bluuebunny/crossref_metadata_2025 huggingface dataset:
A latest developed all permanent magnet ECRIS for atomic physics research at IMP
Authors: Sun L. T. , Zhao H. W. , Zhang Z. M. , Wang H. , Ma B. H. , Li J. Y. , Zhang X. Z. , Feng Y. C. , Guo X. H. , Li X. X. , Ma X. W. , Song M. T. , Zhan W. L.
Published: March 2006

Electron cyclotron resonance (ECR) ion sources have been used for atomic physics research for a long time. With the development of atomic physics research in the Institute of Modern Physics (IMP), additional high performance experimental facilities are required. A 300kV high voltage (HV) platform has been under construction since 2003, and an all permanent magnet ECR ion source is supposed to be put on the platform. Lanzhou all permanent magnet ECR ion source No. 2 (LAPECR2) is a latest developed all permanent magnet ECRIS. It is a 900kg weight and ∅650mm×562mm outer dimension (magnetic body) ion source. The injection magnetic field of the source is 1.28T and the extraction magnetic field is 1.07T. This source is designed to be running at 14.5GHz. The high magnetic field inside the plasma chamber enables the source to give good performances at 14.5GHz. LAPECR2 source is now under commissioning in IMP. In this article, the typical parameters of the source LAPECR2 are listed, and the typical results of the preliminary commissioning are presented.
rf modes and plasma formation of electron cyclotron resonance ion source
Authors: Hayashizaki N. , Hattori T. , Muramatsu M.
Published: March 2006

The plasma chamber of electron cyclotron resonance (ECR) ion sources may be considered as a cavity resonator in radio-frequency (rf) technology. The microwave frequency then has to be tuned to the resonant frequency of a preferable mode. In order to produce ions with higher charge state, the rf characteristics of the plasma chamber should be investigated. As the first study, the rf simulation and the experimental measurement were carried out for a permanent magnet ECR ion source, which was developed at Tokyo Institute of Technology (TokyoTech). The frequency spectrum of microwave power transmission was measured to check the resonance points of the plasma chamber. The mode analysis was performed by a theoretical calculation and with a three-dimensional simulation code. These results and the effect of the electric-field distribution on ECR plasma will be presented.
ARTEMIS-B: A room-temperature test electron cyclotron resonance ion source for the National Superconducting Cyclotron Laboratory at Michigan State University
Authors: Machicoane G. , Cole D. , Ottarson J. , Stetson J. , Zavodszky P.
Published: March 2006

The current scheme for ion-beam injection into the coupled cyclotron accelerator at the NSCL involves the use of two electron cyclotron resonance (ECR) ion sources. The first one is a 6.4GHz fully superconducting that will be replaced within two years by SUSI, a third generation 18GHz superconducting ECR ion source. The other source, ARTEMIS, is a room-temperature source based on the AECR-U design and built in collaboration with the University of Jyväskylä in 1999. Due to cyclotron operation constraint, very little time can be allowed to ion source development and optics studies of the cyclotron injection beam line. In this context, NSCL has decided to build ARTEMIS-B an exact replica of its room-temperature ECR ion source. The goal of this project is threefold. One is to improve the overall reliability of cyclotron operation through tests and studies of various ion source parameters that could benefit beam stability, tuning reproducibility, and of course overall extracted currents performance. Second is to implement and test modifications or upgrade made to the ion source: extraction geometry, new resistive or rf oven design, dual frequency use, liner, etc. Finally, this test source will be used to study various ion optics schemes such as electrostatic quadrupole doublet or triplet at the source extraction or the use of a correction sextupole and assess their effect on the ion beam through the use of an emittance scanner and imaging viewer that will be incorporated into ARTEMIS-B beam line. This article reviews the design and construction of ARTEMIS-B along with some initial commissioning results.
A-PHOENIX, an electron cyclotron resonance ion source for the Spiral 2 facility
Authors: Thuillier T. , Lamy T. , Sortais P. , Suominen P. , Tarvainen O. , Koivisto H.
Published: March 2006

Spiral 2, the radioactive ion-beam facility of GANIL, will start its commissioning in 2009. After a brief recall of Spiral 2 beam requirements, emittance measurements of preliminary 1mA O6+ test beams, done with the PHOENIX source for Spiral 2, are shown and discussed. The 28GHz A-PHOENIX source, designed to better meet the Spiral 2 requirements, is presented and a progress report of its construction is proposed.
Production of charged (singly and multiply) phosphorous beams with electron cyclotron resonance ion source
Authors: Maunoury L. , Kantas S. , Leroy R. , Pacquet J. Y.
Published: March 2006

