Open Access. Powered by Scholars. Published by Universities.®

Physics Commons™

Open Access. Powered by Scholars. Published by Universities.®

Physics Faculty Research & Creative Works

Articles 1051 - 1080 of 1562

Full-Text Articles in Physics

Angle-Resolved X-Ray Circular And Magnetic Circular Dichroisms: Definitions And Applications, Sy Y. Tong, X. Q. Guo, James G. Tobin, George Daniel Waddill Dec 1996

Angle-Resolved X-Ray Circular And Magnetic Circular Dichroisms: Definitions And Applications, Sy Y. Tong, X. Q. Guo, James G. Tobin, George Daniel Waddill

Physics Faculty Research & Creative Works

We introduce definitions of angle-resolved x-ray circular dichroism (ARXCD) and magnetic x-ray circular dichroism (ARMXCD). As defined, the much larger effect of circular dichroism (ARXCD) is separated from the smaller magnetic (ARMXCD) effect. In all materials, ARXCD is zero along mirror planes while nonzero elsewhere. ARMXCD is nonzero only in magnetic materials. The measurement and analysis of ARMXCD allow element specific surface magnetism and surface structure as well as their inter-relationship to be studied as functions of the outgoing electron's direction.

Go to article

Breakdown Of Landau-Ginzburg-Wilson Theory For Certain Quantum Phase Transitions, Thomas Vojta, Dietrich Belitz, Rajesh S. Narayanan, Theodore R. Kirkpatrick Oct 1996

Breakdown Of Landau-Ginzburg-Wilson Theory For Certain Quantum Phase Transitions, Thomas Vojta, Dietrich Belitz, Rajesh S. Narayanan, Theodore R. Kirkpatrick

Physics Faculty Research & Creative Works

The quantum ferromagnetic transition of itinerant electrons is considered. It is shown that the Landau-Ginzburg-Wilson theory described by Hertz and others breaks down due to a singular coupling between fluctuations of the conserved order parameter. This coupling induces an effective long-range interaction between the spins of the form 1/r2d-1. It leads to unusual scaling behavior at the quantum critical point in 1 < d ≤ 3 dimensions, which is determined exactly.

Go to article

Theory Of The Seebeck Coefficient In Lacro₃ And Related Perovskite Systems, D. B. Marsh, Paul Ernest Parris Sep 1996

Theory Of The Seebeck Coefficient In Lacro₃ And Related Perovskite Systems, D. B. Marsh, Paul Ernest Parris

Physics Faculty Research & Creative Works

We consider the Seebeck coefficient in LaCrO3 and related transition-metal-oxide perovskites using a model for electronic conduction based on the electronic structure of the 3d orbitals of the B-site transition-metal cations. Relations for the Seebeck coefficient are presented for those perovskite systems in which electronic conduction is through the t2g states of the B-site transition-metal cations. High- and low-temperature limits for the Seebeck coefficient are identified for the cases of both strong and weak magnetic coupling between electron spins. In these high- and low-temperature limits, the Seebeck coefficient is determined as a function of carrier concentration. Results are …

Go to article

Higher-Order Binding Corrections To The Lamb Shift Of 2p States, Ulrich D. Jentschura, Krzysztof Pachucki Sep 1996

Higher-Order Binding Corrections To The Lamb Shift Of 2p States, Ulrich D. Jentschura, Krzysztof Pachucki

Physics Faculty Research & Creative Works

We present an improved calculation of higher-order corrections to the one-loop self-energy of 2P states in hydrogenlike systems with small nuclear charge Z. The method is based on a division of the integration with respect to the photon energy into a high- and a low-energy part. The high-energy part is calculated by an expansion of the electron propagator in powers of the Coulomb field. The low-energy part is simplified by the application of a Foldy-Wouthuysen transformation. This transformation leads to a clear separation of the leading contribution from the relativistic corrections and removes higher-order terms. The method is applied to …

Go to article

Relation Between Charge-Dipole Interactions And The Sqrt(E)-Dependent Mobility In Molecularly Doped Polymers, Paul Ernest Parris Aug 1996

