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1. Heat and particle flux detachment with stable plasma conditions in the Wendelstein 7-X stellarator fusion experiment

Author

Jakubowski, Marcin, König, Ralf, Schmitz, Oliver, Feng, Yuhe, Krychowiak, Maciej, Otte, Matthias, Reimold, Felix, Dinklage, Andreas, Drewelow, Peter, Effenberg, Florian, Gao, Yu, Niemann, Holger, Schlisio, Georg, Pavone, Andrea, Pedersen, Thomas Sunn, Wenzel, Uwe, Zhang, Daihong, Brezinsek, Sebastijan, Bozhenkov, Sergey, Brunner, Kai Jakob, Carralero, Daniel, Hammond, Ken, Fuchert, Golo, Knauer, Jens, Langenberg, Andreas, Laqua, Heinrich, Marsen, Stefan, Pablant, Novimir, Rahbarnia, Kian, Rudichshauser, Lukas, Stange, Torsten, Wurden, Glen, and team, W7-X

Subjects
Physics - Plasma Physics, Nuclear Experiment
Abstract

Reduction of particle and heat fluxes to plasma facing components is critical to achieve stable conditions for both the plasma and the plasma material interface in magnetic confinement fusion experiments. A stable and reproducible plasma state in which the heat flux is almost completely removed from the material surfaces was discovered recently in the Wendelstein 7-X stellarator experiment. At the same time also particle fluxes are reduced such that material erosion can be mitigated. Sufficient neutral pressure was reached to maintain stable particle exhaust for density control in this plasma state. This regime could be maintained for up to 28 seconds with a minimum feedback control., Comment: Aimed at Physical Review Letters

Published
2020

2. Maximum spin polarization in chromium dimer cations as demonstrated by x-ray magnetic circular dichroism spectroscopy

Author

Zamudio-Bayer, Vicente, Hirsch, Konstantin, Langenberg, Andreas, Niemeyer, Markus, Vogel, Marlene, Ławicki, Arkadiusz, Terasaki, Akira, Lau, J. Tobias, and von Issendorff, Bernd

Subjects
Physics - Chemical Physics, Physics - Atomic and Molecular Clusters
Abstract

X-ray magnetic circular dichroism spectroscopy has been used to characterize the electronic structure and magnetic moment of Cr$_2^+$. Our results indicate that the removal of a single electron from the $4s\sigma_g$ bonding orbital of Cr$_2$ drastically changes the preferred coupling of the $3d$ electronic spins. While the neutral molecule has a zero-spin ground state with a very short bond length, the molecular cation exhibits a ferromagnetically coupled ground state with the highest possible spin of $S=11/2$, and almost twice the bond length of the neutral molecule. This spin configuration can be interpreted as a result of indirect exchange coupling between the $3d$ electrons of the two atoms that is mediated by the single $4s$ electron through a strong intraatomic $3d$-$4s$ exchange interaction. Our finding allows an estimate of the relative energies of two states that are often discussed as ground-state candidates, the ferromagnetically coupled $^{12}\Sigma$ and the low-spin $^2\Sigma$ state., Comment: This is the peer-reviewed, accepted version of the article

Published
2018
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3. Direct Observation of High-Spin States in Manganese Dimer and Trimer Cations by X-ray Magnetic Circular Dichroism Spectroscopy in an Ion Trap

Author

Zamudio-Bayer, Vicente, Hirsch, Konstantin, Langenberg, Andreas, Kossick, Martin, Ławicki, Arkadiusz, Terasaki, Akira, von Issendorff, Bernd, and Lau, J. Tobias

Subjects
Physics - Chemical Physics, Physics - Atomic and Molecular Clusters
Abstract

The electronic structure and magnetic moments of free Mn$_2^+$ and Mn$_3^+$ are characterized by $2p$ x-ray absorption and x-ray magnetic circular dichroism spectroscopy in a cryogenic ion trap that is coupled to a synchrotron radiation beamline. Our results show directly that localized magnetic moments of 5 $\mu_B$ are created by $3d^5 (^6\mathrm{S})$ states at each ionic core, which are coupled in parallel to form molecular high-spin states via indirect exchange that is mediated in both cases by a delocalized valence electron in a singly-occupied $4s$ derived orbital with an unpaired spin. This leads to total magnetic moments of 11 $\mu_B$ for Mn$_2^+$ and 16 $\mu_B$ for Mn$_3^+$, with no contribution of orbital angular momentum.

