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Träfflista för sökning "WFRF:(Janhunen J.) "

Sökning: WFRF:(Janhunen J.)

  • Resultat 1-11 av 11
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1.
  • Fenstermacher, M.E., et al. (författare)
  • DIII-D research advancing the physics basis for optimizing the tokamak approach to fusion energy
  • 2022
  • Ingår i: Nuclear Fusion. - : IOP Publishing. - 0029-5515 .- 1741-4326. ; 62:4
  • Tidskriftsartikel (refereegranskat)abstract
    • DIII-D physics research addresses critical challenges for the operation of ITER and the next generation of fusion energy devices. This is done through a focus on innovations to provide solutions for high performance long pulse operation, coupled with fundamental plasma physics understanding and model validation, to drive scenario development by integrating high performance core and boundary plasmas. Substantial increases in off-axis current drive efficiency from an innovative top launch system for EC power, and in pressure broadening for Alfven eigenmode control from a co-/counter-I p steerable off-axis neutral beam, all improve the prospects for optimization of future long pulse/steady state high performance tokamak operation. Fundamental studies into the modes that drive the evolution of the pedestal pressure profile and electron vs ion heat flux validate predictive models of pedestal recovery after ELMs. Understanding the physics mechanisms of ELM control and density pumpout by 3D magnetic perturbation fields leads to confident predictions for ITER and future devices. Validated modeling of high-Z shattered pellet injection for disruption mitigation, runaway electron dissipation, and techniques for disruption prediction and avoidance including machine learning, give confidence in handling disruptivity for future devices. For the non-nuclear phase of ITER, two actuators are identified to lower the L-H threshold power in hydrogen plasmas. With this physics understanding and suite of capabilities, a high poloidal beta optimized-core scenario with an internal transport barrier that projects nearly to Q = 10 in ITER at ∼8 MA was coupled to a detached divertor, and a near super H-mode optimized-pedestal scenario with co-I p beam injection was coupled to a radiative divertor. The hybrid core scenario was achieved directly, without the need for anomalous current diffusion, using off-axis current drive actuators. Also, a controller to assess proximity to stability limits and regulate β N in the ITER baseline scenario, based on plasma response to probing 3D fields, was demonstrated. Finally, innovative tokamak operation using a negative triangularity shape showed many attractive features for future pilot plant operation.
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  • Janhunen, P., et al. (författare)
  • Invited Article: Electric solar wind sail : Toward test missions
  • 2010
  • Ingår i: Review of Scientific Instruments. - : AIP Publishing. - 0034-6748 .- 1089-7623. ; 81:11, s. 111301-
  • Tidskriftsartikel (refereegranskat)abstract
    • The electric solar wind sail (E-sail) is a space propulsion concept that uses the natural solar wind dynamic pressure for producing spacecraft thrust. In its baseline form, the E-sail consists of a number of long, thin, conducting, and centrifugally stretched tethers, which are kept in a high positive potential by an onboard electron gun. The concept gains its efficiency from the fact that the effective sail area, i.e., the potential structure of the tethers, can be millions of times larger than the physical area of the thin tethers wires, which offsets the fact that the dynamic pressure of the solar wind is very weak. Indeed, according to the most recent published estimates, an E-sail of 1 N thrust and 100 kg mass could be built in the rather near future, providing a revolutionary level of propulsive performance (specific acceleration) for travel in the solar system. Here we give a review of the ongoing technical development work of the E-sail, covering tether construction, overall mechanical design alternatives, guidance and navigation strategies, and dynamical and orbital simulations.
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4.
  • Lê, A D, et al. (författare)
  • Neurobiological processes in alcohol addiction.
  • 2001
  • Ingår i: Alcoholism, clinical and experimental research. - 0145-6008. ; 25:5 Suppl ISBRA
  • Forskningsöversikt (refereegranskat)abstract
