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Start Over Author "Nishizawa, T" Journal physics of plasmas
7 results on '"Nishizawa, T"'

2. Characterizing the flow and turbulence structure near the last closed flux surface in L-mode plasmas of ASDEX Upgrade

Author

Nishizawa, T., Manz, P., Grenfell, G., Griener, M., Wendler, D., Brida, D., Kriete, D., Dux, R., Kobayashi, T., Sasaki, M., and ASDEX Upgrade Team, Max Planck Institute for Plasma Physics, Max Planck Society

Subjects
Condensed Matter Physics
Abstract

Since high density operation is advantageous for building an efficient fusion reactor, understanding the density limit in tokamaks has been seen as one of the most important issues. This paper reports a series of measurements around the last-closed flux surface (LCFS) in L-mode plasmas by using a thermal helium beam diagnostic. Fluctuation analysis has been employed to characterize the poloidal flow and the turbulence structure. A reversal of the poloidal flow in the scrape-off layer and concomitant cooling of the outer divertor plasma are observed as the density is raised. While, in the confined region, the change in the density barely affects the poloidal flow, a higher density shifts the fluctuation power spectral densities toward lower frequencies and wave numbers. The eddy tilting of this region is consistent with what is expected from the magnetic shear effect. A radially coherent low frequency mode appears in the case of the highest density investigated in this study ([Formula: see text] = 0.51), and higher frequencies near the LCFS are modulated by this mode.

Published
2022

3. Edge turbulence measurements in L-mode and I-mode at ASDEX Upgrade.

Author

Bielajew, R., Conway, G. D., Griener, M., Happel, T., Höfler, K., Howard, N. T., Hubbard, A. E., McCarthy, W., Molina Cabrera, P. A., Nishizawa, T., Rodriguez-Fernandez, P., Silvagni, D., Vanovac, B., Wendler, D., Yoo, C., and White, A. E.

Subjects
PLASMA turbulence, TURBULENCE, ELECTRON emission, ELECTRON configuration, EDGES (Geometry)
Abstract

The I-mode confinement regime is promising for future reactor operation due to high energy confinement without high particle confinement. However, the role of edge turbulence in creating I-mode's beneficial transport properties is still unknown. New measurements of edge turbulence ( ρ pol = 0.9 − 1.0) in L-modes and I-modes at low and high densities at ASDEX Upgrade are presented in this paper. A high radial resolution correlation electron cyclotron emission radiometer measures the broadband turbulence throughout the L-mode and I-mode edge and pedestal. The weakly coherent mode (WCM) is measured in both L-mode and I-mode near the last closed flux surface with Te fluctuation levels of 2.3%–4.2%, with a frequency shift between the two phases related to a deeper Er well in I-mode. An n e T e phase diagnostic captures a change of the WCM n e T e phase between L-mode and I-mode from − 171 ° to − 143 °. The thermal He beam diagnostic measures a WCM wavenumber range of −0.5 to −1.0 cm−1. A low-frequency edge oscillation (LFEO) appears in the I-mode phase of these discharges and displays coupling to the WCM, but the LFEO does not appear in the L-mode phase. Linear gyrokinetic simulations of the outer core and pedestal top turbulence indicate that while the dominant turbulent modes in the outer core are ion directed and electrostatic, the turbulence becomes increasingly electron directed and electromagnetic with increasing radius. Collisionality is not found to impact characteristics of the L-mode and I-mode edge turbulence with respect to the presence of the WCM; however, the quality of global confinement decreases with collisionality. [ABSTRACT FROM AUTHOR]

Published
2022
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6. Plasma parameter profile inference from limited data utilizing second-order derivative priors and physic-based constraints.

