bluuebunny/crossref_metadata_2025 huggingface dataset:
Status report on the development of a tubular electron beam ion source
Authors: Donets E. D. , Donets E. E. , Becker R. , Liljeby L. , Rensfelt K.-G. , Beebe E. N. , Pikin A. I.
Published: May 2004

The theoretical estimations and numerical simulations of tubular electron beams in both beam and reflex mode of source operation as well as the off-axis ion extraction from a tubular electron beam ion source (TEBIS) are presented. Numerical simulations have been done with the use of the IGUN and OPERA-3D codes. Numerical simulations with IGUN code show that the effective electron current can reach more than 100 A with a beam current density of about 300–400 A/cm2 and the electron energy in the region of several KeV with a corresponding increase of the ion output. Off-axis ion extraction from the TEBIS, being the nonaxially symmetric problem, was simulated with OPERA-3D (SCALA) code. The conceptual design and main parameters of new tubular sources which are under consideration at JINR, MSL, and BNL are based on these simulations.
Electromagnetic modeling of the extraction region of the ISIS H− ion source
Authors: Faircloth D. C. , Thomason J. W. G. , Whitehead M. O.
Published: May 2004

The ISIS Penning surface plasma source, which routinely produces 35 mA of H− ions during a 200 μs pulse at 50 Hz for uninterrupted periods of up to 50 days, is regarded as one of the leading operational sources in the world. The ISIS source should provide an excellent starting point for a development program to produce H− ion sources with performances exceeding those achieved today, which will be a key requirement for the next generation of high power proton accelerators. One goal is to produce 60 mA of H− ions from the source without large departures from the optimum conditions for source lifetime or increased emittance. As the ISIS source operates in the space-charge limited mode it is predicted that an increase in extraction potential from 17 to 25 kV should be sufficient to achieve this, and a suitable pulsed power supply for the ion source extraction electrode has been manufactured. An understanding of how extract geometry changes affect beam transport is essential for operation at higher extraction potential. An examination has been undertaken of the electromagnetic fields in the extract electrode region using MAFIA finite element analysis software. The effects of changing the extraction potential, gap, and electrode geometry are described.
Two negative ion groups in volume H− sources
Authors: Ivanov A. A.
Published: May 2004

The two-laser photodetachment technique has been used to measure the dynamics of the recovery of negative ion density in the center of the multicusp H− ion source Camembert III after laser irradiation. Several series of experiments in pure hydrogen and hydrogen–argon mixtures for the pressures ranging from 0.85 to 3 mTorr were performed. The curve of the dynamics of H− recovery serves to determine the temperature of negative ions. The single-temperature fits of the experimental curves were not satisfactory, so several changes were introduced into the process of treatment of the experimental data. As a result two negative ion populations with different temperatures were identified. These populations are formed as a result of the existence of two H− production regions with different plasma potentials. The low temperature population (0.03–0.25 eV) corresponds to the ions formed in the central source region. The higher temperature population corresponds to ions formed near the walls or filaments (driver region). This group is then accelerated by the plasma potential into the central plasma region. Thus the well-known difficulty of too high negative ion temperature values obtained with a single parameter fit is resolved.
High proton ratio plasma production in a small negative ion source
Authors: Morishita T. , Inoue T. , Iga T. , Watanabe K. , Imai T.
Published: May 2004

A proton ratio was measured in the small (1.4 l) arc discharge multicusp source at a pressure of 1.4 Pa. A measured proton ratio in an extracted positive ion beam was 50%. By applying the transverse magnetic field as the magnetic filter in the source, the proton ratio drastically increased to 90% even in such a small source. To clarify the proton production processes, coupled rate equations were numerically solved to estimate particle (H+, H2+, H3+, and H0) densities in the various size of ion source. It has been clarified that a main proton production process is different with the source size. In the large size source, which has better confinement of the source plasma, the ionization of H atom becomes effective to increase the proton yield. In the small ion source, the dissociation of H2+ (H2++e→H++H+e) is the dominant process for the proton production. By adopting the magnetic filter in the small source, H2+ production by primary electron impact is suppressed in the extraction region. Molecular ions are dissociated or neutralized by thermal electrons in the extraction region. The main process of the proton production H2++e→H++H+e has the large cross section with the low temperature electrons, thus the high proton yield beam can be extracted.
REXEBIS operation and developments
Authors: Ames F. , Cederkäll J. , Wenander F. J. C. , Wolf B. H. ,   the REX-ISOLED Collaboration
Published: May 2004

At REX-ISOLDE at CERN a unique combination of a Penning trap and an electron beam ion source for the bunching and charge breeding of radioactive ions prior to their acceleration has been put into operation. The task of REXEBIS is to increase the charge state of injected singly charged radioactive ions to a mass to charge ratio A/q<4.5. This enables an efficient acceleration in the following LINAC. Even without optimizing every part a total efficiency of up to 4% for Na ions including the efficiency of the trap and the accelerator could be achieved and the system has been operated reliable and stable for several weeks of beam time. For the EBIS alone the efficiency for the charge breeding in a single state has been determined to be around 10% for elements between Li and Sm and average ion currents of a few pA.
Development of neutral beam injectors for plasma diagnostic in Budker Institute of Nuclear Physics (invited)
Authors: Davydenko V. I. , Ivanov A. A.
Published: May 2004

