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6 results on '"J. Saffert"'

1. A new quasi-stationary, very high density plasma regime on the W7-AS stellarator

Author

A. Weller, G. Kuehner, H. Niedermeyer, M. Kick, J. Baldzuhn, D. Hildebrandt, D. A. Hartmann, H. Maassberg, R. Brakel, M. Endler, R. Burhenn, K. McCormick, H. P. Laqua, E. Speth, N. Rust, F. Schneider, J. Geiger, Thomas Klinger, V. Erckmann, H. J. Hartfuss, A. Werner, J. Saffert, F. Gadelmeier, U. Wenzel, N. Ruhs, H. Ehmler, E. Holzhauer, J. P. Knauer, R. Narayanan, Y. Feng, E. Pasch, F. Sardei, L. Giannone, R. Jaenicke, Friedrich E. Wagner, S Baeumel, E. Wuersching, M. Schubert, M. Hirsch, R. Koenig, P. Grigull, J. Kisslinger, and S. Klose

Subjects
Physics, Steady state, Divertor, Pulse duration, Flux, Plasma, Condensed Matter Physics, Computational physics, law.invention, Magnetic field, Nuclear Energy and Engineering, Physics::Plasma Physics, law, Limiter, Atomic physics, Stellarator
Abstract

Stellarators have the intrinsic property of steady state operation. However, on present-day stellarators the pulse length is usually not only limited due to technical reasons, but also by physical problems. Lack of density control and a subsequent radiation collapse terminate the discharges quite often at high densities. To improve the control of the plasma-wall interaction, the island divertor concept was developed for optimized stellarators. To test this divertor concept on W7-AS, all limiters were removed and replaced by ten divertor modules. In subsequent divertor experiments a promising new plasma operational regime has been discovered which is termed 'high density H-mode' (HDH-mode). During the transition into that regime a clear reduction of ELM-like events and turbulent fluctuations is observed. The HDH-mode combines good energy confinement with very low impurity confinement resulting in low core radiation, but high edge-localized radiation. Consequently, stationary discharges at densities of typically 2 x 10 20 m -3 can be performed within the accessible pulse length of about 1 s. At densities above 3 x 10 20 m -3 a controlled transition from attached to partially detached plasmas is observed. The still edge-localized radiation reaches 90% of the heating power so that the power load onto the divertor target plates is further reduced. At a lower toroidal field of 0.9 T average β-values could be raised from earlier 2% to more than 3% in magnetic field configurations with rather smooth flux surfaces at the plasma boundary. The recently obtained results render excellent prospects for W7-X, the larger superconducting successor experiment of W7-AS.

Published
2002
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2. 140 GHz electron cyclotron resonance heating experiments at the W7-AS stellarator

Author

H. Wolff, A. Dodhy, G. Cattanei, S. Geissler, E. Würsching, A. A. Borschegovsky, S. A. Malygin, H. Verbeek, H. Ringler, F. Sardei, N. Ruhs, P. Pech, H. Niedermeyer, F. Karger, M. Endler, U. Wenzel, R. Burhenn, A. Rudjy, H. Maassberg, S. Sattler, H. J. Hartfuss, G. A. Müller, J. V. Hofmann, J. Baldzuhn, Frank Schneider, R. Jaenicke, M. Tutter, G. Kuehner, T. Geist, G. Herre, D. Zimmermann, H. Kroiss, O. Heinrich, L. Giannone, V. I. Malygin, M. Kick, Ulrich Stroth, T. Ott, V. Erckmann, D. Hildebrandt, D. Dorst, M. Zippe, U. Gasparino, R. Brakel, E. Speth, C. Mahn, K. McCormick, G. Siller, Friedrich E. Wagner, P. Grigull, W. Kasparek, W. Gasparino, J. Saffert, K. Engelhardt, V. I. Ilin, P. G. Schüller, A. Weller, H. P. Penningsfeld, Ulrich Schneider, V. I. Kurbatov, A. Elsner, W. Ohlendorf, H. Hacker, and E. Unger