Relation Between Charge-Dipole Interactions And The Sqrt(E)-Dependent Mobility In Molecularly Doped Polymers, Paul Ernest Parris

Physics Faculty Research & Creative Works

Time-of-flight measurements on a wide variety of molecularly-doped polymers reveal carrier mobilities that exhibit an exponential dependence on the square root of the applied electric field. Recent attempts to explain the observed field dependence have focused on the role played by spatial and energetic disorder. It as also been conjectured that the charge-dipole interactions often identified as the source of energetic disorder could be of sufficient range to lead to correlations in the energies of neighboring hopping sites. We have analytically explored the effect of such correlations on high field carrier transport in random potentials, and discuss how particular features …

Go to article

Neutron Diffraction Structural Study Of Ce₂Fe₁₇₋ₓgaₓ, H. Luo, Z. Hu, William B. Yelon, Sanjay R. Mishra, Gary J. Long, Oran Allan Pringle, D. P. Middleton, K. H. J. Buschow Aug 1996

Neutron Diffraction Structural Study Of Ce₂Fe₁₇₋ₓgaₓ, H. Luo, Z. Hu, William B. Yelon, Sanjay R. Mishra, Gary J. Long, Oran Allan Pringle, D. P. Middleton, K. H. J. Buschow

Physics Faculty Research & Creative Works

Six samples of Ce2Fe17-xGax with nominal Ga content x equal to 0, 0.3, 0.5, 0.7, 1.0, 2.0 have been studied by powder neutron diffraction at room temperature. Both crystalline and magnetic refinements have been carried out. All six samples adopt the Th2Zn17-type rhombohedral structure. The only additional phase found is α-iron. Gallium atoms are found to have high affinity for the iron 18h site, and are absent from the 9d and 18f sites. The Ga substitution for Fe leads to an expansion of both the a and c axes. The Curie …

Go to article

Charge-Dipole Model For The Universal Field Dependence Of Mobilities In Molecularly Doped Polymers, David H. Dunlap, Paul Ernest Parris, Vasudev M. Kenkre Jul 1996

Charge-Dipole Model For The Universal Field Dependence Of Mobilities In Molecularly Doped Polymers, David H. Dunlap, Paul Ernest Parris, Vasudev M. Kenkre

Physics Faculty Research & Creative Works

Using the general result that the mobility μ, of charge carriers driven in a spatially correlated random potential by an electric field E can be expressed in terms of the Laplace transform of a particular correlation function related to the random potential, we demonstrate that the exponential dependence of μ on √E universally observed in molecularly doped polymers arises naturally from the interaction of charge carriers with randomly distributed permanent dipoles.

Go to article

Binary Nucleation Kinetics. Iii. Transient Behavior And Time Lags, Barbara Ellen Wyslouzil, Gerald Wilemski Jul 1996

Binary Nucleation Kinetics. Iii. Transient Behavior And Time Lags, Barbara Ellen Wyslouzil, Gerald Wilemski

Physics Faculty Research & Creative Works

Transient binary nucleation is more complex than unary because of the bidimensionality of the cluster formation kinetics. To investigate this problem qualitatively and quantitatively, we numerically solved the birth-death equations for vapor-to-liquid phase transitions. Our previous work [J. Chem. Phys 103, 1137 (1995)] showed that the customary saddle point and growth path approximations are almost always valid in steady state gas phase nucleation and only fail if the nucleated solution phase is significantly nonideal. The current work demonstrates that in its early transient stages, binary nucleation rarely, if ever, occurs via the saddle point. This affects not only the number …

Go to article

Neutron Diffraction And Magnetic Studies Of Rfe₁₂₋ₓtₓcY (R=Y,Er; T=V,Ti,Mo) Alloys, Z. Hu, William B. Yelon, X. D. Zhang, William Joseph James Apr 1996

Neutron Diffraction And Magnetic Studies Of Rfe₁₂₋ₓtₓcY (R=Y,Er; T=V,Ti,Mo) Alloys, Z. Hu, William B. Yelon, X. D. Zhang, William Joseph James