    • This article represents the proceedings of a symposium at the ISBRA Meeting in Yokohama, Japan. The chairs were A. D. Lê and K. Kiianmaa. The presentations were (1) Alcohol reward and aversion, by C. L. Cunningham; (2) The role of sensitization of neuronal mechanisms in ethanol self-administration, by J. A. Engel, M. Ericson, and B. Söderpalm; (3) Alcohol self-administration in dependent animals: Neurobiological mechanisms, by G. F. Koob, A. J. Roberts, and F. Weiss; (4) Stress and relapse to alcohol, by A. D. Lê; (5) Alcohol-preferring AA and alcohol-avoiding ANA rats differ in locomotor activation induced by repeated morphine injections, by P. Hyytiä, S. Janhunen, J. Mikkola, P. Bäckström, and K. Kiianmaa; and (6) Initial sensitivity and acute functional tolerance to the hypnotic effects of ethanol in mice genetically selected for mild and severe ethanol withdrawal convulsions, by I. Ponomarev and J. C. Crabbe.
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  • Fryer, L. J., et al. (författare)
  • 3D GUMICS Simulations of Northward IMF Magnetotail Structure
  • 2023
  • Ingår i: Journal of Geophysical Research - Space Physics. - : American Geophysical Union (AGU). - 2169-9380 .- 2169-9402. ; 128:8
  • Tidskriftsartikel (refereegranskat)abstract
    • This study presents a re-evaluation of the Kullen and Janhunen (2004, https://doi.org/10.5194/angeo-22-951-2004) global northward interplanetary magnetic field (IMF) simulation, using the Grand Unified Magnetosphere–Ionosphere Coupling Simulation version 4 (GUMICS-4), a global MHD model. We investigate the dynamic coupling between northward IMF conditions and the Earth’s magnetotail and compare the results to observation-based mechanisms for the formation of transpolar arcs. The results of this study reveal that under northward IMF conditions (and northward IMF initialization), a large closed field line region forms in the magnetotail, with similarities to transpolar arc structures observed from spacecraft data. This interpretation is supported by the simultaneous increase of closed flux measured in the magnetotail. However, the reconnection configuration differs in several respects from previously theorized magnetotail structures that have been inferred from both observations and simulations results and associated with transpolar arcs. We observe that dawn–dusk lobe regions form as a result of high-latitude reconnection during the initialization stages, which later come into contact as the change in the IMF By component causes the magnetotail to twist. We conclude that in the GUMICS simulation, transpolar arc-like structures are formed as a result of reconnection in the magnetotail, rather than high-latitude reconnection or due to the mapping of the plasma sheet through a twisted magnetotail as interpreted from previous analysis of GUMICS simulations.
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  • Syrjäsuo, M., Pulkkinen, T.I., Pellinen, R.P., Janhunen, P., Kauristie, K., Viljanen, A., Opgenoorth, H.J., Karllson, P., Wallman, S., Eglitis, P., Nielsen, E. and Thomas, C. (författare)
  • Observations of substorm electrodynamics using the miracle network.
  • 2001
  • Ingår i: The 4th International Conference on Substorms, ICS4. - : Terra Scient. Publ. Comp. Tokyo, Japan. Kaje Hamana, Japan.
  • Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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11.
  • Vaivads, A., et al. (författare)
  • What high altitude observations tell us about the auroral acceleration : A cluster/DMSP conjunction
  • 2003
  • Ingår i: Geophysical Research Letters. - : American Geophysical Union (AGU). - 0094-8276 .- 1944-8007. ; 30:3
  • Tidskriftsartikel (refereegranskat)abstract
    • [1] Magnetic conjugate observations by Cluster and DMSP F14 satellites are used to study the field lines of auroral arc. Cluster is well above the acceleration region and observes upward keV ion beams and bipolar electric structures. The integrated potential at Cluster altitudes shows a dip that is consistent with the keV electron acceleration energy at low altitude. The earthward Poynting flux at Cluster altitudes is comparable to the electron energy flux at low altitudes. Thus, for this event the auroral acceleration can be described as a quasi-stationary potential structure with equipotential lines reaching the Cluster altitudes. The arc forms at the outer edge of the plasma sheet at a density gradient. Multiple Cluster satellite measurements allow us to study the density increase associated with the development of the arc, and to estimate the velocity of the structure. The quasi-potential structure itself may be part of an Alfven wave.
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  • Resultat 1-11 av 11

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