Subjects
Materials science, Mechanical Engineering, Power deposition, Cyclotron, Electron, Neutral beam injection, Electron cyclotron resonance, Magnetic field, law.invention, Nuclear Energy and Engineering, Impurity, law, General Materials Science, Atomic physics, Stellarator, Civil and Structural Engineering
Abstract

Electron cyclotron resonance heating (ECRH) at the W7-AS stellarator is performed two systems of comparable heating power at 70 GHz (0.8 MW, 3 s) and 140 GHz (0.9 MW, 0.4 s). Experiments with 140 GHz open a new parameter window with high density operation up to 1.1 × 1020 m−3. H mode transitions were observed in high density discharges at 2.5 T and at lower density at 1.25 T. The operational window for the stellarator H mode with emphasis on the density and power threshold and the influence of gas puffing on the H transitions are discussed. Perturbation experiments with modulated ECRH power were performed to determine the heat transport and the power deposition profile. Density control is achieved in combined heating with neutral beam injection (NBI) despite the beam particle fuelling, whereas with NBI alone a steady density rise is observed. The impact of combined heating on the impurity confinement was investigated. Electron cyclotron current drive (ECCD) was studied in different magnetic field configurations and the influence of trapped particles on the ECCD efficiency was examined experimentally and compared with theory.

Published
1995
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3. Some aspects of the plasma edge properties of the Wendelstein 7-AS stellarator

Author

R. Brakel, R. Burhenn, G. Cattanei, A. Dodhy, D. Dorst, A. Elsner, K. Engelhardt, V. Erckmann, U. Gasparino, G. Grieger, P. Grigull, H. Hacker, H.J. Hartfuss, H. Jäckel, R. Jaenicke, J. Junker, M. Kick, H. Kroiss, G. Kuehner, I. Lakicevic, A. Lazaros, H. Maassberg, C. Mahn, W. Ohlendorf, H. Renner, H. Ringler, J. Saffert, F. Sardei, M. Tutter, A. Weller, E. Würsching, M. Zippe, R. Behrisch, V. Prozesky, F. Rau, J. Roth, W. Kasparek, G.A. Müller, P.G. Schüller, and M. Thumm

Subjects
Physics, Nuclear and High Energy Physics, Toroid, Plasma, Radiation, law.invention, Nuclear Energy and Engineering, Physics::Plasma Physics, law, Power Balance, Impurity, Orbit (dynamics), Limiter, General Materials Science, Atomic physics, Stellarator
Abstract

The plasma edge region of the W 7-AS stellarator has a complex structure due to “natural” islands. Guiding centre orbit calculations by a Monte Carlo code indicate that there are locally fixed patterns of enhanced particle flow to the wall. Power loss simulations by the DEGAS code satisfactorily reproduce measured power depositions on the main limiters, but in the total power balance including radiation a significant deficiency is found. The role of limiters with respect to impurity fluxes is discussed on the basis of spectroscopic data. A long-term collector probe analysis shows inhomogeneous poloidal and toroidal distributions of deposited materials which are influenced by plasma shots as well as conditioning discharges.

Published
1990

4. Plasma confinement in stellarator systems

Author

A. Elsner, C. Mahn, G. G. Lister, M. Tutter, J. How, G. Mueller, J. H. Feist, H. Ringler, R. Smeulders, D. V. Bartlett, A. N. Dellis, W. Ott, P. Javel, F. Leuterer, R. Jaenicke, P. R. Thomas, G. Grieger, D. Dorst, S. Marlier, G. Cannici, R. Lathe, J. Saffert, B. Lloyd, E. Speth, H. Hacker, A. Weller, H. Jaeckel, A. C. Selden, H. Wobig, E. Wuersching, P. C. Johnson, F. Rau, M. Kick, H. Renner, P. J. Lomas, G. Cattanei, D. J. Lees, J. Sapper, W. Ohlendorf, and J. Junker