A number of hydrogen beam injectors have been developed in Budker Institute of Nuclear Physics, Novosibirsk, for plasma diagnostic in magnetic fusion devices. The developed neutral beams have an energy ranging from 20 to 55 keV, equivalent beam current of 1–4 A, angular beam divergence of ∼10−2 rad, and pulse duration 10−2–10 s. For the beam with a duration of less than 1 s, an arc-discharge plasma box is used in which a low transverse ion temperature plasma is produced by expanding plasma jet. A radio frequency discharge is used for long duration beams. The beams are formed by a four electrode ion optical system. The electrodes are formed as spherical segments in order to provide geometrical focusing of the beam. For better use of the nonuniform plasma emitter, a version of the ion optical system has been developed in which the gaps extend with the radius. This ensures optimal beam formation from an enlarged surface. To provide a beam for active beam emission spectroscopy measurements in large fusion devices, the injector was developed with beam energy up to 55 keV, equivalent beam current (for hydrogen) up to 1.4 A, and pulse duration of up to 10 s. The injector is capable of providing modulated beam with frequency of up to 500 Hz. A distinctive feature of the ion source is that in order to simplify injector design, a thermal inertia-type ion optics system with “thick” electrodes is used.
Experimental comparison between plasma and gas neutralization of high-energy negative ion beams
Authors: Hanada M. , Kashiwagi M. , Inoue T. , Watanabe K. , Imai T.
Published: May 2004

A plasma neutralization efficiency of high-energy negative ion beams was measured in a practical neutralizer with substantial dimensions and compared with a gas neutralization efficiency for fusion application. Hydrogen negative ion beams of 200 keV, 4 mA were neutralized with hydrogen and argon arc plasmas in the plasma neutralizer of 2 m in length and 0.6 m in diameter. To clarify the difference between the plasma and the gas neutralizations, the high-density plasmas were produced at low operating pressure. By means of ∼30 G transverse magnetic fields that were applied locally at openings for beam path, leakage of the primary electrons to the outside of the neutralizer was suppressed sufficiently. The plasma densities were 1011–1012 cm−3 at low operating pressures of 0.002–0.05 Pa for both plasmas while an arc power was ∼40 kW. Neutralization efficiency was increased by using plasmas whose ionization degree was 10%–15%. The maximum neutralization efficiency for hydrogen plasma increased from 55% of the gas neutralization to 65%. The maximum neutralization efficiency for argon plasma increased from 51% of the gas neutralization to 55%. The line densities maximizing the plasma neutralization efficiencies decreased to 65% of those for the gas neutralizations. Neutralization efficiencies in the plasmas and the gases were in good agreement with those calculated from the cross sections. It is concluded that a practical plasma neutralizer with substantial dimensions can increase neutralization efficiency at a low line density as predicted from the numerical analysis based on the cross section data.
Cold-cathode source of ribbon gaseous ion beams
Authors: Emlin D. R. , Gavrilov N. V.
Published: May 2004

A ribbon ion beam source based on a magnetically confined low-pressure glow discharge has been developed. The electrode system of the ion source consists of four series-installed discharge chambers of the inverted magnetron type with a thin-wire anode. Slots are made in walls between the chambers to equalize the linear distribution of the extracted ion current density. A two-electrode multislit ion optical system 44×3 cm in size forms an ion beam having an energy of up to 20 keV. The operation voltage of the glow discharge with a current of up to 1.6 A in a magnetic field of 2–6 mT at a gas pressure (argon) of 0.015–0.03 Pa is 350–650 V. The ion beam current accounts for 8%–14% of the discharge current. The inhomogeneity of the current density distribution along the ribbon beam axis is 10%–20%.
Neutral beam injector for active plasma spectroscopy
Authors: Korepanov S. A. , Abdrashitov G. F. , Beals D. , Davydenko V. I. , Deichuli P. P. , Granetz R. , Ivanov A. A. , Kolmogorov V. V. , Mishagin V. V. , Puiatti M. , Rowan B. , Stupishin N. V. , Shulzhenko G. I. , Valisa M.
Published: May 2004

A diagnostic beam system has been developed for the RFX reversed field pinch, Padova, Italy. Currently the system is loaned to Alcator C-mod, MIT, Boston. The system is primarily used for measurement of the ion temperature by charge-exchange recombination spectroscopy and for magnetic field measurements via motional Stark effect. The system comprises an ion source, beam duct equipped with vacuum pumps and various diagnostics of the beam. The ion source provides 50 keV, 5 A hydrogen beam. Ions are extracted from a plasma created by an arc-discharge source and, after accelerating and focusing, are neutralized in a gas target. A plasma emitter, which is formed by collisionless expansion of a plasma jet on to the grids, has low perpendicular ion temperature. These results are in rather low (0.01 rad) angular divergence of the extracted ion beam. The grids of ion optical system are spherically curved providing geometric focusing of the beam at a distance 4 m. Current density at the focal plane reaches 100 mA/cm2. Arc-discharge plasma box provides highly ionized plasma, so that the extracted beam has about 80% of full energy specie. The injector provides 50 ms duration pulse each 5 min. In order to increase the signal to noise ratio the beam can be modulated with a frequency variable up to 250 Hz.
High current density beamlets from a rf argon source for heavy ion fusion applications
Authors: Kwan J. W. , Grote D. P. , Westenskow G. A.
Published: May 2004

