22,814 research outputs found
Ion laser plasmas
The typical noble gas ion laser plasma consists of a high-current-density glow discharge in a noble gas, in the presence of a magnetic field. Typical CW plasma conditions are current densities of 100 to 2000 A/cm^2, tube diameters of 1 to 10 mm, filling pressures of 0.1 to 1.0 torr, and an axial magnetic field of the order of 1000 G. Under these conditions the typical fractional ionization is about 2 percent and the electron temperature between 2 and 4 eV. Pulsed ion lasers typically use higher current densities and lower operating pressures.
This paper discusses the properties of ion laser plasmas, in terms of both their external discharge parameters and their internal ion and excited state densities. The effect these properties have on laser operation is explained. Many interesting plasma effects, which are important in ion lasers, are given attention. Among these are discharge nonuniformity near tube constrictions, extremely high ion radial drift velocities, wall losses intermediate between ambipolar diffusion and free fall, gas pumping effects, and radiation trapping. The current status of ion laser technology is briefly reviewed
Relation Between Einstein And Quantum Field Equations
We show that there exists a choice of scalar field modes, such that the
evolution of the quantum field in the zero-mass and large-mass limits is
consistent with the Einstein equations for the background geometry. This choice
of modes is also consistent with zero production of these particles and thus
corresponds to a preferred vacuum state preserved by the evolution. In the
zero-mass limit, we find that the quantum field equation implies the Einstein
equation for the scale factor of a radiation-dominated universe; in the
large-mass case, it implies the corresponding Einstein equation for a
matter-dominated universe. Conversely, if the classical radiation-dominated or
matter-dominated Einstein equations hold, there is no production of scalar
particles in the zero and large mass limits, respectively. The suppression of
particle production in the large mass limit is over and above the expected
suppression at large mass. Our results hold for a certain class of conformally
ultrastatic background geometries and therefore generalize previous results by
one of us for spatially flat Robertson-Walker background geometries. In these
geometries, we find that the temporal part of the graviton equations reduces to
the temporal equation for a massless minimally coupled scalar field, and
therefore the results for massless particle production hold also for gravitons.
Within the class of modes we study, we also find that the requirement of zero
production of massless scalar particles is not consistent with a non-zero
cosmological constant. Possible implications are discussed.Comment: Latex, 24 pages. Minor changes in text from original versio
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Beam-Induced Energy Deposition in Muon Storage Rings
Beam-induced radiation effects have been simulated for 20 and 50 GeV muon storage rings designed for a Neutrino Factory. It is shown that by appropriately shielding the superconducting magnets, quench stability, acceptable dynamic heat loads, and low residual dose rates can be achieved. Alternatively, if a specially-designed skew focusing magnet without superconducting coils on the magnet's mid-plane is used, then the energy is deposited preferentially in the warm iron yoke or outer cryostat layers and internal shielding may not be required. In addition to the component irradiation analysis, shielding studies have been performed. Calculations of the external radiation were done for both designs but the internal energy deposition calculations for the 20 GeV Study-2 lattice are still in progress
Vanishing of Gravitational Particle Production in the Formation of Cosmic Strings
We consider the gravitationally induced particle production from the quantum
vacuum which is defined by a free, massless and minimally coupled scalar field
during the formation of a gauge cosmic string. Previous discussions of this
topic estimate the power output per unit length along the string to be of the
order of ergs/sec/cm in the s-channel. We find that this production
may be completely suppressed. A similar result is also expected to hold for the
number of produced photons.Comment: 10 pages, Plain LaTex. Minor improvements. To appear in PR
Toxicity of pyrolysis gases from wood
The toxicity of the pyrolysis gases from nine wood samples was investigated. The samples of hardwoods were aspen poplar, beech, yellow birch, and red oak. The samples of softwoods were western red cedar, Douglas fir, western hemlock, eastern white pine, and southern yellow pine. There was no significant difference between the wood samples under rising temperature conditions, which are intended to simulate a developing fire, or under fixed temperature conditions, which are intended to simulate a fully developed fire. This test method is used to determine whether a material is significantly more toxic than wood under the preflashover conditions of a developing fire
Comovement of International Equity Markets: A Taxonomic Approach
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Non-relativistic quantum systems on topological defects space-times
We study the behavior of non-relativistic quantum particles interacting with
different potentials in the space-times generated by a cosmic string and a
global monopole. We find the energy spectra in the presence of these
topological defects and show how they differ from their free space-time values.Comment: 17 pages, LATEX fil
Growth and Characterization of Ce- Substituted Nd2Fe14B Single Crystals
Single crystals of (Nd1-xCex)2Fe14B are grown out of Fe-(Nd,Ce) flux.
Chemical and structural analysis of the crystals indicates that
(Nd1-xCex)2Fe14B forms a solid solution until at least x = 0.38 with a
Vegard-like variation of the lattice constants with x. Refinements of single
crystal neutron diffraction data indicate that Ce has a slight site preference
(7:3) for the 4g rare earth site over the 4f site. Magnetization measurements
show that for x = 0.38 the saturation magnetization at 400 K, a temperature
important to applications, falls from 29.8 for the parent Nd2Fe14B to 27.6
(mu)B/f.u., the anisotropy field decreases from 5.5 T to 4.7 T, and the Curie
temperature decreases from 586 to 543 K. First principles calculations carried
out within density functional theory are used to explain the decrease in
magnetic properties due to Ce substitution. Though the presence of the
lower-cost and more abundant Ce slightly affects these important magnetic
characteristics, this decrease is not large enough to affect a multitude of
applications. Ce-substituted Nd2Fe14B is therefore a potential high-performance
permanent magnet material with substantially reduced Nd content.Comment: 11 Pages, 8 figures, 5 table
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