Published
2015
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4. Impact of Magnetic Field Configuration on Heat Transport in Stellarators and Heliotrons

Author

WARMER, Felix, TANAKA, Kenji, XANTHOPOULOS, P., NUNAMI, Masanori, NAKATA, Motoki, BEIDLER, Craig, BOZHENKOV, Sergey, BEURSKENS, Marc, BRUNNER, K. J., FORD, O. P., FUCHERT, Golo, FUNABA, Hisamichi, GEIGER, J., GRADIC, D., IDA, Katsumi, IGAMI, Hiroe, KUBO, Shin, LANGENBERG, Andreas, LAQUA, Heinrich, LAZERSON, Samuel, MORISAKI, Tomohiro, OSAKABE, Masaki, PABLANT, Novimir, PASCH, E., PETERSON, Byron J., SATAKE, Shinsuke, SEKI, Ryosuke, SHIMOZUMA, Takashi, SMITH, H. M., STANGE, Torsten, STECHOW, A. von, SUGAMA, Hideo, SUZUKI, Yasuhiro, TAKAHASHI, Hiromi, TOKUZAWA, Tokihiko, TSUJIMURA, Toru, TURKIN, Yuri, WOLF, Robert, YAMADA, Ichihiro, YANAI, Ryoma, YASUHARA, Ryo, YOKOYAMA, Masayuki, YOSHIMURA, Yasuo, YOSHINUMA, Mikirou, ZHANG, Daihong, W7-X Team, LHD Experimental Group, WARMER, Felix, TANAKA, Kenji, XANTHOPOULOS, P., NUNAMI, Masanori, NAKATA, Motoki, BEIDLER, Craig, BOZHENKOV, Sergey, BEURSKENS, Marc, BRUNNER, K. J., FORD, O. P., FUCHERT, Golo, FUNABA, Hisamichi, GEIGER, J., GRADIC, D., IDA, Katsumi, IGAMI, Hiroe, KUBO, Shin, LANGENBERG, Andreas, LAQUA, Heinrich, LAZERSON, Samuel, MORISAKI, Tomohiro, OSAKABE, Masaki, PABLANT, Novimir, PASCH, E., PETERSON, Byron J., SATAKE, Shinsuke, SEKI, Ryosuke, SHIMOZUMA, Takashi, SMITH, H. M., STANGE, Torsten, STECHOW, A. von, SUGAMA, Hideo, SUZUKI, Yasuhiro, TAKAHASHI, Hiromi, TOKUZAWA, Tokihiko, TSUJIMURA, Toru, TURKIN, Yuri, WOLF, Robert, YAMADA, Ichihiro, YANAI, Ryoma, YASUHARA, Ryo, YOKOYAMA, Masayuki, YOSHIMURA, Yasuo, YOSHINUMA, Mikirou, ZHANG, Daihong, W7-X Team, and LHD Experimental Group

Abstract

We assess the magnetic field configuration in modern fusion devices by comparing experiments with the same heating power, between a stellarator and a heliotron. The key role of turbulence is evident in the optimized stellarator, while neoclassical processes largely determine the transport in the heliotron device. Gyrokinetic simulations elucidate the underlying mechanisms promoting stronger ion scale turbulence in the stellarator. Similar plasma performances in these experiments suggests that neoclassical and turbulent transport should both be optimized in next step reactor designs., source:https://doi.org/10.1103/PhysRevLett.127.225001, identifier:0000-0001-9585-5201