Within the framework of biological application linked to ion irradiation, the fabrication of radioactive stents by ion implantation provides a significant improvement of the recovery of arteries after a treatment of stenosed coronary arteries [P. Fehsenfeld et al., Semin Interv Cardiol. 3, 157 (1998); E. Huttel et al., Rev. Sci. Instrum. 73, 825 (2002); M.-A. Golombeck et al., Nucl. Instrum. Methods Phys. Res. B 206, 495 (2003)]. For this appliance, the suitable radioactive ion is P32. Obviously, in order to have a minimum loss of these radioactive ions through the ionization process, it is imperative to have high ionization efficiency. In this article, the production of such singly and multiply charged phosphorous beams is investigated using two different electron cyclotron resonance ion sources: MONO1000∕1001 [P. Jardin et al., Rev. Sci. Instrum. 73, 789 (2002)] and SUPERSHyPIE [J. Y. Pacquet et al., EP Patent No. 97 401294 (pending); R. Leroy et al., 14th International Workshop on ECR Ion Sources, May 1999 (unpublished)]. Spectra and above all efficiencies [J. Y. Pacquet et al., GANIL R 02 07; GANIL R 03 08] (31% of ionization efficiency for phosphorous atoms and compound with MONO1000∕1001 and 43% of ionization efficiency for phosphorous atoms with SUPERSHyPIE) of these beams will be presented as well as the intensities (227eμA for P+ with MONO1000∕1001 and 145eμA for P7+ with SUPERSHyPIE) of such beams.
Gas breakdown in electron cyclotron resonance ion sources
Authors: Skalyga V. A. , Zorin V. G. , Izotov I. V. , Sidorov A. V. , Lamy T. , Sortais P. , Thuillier T.
Published: March 2006

The realization of the beta-beam project (http://beta-beam.web.cern.ch/beta-beam/) assumes the formation of a pulsed ion beam of helium and neon radioactive isotopes. A pulsed electron cyclotron resonance (ECR) source of multicharged ions has been proposed to produce such a beam [P. Sortais et al., Rev. Sci. Instrum. 75, 1610 (2004)]. The rising of plasma density up to a stationary level must be fast enough to actualize this approach. This condition is mandatory to avoid particle losses in the transmission line. In the presented work, the rising time of the plasma density in an ECR ion source from a background level up to 98% of a stationary level is calculated. A zero-dimensional model of plasma formation in a mirror trap [V. Semenov et al., Rev. Sci. Instrum. 73, 635 (2002)] is used, able to make calculation for a wide range of microwave frequencies. Plasma confinement regime can either be classic (Pastoukhov [Rev. Plasma Phys. 13, 203 (1987)]) or gas dynamic, depending on the plasma parameters. The calculations are in good agreement with the experimental results obtained at the SMIS’37 setup. Numerical calculations also show that particle losses can be significantly reduced by pumping effect; thanks to microwave frequency increase above 40GHz.
Direct 10 GHz rf feedthrough plasma device with the NANOGAN III ion source for SPIRAL
Authors: Gaubert G. , Barué C. , Canet C. , Cornell J. , Dubois M. , Dupuis M. , Eleon C. , Flambard J. L. , Huet-Equilbec C. , Jardin P. , Lecesne N. , Leherissier P. , Lemagnen F. , Leroy R. , Pacquet J. Y. , Saint-Laurent M. G. , Villari A. C. C.
Published: March 2006

A new system has been designed to inject the 10 GHz rf power in the NANOGAN III ion source dedicated to the ionization of exotic atoms from the production target of the SPIRAL system at GANIL. The present system, based on a rectangular-to-coaxial transition equipped with a tuning piston, has been replaced by a direct rectangular-to-circular wave guide to feed the plasma of the source. We present the constraints related to the rf injection and a comparison is given of the present and new injection systems.
Drift wave instability in the Helimak experiment
Authors: Perez Jean C. , Horton W. , Gentle K. , Rowan W. L. , Lee K. , Dahlburg Russell B.
Published: March 2006

Electrostatic drift wave linear stability analysis is carried out for the Helimak configuration and compared against experimental data. Density fluctuation and cross-spectrum measurements show evidence of a coherent mode propagating perpendicular to the magnetic field which becomes unstable at k⊥ρs∼0.15. By comparing the experimental results with the wave characteristic of linear two-fluid theory, this mode is identified as an unstable resistive drift wave driven by the density gradient and magnetic grad-B/curvature present in an otherwise magnetohydrodynamic stable steady-state equilibrium.
Modeling of traveling compression regions in the Earth’s magnetotail by the spontaneous fast reconnection model
Authors: Ugai M. , Zheng L.
Published: March 2006

The spontaneous fast reconnection model is applied to the traveling compression regions (TCRs) observed in the Earth’s magnetotail lobe region in association with substorms. For this purpose, virtual satellites are located at spatial points in the (low-β) magnetic field region in the three-dimenisonal simulation domain, so that each satellite directly observes the temporal variations of magnetic fields, obtained from simulations, in accordance with the growth and proceeding of the fast reconnection mechanism. If the virtual satellite is located ahead of the initial plasmoid formation, it observes a pulse-like field compression with the compression rate of more than 10% as well as the bipolar structure of the magnetic field component from northward to southward tilting, when the plasmoid center passes through the satellite location. On the other hand, if it is located behind the plasmoid formation, it observes the unipolar structure of the southward field component. The simulation results are shown to be, both quantitatively and qualitatively, in good agreement with the actual satellite observations. It is demonstrated that the TCR event is the fast reconnection mechanism itself that is seen in the ambient (low-β) magnetic field (magnetotail lobe) region.
Differential turbulent heating of different ions in electron cyclotron resonance ion source plasma
Authors: Elizarov L. I. , Ivanov A. A. , Serebrennikov K. S. , Vostrikova E. A.
Published: March 2006

The article considers the collisionless ion sound turbulent heating of different ions in an electron cyclotron resonance ion source (ECRIS). The ion sound arises due to parametric instability of pumping wave propagating along the magnetic field with the frequency close to that of electron cyclotron. Within the framework of turbulent heating model the different ions temperatures are calculated in gas-mixing ECRIS plasma.
Texas A&M 14.5 and 6.4GHz electron cyclotron resonance ion sources
Authors: May D. P. , Abegglen F. P. , Derrig G. J. , Olsen R. S.
Published: March 2006

