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1999

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Articles 1 - 30 of 347

Full-Text Articles in Physics

Experimental And Phenomenological Study Of Persistent Photoconductivity In Yba2cu3o6 Thin Films, Daniel-Dennis Mcalevy Bubb Dec 1999

Experimental And Phenomenological Study Of Persistent Photoconductivity In Yba2cu3o6 Thin Films, Daniel-Dennis Mcalevy Bubb

Dissertations

Persistent Photoconductivity in YBa2Cu3O6+x thin films is studied by means of infrared photoconductivity measurements after the films have been illuminated with visible light at low temperature. Experimentally, the effect is characterized by the samples' electrical response to infrared light, either causing the resistance to decrease or increase.

A cellular automata model is proposed in explanation of these results and is shown to be consistent with current experimental understanding of this unusual effect, both our results and those of others. The cellular automata model may have application to other unusual optical phenomena exhibited by YBa ...


Dynamics Of The Dbi Spike Soliton, David Kastor, Jennie Traschen Dec 1999

Dynamics Of The Dbi Spike Soliton, David Kastor, Jennie Traschen

David Kastor

We compare oscillations of a fundamental string ending on a D3-brane in two different settings: (1) a test-string radially threading the horizon of an extremal black D3-brane and (2) the spike soliton of the DBI effective action for a D3-brane. Previous work has shown that overall transverse modes of the test-string appear as l=0 modes of the transverse scalar fields of the DBI system. We identify DBI world-volume degrees of freedom that have dynamics matching those of the test-string relative transverse modes. We show that there is a map, resembling T-duality, between relative and overall transverse modes for the ...


Viscoelastic Depinning Of Driven Systems: Mean-Field Plastic Scallops, M. Cristina Marchetti, Alan Middleton, Thomas Prellberg Dec 1999

Viscoelastic Depinning Of Driven Systems: Mean-Field Plastic Scallops, M. Cristina Marchetti, Alan Middleton, Thomas Prellberg

Physics

We have investigated the mean field dynamics of an overdamped viscoelastic medium driven through quenched disorder. The model introduced incorporates coexistence of pinned and sliding degrees of freedom and can exhibit continuous elastic depinning or first order hysteretic depinning. Numerical simulations indicate mean field instabilities that correspond to macroscopic stick-slip events and lead to premature switching. The model is relevant for the dynamics of driven vortex arrays in superconductors and other extended disordered systems.


Nanocomposite Copt:C Films For Extremely High-Density Recording, M. Yu, Yi Liu, A. Moser, D. Weller, David J. Sellmyer Dec 1999

Nanocomposite Copt:C Films For Extremely High-Density Recording, M. Yu, Yi Liu, A. Moser, D. Weller, David J. Sellmyer

David Sellmyer Publications

Nanocomposite CoPt:C films were investigated as potential media for extremely high-density recording. An annealing temperature of over 600 °C is necessary to form nanocomposite CoPt:C films consisting of C matrix and fct CoPt nanocrystallites with grain sizes of 8–20 nm and coercivities of 3–12 kOe. Coercivity and grain size increase with increasing annealing temperature and decreasing C concentration and they are insensitive to film thickness. The average activation volumes are about 0.9×10-18 cm3. The properties of these nanocomposite CoPt:C films can be tailored to satisfy the thermal stability, coercivity, and media ...


Electrical Resistivity Of A Thin Metallic Film, Horacio E. Camblong Dec 1999

Electrical Resistivity Of A Thin Metallic Film, Horacio E. Camblong

Physics and Astronomy

The electrical resistivity of a pure sample of a thin metallic film is found to depend on the boundary conditions. This conclusion is supported by a free-electron model calculation and confirmed by an ab initio relativistic Korringa-Kohn-Rostoker computation. The low-temperature resistivity is found to be zero for a free-standing film (reflecting boundary conditions) but nonzero when the film is sandwiched between two semi-infinite samples of the same material (outgoing boundary conditions). In the latter case, this resistivity scales inversely with the number of monolayers and is due to the background diffusive scattering by a finite lattice.