Published
2023

5. Demonstration of reduced neoclassical energy transport in Wendelstein 7-X

Author

BEIDLER, Craig, SMITH, H. M., ALONSO, Juan Arturo, ANDREEVA, T., BALDZUHN, J., BEURSKENS, Marc, BORCHARDT, Matthias, BOZHENKOV, Sergey, BRUNNER, Kai Jakob, DAMM, Hannes, DREVLAK, M., FORD, Oliver P., FUCHERT, Golo, GEIGER, Joachim, HELANDER, P., HERGENHAHN, Uwe, HIRSCH, M., Höfel, Udo, KAZAKOV, Yevgen, KLEIBER, Ralf, KRYCHOWIAK, Maciej, KWAK, Sehyun, LANGENBERG, Andreas, LAQUA, Heinrich, NEUNER, U., PABLANT, Novimir, PASCH, E., PAVONE, Andrea, PEDERSEN, Thomas Sunn, RAHBARNIA, Kian, SCHILLING, Jonathan, SCOTT, Evan, STANGE, Torsten, SVENSSON, J., THOMSEN, Henning, TURKIN, Yuriy, WARMER, Felix, WOLF, Robert, ZHANG, Daihong, the W7-X Team, BEIDLER, Craig, SMITH, H. M., ALONSO, Juan Arturo, ANDREEVA, T., BALDZUHN, J., BEURSKENS, Marc, BORCHARDT, Matthias, BOZHENKOV, Sergey, BRUNNER, Kai Jakob, DAMM, Hannes, DREVLAK, M., FORD, Oliver P., FUCHERT, Golo, GEIGER, Joachim, HELANDER, P., HERGENHAHN, Uwe, HIRSCH, M., Höfel, Udo, KAZAKOV, Yevgen, KLEIBER, Ralf, KRYCHOWIAK, Maciej, KWAK, Sehyun, LANGENBERG, Andreas, LAQUA, Heinrich, NEUNER, U., PABLANT, Novimir, PASCH, E., PAVONE, Andrea, PEDERSEN, Thomas Sunn, RAHBARNIA, Kian, SCHILLING, Jonathan, SCOTT, Evan, STANGE, Torsten, SVENSSON, J., THOMSEN, Henning, TURKIN, Yuriy, WARMER, Felix, WOLF, Robert, ZHANG, Daihong, and the W7-X Team

Abstract

Research on magnetic confinement of high-temperature plasmas has the ultimate goal of harnessing nuclear fusion for the production of electricity. Although the tokamak1 is the leading toroidal magnetic-confinement concept, it is not without shortcomings and the fusion community has therefore also pursued alternative concepts such as the stellarator. Unlike axisymmetric tokamaks, stellarators possess a three-dimensional (3D) magnetic field geometry. The availability of this additional dimension opens up an extensive configuration space for computational optimization of both the field geometry itself and the current-carrying coils that produce it. Such an optimization was undertaken in designing Wendelstein 7-X (W7-X)2, a large helical-axis advanced stellarator (HELIAS), which began operation in 2015 at Greifswald, Germany. A major drawback of 3D magnetic field geometry, however, is that it introduces a strong temperature dependence into the stellarator’s non-turbulent ‘neoclassical’ energy transport. Indeed, such energy losses will become prohibitive in high-temperature reactor plasmas unless a strong reduction of the geometrical factor associated with this transport can be achieved; such a reduction was therefore a principal goal of the design of W7-X. In spite of the modest heating power currently available, W7-X has already been able to achieve high-temperature plasma conditions during its 2017 and 2018 experimental campaigns, producing record values of the fusion triple product for such stellarator plasmas3,4. The triple product of plasma density, ion temperature and energy confinement time is used in fusion research as a figure of merit, as it must attain a certain threshold value before net-energy-producing operation of a reactor becomes possible1,5. Here we demonstrate that such record values provide evidence for reduced neoclassical energy transport in W7-X, as the plasma profiles that produced these results could not have been obtained in stellarators lackin, source:Beidler, C.D., Smith, H.M., Alonso, A. et al. Demonstration of reduced neoclassical energy transport in Wendelstein 7-X. Nature 596, 221–226 (2021). https://doi.org/10.1038/s41586-021-03687-w, source:https://doi.org/10.1038/s41586-021-03687-w, identifier:0000-0002-4395-239X

Published
2023

6. Core Diagnostics for WENDELSTEIN 7-X Steady-State Exploration Until 18 GJ

Author

HIRSCH, Matthias W., BANNMANN, Sebastian, FUCHERT, Gole, Xiang, Han, HÖFEL, Udo, HUANG, Jia, KNAUER, Jens, KOSCHINSKY, Jean-Paul, KRÄMER-FLECKEN, Andreas, KURSINSKI, Beate, LANGENBERG, Andreas, LAZERSON, Samuel, BEURSKENS, Marc N. A., MEINEKE, Jens, MOSEEV, Dimitry, OOSTERBEEK, Johan, PABLANT, Novimir, PASCH, Eckehard, PAVONE, Andreas, PÖLÖSKEI, Peter, RICHERT, Torsten, STANGE, Torsten, STEFFEN, Matthias, BIEDERMANN, Christoph, STERN, Mathias, VANÓ, Lilla, WOLF, Robert C., XIANG, Haoming M., ZANINI, Marco, BOZHENKOV, Sergey, BRUNNER, Kai-Jakob, CHAUDHARY, Neha, DAMM, Hannes, FORD, Oliver, GUERRERO-ARNAIZ, Juan, and W7-X Team, Max Planck Institute for Plasma Physics, Max Planck Society