The plasma chamber of the Texas A&M 14.5GHz electron cyclotron resonance (ECR) ion source ECR2 has been redesigned recently. Small-diameter (1.8mm), water-carrying copper tubes are interposed between the Nb–Fe–B permanent magnets and the aluminum plasma-chamber wall. This design allows for more protection of the hexapole via water cooling than the previous design and also eliminates all of the troublesome water-to-vacuum seals of the previous design. Both ECR2 and the 6.4GHz electron cyclotron resonance ion source ECR1 have similarly dimensioned aluminum plasma chambers, both incorporate biased disks, but the experience with each has been much different. The performance and the operation of the two sources are compared.
Large-eddy simulation of magnetohydrodynamic turbulence in compressible fluid
Authors: Chernyshov A. A. , Karelsky K. V. , Petrosyan A. S.
Published: March 2006

In the present article, the large eddy simulation (LES) technique for the study of compressible magnetohydrodynamic turbulence is developed. The filtered equations of magnetohydrodynamics of compressible fluid are obtained with the use of a mass-weighted filtering procedure (Favre filtering). Favre-filtered equations for large-scale components of turbulence include subgrid-scale terms describing subgrid phenomena. Different models for closure of subgrid terms are suggested. In this work numerical simulation of filtered magnetohydrodynamic equations and an analysis of the received characteristics of turbulent flow is carried out. The obtained results of numerical computations for different LES models are compared with the results of direct numerical simulation.
Decomposition of solid amorphous hydrogen peroxide by ion irradiation
Authors: Loeffler Mark J. , Teolis Ben D. , Baragiola Raul A.
Published: March 2006

We present laboratory studies of the radiolysis of pure (97%) solid H2O2 films by 50keV H+ at 17K. Using UV-visible and infrared reflectance spectroscopies, a quartz-crystal microbalance, and a mass spectrometer, we measured the absolute concentrations of the H2O, O2, H2O2, and O3 products as a function of irradiation fluence. Ozone was identified by both UV and infrared spectroscopies and O2 from its forbidden transition in the infrared at 1550cm−1. From the measurements we derive radiation yields, which we find to be particularly high for the decomposition of hydrogen peroxide; this can be explained by the occurrence of a chemical chain reaction.
Photo-tuning of lasing from a dye-doped cholesteric liquid crystals by photoisomerization of a sugar derivative having plural azobenzene groups
Authors: Kurihara Seiji , Hatae Yohko , Yoshioka Teppei , Moritsugu Masaki , Ogata Tomonari , Nonaka Takamasa
Published: March 2006

Cholesteric liquid crystal (Ch LC) was prepared by mixing a nematic LC, a sugar derivative having plural azobenzene substituents, and a laser dye. Laser emission from the dye-doped Ch LC was observed at the longer edge of the selective reflection band of the Ch LC. Reversible change in the helical pitch of the Ch LC was caused by the trans-cis photoisomerization of the sugar derivative having plural azobenzene substituents. According to the change in the helical pitch of the Ch LC, the lasing properties were simultaneously affected by the UV and visible light irradiation; laser emission wavelength, intensity, singlemode-multimode.
Development of external electron-beam enhancement of the Penning ionization gauge ion source
Authors: He W. , Zhao H. W. , Liu Zh. W. , Zhao H. Y. , Cao Y. , Zhang Z. M. , Sun L. T. , Zhang X. Zh. , Guo X. H. , Wang H. , Ma B. H. , Li J. Y. , Feng Y. Ch. , Ma L. , Li X. X.
Published: March 2006

To study the injection of additional electrons from an external electron gun into the plasma of a Penning ionization gauge (PIG) ion source, a test bench for the external electron-beam enhancement of the PIG (E-PIG) ion source was set up. A source magnet assembly was built to satisfy the request for magnetic field configuration of the E-PIG ion source. Numerical calculations have been done to optimize the magnetic field configuration so as to fit the primary electrons to be fed into the PIG discharge chamber along the spreading magnetic field lines. Many possible methods for improving the performance and stability of the PIG ion source have been used in the E-PIG ion source, including the use of multicrystal LaB6 cathode and optimized axial magnetic field. This article presents a detailed design of the E-PIG ion source. Substantial enhancement of ion charge state is expected to be observed which demonstrates that the E-PIG is a viable alternative to other much more costly and difficult to operate devices for the production of intense ion beams of higher charge state.
Optical beam profile diagnostic for low energy, long pulse, moderate current electron beams
Authors: Russell Steven J. , Wang Zhi-Fu , Haynes W. Brian , Carlsten Bruce E. , Earley Lawrence M.
Published: March 2006