Physics Faculty Research & Creative Works

RFe12-xTxCy, (R=Y,Er; T=V,Ti,Mo) alloys were prepared by rf induction melting and analyzed using neutron powder diffraction and superconducting quantum interference device (SQUID) measurements. Rietveld analysis of the neutron diffraction data indicates that V, Ti, and Mo atoms all prefer the 8i sites. The refined amount of carbon atoms found in the interstitial sites from neutron diffraction data is significantly less than the nominal carbon content. All samples have the easy direction along the c axis. The Er sublattice couples to the Fe sublattice antiferromagnetically. The average Fe site moments range from 1.3 to 2.8 …

Go to article

Neutron Diffraction Studies Of Ndₙfeₘ₋ₓ₋YVₓalY [(N,M)=(1,12), (2,17), (3,29)], Z. Hu, William B. Yelon, William Joseph James Apr 1996

Neutron Diffraction Studies Of Ndₙfeₘ₋ₓ₋YVₓalY [(N,M)=(1,12), (2,17), (3,29)], Z. Hu, William B. Yelon, William Joseph James

Physics Faculty Research & Creative Works

Several NdnFem-x-yVxAly [(n,m)=(1,12), (2,17), (3,29)] samples were prepared and analyzed using neutron powder diffraction. Rietveld analysis of the neutron diffraction data indicates that the V and Al substituents take those sites with similar environments in all three phases, as observed in our previous study of Ti-substituted compounds. It was confirmed that the diffraction data of the 3:29 compound can be better refined using the A2/m space group than using the P21/c space group. The SQUID measurements show that all samples have Curie temperatures well above room temperature. The neutron diffraction results …

Go to article

Site Affinity Of Substituents In Nd₂Fe₁₇₋ₓtₓ (T=Cu,Zr,Nb,Ti,V) Alloys, William B. Yelon, Z. Hu, William Joseph James, G. K. Marasinghe Apr 1996

Site Affinity Of Substituents In Nd₂Fe₁₇₋ₓtₓ (T=Cu,Zr,Nb,Ti,V) Alloys, William B. Yelon, Z. Hu, William Joseph James, G. K. Marasinghe

Physics Faculty Research & Creative Works

In order to understand the magnetic properties of the substituted rare-earth-iron alloys, it is especially important to know the location of the substitutional atoms within the iron lattice. The site distributions of some nontransition-metal substituents in the substituted Nd2Fe17-xTx alloys have previously been reported. Here we report the site distributions of some transition-metal substituents (Cu,Zr,Nb,Ti,V) in the Nd2Fe17-xTx alloys and compare them with those of the nontransition-metal substituted compounds. Rietveld analysis of neutron powder diffraction data indicates that the nontransition-metal substituents show very similar site affinity at low substituent content. …

Go to article

Critical Behavior Of A Quantum Spherical Model In A Random Field, Thomas Vojta, Michael Schreiber Apr 1996

Critical Behavior Of A Quantum Spherical Model In A Random Field, Thomas Vojta, Michael Schreiber

Physics Faculty Research & Creative Works

We consider the influence of a quenched random field on the critical behavior of a quantum spherical model at the zero-temperature quantum phase transition. We find a complete solution of the model for arbitrary translationally invariant pair interactions. It turns out that the critical behavior for zero as well as finite temperatures is dominated by static random field fluctuations rather than by quantum or thermal fluctuations. Therefore the critical behavior close to the zero-temperature quantum phase transition is identical to that close to a finite-temperature transition. The system does not show a crossover from quantum to classical behavior.