Material-Independent Determination Of Anchoring Properties On Rubbed Polyimide Surfaces, Bharat R. Acharya, Jae-Hoon Kim, Satyendra Kumar Dec 1999

Material-Independent Determination Of Anchoring Properties On Rubbed Polyimide Surfaces, Bharat R. Acharya, Jae-Hoon Kim, Satyendra Kumar

Physics Publications

A material-independent method for determining liquid-crystal (LC) anchoring energy on rubbed polyimide (PI) surfaces has been devised. This method exploits the changes in the easy axis of rubbed PI film induced by exposure to linearly polarized UV (LPUV) Light. The distribution of PI chains in a rubbed film is approximated by a Gaussian function and its width determined from the measured rotation of the LC easy axis as a function of exposure time. A quasimicroscopic free energy of the LC-substrate interface is used to model LC anchoring properties. The experimental and calculated values of the azimuthal anchoring energy are in ...


Quasicrystalline Nature Of Quasicrystal Surfaces: A Photoemission Study, D. Naumović, P. Aebi, :L. Schlapbach, C. Beeli, Thomas A. Lograsso, Dwight W. Delaney Dec 1999

Quasicrystalline Nature Of Quasicrystal Surfaces: A Photoemission Study, D. Naumović, P. Aebi, :L. Schlapbach, C. Beeli, Thomas A. Lograsso, Dwight W. Delaney

Ames Laboratory Publications

Differently prepared surfaces of quasicrystalline i-Al-Pd-Mn are analyzed using angle-resolved photoemission in the x-ray andultraviolet range of photon energies. Depending on the preparation, we find both surfaces with crystalline structure and metallic character, and surfaces with quasicrystalline structural fingerprints and a suppressed density of states at the Fermi level, compatible with a pseudogap.


Interaction Second Virial Coefficients From A Recent H2-Co Potential Energy Surface, J. Gottfried, George C. Mcbane Dec 1999

Interaction Second Virial Coefficients From A Recent H2-Co Potential Energy Surface, J. Gottfried, George C. Mcbane

Peer Reviewed Articles

No abstract provided.


Creation Of An Ultracold Neutral Plasma, Scott D. Bergeson, T. C. Killian, S. Kulin, L. A. Orozco, C. Orzel, S. L. Rolston Dec 1999

Creation Of An Ultracold Neutral Plasma, Scott D. Bergeson, T. C. Killian, S. Kulin, L. A. Orozco, C. Orzel, S. L. Rolston

Faculty Publications

We report the creation of an ultracold neutral plasma by photoionization of laser-cooled xenon atoms. The charge carrier density is as high as 2×10^9 cm^-3, and the temperatures of electrons and ions are as low as 100 mK and 10 uK, respectively. Plasma behavior is evident in the trapping of electrons by the positive ion cloud when the Debye screening length becomes smaller than the size of the sample. We produce plasmas with parameters such that both electrons and ions are strongly coupled.


Oxygen Pressure-Tuned Epitaxy And Optoelectronic Properties Of Laser-Deposited Zno Films On Sapphire, S. Choopun, R. D. Vispute, W. Noch, A. Balsamo, R. P. Sharma, T. Venkatesan, A. Iliadis, David C. Look Dec 1999

Oxygen Pressure-Tuned Epitaxy And Optoelectronic Properties Of Laser-Deposited Zno Films On Sapphire, S. Choopun, R. D. Vispute, W. Noch, A. Balsamo, R. P. Sharma, T. Venkatesan, A. Iliadis, David C. Look

Physics Faculty Publications

Influence of oxygen pressure on the epitaxy, surface morphology, and optoelectronic properties has been studied in the case of ZnO thin films grown on sapphire ~0001! by pulsed-laser deposition. Results of Rutherford backscattering and ion channeling in conjunction with atomic force microscopy clearly indicate that the growth mode, degree of epitaxy, and the defect density strongly depend on the oxygen background pressure during growth. It is also found that the growth mode and the defects strongly influence the electron mobility, free-electron concentration, and the luminescence properties of the ZnO films. By tuning the oxygen pressure during the initial and the ...


Measurement Of The B00 Oscillation Frequency Using L-D*+ Pairs And Lepton Flavor Tags, T. Affolder, Kenneth A. Bloom, Collider Detector At Fermilab Collaboration Dec 1999

Measurement Of The B0B̅0 Oscillation Frequency Using L-D*+ Pairs And Lepton Flavor Tags, T. Affolder, Kenneth A. Bloom, Collider Detector At Fermilab Collaboration

Kenneth Bloom Publications

The oscillation frequency Δmd of B00 mixing is measured using the partially reconstructed semileptonic decay 0l- ν̅ D*+X. The data sample was collected with the CDF detector at the Fermilab Tevatron collider during 1992–1995 by triggering on the existence of two lepton candidates in an event, and corresponds to about 110 pb-1 of p̅p collisions at √s =1.8 TeV. We estimate the proper decay time of the 0 meson from the measured decay length and reconstructed momentum of the l-D*+ system. The charge of the lepton ...