Subjects
ddc:530, Condensed Matter Physics
Published
2022
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7. Advanced electron cyclotron heating and current drive experiments on the stellarator Wendelstein 7-X

Author

Stange Torsten, Laqua Heinrich Peter, Beurskens Marc, Bosch Hans-Stephan, Bozhenkov Sergey, Brakel Rudolf, Braune Harald, Brunner Kai Jakob, Cappa Alvaro, Dinklage Andreas, Erckmann Volker, Fuchert Golo, Gantenbein Gerd, Gellert Florian, Grulke Olaf, Hartmann Dirk, Hirsch Matthias, Höfel Udo, Kasparek Walter, Knauer Jens, Langenberg Andreas, Marsen Stefan, Marushchenko Nikolai, Moseev Dmitry, Pablant Novomir, Pasch Ekkehard, Rahbarnia Kian, Mora Humberto Trimino, Tsujimura Toru, Turkin Yuriy, Wauters Tom, and Wolf Robert

Subjects
Physics, QC1-999
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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8. First neutral beam experiments on Wendelstein 7-X

Author

Lazerson, Samuel A., primary, Ford, Oliver, additional, Äkaslompolö, Simppa, additional, Bozhenkov, Sergey, additional, Slaby, Christoph, additional, Vanó, Lilla, additional, Spanier, Annabelle, additional, McNeely, Paul, additional, Rust, Norbert, additional, Hartmann, Dirk, additional, Poloskei, Peter, additional, Buttenschoゆ, Birger, additional, Burhenn, Rainer, additional, Tamura, Naoki, additional, Bussiahn, Rene, additional, Wegner, Thomas, additional, Drevlak, Michael, additional, Turkin, Yuriy, additional, Ogawa, Kunihiro, additional, Knauer, Jens, additional, Brunner, Kai Jakob, additional, Pasch, Ekkehard, additional, Beurskens, Marc, additional, Damm, Hannes, additional, Fuchert, Golo, additional, Nelde, Philipp, additional, Scott, Evan, additional, Pablant, Novimir, additional, Langenberg, Andreas, additional, Traverso, Peter, additional, Valson, Pranay, additional, Hergenhahn, Uwe, additional, Pavone, Andrea, additional, Rahbarnia, Kian, additional, Andreeva, Tamara, additional, Schilling, Jonathan, additional, Brandt, Christian, additional, Neuner, Ulrich, additional, Thomsen, Henning, additional, Chaudhary, Neha, additional, Höefel, Udo, additional, Stange, Torsten, additional, Weir, Gavin, additional, Marushchenko, Nikolai, additional, Jakubowski, Marcin, additional, Ali, Adnan, additional, Gao, Yu, additional, Niemann, Holger, additional, Puig Sitjes, Aleix, additional, Koenig, Ralf, additional, Schroeder, Ralf, additional, den Harder, Niek, additional, Heinemann, Bernd, additional, Hopf, Christian, additional, Riedl, Rudolf, additional, Wolf, Robert C., additional, and W7-X Team, the, additional

Published
2021
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9. Demonstration of reduced neoclassical energy transport in Wendelstein 7-X