Go to article

Fine-Structure Effect For (E,2e) Collisions, Don H. Madison, V. D. Kravtsov, Stephenie J. Jones, Robert P. Mceachran Apr 1996

Fine-Structure Effect For (E,2e) Collisions, Don H. Madison, V. D. Kravtsov, Stephenie J. Jones, Robert P. Mceachran

Physics Faculty Research & Creative Works

For the case of inelastic electron-atom scattering, it has been known for some time that significant spin effects may be observed even if spin-dependent forces on the projectile can be ignored. These spin effects result from the Pauli principle and this phenomenon has become known as the fine-structure effect. Recently, the question of whether or not these same types of effects should be observed for atomic ionization has been considered and the initial indications are that significant spin asymmetries can also be expected for atomic ionization if the final ion satisfies LS coupling and the final J state of the …

Go to article

Quantum Version Of A Spherical Model: Crossover From Quantum To Classical Critical Behavior, Thomas Vojta Jan 1996

Quantum Version Of A Spherical Model: Crossover From Quantum To Classical Critical Behavior, Thomas Vojta

Physics Faculty Research & Creative Works

We investigate a quantum version of the spherical model which is obtained from the classical Berlin-Kac spherical model by a simple canonical quantization scheme. We find a complete solution of the model for short-range as well as for long-range interactions. At finite temperatures the critical behavior is the same as in the classical spherical model whereas at zero temperature we find a quantum phase transition characterized by new critical exponents. Based on a functional-integral representation of the partition function the free energy of the model is shown to be equivalent to that of the nonlinear σ model in the limit …

Go to article

Effective-Medium Theory For The Electric-Field Dependence Of The Hopping Conductivity Of Disordered Solids, Paul Ernest Parris, B. D. Bookout Jan 1996

Effective-Medium Theory For The Electric-Field Dependence Of The Hopping Conductivity Of Disordered Solids, Paul Ernest Parris, B. D. Bookout

Physics Faculty Research & Creative Works

We derive a general effective-medium theory for describing biased diffusion on a bond-disordered lattice in the presence of an external driving field. In our theory, the effective medium associated with a disordered d-dimensional lattice is characterized, for each value of the applied field, by 2d independent parameters describing, respectively, the net drift velocity vv and the diffusion constant Dvv describing the spread of a carrier packet about its mean value, for each of the d crystal axes. The theory correctly predicts the velocity transition occurring in an exactly soluble model studied by Derrida and, in contrast to other …

Go to article

Upper-Tropospheric Aerosol Sampled During Project Fire Ifo Ii, Donald E. Hagen, Josef Podzimek, Max B. Trueblood Dec 1995

Upper-Tropospheric Aerosol Sampled During Project Fire Ifo Ii, Donald E. Hagen, Josef Podzimek, Max B. Trueblood

Physics Faculty Research & Creative Works

Aerosols can play a role in the cloud formation process through the heterogeneous nucleation mechanism, and in turn, once formed, cirrus clouds can impact the ambient aerosol through scavenging and other collection mechanisms. University of Missouri aerosol sampling facilities were employed on aircraft for in situ collection and characterization of the particulates near cirrus cloud level. Tandem differential mobility analyzer and impactor techniques were used to measure aerosol size distribution, hydration capability, and particle composition information. Evidence of aerosol layering was observed near the tropospause, and there was a tendency toward depletion of the ambient aerosol at both ends of …

Go to article

Coherent Excitation Of The Singlet-Triplet Mixed 1s4f State Of Helium, Jingbo Wang, J. F. Williams, Andris T. Stelbovics, John E. Furst, Don H. Madison Oct 1995

Coherent Excitation Of The Singlet-Triplet Mixed 1s4f State Of Helium, Jingbo Wang, J. F. Williams, Andris T. Stelbovics, John E. Furst, Don H. Madison

Physics Faculty Research & Creative Works

In this paper, we present a detailed theoretical description for the coherent electron-impact excitation, the subsequent time evolution, and the cascading decay process of the singlet-triplet mixed 1s4f state of helium. The excitation amplitude and phase of each sublevel of this state are related to measurable coincidence intensities and polarizations of the emitted photons. It is found that the intensity and polarization of the emitted photons are time modulated due to the singlet and triplet mixing in the 1s4f state.