Detailed Dynamics Of Electron Beams Self-Trapped And Accelerated In A Self-Modulated Laser Wakefield, Shouyuan Chen, M. Krishnan, Anatoly Maksimchuk, R. Wagner, Donald P. Umstadter Dec 1999

Detailed Dynamics Of Electron Beams Self-Trapped And Accelerated In A Self-Modulated Laser Wakefield, Shouyuan Chen, M. Krishnan, Anatoly Maksimchuk, R. Wagner, Donald P. Umstadter

Donald Umstadter Publications

The electron beam generated in a self-modulated laser-wakefield accelerator is characterized in detail. A transverse normalized emittance of 0.06 π mm mrad, the lowest ever for an electron injector, was measured for 2 MeV electrons. The electron beam was observed to have a multicomponent beam profile and energy distribution. The latter also undergoes discrete transitions as the laser power or plasma density is varied. In addition, dark spots that form regular modes were observed in the electron beam profile. These features are explained by analysis and test particle simulations of electron dynamics during acceleration in a three-dimensional plasma wakefield.


Molecular-Dynamics Study Of Phase Transitions In Alkali Azides, M. M. Ossowski, John R. Hardy, R. W. Smith Dec 1999

Molecular-Dynamics Study Of Phase Transitions In Alkali Azides, M. M. Ossowski, John R. Hardy, R. W. Smith

John R. Hardy Papers

An account is presented of our studies of the order-disorder phase transitions in KN3, RbN3, and CsN3. These are based on parameter-free interionic potentials based on the Gordon-Kim modified electron-gas formalism extended to molecular ions. We performed static structural relaxations and supercell molecular dynamics and predicted with reasonable accuracy the temperatures for the onset of the transitions. In particular, we address the question of how the N3- ions reorient to yield the transitions. We found the existence of NaCl-type high-temperature phases in disordered KN3 and RbN3 and argue that this restructuring is preempted by ...


Molecular-Dynamics Study Of Phase Transitions In Alkali Azides, M. M. Ossowski, John R. Hardy, Robert W. Smith Dec 1999

Molecular-Dynamics Study Of Phase Transitions In Alkali Azides, M. M. Ossowski, John R. Hardy, Robert W. Smith

Physics Faculty Publications

An account is presented of our studies of the order-disorder phase transitions in KN3, RbN3, and CsN3. These are based on parameter-free interionic potentials based on the Gordon-Kim modified electron-gas formalism extended to molecular ions. We performed static structural relaxations and supercell molecular dynamics and predicted with reasonable accuracy the temperatures for the onset of the transitions. In particular, we address the question of how the N3- ions reorient to yield the transitions. We found the existence of NaCl-type high-temperature phases in disordered KN3 and RbN3 and argue that this restructuring is preempted by ...


Evidence For Replicate 5p Core Levels In Photoelectron Spectra Of Eu Metal Due To Nonconstant Kinetic-Energy Resonant Auger Decay, S. Haffner, C. G. Olson, David W. Lynch Dec 1999

Evidence For Replicate 5p Core Levels In Photoelectron Spectra Of Eu Metal Due To Nonconstant Kinetic-Energy Resonant Auger Decay, S. Haffner, C. G. Olson, David W. Lynch

Physics and Astronomy Publications

Satellites on the low-binding-energy side of core-level photoelectron emission due to extra 4f screening are a well-known feature in the x-ray photoelectron spectra of valence fluctuation materials and rare-earth metals. A notable exception is Eu metal, where up to now no low-binding-energy satellite has been observed. In this paper we show that in Eu metal the 4d−4f resonance can decay via a resonant Auger decay, which is not a constant kinetic-energy feature due to a rapid change of the strength of 4f screening with excitation energy, establishing a low-binding-energy replica of the 5p core-level photoelectron emission.


