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FREE-FREE GAUNT FACTORS

Description: The hydrogenic (unscreened coulomb) free-free gaunt factors are computed for a wide range of initial energies and photon frequencies. In addition, an average over initial energies with the Maxwell-Boltzmann distribution is performed to give the temperatureaveraged gaunt factors for use in opacity calculations. These are presented as functions of Z/sup 2//kT and h nu /kT. The relation between these gaunt factors and the rate of bremsstrahlung energy production is given, as is the total energy emitted as a function of Z/sup 2//kT. (auth)
Date: November 1, 1957
Creator: Karzas, W.J. & Latter, R.
Partner: UNT Libraries Government Documents Department

A statistical mechanics model for free-for-all airplane passenger boarding

Description: I discuss a model for free-for-all passenger boarding which is employed by some discount air carriers. The model is based on the principles of statistical mechanics where each seat in the aircraft has an associated energy which reflects the preferences of travelers. As each passenger enters the airplane they select their seats using Boltzmann statistics, proceed to that location, load their luggage, sit down, and the partition function seen by remaining passengers is modified to reflect this fact. I discuss the various model parameters and make qualitative comparisons of this passenger boarding model with those that involve assigned seats. The model can be used to predict the probability that certain seats will be occupied at different times during the boarding process. These results might provide a useful description of this boarding method. The model is a relatively unusual application of undergraduate level physics and describes a situation familiar to many students and faculty.
Date: August 1, 2008
Creator: Steffen, Jason H.
Partner: UNT Libraries Government Documents Department

Extension of Boltzmann's theory to a liquid

Description: A theory for the nonequilibrium statistical mechanics of a liquid is presented. This theory consists of coupled evolution equations for the one-particle momentum distribution, and for the two-particle correlation function, and it possesses the same important properties as does Boltzmann's theory, namely the local conservation laws, the local h theorem, and the correct equilibrium solution.
Date: January 1, 1988
Creator: Wallace, D.C.
Partner: UNT Libraries Government Documents Department

Experimental and computational studies of hydrodynamics in three-phase and two-phase fluidized beds

Description: The objective of the present study was to investigate the hydrodynamics of three-phase fluidized beds, their rheology, and experimentally verify a predictive three fluid hydrodynamic model developed at the Illinois Institute of Technology, Chicago. The recent reviews show that there exist no such models in the literature. The IIT hydrodynamic model computes the phase velocities and the volume fractions of gas, liquid, and particulate phases. Model verification involves a comparison of these computed velocities and volume fractions to experimental values. In this thesis, a three fluid model is presented. The input into the model can be particulate viscosities either measured with a Brookfield viscometer or derived using the mathematical techniques of kinetic theory of granular flows pioneered by Savage and others. The computer simulation of a three-phase fluidized bed in an asymmetric mode qualitatively predicts the gas, liquid and solid hold-ups (volume fractions) and flow patterns in the industrially important churn-turbulent (bubbly coalesced) regimes. The computations in a fluidized bed with a symmetric distributor incorrectly showed no bubble coalescence. A combination of X-ray and {gamma}-ray densitometers was used to measure the solids and the liquid volume fractions in a two dimensional bed in the bubble coalesced regime. There is a good agreement between the theory for an asymmetric distributor and the experiments.
Date: December 1, 1994
Creator: Bahary, M.
Partner: UNT Libraries Government Documents Department