Go to article

Comparison Of Branching Ratio And Sum-Rule Analyses Of Magnetic Circular Dichroism In X-Ray-Absorption Spectroscopy, James G. Tobin, George Daniel Waddill, Alan F. Jankowski, Philip A. Sterne, David P. Pappas Sep 1995

Comparison Of Branching Ratio And Sum-Rule Analyses Of Magnetic Circular Dichroism In X-Ray-Absorption Spectroscopy, James G. Tobin, George Daniel Waddill, Alan F. Jankowski, Philip A. Sterne, David P. Pappas

Physics Faculty Research & Creative Works

Two localized picture methods of analyzing the magnetic circular dichroism in x-ray absorption will be applied to experimental results: the branching ratio (BR) and sum rule (SR) approaches. A derivation of the BR formulas and detailed comparison to the SR expressions will be made, including error estimations. The BR approach will be seen to be a limiting case form of the SR spin-moment expression and provide a simple picture of the underlying physics in magnetic x-ray circular dichroism absorption in 3d magnetic materials.

Go to article

Floquet Description Of Multiphoton Processes In Li, D. I. Duncan, J. Greg Story, Thomas F. Gallagher Sep 1995

Floquet Description Of Multiphoton Processes In Li, D. I. Duncan, J. Greg Story, Thomas F. Gallagher

Physics Faculty Research & Creative Works

We have made several different types of measurements of the three-photon ionization of Li produced by 3-ps laser pulses and describe the results using a Floquet picture. Over the photon frequency range 15 000 to 15 800 cm-1, Li represents a strongly coupled three-state system with the 2s ground state coupled to the 2p and 3d states by one and two photons, respectively. Energy analysis of the photoelectrons allows the measurement of the intensity dependent shift of the 2s Floquet state during the laser pulse. The shift shows a strong frequency dependence that is not predicted by first-order …

Go to article

Instability Of The R³Xs¹ Vacuum In Low-Energy Effective String Theory, Mariano Cadoni, Marco Cavaglia Aug 1995

Instability Of The R³Xs¹ Vacuum In Low-Energy Effective String Theory, Mariano Cadoni, Marco Cavaglia

Physics Faculty Research & Creative Works

We present and discuss a Euclidean solution of the low-energy effective string action that can be interpreted as a semiclassical decay process of the ground state of the theory.

Go to article

Coulomb Gap At Finite Temperatures, Masoud Sarvestani, Michael Schreiber, Thomas Vojta Aug 1995

Coulomb Gap At Finite Temperatures, Masoud Sarvestani, Michael Schreiber, Thomas Vojta

Physics Faculty Research & Creative Works

The Coulomb glass, a model of interacting localized electrons in a random potential, exhibits a soft gap, the Coulomb gap, in the single-particle density of states (DOS) g(ε,T) close to the chemical potential µ. In this paper we investigate the Coulomb gap at finite temperatures T by means of a Monte Carlo method. We find that the Coulomb gap fills with increasing temperature. In contrast to previous results the temperature dependence is, however, much stronger than g(µ,T)~TD-1 as predicted analytically. It can be described by power laws with the exponents 1.75 ± 0.1 for the two-dimensional model and 2.7 …

Go to article

Generalization Of The Schwartz-Soffer Inequality For Correlated Random Fields, Thomas Vojta, Michael Schreiber Jul 1995

Generalization Of The Schwartz-Soffer Inequality For Correlated Random Fields, Thomas Vojta, Michael Schreiber

Physics Faculty Research & Creative Works

We investigate the influence of spatial correlations between the values of the random field on the critical behavior of random-field lattice models and derive a generalized version of the Schwartz-Soffer inequality for the averages of the susceptibility and its disconnected part. At the critical point this leads to a modification of the Schwartz-Soffer exponent inequality for the critical exponents η and η- describing the divergences of the susceptibility and its disconnected part, respectively. It now reads η- ≤ 2η-2y where 2y describes the divergence of the random-field correlation function in Fourier space. As an example we exactly calculate …

Go to article

The Kelvin Equation And Self-Consistent Nucleation Theory, Gerald Wilemski Jul 1995