Transport Of Torsional Stress In Dna, Philip C. Nelson Dec 1999

Transport Of Torsional Stress In Dna, Philip C. Nelson

Department of Physics Papers

It is well known that transcription can induce torsional stress in DNA, affecting the activity of nearby genes or even inducing structural transitions in the DNA duplex. It has long been assumed that the generation of significant torsional stress requires the DNA to be anchored, forming a limited topological domain, because otherwise it would spin almost freely about its axis. Previous estimates of the rotational drag have, however, neglected the role of small natural bends in the helix backbone. We show how these bends can increase the drag several thousandfold relative to prior estimates, allowing significant torsional stress even in ...


Photodetachment Of He- In The Vicinity Of The He* (N=3, 4, And 5) Thresholds, Chien-Nan Liu, Anthony F. Starace Dec 1999

Photodetachment Of He- In The Vicinity Of The He* (N=3, 4, And 5) Thresholds, Chien-Nan Liu, Anthony F. Starace

Anthony F. Starace Publications

A comprehensive eigenchannel R-matrix study of photodetachment of He-(1 s2s2p 4P0 (1 ) is presented for the energy region of the Hesnl3l) thresholds, where 3<~n<~5. Over this energy region we present all partial cross sections which have been measured experimentally, including theoretical predictions (1 for the Hes3p 3P ( ) partial cross section, as well as energies and widths for all resonances, and identifications of all major ones. Near the Hen=3) thresholds, we predict two 4De resonances that to our knowledge have previously been neither predicted nor observed, and present results showing their effects on partial cross sections and photoelectron angular distributions; our He (1 ...


Characterisation Of The Effects Of Time And Pressure On A Group Of Electronic Voltage Standards, James Kevin Armstrong Dec 1999

Characterisation Of The Effects Of Time And Pressure On A Group Of Electronic Voltage Standards, James Kevin Armstrong

Masters

Although primary metrology laboratories use standards based on the Josephson effect to maintain a local reference standard for dc voltage, artefact standards are still the standard of choice in many secondary laboratories. The National Metrology Laboratory, Dublin maintains a local reference standard for dc voltage by means of an ensemble of Zener-diode based electronic voltage standard units. Electronic voltage standards have a number of shortcomings over Josephson standards for use as a local reference standard. In particular their output voltages are influenced by several external factors. In order to make optimum use of the NML reference standard it is important ...


Video And Photometric Observations Of A Sprite In Coincidence With A Meteor-Triggered Jet Event, D. M. Suszcynsky, R. Strabley, R. Roussel-Dupre, E. M.D. Symbalisty, R. A. Armstrong, W. A. Lyons, Michael J. Taylor Dec 1999

Video And Photometric Observations Of A Sprite In Coincidence With A Meteor-Triggered Jet Event, D. M. Suszcynsky, R. Strabley, R. Roussel-Dupre, E. M.D. Symbalisty, R. A. Armstrong, W. A. Lyons, Michael J. Taylor

All Physics Faculty Publications

Video and photometric observations of a meteor-triggered “jet” event in association with the occurrence of a sprite were collected during the SPRITES '98 campaign. The event raises interest in the question of possible meteoric triggering of upper atmospheric transients as originally suggested by Muller [1995]. The event consisted of three stages: (1) the observation of a moderately bright meteor, (2) the development of a sprite in the immediate vicinity of the meteor as the meteor reached no lower than ∼70 km altitude, and (3) a slower-forming jet of luminosity that appeared during the late stages of the sprite and propagated ...


Initial State Dependence Of Low-Energy Electron Emission In Fast Ion Atom Collisions, Robert Moshammer, Pablo Daniel Fainstein, Michael Schulz, Wayne M. Schmitt, Holger Kollmus, Rido Mann, Siegbert Hagmann, Joachim Hermann Ullrich Dec 1999

Initial State Dependence Of Low-Energy Electron Emission In Fast Ion Atom Collisions, Robert Moshammer, Pablo Daniel Fainstein, Michael Schulz, Wayne M. Schmitt, Holger Kollmus, Rido Mann, Siegbert Hagmann, Joachim Hermann Ullrich

Physics Faculty Research & Creative Works

Single and multiple ionization of neon and argon atoms by 3.6 MeV/u Au53+ impact has been explored in kinematically complete experiments. Doubly differential cross sections for low-energy electron emission have been obtained for a defined charge state of the recoiling target ion and the receding projectile. Observed target specific structures in the electron continuum are attributable to the nodal structure of the initial bound state momentum distribution. The experimental data are in excellent accord with continuum-distorted-wave eikonal-initial-state single ionization calculations if multiple ionization is considered appropriately.