In a new approach to develop high current beams for heavy ion fusion, beam current at about 0.5 ampere per channel can be obtained by merging an array of high current density beamlets of 5 mA each. We have done computer simulations to study the transport of high current density beamlets and the emittance growth due to this merging process. In our radio frequency (rf) multicusp source experiment, we have produced a cluster of 61 beamlets using minimum gas flow. The current density from a 0.25 cm diameter aperture reached 100 mA/cm2. The normalized 4 rms emittance of 0.0186π mm mrad corresponds to an equivalent ion temperature of 2.08 eV. These results showed that the rf argon plasma source is suitable for producing high current density beamlets that can be merged to form a high current high brightness beam for heavy ion fusion application.
Glow-discharge-driven bucket ion source
Authors: Gavrilov N. V. , Kamenetskikh A. S.
Published: May 2004

A two-stage source of broad beams of gaseous ions employing a glow-discharge plasma cathode and an anode chamber with a peripheral multicusp magnetic field has been studied. A grid, whose potential approached the potential of the screen grid of the ion source, separated the cathode and anode stages. The effect of the energy (0–300 eV), the current of injected electrons (0.2–0.8 A), and the gas pressure (argon) on the plasma parameters and the efficiency of ions extraction from the plasma have been analyzed. The current density of the ions extracted from the magnetic-field-free plasma had a nearly homogeneous distribution (∼10%). The beam of 3 keV argon ions was generated using a two-electrode ion optical system with the area of ∼50 cm2. The beam current was 60 mA at the electron current of the plasma cathode equal to 0.2 A.
Transport velocity of direct current laser induced photodetached electrons in a H− ion source
Authors: Takahashi H. , Kasuya T. , Wada M.
Published: May 2004

The transport velocity of a plasma containing photodetached electrons was measured by injecting a semiconductor laser at power density of 8 W/cm2 into the center of the linearly magnetized cylindrical plasma. The magnetized hydrogen plasma produced with a pair of coils and a ring shaped array of discharge filaments contained the H− density at about 3% of the plasma electron density. For a gas pressure of 1 Pa, the transport velocity of the plasma perturbed by the photodetached electrons decreased from 2500 to 400 m/s as the linear magnetic field was increased from 1.5 to 15 mT. The transport velocity became one half of the original value when the gas pressure was increased from 1 to 2 Pa. The observed transport velocity agreed with the predicted value from diffusion of H− ions in background plasma.
Nonlinear distortion of multicomponent heavy ion beam emittance caused by space charge fields
Authors: Kazarinov Nikolay Yu.
Published: May 2004

The beam of Ca48 ions is obtained in an electron cyclotron resonance (ECR)-ion source with helium as plasma supporting gas. The current of helium ions is often greater than the calcium one. The influence of the helium ions self-fields on emittance of calcium beam during the common transportation from the ECR-ion source to analyzing bending magnet is investigated by macroparticles simulation. For a large magnitude of helium space charge, the calcium ions have a holed-beam shape after analyzing magnet and beam emittance strongly increased. The possibilities of elimination of this effect are discussed.
Initial comparative performances of conventional “surface” and “volume” type, all-permanent-magnet, ECR ion sources (abstract)
Authors: Liu Y. , Alton G. D. , Bilheux H. , Cole J. M. , Meyer F. W.
Published: May 2004

An all-permanent-magnet, 6 GHz “volume-type,” flat central-field concept ECR ion source has been constructed and initially evaluated at the Holifield Radioactive Ion Beam Facility, Oak Ridge National Laboratory. The source is designed so that it can be easily converted from a flat-B configuration to the traditional minimum-B configuration and vice versa, so that comparisons can be made of the performances of the source in the “volume” ECR and “surface” ECR modes of operation under the same conditions. Descriptions of the source, the experimental equipment, and the procedures for evaluation are given, and comparisons of the performances of both volume and surface modes of operation are presented with and without gas mixing. The present studies clearly show that the volume ECR configuration is superior to the surface configuration in terms of charge-state distribution and intensity within a particular charge state, under the same operating conditions.
Universal method for effusive-flow characterization target ion source/vapor transport systems for radioactive ion beam generation (abstract)
Authors: Alton G. D. , Bilheux J.-C. , Liu Y. , Cole J. A. , Williams C.
Published: May 2004

Worldwide interest in the use of accelerated radioactive ion beams (RIBs) for exploring reactions important in understanding the structure of the nucleus and nuclear astrophysical phenomena has motivated the construction of facilities dedicated to their production and acceleration. Many facilities utilize the isotope-separator-on-line (ISOL) method in which species of interest are generated within a solid or liquid target matrix. Experimentally useful RIBs are often difficult to generate by this technique because of the times required for diffusion from the interior of the target material, and to effusively transport the species of interest to the ion source following diffusion release in relation to its lifetime. Therefore, these delay times must be minimized. We have developed an experimental method that can be used to determine effusive-flow times of arbitrary geometry target/vapor transport systems. The technique utilizes a fast valve to measure effusive-flow times as short as 0.1 ms for any chemically active or inactive species through any target system, independent of size, geometry and materials of construction. In this report, we provide a theoretical basis for effusive flow through arbitrary geometry vapor transport systems, describe a universal experimental apparatus for measuring effusive-flow times, and provide time spectra for noble gases through prototype RIB target/vapor-transport systems.
Results of upgrade of the diagnostic neutral beam injector for the TCV tokamak
Authors: Shikhovtsev I. V. , Abdrashitov G. F. , Averboukh I. I. , Davydenko V. I. , Dribinsky S. F. , Duval B. , Ivanov A. A. , Karpushov A. N. , Kolmogorov V. V. , Mishagin V. V. , Podyminogin A. A. , Weisen H.
Published: May 2004

