ZIB

1

Digitale Medien

Electronmagnetohydrodynamic response of a plasma to an external current pulse (1996)

Zhou, H. B. ; Papadopoulos, K. ; Sharma, A. S. ; [weitere]

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

Physics of Plasmas 3 (1996), S. 1484-1494

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ISSN: 1089-7674

Quelle: AIP Digital Archive

Thema: Physik

Notizen: In this paper we examine the dynamic response of a magnetoplasma to an external time-dependent current source in the context of electronmagnetohydrodynamics (EMHD). A combined analytic and numerical technique is developed to address this problem. The set of cold electron plasma and Maxwell's equations are first solved analytically in the (k,ω) space. Inverse Laplace and three-dimensional complex Fast Fourier Transform techniques are used subsequently to numerically transform the radiation fields and plasma currents from the (k,ω) space to the (r,t) space. The results show that the electron plasma responds to a time-varying current source imposed across the magnetic field by exciting whistler/helicon waves and forming an expanding local current loop, driven by field-aligned plasma currents. The current loop consists of two antiparallel field-aligned current channels concentrated at the ends of the imposed current and a cross-field Hall current region connecting these channels. The characteristics of the current closure region are determined by the background plasma density, the magnetic field, and the time scale of the current source. The results are applied to the ionospheric generation of extremely low-frequency (ELF) and very low-frequency (VLF) radiation using amplitude modulated high-frequency heating. It is found that contrary to previous suggestions the dominant radiating moment of the ELF/VLF ionospheric source is an equivalent horizontal magnetic dipole. © 1996 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.872009

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2

Digitale Medien

Gamma ray flashes by plasma effects in the middle atmosphere (2001)

Kaw, P. K. ; Milikh, G. M. ; Sharma, A. S. ; [weitere]

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

Physics of Plasmas 8 (2001), S. 4954-4959

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ISSN: 1089-7674

Quelle: AIP Digital Archive

Thema: Physik

Notizen: In this paper a novel mechanism is identified for the generation of gamma ray flashes observed on the Compton Gamma Ray Observatory satellite. During typical cloud to ground lightning flashes, the electromagnetic pulse can create a self-focused whistler wave channel or duct to guide 10–102/cm−3 of ∼1 MeV electrons (formed by static stratified electric field in clouds at 20 km), to a height of about 30 km where these electrons can create the gamma ray flash by bremsstrahlung. This scenario combines the various observational features of lightning-generated electromagnetic pulses and low altitude energetic electrons to provide a viable nonlinear transport mechanism of energetic electrons to the desired altitude of 30 km for conversion into gamma ray flashes. © 2001 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.1407821

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3

Digitale Medien

Charging of substrates irradiated by particle beams (1997)

Guzdar, P. N. ; Sharma, A. S. ; Guharay, S. K.

Woodbury, NY : American Institute of Physics (AIP)

Applied Physics Letters 71 (1997), S. 3302-3304

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ISSN: 1077-3118

Quelle: AIP Digital Archive

Thema: Physik

Notizen: A simple dynamical model for studying the charging of substrates irradiated by particle beams is developed. The charging potential for positive ion beams can be as large as the beam voltage. For negative ion beams, the charging potential is significantly lower and is governed by the secondary electrons. A closed form expression derived for the charging voltage in the case of negative ion beams agrees well with our numerical work. The results are consistent with observations on charging of isolated substrates during ion implantation with positive and negative ion beams. © 1997 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.120319

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4

Digitale Medien

Global and local geospace modeling in ISTP (1995)

Papadopoulos, K. ; Lyon, J. G. ; Goodrich, C. C. ; [weitere]

Springer

Space science reviews 71 (1995), S. 671-690

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ISSN: 1572-9672

Quelle: Springer Online Journal Archives 1860-2000

Thema: Physik

Notizen: Abstract The objective of the University of Maryland ISTP theory project is the development of the analytical and computational tools, which, combined with the data collected by the space and ground-based ISTP sensors, will lead to the construction of the first causal and predictive global geospace model. To attain this objective a research project composed of four complementary parts is conducted. First the global interaction of the solar wind-magnetosphe re system is studied using three-dimensional MHD simulations. Appropriate results of these simulations are made available to other ISTP investigators through the Central Data Handling Facility (CDHF) in a format suitable for comparison with the observations from the ISTP spacecrafts and ground instruments. Second, simulations of local processes are performed using a variety of non-MHD codes (hybrid, particle and multifluid) to study critical magnetospheric boundary layers, such as the magnetopause and the magnetotail. Third, a strong analytic effort using recently developed methods of nonlinear dynamics is conducted, to provide a complementary semi-empirical understanding of the nonlinear response of the magnetosphere and its parts to the solar wind input. The fourth part will be conducted during and following the data retrieval and its objective is to utilize the data base in conjunction with the above models to produce the next generation of global and local magnetospheric models. Special emphasis is paid to the development of advanced visualization packages that allow for interactive real time comparison of the experimental and computational data. Examples of the computational tools and of the ongoing investigations are presented.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF00751346

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5

Digitale Medien

Thermal instability and transport effects in comets (1996)

Sharma, A. S. ; Milikh, G. M.

Springer

Astrophysics and space science 236 (1996), S. 77-84

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ISSN: 1572-946X

Quelle: Springer Online Journal Archives 1860-2000

Thema: Physik

Notizen: Abstract The localized ion density depletion region observed at comet Halley can be understood in terms of a thermal instability of the cometary plasma due to the excitation of rotational and vibrational levels of water molecules. The electron energy losses due to these processes peak near 4000 K and at higher temperatures a localized cooling leads to the thermal instability due to the increased radiation loss. The resulting increase in recombination leads to the ion density depletion and the estimates for this depletion at comet Halley agree with the observations. The transport effects at the density depletion region due to the diffusion and thermal conductivity are found have time scales larger than the instability time scale and does not affect the formation of the depletion region.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF00644322

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