Dynamics Of A Gravitational Billiard With A Hyperbolic Lower Boundary, Matthew L. Ferguson, B. N. Miller, M. A. Thompson Nov 1999

Dynamics Of A Gravitational Billiard With A Hyperbolic Lower Boundary, Matthew L. Ferguson, B. N. Miller, M. A. Thompson

Matthew L. Ferguson

Gravitational billiards provide a simple method for the illustration of the dynamics of Hamiltonian systems. Here we examine a new billiard system with two parameters, which exhibits, in two limiting cases, the behaviors of two previously studied one-parameter systems, namely the wedge and parabolic billiard. The billiard consists of a point mass moving in two dimensions under the influence of a constant gravitational field with a hyperbolic lower boundary. An iterative mapping between successive collisions with the lower boundary is derived analytically. The behavior of the system during transformation from the wedge to the parabola is investigated for a few ...


Double Twist In Helical Polymer "Soft" Crystals, Christopher Y. Li, Stephen Z. D. Cheng, Jason J. Ge, Feng Bai, John Z. Zhang, Ian K. Mann, Frank W. Harris, Liang-Chy Chien, Donghang Yan, Tianbai He, Bernard Lotz Nov 1999

Double Twist In Helical Polymer "Soft" Crystals, Christopher Y. Li, Stephen Z. D. Cheng, Jason J. Ge, Feng Bai, John Z. Zhang, Ian K. Mann, Frank W. Harris, Liang-Chy Chien, Donghang Yan, Tianbai He, Bernard Lotz

Chemical Physics Publications

In natural and synthetic materials having non-racemic chiral centers, chirality and structural ordering each play a distinct role in the formation of ordered states. Configurational chirality can be extended to morphological chirality when the phase, structures possess low liquid crystalline order. In the crystalline states the crystallization process suppresses the chiral helical morphology due to strong ordering interactions, In this Letter, we report the first observation of helical single lamellar crystals of synthetic non-racemic chiral polymers. Experimental evidence shows that the molecular chains twist along both the long and short axes of the helical lamellar crystals, which is the first ...


Lattice-Stiffening Transition In Copolymer Films Of Vinylidene Fluoride (70%) With Trifluoroethylene (30%), C.N. Borca, Shireen Adenwalla, Jaewu Choi, P.T. Sprungerr, Stephen Ducharme, Lee Robertson, S.P. Palto, Jianglai Liu, Matt Poulsen, V.M. Fridkin, H. You, Peter A. Dowben Nov 1999

Lattice-Stiffening Transition In Copolymer Films Of Vinylidene Fluoride (70%) With Trifluoroethylene (30%), C.N. Borca, Shireen Adenwalla, Jaewu Choi, P.T. Sprungerr, Stephen Ducharme, Lee Robertson, S.P. Palto, Jianglai Liu, Matt Poulsen, V.M. Fridkin, H. You, Peter A. Dowben

Peter Dowben Publications

We report the discovery of a compressibility phase transition at 160 K in crystalline copolymer films of vinylidene fluoride ( 70%) with trifluoroethylene ( 30%). This phase transition is distinct from the known bulk ferroelectric-paraelectric phase transition at 353 K and surface ferroelectric phase transition at 295 K. The new phase transition is characterized by an increase in the effective Debye temperature from 48 to 245 K along the 〈010〉 direction as the temperature falls below 160 K. This phase transition is evident in neutron scattering, x-ray diffraction, angle-resolved photoemission, and in the dipole active phonon modes in electron energy-loss spectroscopy.


Interacting Topological Defects On Frozen Topographies, Mark Bowick, David R. Nelson, Alex Travesset Nov 1999

Interacting Topological Defects On Frozen Topographies, Mark Bowick, David R. Nelson, Alex Travesset

Physics

We propose and analyze an effective free energy describing the physics of disclination defects in particle arrays constrained to move on an arbitrary two-dimensional surface. At finite temperature the physics of interacting disclinations is mapped to a Laplacian Sine-Gordon Hamiltonian suitable for numerical simulations. We then specialize to the case of a spherical crystal at zero temperature. The ground state is analyzed as a function of the ratio of the defect core energy to the Young's modulus. We argue that the core energy contribution becomes less and less important in the limit R >> a, where R is the radius ...