EXPERIMENTAL PROBLEMS IN THE USE OF A POLARIZED PROTONTARGET

Description: I have understood my assignment as a review of some of the work done in high-energy physics with polarized proton targets and a description of some of the special problems connected with polarized targets. Most of my report will be based on the polarized target that I am most familiar with--that constructed by Jeffries, Schultz, Shapiro, and myself. This target is no longer unique; in fact, it is now somewhat old-fashioned in some respects. Other polarized proton targets are in operation at CERN, Saclay, the Rutherford Laboratory, Argonne National Laboratory, the Soviet Union, and there is a target newly in operation at the Brookhaven Laboratory. Other targets are in operation or are in the process of design or construction at a number of other places. Unfortunately, none of these targets consists of pure hydrogen. The target material most often used is made of lanthanum magnesium nitrate, LMN. About a quarter of the weight of this crystal is water; it is the protons within the water molecules that are polarized. Hydrogen constitutes only 3 percent of the weight of the crystal. This means that scattering processes on hydrogen must be distinguished kinematically from scattering processes involving the heavy elements of the target if the target is to be used efficiently in high-energy scattering experiments. In fact, some of the experiments one would very much like to do appear to be very difficult. In LMN the protons are polarized by an indirect process known as dynamic polarization. Neodymium ions are added to the crystal when it is grown from a water solution. The neodymium ions are substituted for lanthanum to the extent of one percent or less. The neodymium ion has an odd number of electrons; it has a doublet ground state, called a Kramers doublet, that acts very much like a ...
Date: September 9, 1966
Creator: Chamberlain, Owen
Partner: UNT Libraries Government Documents Department

Steady State Properties of Lock-On Current Filaments in GaAs

Description: Collective impact ionization has been used to explain lock-on in semi-insulating GaAs under high-voltage bias. The authors have used this theory to study some of the steady state properties of lock-on current filaments. In steady state, the heat gained from the field is exactly compensated by the cooling due to phonon scattering. In the simplest approximation, the carrier distribution approaches a quasi-equilibrium Maxwell-Boltzmann distribution. In this report they examine the validity of this approximation. They find that this approximation leads to a filament carrier density which is much lower than the high density needed to achieve a quasiequilibrium distribution. Further work on this subject is in progress.
Date: February 29, 2000
Creator: KAMBOUR,K.; KANG,SAMSOO; MYLES,CHARLES W. & HJALMARSON,HAROLD P.
Partner: UNT Libraries Government Documents Department

Slowing-in distribution of fast particles released in Maxwellian plasma

Description: The time-independent slowing-in distribution is evaluated for a fast beam of test particles released in an infinite Maxwellian plasma background for various situations including quantum-mechanical and classical scattering regimes. The analysis involves considerations of small angle deflection and large angle scattering events. The results are determined for plasma electrons with thermal velocities larger or smaller than the test particle and plasma ions with thermal velocities lower than the test particle. When plasma electrons and ions are slow the slowing-in distribution behaves as E/sub j//sup $sup 1$/$sub 2$/, where E/sub j/ is the test particle energy. When plasma electrons are faster than the test particles, the high-energy tail acquires a 1/E/sub j/ shape. The origin of the test particle remains arbitrary and hence the results apply for particles produced by fusion events within the plasma proper and for particles externally injected. The total energy distribution is obtained and normalized, and ranges of validity are determined. The calculations are of the Boltzmann type, which is consistent with binary scattering models. The slowing-in distributions are also obtained from the Fokker--Planck equation, and as expected, the results agree with those obtained from the Boltzmann equation for large angle scattering only. (auth)
Date: May 1, 1975
Creator: Husseiny, A.A.; Sabri, Z.A. & Harris, D.R.
Partner: UNT Libraries Government Documents Department