Author

Nishizawa, T., Cavedon, M., Dux, R., Reimold, F., and Toussaint, U. von

Subjects
*MONTE Carlo method, *MARKOV chain Monte Carlo, *LAXATIVES, *KRIGING, *GAUSSIAN processes, *PLASMA diagnostics
Abstract

A Bayesian framework has been used to improve the quality of inferred plasma parameter profiles. An integrated data analysis allows for coherent combinations of different diagnostics, and Gaussian process regression provides a reliable regularization process and systematic uncertainty estimation. In this paper, we propose a new profile inference framework that utilizes our prior knowledge about plasma physics, along with integrated data analysis and a Gaussian process. In order to facilitate the use of the Markov chain Monte Carlo sampling, we use a Gaussian process to define quantities corresponding to the second derivatives of the profiles. We validate the analysis technique by using a synthetic one-dimensional plasma, in which the transport properties are known and demonstrate that the proposed analysis technique can infer plasma parameter profiles from line-integrated measurements only. Furthermore, we can even infer unknown parameters in our physics models when our physics knowledge on the system is incomplete. This analysis framework is applicable to laboratory plasmas and provides a means to investigate plasma parameters, to which standard diagnostics are not directly sensitive. [ABSTRACT FROM AUTHOR]

Published
2021
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7. Performance of Wendelstein 7-X stellarator plasmas during the first divertor operation phase