Currently ongoing at Los Alamos National Laboratory is a program to develop high-power, planar 100–300GHz traveling-wave tubes. An enabling technology for this effort is a sheet electron beam source and much of our effort has been geared toward understanding sheet beam generation and transport. Toward this end we have developed a robust, high resolution optical diagnostic for measuring the transverse density profiles of our electron beams. The diagnostic consists of a thin metal foil followed by an YAG:Ce or YAP:Ce scintillator crystal, both mounted on a vacuum actuator that allows us to position the foil/scintillator combination at arbitrary positions along the beam’s longitudinal axis. The electron beam strikes the metal foil and is stopped, generating Bremsstrahlung x rays that are imaged by the scintillator crystal. This image is then captured by an optical system using a high-speed, intensified gated camera. Using this diagnostic, we have measured beam profiles with resolutions as low as 0.05mm from a 0.51μP electron gun operated between 20 and 120kV.
Designing triple resonance Tesla transformers of arbitrary modal frequency ratio
Authors: Reed John Randolph
Published: March 2006

The purpose of this article is to disclose an automated method to design and investigate multimegavolt triple resonance Tesla transformers. The pulse transformer’s “frequency equation” is presented for the first time. The frequency equation derivation properly models all the inductors, with their self-capacitances, which have yet to be treated in an orthodox manner. The analysis gives new insight into the transformer by showing the relationship between the roots of the frequency equation and the transformer’s modal frequencies. The roots are shown to be subject to manipulation, and so the modal frequencies are controllable. The method efficiently extracts solutions (transformer circuits) from the frequency equation constrained to oscillate at an arbitrary and general modal frequency ratio (to include noninteger). A ratio of the present general interest is 1:2:3. This particular ratio forces the maxima of the three coexisting modal oscillations to align, and their amplitudes sum to produce a local maximum, at a specific time. The same alignment phenomenon occurs with the dual resonance transformer with a modal ratio of 1:2. A pulse transformer is designed as a demonstration. The energy in each of the three oscillations is examined at the moment of peak voltage in the demonstration transformer to show the investigative power of the new equations. This generalized tool will prove useful in the campaign to analytically locate global maximums from the triple resonance transformer’s governing amplitude equation for output voltage.
Picosecond ultrasonics time resolved spectroscopy using a photonic crystal fiber
Authors: Rossignol C. , Rampnoux J. M. , Dehoux T. , Dilhaire S. , Audoin B.
Published: March 2006

We present a time resolved spectroscopy for the picosecond ultrasonics technique. Detection of picosecond coherent phonons using a wavelength continuum generation in a photonic crystal fiber with femtosecond laser pulses is introduced. Measurements are performed on two samples made of tungsten and gallium arsenide for selected wavelengths of probe pulses within a bandwidth of 250nm with an 825nm center wavelength. Characteristic changes of the shape of the acoustic signal due to the selection of the probe wavelength are shown.
Further investigation of energy principle for model current sheets
Authors: Yoon Peter H. , Lui Anthony T. Y.
Published: March 2006

In the present paper we revisit the energy principle associated with magnetic reconnection. In the earlier approach the boundary of the system was freely adjusted to always contain one full period of the magnetic islands. In view of the fact that in simulations of reconnection such an adjustment of the boundary size is not feasible, in the present paper we reconsider a fixed boundary problem. It is shown that the energy conversion is almost negligible in such a situation. It is thus concluded that the choice of appropriate boundary conditions is critically important in the study of the energy conversion by magnetic reconnection. The present finding also points to the likelihood that the study of reconnection in two dimensions in a fixed boundary system may not reveal any appreciable magnetic field-to-particle energy conversion in an overall sense, although the present idealized theoretical approach cannot address the possibility of local heating and acceleration. This does not necessarily mean that the energy conversion by reconnection is not an efficient source of particle energization, for in nature the system is not limited by any artificial boundaries. The present finding instead only points to the possible limitation of studying the reconnection by a two-dimensional fixed-boundary system.
Interaction of the early 3d transition metals Sc, Ti, V, and Cr with N2: An ab initio study
Authors: Kardahakis Stavros , Koukounas Constantine , Mavridis Aristides
Published: March 2006

The interaction of the early 3d transition elements M=Sc, Ti, V, and Cr with N2(XΣg+1) has been studied by coupled-cluster and multiconfigurational techniques in conjunction with quantitative basis sets. We investigated both triatomic (MN2) and tetratomic (M2N2) species but focused mainly on high-spin linear and T-shaped triatomics. The lowest bound states of ScN2(B14),TiN2(Δ5), and VN2(Σ+6) correlate to the first excited state of the M atom, with M−N2 binding energies (De) of 24, 14, and 8kcal∕mol, respectively. In CrN2, the first bound state ∏7 correlates to the sixth excited state of the Cr atom (P7) with De=27kcal∕mol. The M−N2−M bond strength of high-spin linear tetratomics is twice as large the binding energy of the corresponding M−N2 linear triatomics, M=Sc, Ti, V, and Cr.
On the use of transition matrix methods with extended ensembles
Authors: Escobedo Fernando A. , Abreu Charlles R. A.
Published: March 2006

Different extended ensemble schemes for non-Boltzmann sampling (NBS) of a selected reaction coordinate λ were formulated so that they employ (i) “variable” sampling window schemes (that include the “successive umbrella sampling” method) to comprehensibly explore the λ domain and (ii) transition matrix methods to iteratively obtain the underlying free-energy η landscape (or “importance” weights) associated with λ. The connection between “acceptance ratio” and transition matrix methods was first established to form the basis of the approach for estimating η(λ). The validity and performance of the different NBS schemes were then assessed using as λ coordinate the configurational energy of the Lennard-Jones fluid. For the cases studied, it was found that the convergence rate in the estimation of η is little affected by the use of data from high-order transitions, while it is noticeably improved by the use of a broader window of sampling in the variable window methods. Finally, it is shown how an “elastic” window of sampling can be used to effectively enact (nonuniform) preferential sampling over the λ domain, and how to stitch the weights from separate one-dimensional NBS runs to produce a η surface over a two-dimensional domain.
Cryogenic NMR spectroscopy of endohedral hydrogen-fullerene complexes
Authors: Carravetta M. , Johannessen O. G. , Levitt M. H. , Heinmaa I. , Stern R. , Samoson A. , Horsewill A. J. , Murata Y. , Komatsu K.
Published: March 2006