Dual Function Euv Multilayer Mirrors For The Image Mission, David D. Allred, R. Steven Turley, Matthew B. Squires Nov 1999

Dual Function Euv Multilayer Mirrors For The Image Mission, David D. Allred, R. Steven Turley, Matthew B. Squires

Faculty Publications

We have developed a new family of EUV multilayer mirror coatings using uranium. Using this approach we have coated a set of six mirrors for the EUV Imager, a component of the IMAGE mission. This mission is a Medium Explorer (MIDEX) program, which is scheduled for launch early in 2000. The EUV Imager will study the distribution of He+ in the Earth's plasmasphere by detecting its resonantly scattered emission at 30.4 nm (41 eV) and will produce images of the structure and dynamics of the cold plasma on a global scale. There is, however, a bright at 58 ...


Selective Excitation And Thermal Quenching Of The Yellow Luminescence Of Gan, John S. Colton, P. Y. Yu, K. L. Teo, E. R. Weber, P. Perlin, I. Grzegory, K. Uchida Nov 1999

Selective Excitation And Thermal Quenching Of The Yellow Luminescence Of Gan, John S. Colton, P. Y. Yu, K. L. Teo, E. R. Weber, P. Perlin, I. Grzegory, K. Uchida

Faculty Publications

We report the observation of narrower structures in the yellow luminescence of bulk and thin-film n-type GaN, using the technique of selective excitation. These fine structures exhibit thermal quenching associated with an activated behavior. We attribute these fine structures to phonons and electronic excitations of a shallow donor-deep acceptor complex, and determine its activation energy for delocalization. Our results suggest that in addition to distant donor-acceptor pairs, the yellow luminescence can also involve emission complexes of shallow donors and deep acceptors.


Acceleration Of Electrons In A Self-Modulated Laser Wakefield, Shouyuan Chen, M. Krishnan, Anatoly Maksimchuk, Donald P. Umstadter Nov 1999

Acceleration Of Electrons In A Self-Modulated Laser Wakefield, Shouyuan Chen, M. Krishnan, Anatoly Maksimchuk, Donald P. Umstadter

Donald Umstadter Publications

Acceleration of electrons in a self-modulated laser-wakefield is investigated. The generated electron beam is oberved to have a multi-component beam profile and its energy distribution undergoes discrete transitions as the conditions are varied. These features can be explained by simple simulations of electron propagation in a 3-D plasma wave.


Electron Injection By Dephasing Electrons With Laser Fields, E. Dodd, J.K. Kim, Donald P. Umstadter Nov 1999

Electron Injection By Dephasing Electrons With Laser Fields, E. Dodd, J.K. Kim, Donald P. Umstadter

Donald Umstadter Publications

The authors seek to review injection concepts for plasma based acceleration. It is shown that regardless of injection mechanism, resultant beams will be similar due to wave structure. Also, most schemes employ the same basic processes, namely the dephasing of electrons by laser fields, and can thus be analyzed with similar approaches.


Light Scalar Mesons, Joseph Schechter, Deirdre Black, Amir H. Fariborz Nov 1999

Light Scalar Mesons, Joseph Schechter, Deirdre Black, Amir H. Fariborz

Physics

We review how a certain effective chiral Lagrangian approach to pi pi scattering, pi K scattering and eta-prime decay to eta pi pi provides evidence for the existence of light scalars sigma(550) and kappa(900) as well as describing the f0(980) and the a0(980). An attempt to fit these into a nonet suggests that their structure is closer to a dual quark-dual antiquark than to a quark-antiquark. A possible mechanism to explain the next higher mass scalar nonet is also proposed.


Laser Light In, 50-Mev Protons Out, Phillip F. Schewe, Ben Stein, Donald P. Umstadter Nov 1999

Laser Light In, 50-Mev Protons Out, Phillip F. Schewe, Ben Stein, Donald P. Umstadter

Donald Umstadter Publications

At next week's meeting of the American Physical Society Division of Plasma Physics in Seattle, three groups will independently announce their ability to generate powerful, intense streams of ions by shining ultrashort laser pulses on tiny spots of solid material. Potentially, this approach offers an alternative to bulky, expensive ion accelerators for producing high-velocity ions useful for cancer therapy and electronics manufacturing. Using a single pulse of light from Livermore's Petawatt laser, the most powerful in the world, researchers at that laboratory (Scott Wilks, 925-422-2974, wilks@icf.llnl.gov) have reported generating 30 trillion protons with energies up ...