A diagnostic neutral beam injector has been developed at BINP for beam emission spectroscopy measurements in TCV tokamak, Lausanne, Switzerland. The beam has been commissioned in 1999. It operates with a beam energy of up to 50 keV, equivalent neutral beam current (for hydrogen) up to 1 A and pulse duration up to 2 s. Plasma in the ion source is produced by inductively coupled 4.6 MHz radio-frequency discharge. Ions are extracted and accelerated by a four-grid ion optical system with 163 circular 4 mm i.d. apertures. The beam is to provide local measurements of plasma ion temperature, velocity, and impurity densities through active charge exchange recombination spectroscopy. The beam parameters of the diagnostic injector enabled to carry out the measurements at plasma density up to 5×1019 m−3. In order to improve signal to noise ratio in the charge exchange recombination spectroscopy (CXRS) measurements and extend the operational density up to 1020 m−3, the diagnostic injector has been upgraded in 2002. As a result, the neutral beam fraction of full energy was increased from 0.5 to 1 equivalent A (eq A). This paper describes the results of the beam parameters measurements after upgrade.
Development of a high-current microwave ion source for proton linac application systems
Authors: Tanaka M. , Hara S. , Hae T. , Iga T. , Saitou K. , Amemiya K. , Hiramoto K. , Kakiuchi S.
Published: May 2004

A microwave hydrogen ion source was developed to improve reliability, and to increase operation time of proton linac application systems. The ion source needs no filament in the discharge chamber, which leads to better reliability and less maintenance time. The developed source produced a maximum hydrogen ion beam current of 70 mA (high current density of 360 mA/cm2, beam energy of 30 keV) with a 5 mm diam extraction aperture and 1.2 kW microwave power. The proton fraction was increased with an increase in rf power and reached around 90% at 1 kW. Measured 90% beam normalized emittance was 0.4 π mm mrad. Rise times of rf power and beam current to 90% of the final values were about 30 and 35 μs, respectively, at a pulse operation mode with 400 μs pulse width and 100 Hz repetition rate. The dynamic range of beam currents was enlarged (3–63 mA) in the pulse mode with a modified rf wave form to assist ignition of microwave discharge. These performance parameters will be desirable for pulse operation accelerator applications like proton therapy systems. A long time operation stability (150 h) was confirmed with a beam current of 51 mA; change in the current was 2%.
Generation of broad ion beams in sources based on Penning system with nonequipotential cathode
Authors: Nikulin S. P. , Chichigin D. F. , Tretnikov P. V.
Published: May 2004

A method of generation of uniform plasma in low-pressure glow discharges with oscillating electrons has been developed. The method is based on the separation of the cathode into several elements, with potentials of the parts being different. Experimental results show that the use of the nonequipotential cathode in the Penning system enables effective control of spatial plasma distribution. This makes it possible to obtain nearly uniform ion emission current distributions and to form broad beams. Two variants of ion sources are under investigation. The first source generates low energy (∼1 keV) ions, which are often used for cleaning of surfaces. A treated target plays a role in one of the cathodes and acceleration of ions is realized directly in the cathode sheath. The required level of ion energy is provided by applying a corresponding voltage between the target and the anode of the system. The second source generates an ion beam with higher (several tens of keV) energy. Accelerating–decelerating ion optics is used in this variant. The efficiency of ion extraction, defined as the ratio of beam and discharge currents, is equal to 30%.
Highly stripped ion sources for MeV ion implantation
Authors: Batalin V. A. , Bugaev A. S. , Gushenets V. I. , Hershcovitch A. , Johnson B. M. , Kolomiets A. A. , Kuibeda R. P. , Kondratiev B. K. , Kulevoy T. V. , Litovko I. V. , Oks E. M. , Pershin V. I. , Poole H. J. , Petrenko S. V. , Seleznev D. N. , Svarovski A. Ya. , Turchin V. I. , Yushkov G. Yu.
Published: May 2004

A joint research and development effort whose ultimate goal is to develop an intense, high charge state, ion source for mega-electron-volt ion implanters has been initiated. Present day high-energy ion implanters utilize low charge state (usually single charge) ion sources in combination with radio frequency (rf) accelerators. Usually, a MeV Linear Accelerator (MV LINAC) is used for acceleration of a few milliamperes. It is desirable to have instead an intense, high charge state ion source on a relatively low energy platform [direct current (dc) acceleration] to generate high-energy ion beams for implantation. This endeavor is a continuation of earlier research, which resulted in generating ions like Pb+7 and Bi+8 and ion currents exceeding 200 mA. The natural next step is to convert and optimize ion charge state enhancement techniques to generate B, P, As, and Sb ions, and adapt them to a dc implanter. A number of schemes are to be pursued simultaneously. The most promising approach is to be developed into a commercial ion source.
A 29.2 GHz electron cyclotron resonance-primary proton source for the relativistic heavy ion collider optically pumped polarized H− ion source
Authors: Zelenski A. , Alessi J. , LoDestro V. , Ritter J. , Klenov V. , Kokhanovski S. , Zubets V.
Published: May 2004