Multi-scale particle simulation of bounded plasmas

Description: We are using the multi-scale technique to model bounded systems. Certain bounded systems are a naturally suited for the multi-scale method because of the boundary layer that forms at the wall, which is usually a short spatial and time scale structure, can significantly affect the bulk plasma behavior. One goal is to understand the interaction between the bulk plasma and the sheath. If the relevant short time scale physics is local to a few known spatial regions, then one can take advantage of this by advancing particles with variable {Delta}t depending on position, hence reducing computing time. The unmagnetized sheath problem is such a case. The model is a one dimensional bounded slab with kinetic ions and electrons. We start with a collisionless and unmagnetized system for simplicity. The right boundary is a conducting wall that absorbs all particles that come in contact with it. The left boundary is a symmetry point, where the particles are reflected. We allow a specified initial distribution: f(x,v,t = 0). In order to test the numerics of both multi-scale method and boundary conditions we are using the following test problem: a cutoff Maxwellian distribution for the electrons and fixed ions. The system has an analytic solution, so the run may be started from equilibrium. This gives us a benchmark and tests the fast time scale electron sheath dynamics. Results using variable {Delta}t will be given. In the future, we intend to use the more general model to study time dependent bounded plasma problems, such as a plasma expanding toward a conducting wall.
Date: January 1, 1989
Creator: Parker, S.E.; Birdsall, C.K. (California Univ., Berkeley, CA (USA). Electronics Research Lab.); Friedman, A. & Ray, S.L. (Lawrence Livermore National Lab., CA (USA))
Partner: UNT Libraries Government Documents Department

Fluctuations, turbulence and transports in the presence of drift waves

Description: Turbulence spectrum and plasma diffusion have been studied by theoretical analysis as well as by numerical simulations using a drift wave model in which electrons are assumed to follow the Boltzmann distribution, while ions are assumed to move two-dimensionally in the plane perpendicular to the magnetic field. For a plasma near local thermal equilibrium, it is found that while the ion density diffusion is negligibly small, the energy diffusion is much larger and is comparable to the test particle diffusion. In the presence of strong turbulence, deltan approx. n/sub 0/, fluctuation energy is found to cascade toward long wavelength modes which accompanies the density diffusion. The resultant turbulence spectrum is isotropic in two dimensions perpendicular to the magnetic field. However, the particle diffusion coefficient remains small. When the ion density gradient is maintained by freezing the electron background density, it is found that the turbulence spectrum cascades toward smaller wavenumbers only in the direction perpendicular to the density gradient. As a result an anisotropic turbulence spectrum if formed indicating an appearance of zonal flow in this direction.
Date: February 1, 1980
Creator: Okuda, H.; Sato, T.; Hasegawa, A. & Pellat, R.
Partner: UNT Libraries Government Documents Department

Modeling beam-front dynamics at low gas pressures

Description: The dynamics of space charge neutralization at the front of an intense self-focused electron beam pulse exhibits important differences in different gas pressure regimes. At very low pressures, the beam front is in the so-called ion-focused regime (IFR) where all secondary electrons are expelled from the beam region by the radial electric field without causing significant additional ionization. We estimate the upper pressure boundary of this regime by considering the distance scale length for cascade (avalanche) ionization. Data from the FX-25 diode experiments indicate a critical transition pressure (P/sub c/) that agrees with this estimate and with its scaling among various gas types. Normal mobility-limited treatments (local conductivity models) of the secondary electrons at the beam front are not justified until the gas pressure is 10 to 50 times higher than P/sub c/, due to runaway of these secondary electrons in the strong space-charge electric field at the lower pressures. The main conclusion of this study is that a non-local phase space (Boltzmann) treatment of the secondary electrons is required to accurately describe these different beam front regimes and the transitions between them; such a code model is currently under development.
Date: May 13, 1982
Creator: Briggs, R.J. & Yu, S.
Partner: UNT Libraries Government Documents Department

Lattice Boltzmann methods for some 2-D nonlinear diffusion equations:Computational results

Description: In this paper we examine two lattice Boltzmann methods (that are a derivative of lattice gas methods) for computing solutions to two two-dimensional nonlinear diffusion equations of the form {partial derivative}/{partial derivative}t u = v ({partial derivative}/{partial derivative}x D(u){partial derivative}/{partial derivative}x u + {partial derivative}/{partial derivative}y D(u){partial derivative}/{partial derivative}y u), where u = u({rvec x},t), {rvec x} {element of} R{sup 2}, v is a constant, and D(u) is a nonlinear term that arises from a Chapman-Enskog asymptotic expansion. In particular, we provide computational evidence supporting recent results showing that the methods are second order convergent (in the L{sub 1}-norm), conservative, conditionally monotone finite difference methods. Solutions computed via the lattice Boltzmann methods are compared with those computed by other explicit, second order, conservative, monotone finite difference methods. Results are reported for both the L{sub 1}- and L{sub {infinity}}-norms.
Date: January 1, 1990
Creator: Elton, B.H.; Rodrigue, G.H. (California Univ., Davis, CA (USA). Dept. of Applied Science Lawrence Livermore National Lab., CA (USA)) & Levermore, C.D. (Arizona Univ., Tucson, AZ (USA). Dept. of Mathematics)
Partner: UNT Libraries Government Documents Department