We have observed H1 NMR spectra of hydrogen molecules trapped inside modified fullerene cages under cryogenic conditions. Experiments on static samples were performed at sample temperatures down to 4.3K, while magic-angle-spinning (MAS) experiments were performed at temperatures down to 20K at spinning frequencies of 15kHz. Both types of NMR spectra show a large increase in the intramolecular H1–H1 dipolar coupling at temperatures below 50K, revealing thermal selection of a small number of spatial rotational states. The static and MAS spectra were compared to estimate the degree of sample heating in high-speed cryogenic MAS-NMR experiments. The cryogenic MAS-NMR data show that the site resolution of magic-angle-spinning NMR may be combined with the high signal strength of cryogenic operation and that cryogenic phenomena may be studied with chemical site selectivity.
Effect of broadband microwave radiation on the performance of a conventional B-minimum geometry electron cyclotron resonance ion source
Authors: Kawai Y. , Alton G. D. , Tarvainen O. , Suominen P. , Koivisto H.
Published: March 2006

The performances of electron cyclotron resonance ion sources can be enhanced by increasing the physical sizes or numbers of resonant zones embedded within their plasma volumes. Broadband rf power offers a simple, cost effective alternative for increasing the sizes of electron cyclotron resonance (ECR) zones in conventional minimum-B geometry sources over independently powered narrow bandwidth, multiple discrete frequency schemes. In this report, the charge-state enhancing effects of broadband microwave radiation are first demonstrated by comparing the high charge states of Ar ion beams produced by powering a conventional minimum-B geometry, 6.4 GHz ECR ion source with broadband microwave radiation {200 MHz [full width at half maximum (FWHM)]} with those produced by conventional bandwidth [∼1.5MHz (FWHM)] radiation. The results of these studies show that high-charge-state beams (e.g., Ar11+) can be enhanced by factors >2 with broadband microwave radiation over those powered with narrow bandwidth radiation at the same power level, with or without voltage applied to the biased disk. The high charge states exhibit an anomalously strong increase in intensity at an optimum pressure with broadband microwave radiation.
Development and characterization of a laminar aerosol flow tube
Authors: Khalizov Alexei F. , Earle Michael E. , Johnson Wayde J. W. , Stubley Gordon D. , Sloan James J.
Published: March 2006

We have developed a new laminar aerosol flow tube (AFT) to study transformations such as ice nucleation, deliquescence, and efflorescence in model atmospheric aerosols. The apparatus consists of four sections which can be independently cooled to reproduce temperature profiles relevant to the troposphere and stratosphere. An automatic control system maintains the average axial temperature along each section between 100 and 300K, within ±0.1K. Changes in aerosol composition, phase, and size distribution are monitored at the tube exit using infrared spectroscopy (AFT-IR). We used computational fluid dynamics simulations to investigate flow velocity and temperature distributions within the flow tube. Based on these computations, the final design was formulated to eliminate turbulent mixing zones and buoyancy-driven convection cells. The latter can occur even under conditions where the Reynolds number indicates laminar flow. In either case, recirculation causes aerosol residence times and temperature histories to be poorly defined, leading to erroneous interpretation of experimental measurements. The resulting AFT design used copper fins to reduce temperature gradients and axial mixing of aerosol and carrier gas flows in the inlet section to reduce turbulence. The performance of the new AFT is significantly better than for previous designs.
Inversion of velocity map ion images using iterative regularization and cross validation
Authors: Renth F. , Riedel J. , Temps F.
Published: March 2006

Two methods for improved inversion of velocity map images are presented. Both schemes use two-dimensional basis functions to perform the iteratively regularized inversion of the imaging equation in matrix form. The quality of the reconstructions is improved by taking into account the constraints that are derived from prior knowledge about the experimental data, such as non-negativity and noise statistics, using (i) the projected Landweber [Am. J. Math. 73, 615 (1951)] and (ii) the Richardson-Lucy [J. Opt. Soc. Am. 62, 55 (1972); Astron. J. 79, 745 (1974)] algorithms. It is shown that the optimum iteration count, which plays the role of a regularization parameter, can be determined by partitioning the image into quarters or halves and a subsequent cross validation of the inversion results. The methods are tested with various synthetic velocity map images and with velocity map images of the H-atom fragments produced in the photodissociation of HBr at λ=243.1nm using a (2+1) resonantly enhanced multiphoton ionization (REMPI) detection scheme. The versatility of the method, which is only determined by the choice of basis functions, is exploited to take into account the photoelectron recoil that leads to a splitting and broadening of the velocity distribution in the two product channels, and to successfully reconstruct the deconvolved velocity distribution. The methods can also be applied to the cases where higher order terms in the Legendre expansion of the angular distribution are present.
Solitary wave propagation in solar flux tubes
Authors: Erdélyi Robert , Fedun Viktor
Published: March 2006