The Kelvin Equation And Self-Consistent Nucleation Theory, Gerald Wilemski

Physics Faculty Research & Creative Works

Issues of self-consistency are reviewed for several unary equilibrium size distributions based on the capillarity approximation. Some apparent difficulties of interpretation are resolved. In terms of the kinetic approach to nucleation theory, the influence of self-consistency on the nucleation rate is shown to arise entirely from differences in the dimer evaporation rates for nearly all versions of classical theory. The nucleation rate behavior of the Kelvin model is explored. In this model, the Kelvin equation is used to prescribe all cluster evaporation rates. Nucleation rates predicted by the Kelvin model are quantitatively similar to those of the self-consistent classical (SCC) …

Go to article

Binary Nucleation Kinetics. Ii. Numerical Solution Of The Birth-Death Equations, Barbara Ellen Wyslouzil, Gerald Wilemski Jul 1995

Binary Nucleation Kinetics. Ii. Numerical Solution Of The Birth-Death Equations, Barbara Ellen Wyslouzil, Gerald Wilemski

Physics Faculty Research & Creative Works

We numerically solve the complete set of coupled differential equations describing transient binary nucleation kinetics for vapor-to-liquid phase transitions. We investigate binary systems displaying both positive and negative deviations from ideality in the liquid phase and obtain numerical solutions over a wide range of relative rates of monomer impingement. We emphasize systems and conditions that either have been or can be investigated experimentally. In almost every case, we find behavior consistent with Stauffer's idea that the major particle flux passes through the saddle point with an orientation angle that depends on the rates of monomer impingement. When this is true, …

Go to article

Binary Nucleation Kinetics. I. Self-Consistent Size Distribution, Gerald Wilemski, Barbara Ellen Wyslouzil Jul 1995

Binary Nucleation Kinetics. I. Self-Consistent Size Distribution, Gerald Wilemski, Barbara Ellen Wyslouzil

Physics Faculty Research & Creative Works

Using the principle of detailed balance, we derive a new self-consistency requirement, termed the kinetic product rule, relating the evaporation coefficients and equilibrium cluster distribution for a binary system. We use this result to demonstrate and resolve an inconsistency for an idealized Kelvin model of nucleation in a simple binary mixture. We next examine several common forms for the equilibrium distribution of binary clusters based on the capillarity approximation and ideal vapor behavior. We point out fundamental deficiencies for each expression. We also show that each distribution yields evaporation coefficients that formally satisfy the new kinetic product rule but are …

Go to article

Observation Of Postcollision Effects In The Scattered Projectile Spectra For Ionizing Proton-Helium Collisions, Tibor Vajnai, A. D. Gaus, Joachim A. Brand, W. T. Htwe, Don H. Madison, Ronald E. Olson, Jerry Peacher, Michael Schulz May 1995

Observation Of Postcollision Effects In The Scattered Projectile Spectra For Ionizing Proton-Helium Collisions, Tibor Vajnai, A. D. Gaus, Joachim A. Brand, W. T. Htwe, Don H. Madison, Ronald E. Olson, Jerry Peacher, Michael Schulz

Physics Faculty Research & Creative Works

We have measured and calculated doubly differential single ionization cross sections as a function of the scattering angle and the projectile energy loss for 50 to 150 keV proton-helium collisions. These cross sections show unexpected structures as a function of both the energy loss and the scattering angle, which are interpreted as due to the postcollision interaction. Although the effects of postcollision interactions have previously been observed in electron spectra, this is the first observation of such effects for the scattered protons.

Go to article

Differential Double-Excitation Cross Sections In 50-150-Kev Proton-Helium Collisions, Michael Schulz, W. T. Htwe, A. D. Gaus, Jerry Peacher, Tibor Vajnai Mar 1995

Differential Double-Excitation Cross Sections In 50-150-Kev Proton-Helium Collisions, Michael Schulz, W. T. Htwe, A. D. Gaus, Jerry Peacher, Tibor Vajnai