Author

BEIDLER, Craig, SMITH, H. M., ALONSO, Juan Arturo, ANDREEVA, T., BALDZUHN, J., BEURSKENS, Marc, BORCHARDT, Matthias, BOZHENKOV, Sergey, BRUNNER, Kai Jakob, DAMM, Hannes, DREVLAK, M., FORD, Oliver P., FUCHERT, Golo, GEIGER, Joachim, HELANDER, P., HERGENHAHN, Uwe, HIRSCH, M., Höfel, Udo, KAZAKOV, Yevgen, KAZAKOV, Yevgen O., KLEIBER, Ralf, KRYCHOWIAK, Maciej, KWAK, Sehyun, LANGENBERG, Andreas, LAQUA, Heinrich, NEUNER, U., PABLANT, Novimir, PASCH, E., PAVONE, Andrea, PEDERSEN, Thomas Sunn, RAHBARNIA, Kian, SCHILLING, Jonathan, SCOTT, Evan, STANGE, Torsten, SVENSSON, J., THOMSEN, Henning, TURKIN, Yuriy, WARMER, Felix, WOLF, Robert, ZHANG, Daihong, the W7-X Team, BEIDLER, Craig, SMITH, H. M., ALONSO, Juan Arturo, ANDREEVA, T., BALDZUHN, J., BEURSKENS, Marc, BORCHARDT, Matthias, BOZHENKOV, Sergey, BRUNNER, Kai Jakob, DAMM, Hannes, DREVLAK, M., FORD, Oliver P., FUCHERT, Golo, GEIGER, Joachim, HELANDER, P., HERGENHAHN, Uwe, HIRSCH, M., Höfel, Udo, KAZAKOV, Yevgen, KAZAKOV, Yevgen O., KLEIBER, Ralf, KRYCHOWIAK, Maciej, KWAK, Sehyun, LANGENBERG, Andreas, LAQUA, Heinrich, NEUNER, U., PABLANT, Novimir, PASCH, E., PAVONE, Andrea, PEDERSEN, Thomas Sunn, RAHBARNIA, Kian, SCHILLING, Jonathan, SCOTT, Evan, STANGE, Torsten, SVENSSON, J., THOMSEN, Henning, TURKIN, Yuriy, WARMER, Felix, WOLF, Robert, ZHANG, Daihong, and the W7-X Team

Abstract

0000-0002-4395-239X, Research on magnetic confinement of high-temperature plasmas has the ultimate goal of harnessing nuclear fusion for the production of electricity. Although the tokamak1 is the leading toroidal magnetic-confinement concept, it is not without shortcomings and the fusion community has therefore also pursued alternative concepts such as the stellarator. Unlike axisymmetric tokamaks, stellarators possess a three-dimensional (3D) magnetic field geometry. The availability of this additional dimension opens up an extensive configuration space for computational optimization of both the field geometry itself and the current-carrying coils that produce it. Such an optimization was undertaken in designing Wendelstein 7-X (W7-X)2, a large helical-axis advanced stellarator (HELIAS), which began operation in 2015 at Greifswald, Germany. A major drawback of 3D magnetic field geometry, however, is that it introduces a strong temperature dependence into the stellarator’s non-turbulent ‘neoclassical’ energy transport. Indeed, such energy losses will become prohibitive in high-temperature reactor plasmas unless a strong reduction of the geometrical factor associated with this transport can be achieved; such a reduction was therefore a principal goal of the design of W7-X. In spite of the modest heating power currently available, W7-X has already been able to achieve high-temperature plasma conditions during its 2017 and 2018 experimental campaigns, producing record values of the fusion triple product for such stellarator plasmas3,4. The triple product of plasma density, ion temperature and energy confinement time is used in fusion research as a figure of merit, as it must attain a certain threshold value before net-energy-producing operation of a reactor becomes possible1,5. Here we demonstrate that such record values provide evidence for reduced neoclassical energy transport in W7-X, as the plasma profiles that produced these results could not have been obtained in stellarators lackin