Subjects
Physics, Nuclear physics, Plasma heating, law, Plasma confinement, Plasma, Atomic physics, Electrical conductor, Stellarator, law.invention, Plasma control, Magnetic field, Plasma current
Abstract

The stellarator is a plasma confinement system in which the magnetic field configuration is produced by currents in conductors outside the plasma. Plasma current is not necessarily required for confinement or for heating the plasma. Results from the CLEO and W VIIA experiments are presented to illustrate the progress in the understanding of containment and heating in the stellarator configuration.

Published
1981
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5. Plasma heating in JET

Author

A Ainsworth, H Altmann, R J Anderson, J Arbez, D Bartlett, W Bailey, K Behringer, E Bertolini, P Bertoldi, C H Best, V Bhatnagar, R J Bickerton, G Boissin, T Bonicelli, S Booth, A Boschi, G Bosia, M Botman, H Brelen, H Brinkschulte, M L Browne, M Brusati, T Budd, M Bures, P Butcher, H Buttgereit, D Cacaut, C Caldwell-Nichols, D Campbell, J Carwardine, G Celentano, C D Challis, A Cheetman, J Christiansen, C Christodoulopoulos, P Chuilon, R Claesen, J P Coad, M Cooke, J G Cordey, W Core, S Corti, A E Costley, G Cottrell, J Dean, E Deksnis, G Deschamps, K J Dietz, J Dobbing, S E Dorling, D F Duechs, G Duesing, H Duquenoy, L de Kock, A Edwards, W Engelhardt, F Erhorn, B Eriksson, H Falter, T Hellsten, J L Hemmerich, R Hemsworth, F Hendriks, R F Herzog, L Horton, J How, M Huart, A Hubbard, M Hugon, P Jones, J Kaeline, A Kaellne, A Kaye, B E Keen, M Keilhacker, G Kinahan, A Konstantellos, P Kupschus, P Lallia, J R Last, N Foden, C Froger, K Fullard, A Galetsas, A Gallacher, A Gibson, R D Gill, A Geode, A Gondhalekar, N A Gottardi, C Gowers, R Granetz, B Green, S Gregoli, F S Griph, R Haange, C J Hancock, P Harbour, R F Herog, J Kaellne, L Lauro-Taroni, E Lazzaro, R C Lobel, P Lomas, M Lorenzo-Gottardi, C Lowry, G Magyar, D Maissonneir, M Malacarne, V Marchese, P Massmann, P McMullen, M J Mead, P Meriguet, V Merlo, S Mills, P Millward, A Moissonnier, P L Mondini, P Morgan, G Murphy, M F Nave, L Nickesson, P Nielson, P Noll, S Nowak, W Obert, B Oliver, M Olsson, J O'Rourke, M G Pacco, J Paillere, L Pannacione, S Papastergiou, D Pasini, M Pescatore, J Planncoulaine, J P Poffe, R Prentice, T Raimondi, C Raymond, P H Rebut, J Removille, W Riediker, R Roberts, A Rolfe, R T Ross, G Sadler, J Saffert, N Salmon, A Sand, A Santagiustina, R Saunders, M Schmid, F C Schueller, K Selin, R Shaw, D Sigournay, R Simonini, P Smeulders, L Sonnerup, K Sonnenberg, M Stamp, C A Steed, D Stork, P E Stott, T E Stringer, D Summers, A Tanga, A Taroni, A Terrington, A Tesini, P R Thomas, E Thompson, F Tibone, R Tivery, E Usselmann, H Van der Beken, M Von Hellerman, J E Van Montfoort, T Wade, C Walker, B A Wallander, M Walravens, K Walter, M L Watkins, M Watson, D Webberley, J Wesson, J Wilks, T Winkel, C Woodward, M Wykes, D Young, L Zennelili, J Zwart, B Beaumont, D Gambier, D Moreau, J Ehrenberg, H Jaeckel, S Kissel, U Kuephnapfel, R Mueller, A Staebler, A Weller, J H Hamnen, M Evrared, M Gadeberg, K Thomsen, P Dupperrex, G Tonetti, N Lopez-Cardozo, B Tubbing, J Von Seggern, J Tagle, F Bombarda, G Bracco, R Giannella, R Carolan, M Cox, M Forrest, D Goodall, N Hawkes, P Haynes, J Hugill, K D Lawson, G McCracken, J Partridge, N Peacock, J Snipes, T Todd, H Schamel, H Summers, and S Tsuji

