bluuebunny/crossref_metadata_2025 huggingface dataset:
The dielectric self-consistent field method. II. Application to the study of finite range effects
Authors: Boresch Stefan , Steinhauser Othmar
Published: July 2002

The dielectric self-consistent field (DSCF) method is used to study finite range corrections for the electrostatic contribution to solvation free energies. Detailed results obtained from calculations using Ewald summation (EW) and a generalized reaction field (GRF) technique are reported for the solvation of a spherical ion, glycine and an alanine octapeptide in an ideal α-helical conformation. For the peptide EW calculations are carried out with both conducting (“tinfoil”) dielectric boundary conditions and adjusted dielectric boundary conditions. The emphasis of this work is on solutes without net charge, but with a large dipole moment. It is shown that in this case—similarly to ionic solvation—the self-energy correction needs to be modified by a thermodynamic correction that accounts for the dielectric constant of the solvent. An analytical expression for this term is worked out. The results obtained for glycine and the alanine octapeptide demonstrate that its use improves the system-size independence of solvation free energies calculated with EW compared with just the self energy correction; the GRF results are less satisfactory. We further show the connection between finite range corrections and artifacts in the total electrostatic energy of a system resulting from the use of modified electrostatic interactions. The direct comparison of EW with GRF shows that at present EW is the best method to use in simulations with explicit solvent and periodic boundary conditions.
Enhancement of mode-converted electron Bernstein wave emission during National Spherical Torus Experiment H-mode plasmas
Authors: Taylor G. , Efthimion P. C. , Jones B. , LeBlanc B. P. , Maingi R.
Published: July 2002

A sudden, threefold increase in emission from fundamental electrostatic electron Bernstein waves (EBW) which mode convert and tunnel to the electromagnetic X-mode has been observed during high energy and particle confinement (H-mode) transitions in the National Spherical Torus Experiment (NSTX) plasma [M. Ono, S. Kaye, M. Peng et al., in Proceedings of the 17th IAEA Fusion Energy Conference (IAEA, Vienna, Austria, 1999), Vol. 3, p. 1135]. The mode-converted EBW emission viewed normal to the magnetic field on the plasma midplane increases when the density profile steepens in the vicinity of the mode conversion layer, which is located in the plasma scrape off. The measured conversion efficiency during the H-mode is consistent with the calculated EBW to X-mode conversion efficiency derived using edge density data. Calculations indicate that there may also be a small residual contribution to the measured X-mode electromagnetic radiation from polarization-scrambled, O-mode emission, converted from EBWs.
Capillary effects at newly formed liquid–liquid contacts
Authors: Rein Martin
Published: July 2002

Capillary processes occurring right after the instant of contact between two liquids are studied. The geometry considered is that of a drop touching the plane free surface of a pool. Based on energy arguments we first show that right after the instant of contact pool liquid can spread up the surface of the drop. The dynamics of the fluid motion caused by capillarity are then described by a Lagrangian equation of motion and compared to experimental data of the literature.
Laboratory and numerical investigations on Bénard–Marangoni convection in circular vessels
Authors: Pasquetti R. , Cerisier P. , Le Niliot C.
Published: July 2002

This study is concerned with supercritical Bénard–Marangoni flows of a high Prandtl number (Pr≈4000) fluid in cylinders of small to medium aspect ratio, 5⩽A⩽10. Laboratory experiments and numerical simulations, handled with an accurate spectral solver of the unsteady three-dimensional Boussinesq equations, are used to get a good understanding of the flow behavior. Experimental and numerical results are successively presented and then discussed. The confinement effects are especially pointed out and carefully analyzed.
Long mean-free path collisional stability of electromagnetic modes in axisymmetric closed magnetic field configurations
Authors: Simakov Andrei N. , Hastie R. J. , Catto Peter J.
Published: July 2002

An axially symmetric plasma confined by a poloidal magnetic field with closed field lines is considered. A kinetic analysis of electromagnetic modes is performed for an “intermediate collisionality” ordering in which the particle collision frequency is much smaller than the transit or bounce frequency, but much larger than the mode, magnetic drift, and diamagnetic drift frequencies. A second order integrodifferential ballooning equation for electromagnetic modes is derived, which describes “high-frequency” ideal magnetohydrodynamic (MHD) and “low-frequency” entropy modes. The equation recovers the corresponding ideal MHD ballooning equation for the mode frequency greater than the magnetic drift and diamagnetic drift frequencies, and generalizes the results of an earlier electrostatic treatment of the entropy mode to arbitrary plasma beta. Ion gyrorelaxation collisional modifications to the entropy mode are also evaluated for arbitrary plasma beta and specific results are presented for both a point dipole and Z pinch.
Radiation hard diamond laser beam profiler with subnanosecond temporal resolution
Authors: Schein J. , Campbell K. M. , Prasad R. R. , Binder R. , Krishnan M.
Published: July 2002