A 29.2 GHz dc electron cyclotron resonance (ECR) source produces a primary proton beam in the relativistic heavy ion collider (RHIC) optically pumped polarized H− ion source. A proton beam of a 50–100 mA is extracted from the ECR plasma at 2.0–3.0 keV energy by a 121-hole, three-grid ion extraction system. Polarized beam injection to RHIC requires only 300–500 μs pulses at 0.2–6 2/3 Hz repetition rate. Pulsed source operation was studied and resulted in a significant current increase at greatly reduced average microwave power and hydrogen gas consumption. A molecular H2+ ion beam component out of the ECR source might cause polarization dilution, when H20 molecular beam is dissociated in the sodium ionizer cell with the production of H− ions (having half the energy of the main component) with lower polarization. Admixture of oxygen gas reduces the H2+ beam component. A reduction to less than 5% was observed also in pulsed ECR operation. As a result of the ECR-source optimization, the RHIC optically pumped polarized H+ ion source intensity was increased up to 0.5–1.0 mA at routine operation (maximum current 1.5 mA). A polarization of 80% was measured in a 200 MeV polarimeter.
Beam emittance measurements of transformer coupled plasma ion source for focused ion beam
Authors: Kim Yoon Jae , Hong I. S. , Kim H. S. , Hwang Y. S.
Published: May 2004

A transformer coupled plasma (TCP) ion source has been tested in order to test its feasibility as a high brightness ion source for focused ion beam. When operating the TCP ion source with filter magnets in front of plasma electrode for a negative ion source, lower emittances are expected. Extracted beam emittances are measured with an Allison-type scanning device for various plasma parameters and extraction conditions. The normalized emittance has been measured to be around 0.2 (π mm mrad) with beam currents of up to 0.55 mA. In particular, noting that multicusp magnets have a role in decreasing the emittance as well as increasing plasma discharge efficiency, transverse magnetic field has been confirmed to be a useful tool for decreasing emittance via electron energy control.
On large streamwise structures in a wall jet flowing over a circular cylinder
Authors: Neuendorf R. , Lourenco L. , Wygnanski I.
Published: May 2004

This paper describes an experimental search for large streamwise vortices in a turbulent wall jet flowing over a convex surface. The existence of these vortices resulting from a centrifugal instability was suspected but never previously observed in this flow. They eluded detection because they meander across the span, as they become larger, with increasing distance from the nozzle. A particle image velocimeter, used in air, enabled the mapping of these vortices establishing their circulation and their evolution in the direction of streaming. Although the longitudinal structures educed do not contribute to mean spanwise distortion of the flow, they are strong enough to augment the Reynolds stresses that increase the rate of spread of the jet and its turbulent intensities. Since the temporal resolution of the instrument is not yet adequate to track the motion of large vortices, the turbulent characteristics surrounding a pair of educed counter-rotating vortices were observed in a frame of reference that is statistically stationary relative to the vortex cores.
Is a plane liquid curtain algebraically absolutely unstable?
Authors: Luchini Paolo
Published: May 2004

The dispersion relation of capillary waves in a plane moving liquid curtain is critically re-analyzed with an eye to its behavior near the origin of wavenumber space and the large-time asymptotics of the corresponding Green’s function. Evidence is found that recent and less recent theories supporting the existence of a zero-wavenumber algebraic absolute instability contain serious inconsistencies.
Switching of nonneutral plasma diodes. II. Numerical results
Authors: Kuznetsov V. I. , Ender A. Ya. , Schamel H. , Akimov P. V.
Published: May 2004

The switching of a pure electron diode between two equilibria of different current status is numerically investigated by means of an updated Vlasov code. The emphasis is on finite jumps of the applied voltage as well as on jumps in the vicinity of a critical point, namely, the space-charge-limited (SCL) point, which marks the transition between a high current normal C branch—a state without electron reflection—and a low current stable B branch—a state where electrons are partially reflected. The main result obtained is a strong delay of the transition time in case of a switching close to an SCL point. In case of a switching to an unstable part of the B branch, large amplitude coherent oscillations arise corresponding to limit cycles in the language of nonlinear dynamics.
Canonical decompositions of n-qubit quantum computations and concurrence
Authors: Bullock Stephen S. , Brennen Gavin K.
Published: May 2004

The two-qubit canonical decomposition SU(4)=[SU(2)⊗SU(2)]Δ[SU(2)⊗SU(2)] writes any two-qubit unitary operator as a composition of a local unitary, a relative phasing of Bell states, and a second local unitary. Using Lie theory, we generalize this to an n-qubit decomposition, the concurrence canonical decomposition (CCD) SU(2n)=KAK. The group K fixes a bilinear form related to the concurrence, and in particular any unitary in K preserves the tangle |〈φ|¯(−iσ1y)⋯(−iσny)|φ〉|2 for n even. Thus, the CCD shows that any n-qubit unitary is a composition of a unitary operator preserving this n-tangle, a unitary operator in A which applies relative phases to a set of GHZ states, and a second unitary operator which preserves the tangle. As an application, we study the extent to which a large, random unitary may change concurrence. The result states that for a randomly chosen a∈A⊂SU(22p), the probability that a carries a state of tangle 0 to a state of maximum tangle approaches 1 as the even number of qubits approaches infinity. Any v=k1ak2 for such an a∈A has the same property. Finally, although |〈φ|¯(−iσ1y)⋯(−iσny)|φ〉|2 vanishes identically when the number of qubits is odd, we show that a more complicated CCD still exists in which K is a symplectic group.
Nanoparticle transport and deposition in bifurcating tubes with different inlet conditions
Authors: Shi H. , Kleinstreuer C. , Zhang Z. , Kim C. S.
Published: May 2004