The aim of the present work is to investigate the excitation, time-dependent dynamic evolution, and interaction of nonlinear propagating (i.e., solitary) waves on vertical cylindrical magnetic flux tubes in compressible solar atmospheric plasma. The axisymmetric flux tube has a field strength of 1000G at its footpoint, which is typical for photospheric regions. Nonlinear waves that develop into solitary waves are excited by a footpoint driver. The propagation of the nonlinear signal is investigated by solving numerically a set of fully nonlinear 2.0D magnetohydrodynamic (MHD) equations in cylindrical coordinates. For the initial conditions, axisymmetric solutions of the linear dispersion relation for wave modes in a magnetic flux tube are applied. In the present case, we focus on the sausage mode only. The dispersion relation is solved numerically for a range of plasma parameters. The equilibrium state is perturbed by a Gaussian at the flux tube footpoint. Two solitary solutions are found by solving the full nonlinear MHD equations. First, the nonlinear wave propagation with external sound speed is investigated. Next, the solitary wave propagating close to the tube speed, also found in the numerical solution, is studied. In contrast to previous analytical and numerical works, here no approximations were made to find the solitary solutions. A natural application of the present study may be spicule formation in the low chromosphere. Future possible improvements in modeling and the relevance of the photospheric chromospheric transition region coupling by spicules is suggested.
On intense electron beam propagation through gas jets
Authors: Krasheninnikov S. I. , Frolov B. K.
Published: March 2006

The structure of the ionization front created by an expanding high-intensity electron beam as it travels through ∼1atm gas is considered theoretically. The velocity of the front, Vf, on the order of a few 10∧9cm∕s, is determined by the electric field ionization process. When decreasing the gas density, the velocity Vf decreases relatively slowly up to some threshold, after which it starts rapidly falling. The magnitude of Vf is higher for argon than for helium. These findings are supported by experimental observations.
A study of the radical-radical reaction dynamics of O(P3)+t-C4H9→OH+iso-C4H8
Authors: Nam Mi-Ja , Youn Sung-Eui , Choi Jong-Ho
Published: March 2006

The radical-radical reaction dynamics of ground-state atomic oxygen [O(P3)] with t-butyl radicals (t-C4H9) in the gas phase were investigated using high-resolution laser spectroscopy in a crossed-beam configuration, together with ab initio theoretical calculations. The radical reactants, O(P3) and t-C4H9, were produced by the photodissociation of NO2 and the supersonic flash pyrolysis of the precursor, azo-t-butane, respectively. A new exothermic channel, O(P3)+t-C4H9→OH+iso-C4H8, was identified and the nascent rovibrational distributions of the OH (XΠ2:υ″=0,1,2) products were examined. The population analyses for the two spin-orbit states of F1(Π3∕22) and F2(Π1∕22) showed that the υ″=0 level is described by a bimodal feature composed of low- and high-N″ rotational components, whereas the υ″=1 and 2 levels exhibit unimodal distributions. No noticeable spin-orbit or Λ-doublet propensities were observed in any vibrational state. The partitioning ratio of the vibrational populations (Pυ″) with respect to the low-N″ components of the υ″=0 level was estimated to be P0:P1:P2=1:1.17±0.24:1.40±0.11, indicating that the nascent internal distributions are highly excited. On the basis of the comparison of the experimental results with the statistical theory, the reaction mechanism at the molecular level can be described in terms of two competing dynamic pathways: the major, direct abstraction process leading to the inversion of the vibrational populations, and the minor, short-lived addition-complex process responsible for the hot rotational distributions. After considering the reaction exothermicity, the barrier height, and the number of intermediates along the addition reaction pathways on the lowest doublet potential energy surface, the formation of CH3COCH3(acetone)+CH3 was predicted to be dominant in the addition mechanism.
A novel self-consistent-field lattice model for block copolymers
Authors: Chen Ji-Zhong , Zhang Cheng-Xiang , Sun Zhao-Yan , Zheng Yi-Song , An Li-Jia
Published: March 2006

We develop a self-consistent-field lattice model for block copolymers and propose a novel and general method to solve the self-consistent-field equations. The approach involves describing the polymer chains in a lattice and employing a two-stage relaxation procedure to evolve a system as rapidly as possible to a free-energy minimum. In order to test the validity of this approach, we use the method to study the microphases of rod-coil diblock copolymers. In addition to the lamellar and cylindrical morphologies, micellar, perforated lamellar, gyroid, and zigzag structures have been identified without any prior assumption of the microphase symmetry. Furthermore, this approach can also give the possible orientation of the rods in different structures.
Nonreactive molecular dynamics force field for crystalline hexahydro-1,3,5-trinitro-1,3,5 triazine
Authors: Boyd Sylke , Gravelle Matthew , Politzer Peter
Published: March 2006

