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1

Digitale Medien

Rotational and magnetic shear stabilization of magnetohydrodynamic modes and turbulence in DIII-D high performance discharges (1996)

Lao, L. L. ; Burrell, K. H. ; Casper, T. S. ; [weitere]

[S.l.] : American Institute of Physics (AIP)

Physics of Plasmas 3 (1996), S. 1951-1958

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ISSN: 1089-7674

Quelle: AIP Digital Archive

Thema: Physik

Notizen: The confinement and the stability properties of the DIII-D tokamak [Plasma Physics and Controlled Nuclear Fusion Research 1986 (International Atomic Energy Agency, Vienna, 1987), Vol. 1, p. 159] high-performance discharges are evaluated in terms of rotational and magnetic shear, with an emphasis on the recent experimental results obtained from the negative central magnetic shear (NCS) experiments. In NCS discharges, a core transport barrier is often observed to form inside the NCS region accompanied by a reduction in core fluctuation amplitudes. Increasing negative magnetic shear contributes to the formation of this core transport barrier, but by itself is not sufficient to fully stabilize the toroidal drift mode (trapped-electron-ηi mode) to explain this formation. Comparison of the Doppler shift shear rate to the growth rate of the ηi mode suggests that the large core E×B flow shear can stabilize this mode and broaden the region of reduced core transport. Ideal and resistive stability analysis indicates the performance of NCS discharges with strongly peaked pressure profiles is limited by the resistive interchange mode to low βN≤2.3. This mode is insensitive to the details of the rotational and the magnetic shear profiles. A new class of discharges, which has a broad region of weak or slightly negative magnetic shear (WNS), is described. The WNS discharges have broader pressure profiles and higher β values than the NCS discharges, together with high confinement and high fusion reactivity. © 1996 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.871991

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2

Digitale Medien

Symmetry experiments in gas-filled hohlraums at NOVA (1996)

Delamater, N. D. ; Murphy, T. J. ; Hauer, A. A. ; [weitere]

[S.l.] : American Institute of Physics (AIP)

Physics of Plasmas 3 (1996), S. 2022-2028

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ISSN: 1089-7674

Quelle: AIP Digital Archive

Thema: Physik

Notizen: Understanding drive symmetry in gas-filled hohlraums is currently of interest because the baseline design of the indirect drive ignition target for the planned National Ignition Facility uses a gas-filled hohlraum. This paper reports on the results of a series of experiments performed at the Nova laser [C. Bibeau et al. Appl. Opt. 31, 5799 (1992)] facility at Lawrence Livermore National Laboratory with the goal of understanding time-dependent drive symmetry in gas filled hohlraums. Time-dependent symmetry data from capsule implosions and reemission targets in gas-filled hohlraums are discussed. Results of symmetry measurements using thin wall gas-filled hohlraums are also discussed. The results show that the gas is effective in impeding the motion of the wall blowoff material, and that the resulting implosion performance of the capsule is not significantly degraded from vacuum results. The implosion symmetry in gas differs from vacuum results with similar laser pointing indicating a shift in beam position on the hohlraum wall and hotter drive at the capsule's poles than at the equator. A theory has been proposed to explain the observed shift as a plasma physics effect: beam steering due to filamentation and transverse plasma flows. © 1996 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.871999

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3

Digitale Medien

Radiation drive in laser-heated hohlraums (1996)

Suter, L. J. ; Kauffman, R. L. ; Darrow, C. B. ; [weitere]

[S.l.] : American Institute of Physics (AIP)

Physics of Plasmas 3 (1996), S. 2057-2062

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ISSN: 1089-7674

Quelle: AIP Digital Archive

Thema: Physik

Notizen: Nearly 10 years of Nova [E. M. Campbell, Laser Part. Beams 9, 209 (1991)] experiments and analysis have lead to a relatively detailed quantitative and qualitative understanding of radiation drive in laser-heated hohlraums. Our most successful quantitative modeling tool is two-dimensional (2-D) LASNEX numerical simulations [G. B. Zimmerman and W. L. Kruer, Comments Plasma Phys. Controlled Fusion 2, 51 (1975)]. Analysis of the simulations provides us with insight into the physics of hohlraum drive. In particular we find hohlraum radiation conversion efficiency becomes quite high with longer pulses as the accumulated, high-Z blow-off plasma begins to radiate. Extensive Nova experiments corroborate our quantitative and qualitative understanding. © 1996 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.872002

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4

Digitale Medien

Demonstration of high-performance negative central magnetic shear discharges in the DIII-D tokamak (1996)

Rice, B. W. ; Burrell, K. H. ; Lao, L. L. ; [weitere]

[S.l.] : American Institute of Physics (AIP)

Physics of Plasmas 3 (1996), S. 1983-1991

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ISSN: 1089-7674

Quelle: AIP Digital Archive

Thema: Physik

Notizen: Reliable operation of discharges with negative central magnetic shear has led to significant increases in plasma performance and reactivity in both low confinement, L-mode, and high confinement, H-mode, regimes in the DIII-D tokamak [Plasma Physics and Controlled Nuclear Fusion Research 1986 (International Atomic Energy Agency, Vienna, 1987), Vol. 1, p. 159]. Using neutral beam injection early in the initial current ramp, a large range of negative shear discharges have been produced with durations lasting up to 3.2 s. The total noninductive current (beam plus bootstrap) ranges from 50% to 80% in these discharges. In the region of shear reversal, significant peaking of the toroidal rotation [fφ(0)∼30–60 kHz] and ion temperature [Ti(0)∼15–22 keV] profiles are observed. In high-power discharges with an L-mode edge, peaked density profiles are also observed. Confinement enhancement factors up to H≡τE/τITER-89P∼2.5 with an L-mode edge, and H∼3.3 in an edge localized mode (ELM)-free H mode, are obtained. Transport analysis shows both ion thermal diffusivity and particle diffusivity to be near or below standard neoclassical values in the core. Large pressure peaking in the L mode leads to high disruptivity with βN≡βT/(I/aB)≤2.3, while broader pressure profiles in the H mode gives low disruptivity with βN≤4.2. © 1996 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.871994