Transport and deposition of ultrafine particles in straight, bent and bifurcating tubes are considered for different inlet Reynolds numbers, velocity profiles, and particle sizes, i.e., 1 nm⩽dp⩽150 nm. A commercial finite-volume code with user-supplied programs was validated with analytical correlations and experimental data sets for nanoparticle depositions, considering a straight tube, a tubular 90° bend, and a G3-G5 double bifurcation with both planar and nonplanar configurations. The focus is on the airflow structures as well as nanoparticle deposition patterns and deposition efficiencies, which were analyzed for planar and nonplanar bifurcating lung airway models representing part of the upper bronchial tree. Deposition takes place primarily by Brownian diffusion, and thus deposition efficiencies increase with decreasing nanoparticle size and lower inlet Reynolds numbers. Deposition in the nonplanar configuration differs only slightly from that in the planar configuration. When compared with axisymmetric inlet conditions, the more realistic, skewed inlet velocity and particle profiles generate nearly axisymmetric deposition patterns as well. This work may elucidate basic physical insight of ultrafine particle transport and deposition relevant to environmental, industrial and biomedical studies.
Potential structure of a plasma in an internal conductor device under the influence of a biased electrode
Authors: Saitoh H. , Yoshida Z. , Himura H. , Morikawa J. , Fukao M.
Published: May 2004

The present study examined the electric field structure in a magnetized plasma in a prototype ring trap (Proto-RT) device with an internal ring electrode. A radial electric field of up to 3 kV m−1 was produced in the broad region between the electrode and vessel wall when the ring electrode was negatively biased. The resultant E×B toroidal rotational speed is comparable to the ion sound speed. Positive biasing, however, created a gap between the plasma and the electrode, failing to produce an internal electric field.
Plasma wave and second-harmonic generation of intense laser beams due to relativistic effects
Authors: Salih Hyder A. , Sharma R. P. , Rafat M.
Published: May 2004

This article studies the relativistic self-focusing of an intense laser beam in underdense plasma. Due to relativistic self-focusing of the laser beam, a transverse intensity gradient is created, and this can generate a plasma wave at the pump wave frequency. The mechanism of the plasma wave, second-harmonic generation, and the parameters which govern the second-harmonic yield, have been studied in detail. For a typical laser with wavelength (λ=1.053 μm), intensity (1018 W cm−2) and a plasma having density (ωp/ω0=0.25), the second-harmonic intensity was found to be around (1014 W cm−2).
Thermomagnetic convection in a square enclosure using a line dipole
Authors: Ganguly Ranjan , Sen Swarnendu , Puri Ishwar K.
Published: May 2004

We have simulated thermomagnetic convection in a differentially heated square cavity with an infinitely long third dimension. The cavity is under the influence of an imposed two-dimensional magnetic field that conforms to the Maxwell’s equations. Our objective is to characterize the thermomagnetic convection in terms of the geometric length scales, magnetic fluid properties, temperature differences, and strengths of the imposed magnetic fields. Fluid motion occurs due to both the gradients of the magnetic field and the temperature. Colder fluid that has a larger magnetic susceptibility is attracted toward regions with larger field strength during thermomagnetic convection, which displaces warmer fluid of lower susceptibility. The height-averaged Nusselt number Nuav increases with increasing magnetic dipole strength and temperature but decreases with increasing fluid viscosity. Thermomagnetic heat transfer increases when the length scale decreases if the dipole strength of the source magnet is constant. This makes thermomagnetic convection a potentially viable option for microscale heat transfer applications. Thermomagnetic convection can be correlated with a dimensionless magnetic Rayleigh number Ram=(μ0ρ0βρχm,0m2 ΔT Pr/η2h2) and heat transfer due to this form of convection in the range Ram=2×104–2×107 is as effective as buoyancy-induced convection in the range Ra=1000–106.
Linear stability analysis for a rotating cylinder with a rotating magnetic field
Authors: Walker J. S. , Martin Witkowski L.
Published: May 2004

This paper treats the first hydrodynamic instability for a uniform-density, electrically conducting liquid in a finite-length cylinder which is rotating about its centerline. There is a uniform, transverse magnetic field which rotates about the cylinder’s centerline and which produces a steady, axisymmetric, azimuthal body force on the liquid. For the initial transition from a steady, axisymmetric flow to a periodic, nonaxisymmetric flow, results for the critical value of the magnetic Taylor number and for the frequency of the critical disturbance are presented as functions of the Reynolds number for the cylinder rotation. Rotations of the cylinder and of the magnetic field in the same azimuthal direction and in opposite directions are considered.
Properties of continuous Fourier extension of the discrete cosine transform and its multidimensional generalization
Authors: Atoyan A. , Patera J.
Published: May 2004