Author

Wolf, R. C., Alonso, A., Akaslompolo, S., Baldzuhn, J., Beurskens, M., Beidler, C. D., Biedermann, C., Bosch, H. -S., Bozhenkov, S., Brakel, R., Braune, H., Brezinsek, S., Brunner, K. -J., Damm, H., Dinklage, A., Drewelow, P., Effenberg, F., Feng, Y., Ford, O., Fuchert, G., Gao, Y., Geiger, J., Grulke, O., Harder, N., Hartmann, D., Helander, P., Heinemann, B., Hirsch, M., Hofel, U., Hopf, C., Ida, K., Isobe, M., Jakubowski, M. W., Kazakov, Y. O., Killer, C., Klinger, T., Knauer, J., Konig, R., Krychowiak, M., Langenberg, A., Laqua, H. P., Lazerson, S., Mcneely, P., Marsen, S., Marushchenko, N., Nocentini, R., Ogawa, K., Orozco, G., Osakabe, M., Otte, M., Pablant, N., Pasch, E., Pavone, A., Porkolab, M., Puig Sitjes, A., Rahbarnia, K., Riedl, R., Rust, N., Scott, E., Schilling, J., Schroeder, R., Stange, T., Von Stechow, A., Strumberger, E., Sunn Pedersen, T., Svensson, J., Thomson, H., Turkin, Y., Vano, L., Wauters, T., Wurden, G., Yoshinuma, M., Zanini, M., Zhang, D., Andreeva, T., Brandt, C., Burhenn, R., Buttenschon, B., Geiger, B., Tamura, N., Thomsen, H., Wegner, T., Abramovic, I., Alcuson, J., Aleynikov, P., Aleynikova, K., Ali, A., Anda, G., Ascasibar, E., Bahner, J. P., Baek, S. G., Balden, M., Banduch, M., Barbui, T., Behr, W., Beidler, C., Benndorf, A., Biel, W., Blackwell, B., Blanco, E., Blatzheim, M., Ballinger, S., Bluhm, T., Bockenhoff, D., Boswirth, B., Bottger, L. -G., Borchardt, M., Borsuk, V., Boscary, J., Brand, H., Brauer, T., Bussiahn, R., Bykov, V., Cai, J., Calvo, I., Cannas, B., Cappa, A., Carls, A., Carralero, D., Carraro, L., Carvalho, B., Castejon, F., Charl, A., Chaudhary, N., Chauvin, D., Chernyshev, F., Cianciosa, M., Citarella, R., Claps, G., Coenen, J., Cole, M., Cole, M. J., Cordella, F., Cseh, G., Czarnecka, A., Czerski, K., Czerwinski, M., Czymek, G., Da Molin, A., Da Silva, A., De La Pena, A., Degenkolbe, S., Dhard, C. P., Dibon, M., Dittmar, T., Drevlak, M., Drews, P., Durodie, F., Edlund, E., Van Eeten, P., Ehrke, G., Elgeti, S., Endler, M., Ennis, D., Esteban, H., Estrada, T., Fellinger, J., Flom, E., Fernandes, H., Fietz, W. H., Figacz, W., Fontdecaba, J., Fornal, T., Frerichs, H., Freund, A., Funaba, T., Galkowski, A., Gantenbein, G., Garcia Regana, J., Gates, D., Giannella, V., Gogoleva, A., Goncalves, B., Goriaev, A., Gradic, D., Grahl, M., Green, J., Greuner, H., Grosman, A., Grote, H., Gruca, M., Guerard, C., Hacker, P., Han, X., Harris, J. H., Hathiramani, D., Hein, B., Henneberg, S., Henkel, M., Hernandez Sanchez, J., Hidalgo, C., Hollfeld, K. P., Holting, A., Hoschen, D., Houry, M., Howard, J., Huang, X., Huang, Z., Hubeny, M., Huber, M., Hunger, H., Ilkei, T., Illy, S., Israeli, B., Jablonski, S., Jakubowski, M., Jelonnek, J., Jenzsch, H., Jesche, T., Jia, M., Junghanns, P., Kacmarczyk, J., Kallmeyer, J. -P., Kamionka, U., Kasahara, H., Kasparek, W., Kenmochi, N., Kirschner, A., Kleiber, R., Knaup, M., Knieps, A., Kobarg, T., Kocsis, G., Kochl, F., Kolesnichenko, Y., Konies, A., Kornejew, P., Koschinsky, J. -P., Koster, F., Kramer, M., Krampitz, R., Kramer-Flecken, A., Krawczyk, N., Kremeyer, T., Krom, J., Ksiazek, I., Kubkowska, M., Kuhner, G., Kurki-Suonio, T., Kurz, P. A., Kwak, S., Landreman, M., Lang, P., Lang, R., Langish, S., Laqua, H., Laube, R., Lechte, C., Lennartz, M., Leonhardt, W., Li, C., Li, Y., Liang, Y., Linsmeier, C., Liu, S., Lobsien, J. -F., Loesser, D., Loizu Cisquella, J., Lore, J., Lorenz, A., Losert, M., Lucke, A., Lumsdaine, A., Lutsenko, V., Maassberg, H., Marchuk, O., Matthew, J. H., Marushchenko, M., Masuzaki, S., Maurer, D., Mayer, M., Mccarthy, K., Meier, A., Mellein, D., Mendelevitch, B., Mertens, P., Mikkelsen, D., Mishchenko, A., Missal, B., Mittelstaedt, J., Mizuuchi, T., Mollen, A., Moncada, V., Monnich, T., Morisaki, T., Moseev, D., Murakami, S., Nafradi, G., Nagel, M., Naujoks, D., Neilson, H., Neu, R., Neubauer, O., Neuner, U., Ngo, T., Nicolai, D., Nielsen, S. K., Niemann, H., Nishizawa, T., Nuhrenberg, C., Nuhrenberg, J., Obermayer, S., Offermanns, G., Olmanns, J., Ongena, J., Oosterbeek, J. W., Pacios Rodriguez, L., Panadero, N., Panadero Alvarez, N., Papenfuss, D., Paqay, S., Pawelec, E., Pedersen, T. S., Pelka, G., Perseo, V., Peterson, B., Pilopp, D., Pingel, S., Pisano, F., Plaum, B., Plunk, G., Poloskei, P., Proll, J., Puiatti, M. -E., Purps, F., Rack, M., Recsei, S., Reiman, A., Reimold, F., Reiter, D., Remppel, F., Renard, S., Riemann, J., Risse, K., Rohde, V., Rohlinger, H., Rome, M., Rondeshagen, D., Rong, P., Roth, B., Rudischhauser, L., Rummel, K., Rummel, T., Runov, A., Ryc, L., Ryosuke, S., Sakamoto, R., Salewski, M., Samartsev, A., Sanchez, E., Sano, F., Satake, S., Schacht, J., Satheeswaran, G., Schauer, F., Scherer, T., Schlaich, A., Schlisio, G., Schluck, F., Schluter, K. -H., Schmitt, J., Schmitz, H., Schmitz, O., Schmuck, S., Schneider, M., Schneider, W., Scholz, P., Schrittwieser, R., Schroder, M., Schroder, T., Schumacher, H., Schweer, B., Sereda, S., Shanahan, B., Sibilia, M., Sinha, P., Siplia, S., Slaby, C., Sleczka, M., Smith, H., Spiess, W., Spong, D. A., Spring, A., Stadler, R., Stejner, M., Stephey, L., Stridde, U., Suzuki, C., Szabo, V., Szabolics, T., Szepesi, T., Szokefalvi-Nagy, Z., Tancetti, A., Terry, J., Thomas, J., Thumm, M., Travere, J. M., Traverso, P., Tretter, J., Trimino Mora, H., Tsuchiya, H., Tsujimura, T., Tulipan, S., Unterberg, B., Vakulchyk, I., Valet, S., Van Milligen, B., Van Vuuren, A. J., Vela, L., Velasco, J. -L., Vergote, M., Vervier, M., Vianello, N., Viebke, H., Vilbrandt, R., Vorkoper, A., Wadle, S., Wagner, F., Wang, E., Wang, N., Wang, Z., Warmer, F., Wegener, L., Weggen, J., Wei, Y., Weir, G., Wendorf, J., Wenzel, U., Werner, A., White, A., Wiegel, B., Wilde, F., Windisch, T., Winkler, M., Winter, A., Winters, V., Wolf, S., Wright, A., Xanthopoulos, P., Yamada, H., Yamada, I., Yasuhara, R., Yokoyama, M., Zarnstorff, M., Zeitler, A., Zhang, H., Zhu, J., Zilker, M., Zocco, A., Zoletnik, S., Zuin, M., Science and Technology of Nuclear Fusion, Turbulence in Fusion Plasmas, and W7-X Team, Max Planck Institute for Plasma Physics, Max Planck Society