Effect of ion speed distribution on the spectral shape of the 2. 5 MeV neutron line produced by DD fusion

Description: Ion mean energy may be determined from Doppler broadening of the 2.5 MeV neutron line in Maxwellian deuterium plasma. Since many plasmas are non-Maxwellian a Monte Carlo simulation has been used to predict the spectral shape produced by a variety of simple speed distributions with mean energies in the range 1 to 100 keV. The results are Gaussian to high order and their width varies as the square root of the mean ion energy. However, the line width varies substantially among different ion speed distributions with the same mean energy. The similarity in shape of these spectra prevent the determination of the speed distribution type from detailed measurements of the neutron spectrum. 24 refs., 4 figs., 2 tabs.
Date: February 1, 1986
Creator: Slaughter, D.
Partner: UNT Libraries Government Documents Department

Electron cyclotron heating at down-shifted frequencies in existing tokamak devices

Description: Plasma heating in existing tokamak devices by electron cyclotron waves with frequency (f) significantly smaller than the electron gyrofrequency (f/sub c/) is investigated for the case of Maxwellian plasmas. It is shown that for central electron temperatures larger than 3 keV, strong absorption of extraordinary waves can occur at values of toroidal field for which the condition f = f/sub c/ is not satisfied in the plasma region. The cases of f = 60 GHz and f = 100 GHz are discussed for the PLT and TFTR devices as representative of medium (approx. =30 kG) and high (approx. =50 kG) magnetic field tokamaks, respectively. Numerical calculations with a ray tracing code indicate that most of the rf energy is absorbed in a central plasma region. These results are of practical interest because they significantly simplify the main technical problem of ECH in a tokamak reactor, i.e., the development of high frequency and high power microwave sources.
Date: June 1, 1985
Creator: Mazzucato, E.; Fidone, I.; Giruzzi, G. & Krivenski, V.
Partner: UNT Libraries Government Documents Department

EDOT: a code to calculate charge particle slowing down in a plasma

Description: EDOT is a code that calculates the slowing down of a test particle in a Maxwellian plasma utilizing continuous slowing down theory. Both nuclear scattering and reactions are included. The output includes slowing down parameters as well as spectra of knock-on ions and in-flight reaction probabilities. The theory, input, and output for the code are described.
Date: August 5, 1977
Creator: Perkins, S. T.
Partner: UNT Libraries Government Documents Department

Theoretical descriptions of neutron emission in fission

Description: Brief descriptions are given of the observables in neutron emission in fission together with early theoretical representations of two of these observables, namely, the prompt fission neutron spectrum N(E) and the average prompt neutron multiplicity {bar {nu}}{sub p}. This is followed by summaries, together with examples, of modern approaches to the calculation of these two quantities. Here, emphasis is placed upon the predictability and accuracy of the new approaches. In particular, the dependencies of N(E) and {bar {nu}}{sub p} upon the fissioning nucleus and its excitation energy are discussed. Then, recent work in multiple-chance fission and other recent work involving new measurements are presented and discussed. Following this, some properties of fission fragments are mentioned that must be better known and better understood in order to calculate N(E) and {bar {nu}}{sub p} with higher accuracy than is currently possible. In conclusion, some measurements are recommended for the purpose of benchmarking simultaneous calculations of neutron emission and gamma emission in fission. 32 refs., 26 figs.
Date: January 1, 1990
Creator: Madland, D.G.
Partner: UNT Libraries Government Documents Department