A two-dimensional detector array has been fabricated from a single 10-mm-diam by 100-μm-thick chemical vapor deposition diamond disk by applying a 1×1 mm2 metallization grid of 4×4 pixels with centered bias connections. This diamond has been exposed to high power pulsed laser radiation. It has been shown that this kind of diamond array operates as a radiation hard, ultrafast laser beam profiler and can obtain spatial profiles with 500 ps temporal resolution. Ten spatial profiles were obtained within a single 5 ns duration laser pulse, revealing in detail the temporal and spatial development of the laser beam intensity. No attenuation is necessary for this profiler when making single-shot measurements at intensities up to ∼100 MW/cm2.
An experimental method to investigate the structure and kinetics of patterned surfaces using laser light diffraction
Authors: Klemradt Uwe , Aspelmeyer Markus , Wood Lowell T. , Moss Simon C.
Published: July 2002

We describe a novel experimental method using the diffraction of a He–Ne laser beam to study surfaces patterned with structures on mesoscopic to macroscopic length scales. The technique provides high spatial and temporal resolution; it is not limited to periodic, artificial structures, but is also well suited to study the development of self-organized surface relief. Measurements can be performed under in situ conditions in a diffraction mode or an imaging mode, providing (1) qualitative and quantitative information on the surface structures, (2) information on time-dependent surface changes with a resolution of 10 μs or better, (3) observation of incubation processes (including determination of incubation time) in first-order, displacive phase transformations, and (4) observation of the surface in real space, in particular, the pattern evolution as a function of temperature or other parameters. As an example we show results of the application of our method to a Ni0.63Al0.37 single crystal undergoing a martensitic transformation.
High pressure hydrogen loading cell for photoconductivity measurements down to the milliKelvin regime
Authors: Th. Hoekstra A. F. , Rosenbaum T. F. , Roy A. S.
Published: July 2002

A gas loading cell has been developed to load rare earth thin film samples with hydrogen at pressures up to 200 bars at room temperature. A miniature valve closes the gas inlet, after which the cell is suspended from the cold tail of a He3 flow cryostat into the bore of a 16 T superconducting magnet. An ultraviolet stroboscope outside the cryostat illuminates the sample by way of an optical fiber to a window in the cell. Electrical feedthroughs permit photoconductivity and magnetotransport measurements over three decades in temperature. Extension to other materials, different gas atmospheres, and helium dilution refrigerator temperatures is straightforward.
Imprint reduction using an intensity spike in OMEGA cryogenic targets
Authors: Collins T. J. B. , Skupsky S.
Published: July 2002

A novel technique for reducing laser imprint in OMEGA [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)] cryogenic targets has been developed. A typical direct-drive inertial confinement fusion target consists of a shell of deuterium–tritium ice with a thin outer layer of polystyrene (CH). The presence of the CH layer gives rise to a brief period of early-time Rayleigh–Taylor instability. This effectively increases the amount of laser imprint by about a factor of 2 for typical target configurations, and especially for the nonuniformity modes considered most dangerous for target performance. Two-dimensional hydrodynamic simulations show that by introducing a short, high-intensity spike at the start of the implosion, this early-time growth can be significantly reduced with only a modest decrease in the calculated one-dimensional neutron yield.
Resistive wall instabilities and tearing mode dynamics in the EXTRAP T2R thin shell reversed-field pinch
Authors: Malmberg J.-A. , Brunsell P. R.
Published: July 2002

Observations of resistive wall instabilities and tearing mode dynamics in the EXTRAP T2R thin shell (τw=6 ms) reversed field pinch are described. A nonresonant mode (m=1,n=−10) with the same handedness as the internal field grows nearly exponentially with an average growth time of about 2.6 ms (less than 1/2 of the shell time) consistent with linear stability theory. The externally nonresonant unstable modes (m=1,n>0), predicted by linear stability theory, are observed to have only low amplitudes (in the normal low-Θ operation mode of the device). The radial field of the dominant internally resonant tearing modes (m=1,n=−15 to n=−12) remain low due to spontaneous fast mode rotation, corresponding to angular phase velocities up to 280 krad/s. Phase aligned mode structures are observed to rotate toroidally with an average angular velocity of 40 krad/s, in the opposite direction of the plasma current. Toward the end of the discharge, the radial field of the internally resonant modes grows as the modes slow down and become wall-locked, in agreement with nonlinear computations. Fast rotation of the internally resonant modes has been observed only recently and is attributed to a change of the front-end system (vacuum vessel, shell, and TF coil) of the device.
A position-sensitive particle detector for Coulomb excitation experiment
Authors: Toh Y. , Oshima M. , Hayakawa T. , Hatsukawa Y. , Katakura J. , Matsuda M. , Iimura H. , Kusakari H. , Nishimiya D. , Sugawara M. , Zhang Y. H.
Published: July 2002