A versatile method is described for the practical computation of the exact discrete Fourier transforms (DFT), both the direct and the inverse ones, of a continuous function g given by its values gj at the points of a uniform grid FN generated by conjugacy classes of elements of finite adjoint order N in the fundamental region F of compact semisimple Lie groups. The present implementation of the method is for the groups SU(2), when F is reduced to a one-dimensional segment, and for SU(2)×SU(2)×⋯×SU(2) in multidimensional cases. This simplest case turns out to be a version of the discrete cosine transform (DCT). Implementations, abbreviated as DGT for Discrete Group Transform, based on simple Lie groups of higher ranks, are to be considered separately. DCT is often taken to be simply a specific type of the standard DFT. Here we show that the DCT is very different from the standard DFT when the properties of the continuous extensions of the two inverse discrete transforms are studied. The following properties of the continuous extension of DCT (called CEDCT) from the discrete tj∈FN to all t∈F are proven and exemplified. Like the standard DFT, the DCT also returns the exact values of {gj} on the N+1 points of the grid. However, unlike the continuous extension of the standard DFT: (a) The CEDCT function fN(t) closely approximates g(t) between the points of the grid as well; (b) for increasing N, the derivative of fN(t) converges to the derivative of g(t); (c) for CEDCT the principle of locality is valid. In this article we also use the continuous extension of the two-dimensional (2D) DCT, SU(2)×SU(2), to illustrate its potential for interpolation as well as for the data compression of 2D images.
Two-dimensional numerical investigations of small-amplitude disturbances in a boundary layer at Ma=4.8: Compression corner versus impinging shock wave
Authors: Pagella Alessandro , Babucke Andreas , Rist Ulrich
Published: May 2004

Two-dimensional direct numerical simulations and linear stability theory investigations have been carried out for a compression ramp at Ma=4.8 and compared to earlier results of a laminar boundary layer with impinging shock wave. The inflow parameters in both flows were identical; the ramp angle of the compression corner was chosen to cause a separation bubble, which has exactly the same length compared to the case with impinging shock. It turned out, that the two cases are almost identical for the base flow properties. This is in accordance with similarity assumptions, e.g., free interaction theory, which for smaller Reynolds numbers states, that the boundary layer should be independent of the sort of shock-boundary layer interaction. However, linear stability theory results differ near the corner and the impinging shock, respectively. Direct numerical simulations of small-amplitude disturbances, which were introduced into the laminar boundary layer, also behave in a very similar way. Amplitude distributions exhibit the same characteristics. The according distributions of the ramp flow have slightly larger amplitudes than the case with impinging shock.
Integrated optical devices design by genetic algorithm
Authors: Sanchis L. , Håkansson A. , López-Zanón D. , Bravo-Abad J. , Sánchez-Dehesa José
Published: May 2004

In this work, we use multiple scattering in conjunction with a genetic algorithm to reliably determine the optimized photonic-crystal-based structure able to perform a specific optical task. The genetic algorithm operates on a population of candidate structures to produce new candidates with better performance in an iterative process. The potential of this approach is illustrated by designing a spot size converter that has a very low F number (F=0.47) and a conversion ratio of 11:1. Also, we have designed a coupler device that introduces the light from the optical fiber into a photonic-crystal-based waveguide with a coupling efficiency over 87% for a wavelength that can be tuned to 1.5 μm.
Three-dimensional dynamics of relativistic flows in pair plasmas with force-free magnetic configuration
Authors: Sakai Jun-Ichi , Matsuo Akira
Published: May 2004

Dynamics of the relativistic flow in pair plasmas with force-free magnetic configuration is investigated by using a three-dimensional fully relativistic electromagnetic particle-in-cell code. This study is an extension of the work by Haruki and Sakai [Phys. Plasmas 8, 1538 (2001)] that was done in a two-dimensional force-free magnetic configuration. They found that during the early stage of the interaction there occurs the streaming instability, which induces the electromagnetic perturbations associated with generation of quasi-static magnetic field. In the nonlinear stage the force-free magnetic field becomes unstable against the firehose instability and then magnetic islands are formed through magnetic reconnection. The dissipated magnetic field energy is converted to the plasma heating as well as the high-energy particle production. It is found that the three-dimensional configuration could result in completely different dynamics, except for the initial phase where the streaming instability develops. It is also found that the dynamical interaction between the force-free magnetic configuration and the relativistic plasma flows develops sequentially through four different physical processes: (I) The phase of streaming instability, (II) the phase of magnetic reconnection triggered by the first streaming instability, (III) the phase of Alfvén wave excitation through the magnetic reconnection process, and (IV) the phase of dissipation of the Alfvén waves through the magnetic reconnection. It is shown that three-dimensional Alfvén waves with helical magnetic structures can be excited through complicated three-dimensional tearing instability triggered from the streaming instability. During these dynamical processes the pair plasma can be heated through the magnetic reconnection and also the high-energy particles are generated. The interaction process between the force-free collisionless plasmas and the relativistic plasma flows may play an important role for the effective magnetic field energy dissipation, formation of filament structures, and high-energy particle production in astrophysical plasmas.
Neurons culturing and biophotonic sensing using porous silicon
Authors: Ben-Tabou de Leon S. , Sa’ar A. , Oren R. , Spira M. E. , Yitzchaik S.
Published: May 2004

