been observed when changing the power deposition from on- to off-axis heating with energy confinement times τ E being mainly unaffected. In addition, the scaling of impurity transport properties with respect to a variation of heating power P ECRH and electron density n e has been investigated by keeping the heating power deposition on-axis. The observed τ I scaling compares well to known τ I scaling laws observed in other machines. A comparison of τ I and τ E yields an averaged ratio of τ E /τ I = 1.3 and transport times in the range of τ I = 40–130 ms and τ E = 40–190 ms. Comparing those absolute values to neoclassical predictions supports the recently observed nature of anomalous transport in Wendelstein 7-X, given within the up to now investigated operational parameters.

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27. Key results from the first plasma operation phase and outlook for future performance in Wendelstein 7-X

Author

H. Thomsen, Yu. Turkin, H. Trimino Mora, N. A. Pablant, Kian Rahbarnia, J. P. Knauer, Thomas Sunn Pedersen, Hans-Stephan Bosch, Ulrich Neuner, J. Geiger, Andreas Dinklage, G. Fuchert, S. A. Bozhenkov, M. Hirsch, R. C. Wolf, Thomas Klinger, P. Kornejew, Andreas Langenberg, and W7-X Team, Max Planck Institute for Plasma Physics, Max Planck Society

Subjects
Physics, Nuclear engineering, Phase (waves), Nanotechnology, Plasma, Condensed Matter Physics, 01 natural sciences, 010305 fluids & plasmas, law.invention, Triple product, law, 0103 physical sciences, Limiter, Wendelstein 7-X, 010306 general physics, Review Papers, Stellarator
Abstract

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.

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