Published
2021

10. Impact of Magnetic Field Configuration on Heat Transport in Stellarators and Heliotrons

Author

WARMER, Felix, TANAKA, Kenji, XANTHOPOULOS, P., NUNAMI, Masanori, NAKATA, Motoki, BEIDLER, Craig, BOZHENKOV, Sergey, BEURSKENS, Marc, BRUNNER, K. J., FORD, O. P., FUCHERT, Golo, FUNABA, Hisamichi, GEIGER, J., GRADIC, D., IDA, Katsumi, IGAMI, Hiroe, KUBO, Shin, LANGENBERG, Andreas, LAQUA, Heinrich, LAZERSON, Samuel, MORISAKI, Tomohiro, OSAKABE, Masaki, PABLANT, Novimir, PASCH, E., PETERSON, Byron, PETERSON, Byron J., SATAKE, Shinsuke, SEKI, Ryosuke, SHIMOZUMA, Takashi, SMITH, H. M., STANGE, Torsten, STECHOW, A. von, SUGAMA, Hideo, SUZUKI, Yasuhiro, TAKAHASHI, Hiromi, TOKUZAWA, Tokihiko, TSUJIMURA, Toru, TURKIN, Yuri, WOLF, Robert, YAMADA, Ichihiro, YANAI, Ryoma, YANAI, Ryohma, YASUHARA, Ryo, YOKOYAMA, Masayuki, YOSHIMURA, Yasuo, YOSHINUMA, Mikirou, ZHANG, Daihong, W7-X Team, LHD Experimental Group, WARMER, Felix, TANAKA, Kenji, XANTHOPOULOS, P., NUNAMI, Masanori, NAKATA, Motoki, BEIDLER, Craig, BOZHENKOV, Sergey, BEURSKENS, Marc, BRUNNER, K. J., FORD, O. P., FUCHERT, Golo, FUNABA, Hisamichi, GEIGER, J., GRADIC, D., IDA, Katsumi, IGAMI, Hiroe, KUBO, Shin, LANGENBERG, Andreas, LAQUA, Heinrich, LAZERSON, Samuel, MORISAKI, Tomohiro, OSAKABE, Masaki, PABLANT, Novimir, PASCH, E., PETERSON, Byron, PETERSON, Byron J., SATAKE, Shinsuke, SEKI, Ryosuke, SHIMOZUMA, Takashi, SMITH, H. M., STANGE, Torsten, STECHOW, A. von, SUGAMA, Hideo, SUZUKI, Yasuhiro, TAKAHASHI, Hiromi, TOKUZAWA, Tokihiko, TSUJIMURA, Toru, TURKIN, Yuri, WOLF, Robert, YAMADA, Ichihiro, YANAI, Ryoma, YANAI, Ryohma, YASUHARA, Ryo, YOKOYAMA, Masayuki, YOSHIMURA, Yasuo, YOSHINUMA, Mikirou, ZHANG, Daihong, W7-X Team, and LHD Experimental Group

Abstract

0000-0001-9585-5201, We assess the magnetic field configuration in modern fusion devices by comparing experiments with the same heating power, between a stellarator and a heliotron. The key role of turbulence is evident in the optimized stellarator, while neoclassical processes largely determine the transport in the heliotron device. Gyrokinetic simulations elucidate the underlying mechanisms promoting stronger ion scale turbulence in the stellarator. Similar plasma performances in these experiments suggests that neoclassical and turbulent transport should both be optimized in next step reactor designs.

Published
2021

11. Impact of the temperature ratio on turbulent impurity transport in Wendelstein 7-X

Author

Wegner, Thomas, primary, Alcuson, Jorge Alberto, additional, Geiger, Benedikt, additional, von Stechow, Adrian, additional, Xanthopoulos, Pavlos, additional, Angioni, Clemente, additional, Beurskens, Marc N A, additional, Böttger, Lukas, additional, Bozhenkov, Sergey A, additional, Brunner, Kai Jakob, additional, Burhenn, Rainer, additional, Buttenschön, Birger, additional, Damm, Hannes, additional, Edlund, Eric M, additional, Ford, Oliver P, additional, Fuchert, Golo, additional, Grulke, Olaf, additional, Huang, Zhouji, additional, Knauer, Jens P, additional, Kunkel, Falk, additional, Langenberg, Andreas, additional, Pablant, Novimir Antoniuk, additional, Pasch, Ekkehard, additional, Rahbarnia, Kian, additional, Schilling, Jonathan, additional, Thomsen, H, additional, and Vano, Lilla, additional

Published
2020
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12. Experimental and theoretical 2p core-level spectra of size-selected gas-phase aluminum and silicon cluster cations: chemical shifts, geometric structure, and coordination-dependent screening

Author

Walter, Michael, primary, Vogel, Marlene, additional, Zamudio-Bayer, Vicente, additional, Lindblad, Rebecka, additional, Reichenbach, Thomas, additional, Hirsch, Konstantin, additional, Langenberg, Andreas, additional, Rittmann, Jochen, additional, Kulesza, Alexander, additional, Mitrić, Roland, additional, Moseler, Michael, additional, Möller, Thomas, additional, von Issendorff, Bernd, additional, and Lau, J. Tobias, additional