For Coulomb excitation experiments using a γ-ray detector array, a position-sensitive particle detector system that has a good angular resolution, capability of managing a high-counting rate, robustness for a radiation damage, compactness (under 110 mm φ) and easiness of handling is necessary. For this purpose we developed a new device utilizing plastic and yttrium aluminum perovskite activated by cerium (formula YAlO3:Ce abbreviated YAP Ce) scintillators and a position-sensitive photomultiplier tube. The detector system could operate at a high-counting rate (about 105), and with a good position resolution of 0.5–1.2 mm, which was enough for Doppler correction of the γ rays. It could sustain the radiation damage caused by Coulomb excitation experiments with heavy ions for more than 50 days. The detector chamber was well fitted in the 110 mm φ diameter of the internal space of a compact γ-ray detector array, GEMINI. This was much easier to handle than the position-sensitive gas counter. In Coulomb excitation experiment utilizing this device, the nucleus Ge74 has been Coulomb excited using a Pb target. The transitional E2 matrix elements have been determined and the device has turned out to be useful in Coulomb excitation experiments with heavy-ion beams.
High sensitivity Faraday rotation technique for measurements of magnetic fields with immunity to x-ray effects
Authors: Intrator T. , Marshall B. , Clark D. , McCuistan T. , Anderson B. , Broste B. , Forman K. , Taccetti M.
Published: July 2002

A novel high sensitivity diagnostic for magnetic fields using a high Verdet constant ZnSe crystal is demonstrated. It was thought that x-ray effects might render this particular diagnostic realization suspect for fast rise time magnetic fields. Tests with x-ray fluxes up to 180 millirad at photon-energies up to 200 keV indicate immunity from these effects.
Lock-in imaging of multicycle integration focal plane array
Authors: Chin Ken K. , Ou Haijiang
Published: July 2002

Lock-in imaging using multicycle integration focal plane array (MIFPA) is demonstrated to detect extremely weak image and/or spectroscopic signals. Each pixel of the MIFPA has a correlated multicycle integrator to play the roles of lock-in’s phase-sensitive detector and low-pass filter. In lock-in imaging, the signal current is accumulated while the dark or background current is canceled. As a result, the total integration time is increased by several orders, which is equivalent to the reduction of bandwidth by several orders. All advantages associated with the lock-in amplifier are achieved by imaging with MIFPA. Key issues of the MIFPA technology, including the design and performance of the correlated multicycle integrator, are discussed.
Argon ionization cross sections for charge state distribution modeling in electron cyclotron resonance ion source
Authors: Bogatu I. N. , Edgell D. H. , Kim J. S. , Pardo R. C. , Vondrasek R.
Published: July 2002

An updated and more accurate database for single- and double-ionization cross sections for almost all argon ions has been developed for the modeling of the charge state distribution (CSD) within an electron cyclotron resonance ion source. When the highly non-Maxwellian anisotropic electron-distribution function, is modeled by a Fokker–Planck code, one has to use the ionization cross sections instead of the Maxwellian rate coefficients. Most of the fitting coefficients used within the well-established semi-empirical formulas for direct ionization and double ionization have been recalculated using more accurate crossed-beam experimental data available. The shift of the CSD to higher-charge states due to the contribution of excitation autoionization and double ionization is presented by comparing the GEM code modeling using the Lotz formula and the cross sections with updated fitting coefficients.
An apparatus for the measurement of the gas permeability of foam films
Authors: Krustev R. , Müller H. J.
Published: July 2002

A device is described which allows the measurement of the gas permeability of a single foam film upon variation of its thickness and specific interaction film free energy. A variable external pressure is applied on the film, which results in corresponding variations of the film thickness and the specific interaction film free energy. The apparatus allows the gas permeability of foam films to be investigated at different desired values of these quantities. The method can be used to gain information about the structure of the foam film. Small changes in the adsorption density in the stabilizing surfactant monolayers of the film result in dramatic changes of the permeability. Therefore measurements of the permeability coefficient may be used as a tool to detect variations in composition and structure of the film monolayers. This apparatus will also be extremely useful for the study of the permeation of pure gases and vapors and of gas separation by foam films for purposes of chemical technology or medicine.
Production of various species of focused ion beam
Authors: Ji Q. , King T.-J. , Leung K.-N. , Wilde S. B.
Published: July 2002