An empirical nonreactive force field has been developed for molecular dynamics (MD)/Monte Carlo simulation of the formation, diffusion, and agglomeration of point defects in the crystal lattice of the α modification of hexahydro-1,3,5-trinitro-1,3,5 triazine (RDX) using flexible molecules. Bond stretching and angle bending are represented by Morse and harmonic functions, and torsion by a truncated cosine series. Nonbonded interactions, both inter- and intramolecular, are described by Buckingham potentials separately parametrized. Intermolecular electrostatic interactions are treated via a Coulomb term coupled with a smooth 15.0Å cutoff radius. Parameters were taken in part from earlier published works and were determined partly by fitting to known molecular and crystal properties of RDX. In MD simulations at constant pressure and temperature, the model was able to stabilize and maintain the correct crystal structure, symmetry, and molecular conformation of α-RDX. Vibrational frequencies, lattice binding energy and dimensions, coefficients of thermal expansion, and several unusually short intermolecular distances are all reproduced in satisfactory agreement with experimental data.
Systematic study of the size and spacing dependence of Ag nanoparticle enhanced fluorescence using electron-beam lithography
Authors: Corrigan T. D. , Guo S.-H. , Szmacinski H. , Phaneuf R. J.
Published: March 2006

We study the enhancement of fluorescence by Ag nanopillars on a semiconducting substrate in which the pillar size, shape, and spacing is varied systematically using electron-beam lithography. Local maxima in the enhancement versus lateral size, as large as a factor of ∼20 are observed, and vary both with the shape of the pillars and the wavelength of the excitation. We find that the size, shape, and spacing dependence is in qualitative agreement with a model based upon resonant coupling with particle plasmon polaritons. We also find increased enhancement for particle shapes producing high local electric fields.
Investigation of laser ion acceleration inside irradiated solid targets by neutron spectroscopy
Authors: Youssef A. , Kodama R. , Tampo M.
Published: March 2006

Origins and acceleration directions of accelerated ions inside solid LiF, CH-LiF, and LiF-CH targets irradiated by a 450fs, 20J, 1053nm laser at an intensity of 3×1018W∕cm2 have been investigated by neutron spectroscopy. The irradiated targets generate neutrons through the reaction Li7 (p,n)Be7 between accelerated protons and background Li7 ions inside the target. The produced neutron spectra observed from two different observation angles 20° and 120° to the target rear-side normal. From the measured and calculated spectra, by three-dimensional Monte Carlo code, the maximum energy, the total number, and the slope temperature of the accelerated ions are investigated. The results indicate that ions are not only accelerated from the front surface toward the rear surface, but also from the rear surface toward the front surface with comparable maximum energy and higher number.
Theory of dust self-organized convection in cylindrical discharges. II. Dust convective structures
Authors: Tsytovich V. N. , Vladimirov S. V. , Vaulina O. S. , Petrov O. F. , Fortov V. E.
Published: March 2006

The convection of dust particles in a plasma is related to the spatial gradients of dust charge distributions existing due to different plasma conditions in different parts of dusty structures. Here, the set of nonlinear equations is derived to describe the dust convective structures appearing as perturbations of the basic nonlinear structures obtained in Part I. On its basis, various cases of the dust convection in cylindrical dusty structures in a plasma are obtained. It is demonstrated that there is the broad range of plasma and dust parameters where the self-organized dust convection exist.
Multiscale interaction of a tearing mode with drift wave turbulence: A minimal self-consistent model
Authors: McDevitt C. J. , Diamond P. H.
Published: March 2006

A minimal self-consistent model of the multiscale interaction of a tearing mode with drift wave turbulence is presented. A tearing instability in a cylindrical plasma interacting with electrostatic drift waves is considered, for reasons of simplicity. Wave kinetics and adiabatic theory are used to treat the feedback of tearing mode flows on the drift waves via shearing and radial advection. The stresses exerted by the self-consistently evolved drift wave population density on the tearing mode are calculated by mean field methods. The principal effect of the drift waves is to pump the resonant low-m mode via a negative viscosity, consistent with the classical notion of an inverse cascade in quasi-two-dimensional turbulence. This process can occur alone or in synergy with current gradient drive of the low-m mode. Speculations of the relation of this multiscale process to the more general issue of the fate of energy transferred to large scales by an inverse cascade are presented. The existence of nonlinearly driven vortices pinned to low-q surfaces as a class of highly anisotropic dissipative structures which terminate the inverse cascade is proposed. The evolution of a finite size magnetic island is discussed.
α
, γ, and normal, abnormal glow discharge modes in radio-frequency capacitively coupled discharges at atmospheric pressure
Authors: Moon Se Youn , Rhee J. K. , Kim D. B. , Choe W.
Published: March 2006

Discharge modes, α and γ, of a radio-frequency helium capacitively coupled discharge at atmospheric pressure were investigated with the discharge gap distance between electrodes varied from 1 to 5mm. As similarly observed in other experiments, the α and γ mode and the α–γ mode transition were observed with large drops in the voltage (310–179V) and the phase angle between the voltage and current (54°–18°), and a contraction of the plasma volume (8.5–0.17cm3, at 3mm gap distance). The discharge voltage where the α–γ mode transition occurred versus the gap distance showed a similar behavior with the Paschen curve for a gas breakdown. Depending on the gap distance, normal and abnormal glow regimes were observed in the αmode. At 1 and 2mm, the α mode remained in the abnormal glow discharge until the α–γ mode transition occurred as the discharge current increases. At 3mm, however, the α mode was excited as a normal glow discharge with a constant current density (17mA∕cm2) but it became an abnormal glow discharge as the current increased. At 4mm, the α mode was sustained as a normal glow discharge, then the transition to the γ mode occurred. Using a simple resistor-capacitor circuit model and a α sheath breakdown model, the discharge modes and the mode transition properties were studied.
Effect of axial magnetic field variations on asymmetry-induced transport in a non-neutral plasma trap
Authors: Eggleston D. L. , McMurtry K. J. , Kabantsev A. A. , Driscoll C. F.
Published: March 2006