Published
2019
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13. Magnetic Moments of Free, Size-Selected Iron, Cobalt, and Nickel Clusters

Author

Langenberg, Andreas, Lau, Tobias, Technische Universität Berlin, Fakultät II - Mathematik und Naturwissenschaften, Möller, Thomas, von Issendorff, Bernd, Dähne, Mario, and Langenberg, Andreas

Subjects
ddc:530
Abstract

In dieser Arbeit wurde erfolgreich ein Experiment zur Messung Spin-Bahn aufgelöster magnetischer Momente von freien, massenselektierten Clustern mittels XMCD-Spekroskopie aufgebaut. Erste Messungen an kationischen Eisen-, Cobalt- und Nickelclustern im mittleren Größenbereich (Fe+10−15, Co+10−15, Ni+10−15) zeigen, dass diese Cluster anders als im Festkörper starke Ferromagneten mit vollständig gefülltem Majoritätsband und maximalen Spinmomenten von μs = 1.0 μB pro 3d Loch sind, was durch die geringe Koordination der Atome in Clustern verursacht wird. Als Ausnahme wird bei Fe+13 ein um 1.0 ± 0.4 μB pro Atom reduziertes Spinmoment beobachtet, was im Zusammenhang mit der hohen Symmetrie der Ikosaederstruktur steht. Bei sehr kleinen Clustern (Fe+2−6 und Co+2−6) kommt es vermutlich in Folge reduzierter mittlerer Bindungslängen zu unvollständig gefüllten Majoritätsbändern und verringerten Spinmomenten von μs < 1.0 μB pro 3d Loch. Die magnetischen Bahnmomente von Clustern sind im Vergleich zu Atomen bereits für sehr kleine Eisencluster stark reduziert und erreichen nur 5-25% des atomaren Wertes. Verursacht wird dies durch die Aufhebung der sphärischen Symmetrie im Kristallfeld benachbarter Atome. Bei kleinen Cobaltclustern wie Co+3 entsprechen die Bahnmomente dagegen bis zu 43% des atomaren Wertes und sind bis zur Clustergröße n ≤ 6 im Vergleich zu Eisenclustern systematisch erhöht. Ein Vergleich berechneter Spinmomente zeigt eine gute Übereinstimmung zwischen Theorie und Experiment für Eisencluster, aber eine systematische Diskrepanz für Cobalt- und Nickelcluster, wo Rechnungen die hier gemessenen Spinmomente im Durchschnitt um circa 0.5μB pro Atom unterschätzen. Die Ergebnisse von Stern-Gerlach Experimenten sind im Vergleich zu den hier gemessenen Gesamtmomenten für Eisen-, Cobalt- und Nickelcluster durchschnittlich um 0.5 μB verringert, was vermutlich durch eine unzureichende Thermalisierung der Cluster in den Stern-Gerlach Experimenten verursacht wird. In this work, an experiment for measuring spin and orbital resolved magnetic moments of free, mass selected clusters by means of XMCD-spectroscopy has been set up. First results on medium sized, cationic iron-, cobalt-, and nickel clusters (Fe+10−15, Co+10−15, Ni+10−15) show that in contrast to the bulk these clusters are strong ferromagnets with a completely filled majority spin band and a maximum spin moment of μs = 1.0 μB per 3d hole, that is induced by the low coordinated atoms of the clusters. As an exception, Fe+13 has a reduced spin moment of about 1.0 ± 0.4 μB per atom, that is related to the highly symmetric, icosahedral structure of Fe+13. For small clusters, majority spin bands are not saturated leading to reduced spin moments of μs < 1.0μB per 3d hole as a consequence of shrunken average nearest neighbour distances. A comparison of magnetic orbital moments of clusters and atoms reveals that already for small iron clusters, orbital moments are strongly reduced to 5-25% of its atomic value, induced by the breakup of spherical symmetry in the crystal field of nearby atoms. In contrast to iron clusters, orbital moments of small cobalt clusters like Co+3 correspond to up to 43% of the atomic value and a systematic enhancement compared to iron clusters is observed for clustersizes n ≤ 6. Calculations of spin moments of iron clusters achieve a good agreement between theory and experiment. For cobalt and nickel clusters, theory systematically underestimates the measured spin magnetic moments by about 0.5 μB per atom. Results from Stern-Gerlach deflection experiments are compared to our derived total magnetic momentes of iron, cobalt, and nickel clusters reduced by 0.5 μB per atom, that might be caused by an insufficient thermalization of the clusters in Stern-Gerlach experiments.

