The Alpha Magnetic Spectrometer (AMS) was flown on the space shuttle Discovery during flight STS-91 (June 1998) in a 51.7° orbit at altitudes between 320 and.A search for antihelium nuclei in the ...rigidity range 1–was performed. No antihelium nuclei were detected at any rigidity. An upper limit on the flux ratio of antihelium to helium of <1.1×10−6 was obtained.The high energy proton, electron, positron, helium, antiproton and deuterium spectra were accurately measured.For each particle and nuclei two distinct spectra were observed: a higher energy spectrum and a substantial second spectrum. Positrons in the second spectrum were found to be much more abundant than electrons. Tracing particles from the second spectra shows that most of them travel for an extended period of time in the geomagnetic field, and that the positive particles (p and e+) and negative ones (e−) originate from two complementary geographic regions. The second helium spectrum flux over the energy range 0.1–was measured to be . Over 90 percent of the helium flux was determined to be at the 90% confidence level. (Elsevier)
Measurement of the chemical and isotopic composition of cosmic rays is essential for the precise understanding of their propagation in the galaxy. While the model parameters are mainly determined ...using the B/C ratio, the study of extended sets of ratios can provide stronger constraints on the propagation models. In this paper, the relative abundances of light-nuclei lithium, beryllium, boron, and carbon are presented. The secondary-to-primary ratios Li/C, Be/C, and B/C have been measured in the kinetic energy range 0.35-45 GeV nucleon--1. The isotopic ratio 7Li/6Li is also determined in the magnetic rigidity interval 2.5-6.3 GV. The secondary-to-secondary ratios Li/Be, Li/B, and Be/B are also reported. These measurements are based on the data collected by the Alpha Magnetic Spectrometer AMS-01 during the STS-91 space shuttle flight in 1998 June. Our experimental results are in substantial agreement with other measurements, where they exist. We describe our light-nuclei data with a diffusive-reacceleration model. A 10%-15% overproduction of Be is found in the model predictions and can be attributed to uncertainties in the production cross-section data.
The Russian program for development of low aspect ratio tokamaks (spherical tokamaks) is presented. The urgency of the theme is conditioned by the results of theoretical research and experimental ...data obtained from small-scale installations where the direction has proved to be greatly promising. The present work describes a number of spherical tokamak projects governed by certain logic. The intended research is supposed to solve the issues of maintaining the advantages of such tokamaks for mega-ampere range installations, overcoming the current difficulties typical for such tokamaks, and, finally, considering the possibility of building an inexpensive compact thermonuclear reactor.
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We discuss the deep topological reasons why dislocation quadrupoles should be used for the construction of dislocations containing edge components. We demonstrate that contrary to all ...other currently used methods, this approach exactly preserves the topology of the order parameter field (atomic displacements in a crystal with defects relative to a defect-free crystal) of a dislocation-free crystal with periodic boundary conditions even for small simulation volumes and, thus, restores the verity of the material frame indifference principle, broken in other techniques. Using dislocation quadrupoles for edge and mixed dislocations, we have developed a careful procedure for relaxation of atomic positions around a dislocation core which enables one to achieve arbitrary low dislocation densities characteristic for real crystals. As a demonstration of the method capabilities, we have constructed a simulation volume with as low dislocation density as 1.5·1014m-2, which is realistic in deformed crystals, and one can easily lower this value as desired. All details of dislocation construction process are explicitly specified, making it very easy to reproduce our results. FCC Al crystal is used as a test case.
The paper presents the results of the system research on the coordinated development of nuclear and fusion power engineering in the current century. Considering the increasing problems of resource ...procurement, including limited natural uranium resources, it seems reasonable to use fusion reactors as high-power neutron sources for production of nuclear fuel in a blanket. It is shown that the share of fusion sources in this structural configuration of the energy system can be relatively small. A fundamentally important aspect of this solution to the problem of closure of the fuel cycle is that recycling of highly active spent fuel can be abandoned. Radioactivity released during the recycling of the spent fuel from the hybrid reactor blanket is at least two orders of magnitude lower than during the production of the same number of fissile isotopes after the recycling of the spent fuel from a fast reactor.
The prospects of various energy sources have to be evaluated on the basis of economical, energy and political factors, and ecological consequences. The gradual replacement of energy technologies ...based on burning of fossil fuels by the new ‘clean’ ones not yielding greenhouse gases is called for so as to conserve the atmosphere at least in the present state. From this point, one of the most promising energy technologies is controlled fusion. Today, we are in the stage of transition from proof-of-principle plasma physics experiments to practical realization of this concept. The place of future fusion power reactors in the global system is being discussed widely. In 1985, the Government Agreement on the design of the International Thermonuclear Experimental Reactor (ITER) was signed by Russia, Japan, The European Community, and the United States of America. That was the starting point of this enormous project; and now we are in the second phase, i.e. the Engineering Design Activities, to be completed by 1998. The focal point for design is the Joint Central Team, with about 200 scientists and engineers from Russia, Japan, the European Community, and the USA working jointly. The national Home Teams provide strong support for the design and research and development programs on the basis of equal contributions to the Project. One of the key problems to be solved concerns fusion reactor materials, including the creation of a complete database on appropriate materials irradiated up to a neutron fluence of 10
23 n · cm
−3, the development of new alloys and relevant engineering technologies.
We study the stability of Couette flow between two cylinders in the presence of axial magnetic field in local WKB approximation. We find the analytical expression of the critical angular velocity ...minimized over the wave number and the imposed magnetic field as a function of the measure of deviation of the rotation law from the Rayleigh line. The result found is in a good agreement with the previously known numerical results based on the global analysis. We perform a minimization of the critical Reynolds number over the wave number at fixed magnetic field both analytically and numerically. We show that a compromise between resistive suppression of magneto-rotational instability at weak magnetic field and the increase of the critical Reynolds number with the increase of magnetic field is possible. It takes place at moderate values of magnetic field of order 3
×
10
2 gauss giving the critical Reynolds number of order
4
×
10
4
.
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