It has been suggested that magnetically trapped particles play a role in the asymmetry-induced radial transport observed in the Occidental non-neutral plasma trap. This magnetic trapping would occur due to a small increase (β≡δB∕B≈0.4%) in magnetic field at the center of our solenoid and would keep low velocity particles confined to the ends of the trap. To test this suggestion, three coils of additional windings have been added to the trap solenoid thus allowing adjustment of the axial field variation δB. The effect of these adjustments on typical radial flux resonances is investigated. Making B as uniform as possible reduces β by a factor of 5.9, but this produces little change in the transport. Varying β over the broader range from −8.5% to 9.5% gives variations of 20%–90% in the magnitude, peak frequency, and width of the flux resonances, but these variations do not match the predictions of a simple model of trapped particle transport based on isotropic particle distributions.
Effect of hydrogen dilution on carrier transport in hydrogenated boron-doped nanocrystalline silicon-silicon carbide alloys
Authors: Myong Seung Yeop , Lim Koeng Su , Konagai Makoto
Published: March 2006

The effect of the hydrogen dilution ratio on characteristics of hydrogenated boron-doped nanocrystalline silicon-silicon carbide alloy (p-nc-Si–SiC:H) films is investigated. Hydrogen coverage near the growing surface causes nanocrystallization by retarding the reactions of the precursors. It was found that p-nc-Si–SiC:H alloys have two different kinds of carrier transport mechanisms: one is the thermally activated hopping conduction between neighboring crystallites near room temperature and the other is the band tail hopping conduction below 150K. However, the film at the onset of the nanocrystalline growth exhibits a different behavior due to a large band tail disorder.
Ponderomotive acceleration of electrons in the interaction of arbitrarily polarized laser pulse with a tenuous plasma
Authors: Sazegari V. , Mirzaie M. , Shokri B.
Published: March 2006

The forward ponderomotive force associated with an intense short laser pulse, propagating in a tenuous plasma, accelerates the electrons to velocities higher than the group velocity of the laser. In this work, a simple general solution for ponderomotive acceleration is presented for arbitrary polarization. The circular polarization is more efficient than linear polarization, since the threshold laser intensity needed for electron acceleration is lower for a circularly polarized laser pulse.
Thermodynamic and electrostatic analysis of threading dislocations in epitaxial ferroelectric films
Authors: Misirlioglu I. B. , Alpay S. P. , Aindow M. , Nagarajan V.
Published: March 2006

The role of threading dislocations on the electrical properties of epitaxial ferroelectric films is analyzed using a thermodynamic formalism and basic electrostatics. The modeling is carried out for a 300nm thick (001) PbZr0.2Ti0.8O3 on (001) SrTiO3 which displays a large population of threading dislocations as determined by transmission electron microscopy. Results show that although the phase transformation characteristics of ferroelectric films containing threading dislocations are altered such that the transformation is “smeared” over a temperature interval due to local strain variations, these defects do not have as profound an effect on the electrical properties as the misfit dislocations.
System size and control parameter effects in reverse perturbation nonequilibrium molecular dynamics
Authors: Mountain Raymond D.
Published: March 2006

The issue of system size effects in the reverse perturbation nonequilibrium molecular dynamics method for determining transport coefficients of fluids is examined for the case of the Lennard-Jones model. It is found that when adequate precautions are observed in obtaining linear temperature or momentum profiles, a 250 atom system is adequate for determining the thermal conductivity and the shear viscosity. Also, a means of determining the uncertainties in the transport coefficients is described. The conclusion is that this method is computationally competitive with other simulation methods for estimating transport coefficients.
Striations in dielectric barrier discharge systems with a hollow anode
Authors: Khudik V. N. , Shvydky A. , Theodosiou C. E.
Published: March 2006

The dynamics of the charging of an elongated hollow anode covered with a dielectric layer by an electron current is studied via three-dimensional particle-in-cell/Monte Carlo kinetic simulations. It is shown that this process is accompanied by the successive formation of striations in the plasma created by the electron impact ionization of the background gas. A number of specially designed numerical experiments are performed to further explore the nature of this phenomenon. An experimental setup where this type of striations should be observed is suggested.
Ultrahigh-speed optical frequency domain imaging and application to laser ablation monitoring
Authors: Oh W. Y. , Yun S. H. , Vakoc B. J. , Tearney G. J. , Bouma B. E.
Published: March 2006

We demonstrate a linear laser resonator incorporating a semiconductor optical amplifier and scanning filter for high repetition rate, broad wavelength, unidirectional scanning. The laser operates at up to 115kHz repetition rates and demonstrates a tuning-speed-independent power of >30mW. We apply this laser to enable ultrahigh-speed optical frequency domain imaging of the dynamics of laser ablation of biological tissue. The imaging system acquires single longitudinal scans (A-lines) in 8.7μs and complete cross-sectional images comprising 575A-lines at a rate of 200 frames per second.
Physical mechanism of current-free double layers
Authors: Chen Francis F.
Published: March 2006

Undriven double layers observed in plasmas expanding along magnetic fields are the result of a sheath instability connected with the Bohm criterion. Diverging magnetic field lines cause the presheath acceleration of ions, causing a potential jump resembling that of a double layer. The process stops when it runs out of energy.