Published
2013

14. Higher Ionization Energies from Sequential Vacuum-Ultraviolet Multiphoton Ionization of Size-Selected Silicon Cluster Cations

Author

Kasigkeit, Christian, primary, Hirsch, Konstantin, additional, Langenberg, Andreas, additional, Möller, Thomas, additional, Probst, Jürgen, additional, Rittmann, Jochen, additional, Vogel, Marlene, additional, Wittich, Jörg, additional, Zamudio-Bayer, Vicente, additional, von Issendorff, Bernd, additional, and Lau, J. Tobias, additional

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

Author

Stange, Torsten, Laqua, Heinrich Peter, Beurskens, Marc, Bosch, Hans-Stephan, Bozhenkov, Sergey, Brakel, Rudolf, Braune, Harald, Brunner, Kai Jakob, Cappa, Alvaro, Dinklage, Andreas, Erckmann, Volker, Fuchert, Golo, Gantenbein, Gerd, Gellert, Florian, Grulke, Olaf, Hartmann, Dirk, Hirsch, Matthias, Höfel, Udo, Kasparek, Walter, Knauer, Jens, Langenberg, Andreas, Marsen, Stefan, Marushchenko, Nikolai, Moseev, Dmitry, Pablant, Novomir, Pasch, Ekkehard, Rahbarnia, Kian, Mora, Humberto Trimino, Tsujimura, Toru, Turkin, Yuriy, Wauters, Tom, and Wolf, Robert

Subjects
7. Clean energy

18. Letter

Author

W7-X Team, Wegner, Thomas, Alcuson, Jorge Alberto, Geiger, Benedikt, Stechow, Adrian von, Xanthopoulos, Pavlos, Angioni, Clemente, Beurskens, Marc N. A., Böttger, Lukas, Bozhenkov, Sergey A., Brunner, Kai Jakob, Burhenn, Rainer, Buttenschön, Birger, Damm, Hannes, Edlund, Eric M., Ford, Oliver P., Fuchert, Golo, Grulke, Olaf, Huang, Zhouji, Knauer, Jens P., Kunkel, Falk, Langenberg, Andreas, Pablant, Novimir Antoniuk, Pasch, Ekkehard, Rahbarnia, Kian, Schilling, Jonathan, Thomsen, H., Vano, Lilla, Gantenbein, Gerd, Huber, Martina, Illy, Stefan, Jelonnek, John, Kobarg, Thorsten, Lang, Rouven, Leonhardt, Wolfgang, Mellein, Daniel, Papenfuß, Daniel, Scherer, Theo, Thumm, Manfred, Wadle, Simone, Weggen, Jörg, and W7-X Team, Max Planck Institute for Plasma Physics, Max Planck Society

Subjects
Nuclear and High Energy Physics, Electron density, Technology, Materials science, Condensed matter physics, Plasma, Condensed Matter Physics, 7. Clean energy, 01 natural sciences, Instability, 010305 fluids & plasmas, law.invention, Ion, Impurity, law, Physics::Plasma Physics, 0103 physical sciences, Electron temperature, Wendelstein 7-X, 010306 general physics, ddc:600, Stellarator
Abstract

First experimental observations in the Wendelstein 7-X stellarator indicate that the impurity confinement can be explained by turbulent processes. In particular, plasma discharges with increased ion to electron temperature ratio are accompanied by reduced electron density fluctuation amplitudes and anomalous impurity diffusion, suggesting a lower turbulent transport. Employing gyro-kinetic numerical simulations, we argue that the temperature Ratio plays a key role for reducing the ion temperature gradient instability in Wendelstein 7-X, leading to an enhanced impurity confinement.

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

Author

Sunn Pedersen T, Dinklage A, Turkin Y, Wolf R, Bozhenkov S, Geiger J, Fuchert G, Bosch HS, Rahbarnia K, Thomsen H, Neuner U, Klinger T, Langenberg A, Trimiño Mora H, Kornejew P, Knauer J, Hirsch M, and Pablant N

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.

Published
2017
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