Subjects
Jet (fluid), Settore FIS/03, Materials science, Nuclear Energy and Engineering, Resonance, Electron temperature, Plasma, Sawtooth wave, Electron, Atomic physics, Condensed Matter Physics, Neutral beam injection, Ion
Abstract

Heating the JET plasma well above temperatures reached in the ohmic phase is the aim of the two additional heating systems planned for JET: ion cyclotron resonance heating (ICRF) and neutral beam injection (NBI). Operations with the latter started in February 1986, initially with hydrogen injection, up to a power level of 7 MW. ICRF power has been delivered to the plasma by three antennae and has reached power levels of 6 MW for 2 s. In most experiments, the frequency of the waves is adjusted to position the minority ion resonance layer close to the centre of the discharge, resulting in a centrally peaked power deposition profile. Results have also shown that the increase of the volume averaged electron temperature was much less dependent on the radial position of the ion resonance layer than were the central temperatures of both ions and electrons which can both approach 5 keV. In cases of 'on axis' heating, large increases in the sawtooth activity is observed with sawtooth periods exceeding 0.3 s. Initial results with NBI have shown a decrease of the global energy confinement time with additional power similar to the one observed with ICRF heating.

Published
1986
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6. Initial operation of the Wendelstein 7AS advanced stellarator

Author

H Renner, E Anabitarte, E Ascasibar, S Besshou, R Brakel, R Burhenn, G Cattanei, A Dodhy, D Dorst, A Elsner, K Engelhardt, V Erckmann, D Evans, U Gasparino, G Grieger, P Grigull, H Hacker, H Hailer, H J Hartfuss, H Jackel, R Jaenicke, S Jiang, J Junker, M Kick, H Kroiss, G Kuehner, I Lakicevic, H Maassberg, C Mahn, R Martin, G Muller, H Munch, A Navarro, M Ochando, W Ohlendorf, M Petrov, F Rau, H Ringler, J Saffert, J Sanchez, J Sapper, A V Saposhnikov, F Sardei, I S Sbitnikova, I Schoenewolf, K Schwoerer, F Tabares, M Tutter, A Weller, H Wobig, E Wursching, M Zippe, J H Feist, K Freudenberger, R C Kunze, W Ott, F -P Penningsfeld, E Speth, W Melkus, W Kasparek, G A Muller, P G Schuller, M Thumm, R Wienecke, J Baumler, W Becker, F Braun, R Fritsch, F Hofmeister, A Murphy, J M Noterdaeme, S Puri, F Ryter, H Wedler, and F Wesner

Subjects
Surface mapping, Physics, Nuclear Energy and Engineering, law, Phase (waves), Plasma, Current (fluid), Condensed Matter Physics, Stellarator, Bootstrap current, law.invention, Plasma current, Computational physics
Abstract

The first plasma experiments on the W7AS advanced stellarator were conducted in October 1988, after magnetic surface mapping. The characteristics of the device are described. During the first phase of operation, 70 GHz ECF was used to generate and heat a 'currentless' plasma which was maintained in quasi-steady state for typically 0.5 s. Effects of the magnetic configuration on the confinement and measures to deal with the observed plasma current (bootstrap current and ECF-driven current) were investigated. Preliminary results of transport analysis are presented and compared with predictions of transport models.

Published
1989
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