Effect of deviations from the Maxwell distribution on neutron production in laser targets

Description: Because of the brief duration of laser implosions and the small size of the pellets, one may be concerned that the ions never reach a Maxwell distribution or that the tail is lost by diffusion. This might have a large effect on <sigma v>, which depends heavily on the tail. We have calculated the ion distribution and the DT <sigma v>. Results are presented for the ratio of <sigma v> for a monoenergetic isotropic distribution to that for a Maxwell distribution, for the rate of approach of <sigma v> to the equilibrium value, and for the decay of <sigma v> due to fast ion losses. The main effect in the last case is due to energy losses, not to non-Maxwellian distribution. The effect is substantially different than previously reported.
Date: November 1, 1978
Creator: Henderson, D.B. & Petschek, A.G.
Partner: UNT Libraries Government Documents Department

SGV: a code to evaluate plasma reaction rates to a specified accuracy

Description: A FORTRAN code to evaluate binary reaction rates (sigmav) for a plasma to a specified accuracy is described. Distribution functions permitted are (1) two Maxwellian species at different temperatures, (2) beam-Maxwellian, (3) cold gas with Maxwellian, and (4) beam-plasma with mirror distribution of the form f(v) varies as f(v) M (cos theta). Several functional forms are permitted for f(v) and M(cos theta). Cross-section subroutines for a number of interactions involving hydrogen, helium, and electrons are included, as is a routine allowing input of numerical data. The code is written as a subroutine to allow ready incorporation into larger plasma codes.
Date: September 22, 1978
Creator: Devoto, R.S. & Hanson, J.D.
Partner: UNT Libraries Government Documents Department

Optimization of nonthermal fusion power consistent with energy channeling

Description: If the energy of charged fusion products can be diverted directly to fuel ions, non-Maxwellian fuel ion distributions and temperature differences between species will result. To determine the importance of these nonthermal effects, the fusion power density is optimized at constant-{beta} for nonthermal distributions that are self-consistently maintained by channeling of energy from charged fusion products. For D-T and D-{sup 3}He reactors, with 75% of charged fusion product power diverted to fuel ions, temperature differences between electrons and ions increase the reactivity by 40-70%, while non- Maxwellian fuel ion distributions and temperature differences between ionic species increase the reactivity by an additional 3-15%.
Date: February 1, 1995
Creator: Snyder, P. B.; Herrmann, M. C. & Fisch, N. J.
Partner: UNT Libraries Government Documents Department

Simulations of second-order Fermi acceleration of electrons: Solving the injection problem

Description: The boosting of electrons from a Maxwellian distribution into a suprathermal power-law tail has long been recognized as an important bottleneck governing the subsequent acceleration of some of these electrons to relativistic energies. This is the seed or injection problem. I study this boosting process using a test-particle simulation code, following the full equations of motion of tens of thousands of electrons chosen from a thermal population as they move through general time-dependent magnetic fields. Inhomogeneities in the magnetic field are provided by finite swarms of moving current loops with Maxwellian velocity distributions and power-law distributions of loop size and dipole moment strength. Whether bulk heating or boosting occurs is found to depend on the size of the swarm thermal speed compared to the electron thermal speed. When the swarm thermal speed is comparable to the electron thermal speed the entire electron population is heated by encounters with the rapidly moving current loops, approximately preserving the Maxwellian character of the electron distribution. On the other hand, at very low swarm thermal speeds there is no bulk heating; instead one percent or fewer of the electrons are boosted into a power-law suprathermal tail with a differential energy spectral index between 1 and 2. Individual boosts of 2000 and more have been observed in samples of 50,000 electrons. Most of the strongly boosted electrons have initial energies that are well below the peak of the initial Maxwellian.
Date: December 31, 1991
Creator: Gisler, G. R.
Partner: UNT Libraries Government Documents Department