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5

Digitale Medien

Laser–plasma interactions in ignition-scale hohlraum plasmas (1996)

MacGowan, B. J. ; Afeyan, B. B. ; Back, C. A. ; [weitere]

[S.l.] : American Institute of Physics (AIP)

Physics of Plasmas 3 (1996), S. 2029-2040

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ISSN: 1089-7674

Quelle: AIP Digital Archive

Thema: Physik

Notizen: Scattering of laser light by stimulated Brillouin scattering (SBS) and stimulated Raman scattering (SRS) is a concern for indirect drive inertial confinement fusion (ICF). The hohlraum designs for the National Ignition Facility (NIF) raise particular concerns due to the large scale and homogeneity of the plasmas within them. Experiments at Nova have studied laser–plasma interactions within large scale length plasmas that mimic many of the characteristics of the NIF hohlraum plasmas. Filamentation and scattering of laser light by SBS and SRS have been investigated as a function of beam smoothing and plasma conditions. Narrowly collimated SRS backscatter has been observed from low density, low-Z, plasmas, which are representative of the plasma filling most of the NIF hohlraum. SBS backscatter is found to occur in the high-Z plasma of gold ablated from the wall. Both SBS and SRS are observed to be at acceptable levels in experiments using smoothing by spectral dispersion (SSD). © 1996 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.872000

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6

Digitale Medien

Direct-drive laser-fusion experiments with the OMEGA, 60-beam, 〉40 kJ, ultraviolet laser system (1996)

Soures, J. M. ; McCrory, R. L. ; Verdon, C. P. ; [weitere]

[S.l.] : American Institute of Physics (AIP)

Physics of Plasmas 3 (1996), S. 2108-2112

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ISSN: 1089-7674

Quelle: AIP Digital Archive

Thema: Physik

Notizen: OMEGA, a 60-beam, 351 nm, Nd:glass laser with an on-target energy capability of more than 40 kJ, is a flexible facility that can be used for both direct- and indirect-drive targets and is designed to ultimately achieve irradiation uniformity of 1% on direct-drive capsules with shaped laser pulses (dynamic range (approximately-greater-than)400:1). The OMEGA program for the next five years includes plasma physics experiments to investigate laser–matter interaction physics at temperatures, densities, and scale lengths approaching those of direct-drive capsules designed for the 1.8 MJ National Ignition Facility (NIF); experiments to characterize and mitigate the deleterious effects of hydrodynamic instabilities; and implosion experiments with capsules that are hydrodynamically equivalent to high-gain, direct-drive capsules. Details are presented of the OMEGA direct-drive experimental program and initial data from direct-drive implosion experiments that have achieved the highest thermonuclear yield (1014 DT neutrons) and yield efficiency (1% of scientific breakeven) ever attained in laser-fusion experiments. © 1996 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.871662

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7

Digitale Medien

Resistivity and its temperature dependence of nanostructured NiAl at temperatures from 77 to 300 K (1996)

Qin, X. Y. ; Zhang, L. D. ; Wu, B. M. ; [weitere]

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 80 (1996), S. 4776-4778

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ISSN: 1089-7550

Quelle: AIP Digital Archive

Thema: Physik

Notizen: Direct current resistivity and its temperature dependence for nanostructured NiAl (n-NiAl) was investigated at temperatures from 77 to 300 K. The resistivity of n-NiAl (size 5–6 nm) was higher than that of polycrystalline NiAl and increased with decreasing density. For the n-NiAl with relative density D(approximately-greater-than)70%, the resistivity decreased with decreasing temperature, manifesting metallic behavior. However, its temperature coefficient of resistivity decreased monotonically with decreasing density, and changed sign from positive to negative at densities 68%–70%, below which it displays on nonmetallic behavior. These results can be well interpreted by dominant grain boundary scattering. © 1996 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.363417

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8

Digitale Medien

Toward high-performance computational chemistry: II. A scalable self-consistent field program (1996)

Harrison, Robert J. ; Guest, Martyn F. ; Kendall, Rick A. ; [weitere]

New York, NY [u.a.] : Wiley-Blackwell

Journal of Computational Chemistry 17 (1996), S. 124-132

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ISSN: 0192-8651

Schlagwort(e): Chemistry ; Theoretical, Physical and Computational Chemistry

Quelle: Wiley InterScience Backfile Collection 1832-2000

Thema: Chemie und Pharmazie , Informatik

Notizen: We discuss issues in developing scalable parallel algorithms and focus on the distribution, as opposed to the replication, of key data structures. Replication of large data structures limits the maximum calculation size by imposing a low ratio of processors to memory. Only applications which distribute both data and computation across processors are truly scalable. The use of shared data structures that may be independently accessed by each process even in a distributed memory environment greatly simplifies development and provides a significant performance enhancement. We describe tools we have developed to support this programming paradigm. These tools are used to develop a highly efficient and scalable algorithm to perform self-consistent field calculations on molecular systems. A simple and classical strip-mining algorithm suffices to achieve an efficient and scalable Fock matrix construction in which all matrices are fully distributed. By strip mining over atoms, we also exploit all available sparsity and pave the way to adopting more sophisticated methods for summation of the Coulomb and exchange interactions. © 1996 by John Wiley & Sons, Inc.

Zusätzliches Material: 5 Ill.

Materialart: Digitale Medien

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