The ability to generate various ion species makes the multicusp plasma ion source an excellent candidate for maskless resistless lithography application. In this article, the mass spectra of both positive and negative ions for phosphorus, BF3, and oxygen multicusp plasmas are presented. It is shown that over 90% P+ ions are produced. The production of BF2+ and O2+ increases with increasing gas pressure, and decreases with increasing source power. With optimization of source operating parameters, approximately 85% BF2+ and over 90% O2+ have been achieved.
Model-based predictors for improved automated beam generation and tuning of high current ion implanters
Authors: Graf M. A. , Tieger D. R. , Hsieh T. J. , Rutishauser H. , Ring P.
Published: July 2002

Reliable and efficient beam generation and setup can provide significant cost-of-ownership advantages for modern high current ion implantation in the semiconductor industry. Automated tuning algorithms which make use of fundamental models to aid the decision-making process can be more effective at producing robust tuning solutions over the wide range of operating parameters typically called for in this industry. The ability to predict ion source, extraction, and beamline behavior over a range of energies from 0.2 to 160 keV, beam currents from 0.01 to 25 mA, using six or more ion species, over the full lifetime of the ion source, allows the full flexibility of the implant tool to be realized. Empirical and fundamental models which describe this behavior on a variety of Axcelis high current ion implant platforms are presented, and the ways in which these models may be used to improve overall implanter performance are demonstrated.
Experimental characterization of a thermionic-arc discharge ionization device for flowing gases
Authors: Deaconu Stelu , Coleman Hugh W. , Wu S. T.
Published: July 2002

The working characteristic of a new hollow cathode, thermionic-arc dc discharge ionization device was investigated experimentally. Under typical operating conditions the device produces a steady, field-free plasma plume by ionizing a flowing gas column. Experiments were performed with argon, nitrogen, and helium, the typical discharge pressures being 0.2–0.6 Torr. The discharge exploits the inherent stability of the point to plane geometry and the ionization efficiency of the hollow cathode. Electrically, the discharge is fed from a constant–voltage power supply and maintained below the interelectrode gap breakdown threshold. Thus the discharge current is given by Ohm’s law and is a function of the applied field and local plasma parameters. This modus operandi increases the ionization efficiency by maintaining a local thermal nonequilibrium in the discharge. The degree of nonequilibrium maintained in the plume downstream the cathode was higher in nitrogen (Te/Tgas≅8–10) than in argon (Te/Tgas≅3–4), and is attributed to a lower collision frequency in the nitrogen plume. At an input power level of 0.9 kW plasmas with electron densities of 1017 part/m3 in nitrogen and 1018 part/m3 in argon were recorded in the plume outside the high-field cathode region. Helium discharge displayed the highest nonequilibrium level (Te/Tgas≅100) but at the same time showed the largest degree of instability and the lowest electron density levels 1015 part/m3. The experiments indicate that the stability and the ionization efficiency of the discharge are enhanced by a supersonic flow field. Flow surveys have shown that the more stable argon and nitrogen plumes were slightly supersonic in the range of pressure investigated while helium flow remained subsonic throughout. The important consequence to the supersonic flow is the development of a normal shock in front of the cathode filament. Analysis of the data indicates that the normal shock is an effective stabilizing boundary.
A comparison of peak frequency-time plots produced with Hilbert and wavelet transforms
Authors: Guillaume D. W.
Published: July 2002

Practical techniques for producing both Hilbert and wavelet transform representations of peak frequency are given. Peak frequency-time plots of simple model signals are produced using both transforms and are presented and compared. This study shows that the peak frequency-time plots produced using the wavelet transform are superior to those produced using the Hilbert transform since the wavelet representation does not show large false frequency indications when the model time series undergoes a large abrupt frequency change. Further, when multiple dominant frequencies are present in the model time series, the wavelet based peak frequency-time plot more clearly identifies the higher of the dominant frequencies while the Hilbert based peak frequency-time plot is affected by the lower frequency and leads to less clear results.
High intensity ion beams from an atmospheric pressure inductively coupled plasma
Authors: Al Moussalami S. , Chen W. , Collings B. A. , Douglas D. J.
Published: July 2002