We report on culturing of Aplysia neurons on porous silicon substrates. Good adhesion of the neurons to the porous silicon substrate and a formation of neuron-semiconductor contact have been accomplished. Cultured neurons survived for at least one week on porous silicon showing normal passive membrane properties and generation of action potentials. We have investigated the possibility of using the photoluminescence from porous silicon for transducing neuronal activity into photonic signals. We found that photoluminescence quenching occurs for cathodic current polarization using aqueous salt-based liquid solution contact. The quenching process is due to diffusion of electrons into the porous silicon, giving rise to Auger nonradiative recombination in the silicon nanocrystallites. The decay time of the photoluminescence was found to be relatively slow due to diffusive nature of the process.
Approximate analytical solutions for the space-charge-limited current in one-dimensional and two-dimensional cylindrical diodes
Authors: Chen Xupeng , Dickens James , Hatfield L. L. , Choi Eun-Ho , Kristiansen M.
Published: May 2004

In high-power microwave diode design, the space-charge-limited current is important because of its relation to the diode impedance, and the formation of the virtual cathode. Although the Langmuir–Blodgett law, as a numerical solution, is helpful, a simple functional expression would be more convenient for practical research. In this paper, a physical approximation has been introduced to analyze the nonlinear Poisson’s equation in a one-dimensional (1-D) cylindrical vacuum diode. With the help of this physical approximation, a solution for the space-charge-limited current for 1-D cylindrical diodes has been investigated and developed. In addition, a comparison between our approximate result and the Langmuir–Blodgett numerical solution shows that the physical approximation method is valid in nonlinear differential equation analyses. This physical approximation can be used to analyze similar nonlinear differential equations. Also, a correction for the space-charge-limited current in a two-dimensional cylindrical diode is obtained within a limitation.
Slater sum for the one-dimensional sech2 potential in relation to the kinetic energy density
Authors: Howard I. A. , Minguzzi A. , March N. H. , Tosi M. P.
Published: May 2004

In earlier work on the one-dimensional sech2 potential energy [I. A. Howard and N.H. March, Int. J. Quantum Chem. 91, 119 (2003)] it has been shown that both electron density ρ(x) and kinetic energy t(x) are low-order polynomials in the potential V(x), for a small number of bound states. Here all attention is focused on the continuum states for the sech2 potential with a single bound state. The tool employed is the Slater sum, which satisfies a partial differential equation. This is first solved explicitly for the bound state, and then the solution is generalized to apply to the continuum. Again, considerable simplification is exhibited for this specific choice of potential. A brief discussion is included of a central sech2(r) potential.
Classification of the pseudosymmetric space–times
Authors: Haesen Stefan , Verstraelen Leopold
Published: May 2004

The pseudosymmetry condition on a manifold is a generalization of the notion of spaces of constant curvature. A complete algebraic classification of the pseudosymmetric space–times based on the Petrov type of the Weyl tensor and the Segré type of the Ricci tensor is presented.
Head-on injection of a high quality electron beam by the interaction of two laser pulses
Authors: Kotaki H. , Masuda S. , Kando M. , Koga J. K. , Nakajima K.
Published: May 2004

High quality intense relativistic electron beams are generated by the interaction of two colliding laser pulses to inject plasma electrons into a wakefield excited by one of the laser pulses. The mechanism of the injection is analyzed theoretically and the generation of a high quality electron beam is verified by the numerical simulation. An electron beam has a small energy spread of 1%, ultrashort pulse duration less than 10 fs and normalized transverse emittance less than 1 π mm mrad.
Room-temperature ferromagnetism in ion-implanted Co-doped TiO2(110) rutile
Authors: Shutthanandan V. , Thevuthasan S. , Heald S. M. , Droubay T. , Engelhard M. H. , Kaspar T. C. , McCready D. E. , Saraf L. , Chambers S. A. , Mun B. S. , Hamdan N. , Nachimuthu P. , Taylor B. , Sears R. P. , Sinkovic B.
Published: May 2004

Ferromagnetic Co-doped rutile TiO2 single crystals were synthesized by high-temperature ion implantation and characterized by a variety of techniques. Co is uniformly distributed to a depth of ∼300 nm with an average concentration of ∼2 at. %, except in the near-surface region, where the concentration is ∼3 at. %. Ferromagnetic behavior is exhibited at room temperature with an effective saturation magnetization of ∼0.6 μB/Co atom. The Co is in a formal oxidation state of +2 throughout the implanted region, and no Co(O) is detected.
Three-photon excited band edge and trap emission of CdS semiconductor nanocrystals
Authors: Chon James W. M. , Gu Min , Bullen Craig , Mulvaney Paul
Published: May 2004

We report on three-photon excited band edge and trap emission of CdS semiconductor nanocrystals. While the band edge emission intensity clearly shows a cubic dependence on excitation intensity, demonstrating three-photon absorption process, the trap emission does not exhibit such a cubic dependence. A simple theoretical model based on the assumption that there exist a limited number of trap states in nanocrystals shows good agreement with the experiment, suggesting that the number of trap states play an important role in their emission intensity dependence of multiphoton excitation. The three-photon absorption cross section of CdS nanocrystals is measured to be ∼10−79 cm6 s2 photon−2, which is three to four orders of magnitude higher than those of the previously reported common UV fluorescent dyes.