Subjects
Physics, Technology, Plasma parameters, Divertor, Nuclear engineering, Plasma, Condensed Matter Physics, 01 natural sciences, 7. Clean energy, Electron cyclotron resonance, 010305 fluids & plasmas, law.invention, Magnetic field, law, 0103 physical sciences, Limiter, Wendelstein 7-X, 010306 general physics, ddc:600, Stellarator
Abstract

Wendelstein 7-X is the first comprehensively optimized stellarator aiming at good confinement with plasma parameters relevant to a future stellarator power plant. Plasma operation started in 2015 using a limiter configuration. After installing an uncooled magnetic island divertor, extending the energy limit from 4 to 80 MJ, operation continued in 2017. For this phase, the electron cyclotron resonance heating (ECRH) capability was extended to 7 MW, and hydrogen pellet injection was implemented. The enhancements resulted in the highest triple product (6.5 × 1019 keV m-3 s) achieved in a stellarator until now. Plasma conditions [Te(0) ≈ Ti(0) ≈ 3.8 keV, τE > 200 ms] already were in the stellarator reactor-relevant ion-root plasma transport regime. Stable operation above the 2nd harmonic ECRH X-mode cutoff was demonstrated, which is instrumental for achieving high plasma densities in Wendelstein 7-X. Further important developments include the confirmation of low intrinsic error fields, the observation of current-drive induced instabilities, and first fast ion heating and confinement experiments. The efficacy of the magnetic island divertor was instrumental in achieving high performance in Wendelstein 7-X. Symmetrization of the heat loads between the ten divertor modules could be achieved by external resonant magnetic fields. Full divertor power detachment facilitated the extension of high power plasmas significantly beyond the energy limit of 80 MJ.

Published
2019

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