Physics Faculty Research & Creative Works

We have measured projectile-energy-loss spectra for 50-, 100-, and 150-keV p+He collisions. From the data we obtained differential double-excitation cross sections as a function of projectile scattering angle. At 150 keV a pronounced peak structure was observed at about 0.7 mrad for double excitation to the (2p2) 1D and (2s2p) 1P states. Our data provide indications for the dominance of a first-order mechanism involving the electron-electron interaction in double excitation for 150 keV at small scattering angles. At lower projectile energies and larger scattering angles a second-order mechanism appears to be of the same order of …

Go to article

State Selective Scattering Angle Dependent Capture Cross Sections Measured By Cold Target Recoil Ion Momentum Spectroscopy, Volker Mergel, Reinhard Dorner, Joachim Hermann Ullrich, Ottmar Jagutzki, Sergio Lencinas, S. Nuttgens, Lutz Spielberger, Marc Unverzagt, C. Lewis Cocke, Ronald E. Olson, Michael Schulz, Udo Buck, E. Zanger, W. Theisinger, M. Isser, S. Geis, Horst Schmidt-Bocking Mar 1995

State Selective Scattering Angle Dependent Capture Cross Sections Measured By Cold Target Recoil Ion Momentum Spectroscopy, Volker Mergel, Reinhard Dorner, Joachim Hermann Ullrich, Ottmar Jagutzki, Sergio Lencinas, S. Nuttgens, Lutz Spielberger, Marc Unverzagt, C. Lewis Cocke, Ronald E. Olson, Michael Schulz, Udo Buck, E. Zanger, W. Theisinger, M. Isser, S. Geis, Horst Schmidt-Bocking

Physics Faculty Research & Creative Works

We have developed a new kind of recoil ion momentum spectroscopy technique, using a precooled supersonic gas jet target, to determine state selective, scattering angle dependent cross sections for swift ion-atom collisions ( 0. 25 , ..., , 1 MeV He2+ on He), by measuring the transverse and longitudinal momentum of the recoil ion. A longitudinal momentum resolution of ± 0.13 a. u. was achieved, about a factor of 30 better than ever obtained before, which enables a clear separation of K and L shell capture. In the transverse direction a resolution corresponding to a projectile scattering angle uncertainty …

Go to article

Electric-Field Enhancement Of Dielectronic Recombination From A Continuum Of Finite Bandwidth, J. Greg Story, Bernard J. Lyons, Thomas F. Gallagher Mar 1995

Electric-Field Enhancement Of Dielectronic Recombination From A Continuum Of Finite Bandwidth, J. Greg Story, Bernard J. Lyons, Thomas F. Gallagher

Physics Faculty Research & Creative Works

A small electric field is shown to increase the dielectronic recombination, via autoionizing Rydberg states, of an electron from a continuum of finite bandwidth. The continuum of finite bandwidth is a broad autoionizing state which is part of a series converging to a higher limit, and the field enhancement of the rate occurs because the field converts the nl Rydberg states to nk Stark states, increasing the number of contributing recombination paths. The experimental results are in excellent agreement with the predictions of an isolated resonance approximation treatment and show clearly both the positive effect of Stark mixing and the …

Go to article

The Light Ion Pulsed Power Induction Accelerator For Etf, Ronald E. Olson, M. G. Mazarakis, C. L. Olson, D. L. Smith, L. F. Bennett Jan 1995

The Light Ion Pulsed Power Induction Accelerator For Etf, Ronald E. Olson, M. G. Mazarakis, C. L. Olson, D. L. Smith, L. F. Bennett

Physics Faculty Research & Creative Works

The light ion Engineering Test Facility (ETF) driver concept, based on Hermes III and RHEPP technologies, is a scaled-down version of the LMF design incorporating repetition rate capabilities of up to 10 Hz. The preconceptual design presented here provides 250 TW peak power to the ETF target during 8 ns, equal to 2 MJ total ion beam energy. Linear inductive voltage addition driving a self-magnetically insulated transmission line (MITL) is utilized to generate the 36 MV peak voltage needed for lithium ion beams. The ~3 MA ion current is achieved by utilizing many accelerating modules in parallel. Since the current …

Go to article

First Prev Next Last