Studies of dynamic processes related to active experiments in space plasmas

This is the final report for grant NAGw-2055, 'Studies of Dynamic Processes Related to Active Experiments in Space Plasmas', covering research performed at the University of Michigan. The grant was awarded to study: (1) theoretical and data analysis of data from the CHARGE-2 rocket experiment (1keV; 1-46 mA electron beam ejections) and the Spacelab-2 shuttle experiment (1keV; 100 mA); (2) studies of the interaction of an electron beam, emitted from an ionospheric platform, with the ambient neutral atmosphere and plasma by means of a newly developed computer simulation model, relating model predictions with CHARGE-2 observations of return currents observed during electron beam emissions; and (3) development of a self-consistent model for the charge distribution on a moving conducting tether in a magnetized plasma and for the potential structure in the plasma surrounding the tether. Our main results include: (1) the computer code developed for the interaction of electrons beams with the neutral atmosphere and plasma is able to model observed return fluxes to the CHARGE-2 sounding rocket payload; and (2) a 3-D electromagnetic and relativistic particle simulation code was developed

Solar-Terrestrial Science Strategy Workshop

The conclusions and recommendations reached at the Solar Terrestrial Science Strategy Workshop are summarized. The charter given to this diverse group was: (1) to establish the level of scientific understanding to be accomplished with the completion of the current and near term worldwide programs; (2) identify the significant scientific questions to be answered by future solar terrestrial programs, and the programs required to answer these questions; and (3) map out a program strategy, taking into consideration currently perceived space capabilities and constraints, to accomplish the identified program

Report from ionospheric science

The general strategy to advance knowledge of the ionospheric component of the solar terrestrial system should consist of a three pronged attack on the problem. Ionospheric models should be refined by utilization of existing and new data bases. The data generated in the future should emphasize spatial and temporal gradients and their relation to other events in the solar terrestrial system. In parallel with the improvement in modeling, it will be necessary to initiate a program of advanced instrument development. In particular, emphasis should be placed on the area of improved imaging techniques. The third general activity to be supported should be active experiments related to a better understanding of the basic physics of interactions occurring in the ionospheric environment. These strategies are briefly discussed

On the "Causality Argument" in Bouncing Cosmologies

We exhibit a situation in which cosmological perturbations of astrophysical relevance propagating through a bounce are affected in a scale-dependent way. Involving only the evolution of a scalar field in a closed universe described by general relativity, the model is consistent with causality. Such a specific counter-example leads to the conclusion that imposing causality is not sufficient to determine the spectrum of perturbations after a bounce provided it is known before. We discuss consequences of this result for string motivated scenarios.Comment: 4 pages, 1 figure, ReVTeX, to appear in Phys. Rev. Let

Report from space plasma science

Space plasma science, especially plasma experiments in space, is discussed. Computational simulations, wave generation and propagation, wave-particle interactions, charged particle acceleration, particle-particle interactions, radiation transport in dense plasmas, macroscopic plasma flow, plasma-magnetic field interactions, plasma-surface interactions, prospects for near-term plasma science experiments in space and three-dimensional plasma experiments are among the topics discussed

Recent results from studies of electron beam phenomena in space plasmas

Experiments involving the ejection of beams of electrons from spacecraft have been performed for more than 2 decades in order to study fundamental plasma physical processes as well as for a range of diagnostic- and application-oriented purposes. This paper reviews some of the key issues that have been pursued in the past 10 years. These include questions regarding spacecraft charging and beam dynamics, the interaction of beams with neutral gas and plasmas, and the electromagnetic radiation generated by continuous and pulsed electron beams. It is shown how our understanding of these phenomena has matured, thereby providing a solid foundation for future experiments involving the use of electron beams.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/30225/1/0000617.pd

The possibility of supersonic plasma flow in a collapsing post-sunset ionosphere

As a result of the rapidly decreasing pressure in the topside ionosphere during twilight hours, a rapid downward flow of hydrogen plasma from the protonosphere takes place. In the case of steady state, isothermal, frictionless flow the criterion for the existence of a critical point (transition to supersonic flow) above 1000 km is that the plasma temperature be lower than a certain limiting temperature Ti which is a function of the field line considered. In the latitude region between 40[deg] and 70[deg] this upper temperature limit varies from 963[deg]K to 1066[deg]K. Since these temperatures are considerably lower than the observed temperatures, it follows that in the case of steady state, isothermal flow the velocities will always remain subsonic. When the effect of the neglected terms is examined, the temperature gradient is shown to exert the strongest influence on the nature of the flow. For each latitude there is shown to exist a certain gradient ([part]T/[part]r)0 such that, if [part]T/[part]rT/[part]r)0 the criterion for a critical point to exist above 1000 km is again that the temperature at the critical point be less than some limiting temperature tl. If, however, [part]T/[part]r>([part]T/[part]r)O, then the criterion turns out to be that the temperature at the critical point be larger than Tl. The values of ([part]T/[part]r)0 are between 9 x 10-6[deg]K cm-1 and 6.75 x 10-6[deg]K cm-1 for latitudes between 40[deg] and 70[deg]. For values of the temperature gradient above about 4 x 10-6[deg]K cm-1 the criterion is satisfied for physically realistic temperatures (above 1500[deg]K), i.e. a critical point may exist above 1000 km. On this basis it is concluded that there is a definite possibility that supersonic downward flows in a post-sunset topside ionosphere may occur.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/34189/1/0000478.pd

Axions In String Theory

In the context of string theory, axions appear to provide the most plausible solution of the strong CP problem. However, as has been known for a long time, in many string-based models, the axion coupling parameter F_a is several orders of magnitude higher than the standard cosmological bounds. We re-examine this problem in a variety of models, showing that F_a is close to the GUT scale or above in many models that have GUT-like phenomenology, as well as some that do not. On the other hand, in some models with Standard Model gauge fields supported on vanishing cycles, it is possible for F_a to be well below the GUT scale.Comment: 62 pages, v2; references, acknowledgements and minor corrections adde

Critical Behavior of the Meissner Transition in the Lattice London Superconductor

We carry out Monte Carlo simulations of the three dimensional (3D) lattice London superconductor in zero applied magnetic field, making a detailed finite size scaling analysis of the Meissner transition. We find that the magnetic penetration length \lambda, and the correlation length \xi, scale as \lambda ~ \xi ~ |t|^{-\nu}, with \nu = 0.66 \pm 0.03, consistent with ordinary 3D XY universality, \nu_XY ~ 2/3. Our results confirm the anomalous scaling dimension of magnetic field correlations at T_c.Comment: 4 pages, 5 ps figure

TSS-1 - Orbiter current and voltage experiments

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76697/1/AIAA-1993-702-280.pd