This work is directed towards substantially improving the sensitivity of an inductively coupled plasma mass spectrometer (ICP-MS). Ions produced in the ICP at atmospheric pressure have been extracted with comparatively high current densities. The conventional approach to ion extraction, based on a skimmed molecular beam, has been abandoned, and a high extraction field arrangement has been adopted. Although the new approach is not optimized, current densities more than 180 times greater than that of a conventional interface have been extracted and analyte sensitivities ∼10–100× greater than those reported previously for quadrupole ICP-MS have been measured.
Photodissociation of O2 in the Herzberg continuum. I. Ab initio calculation of potential energy curves and properties
Authors: van Vroonhoven Mirjam C. G. N. , Groenenboom Gerrit C.
Published: July 2002

We present ab initio complete active space self-consistent-field plus multireference configuration interaction (CASSCF+MRCI) potential energy curves for the eight electronically excited ungerade states of oxygen (A 3Σu+, c 1Σu−, A′ 3Δu, Πu1, Πu3, Πu5, Πu-5, and 2 3Σu+) that correlate with the O(3P)+O(3P) dissociation limit. We also report the R-dependent spin–orbit couplings between these states and the R-dependent radial derivative coupling matrix element 〈2 3Σu+|∂/∂R| A 3Σu+〉. The near degeneracy in the long range of the same-symmetry states 2 3Σu+ and A 3Σu+ may result in unphysical mixing of these states in a CASSCF calculation. We derive the correct asymptotic behavior of these states as dictated by the quadrupole–quadrupole interaction and we show how a correct long range description of these states can be achieved numerically by employing undistorted molecular orbitals. Bound state calculations using Herzberg I, II, and III potentials show excellent agreement with all available spectroscopic data. In the accompanying paper the potentials and couplings will be employed in a semiclassical study of the photodissociation of O2 in the Herzberg continuum.
Temporal change of an extracted H− current by injecting pulse laser light into the extraction region of an H− ion source
Authors: Matsumoto Y. , Wada M. , Kasuya T. , Sasao M.
Published: July 2002

The temporal change of the H− beam current extracted from a volume-production-type negative ion source by injecting a Nd-YAG laser beam into the ion source plasma was measured. The measured change was about 0.3% of the dc H− beam current. The validity of the method was confirmed using Ar plasma which showed no photodetachment signal. The contribution of the local H− density upon the extracted beam was investigated by changing the distance between the center of the laser beam and the plasma grid. The result showed that the contribution took the maximum at about 8 mm distance from the laser beam center to the plasma grid surface.
A high-capacity magnetic pump for gas circulation in closed systems
Authors: Ding Yuqing , LeVan M. Douglas
Published: July 2002

This note describes a new pump designed primarily to recirculate gas in a closed-loop system. The pump consists of a main pump body and an exterior check-valve bridge. The main body, consisting simply of a cylinder and magnetic piston, drives gas in two directions, while the exterior check-valve bridge rectifies the flow to one direction. Large flow rates of up to 7 L/min can be obtained with the prototype pump. The design can easily be scaled to produce pumps for larger or smaller flow rates.
Direction of ion ∇B drift and power threshold in high confinement mode in diverted tokamaks
Authors: Shaing K. C.
Published: July 2002

An explanation of the dependence of the power threshold on the direction of the ion ∇B drift in diverted tokamaks is presented by using the high confinement mode (H-mode) theory based on the orbit loss triggered electric field bifurcation and the subsequent turbulence suppression. Here, B is the magnetic field strength. It is shown that ion collisionality, which defines the onset of the orbit loss, depends on the direction of the ion ∇B drift. Through this dependence, the power threshold also depends on the direction of the ion ∇B drift. A possible method to test this explanation experimentally is suggested.
On a variational approach to the extraction of quadratures from broadband reflectometry signals
Authors: Figueiredo António C. A. , Bizarro João P. S.
Published: July 2002

A variational method is employed to retrieve the phase from broadband reflectometry signals. The method yields the so-called in-phase and quadrature components of a signal (the signal quadratures in short), by stipulating that these should have the smallest possible amount of functional variation, whereby the signal carrier frequency is also recovered as a by-product. The variational approach is based on the reasonable assumption that, for given data, the quadratures are expected to be as slow as possible, as they contain the slow modulations of amplitude and phase, while rapid variations are accounted for by the carrier frequency. The advantages and shortcomings of the variational method are discussed, and a pertinent comparison with the analytic signal—recently proposed as a means to extract the phase from broadband reflectometry signals—is also carried out. The application of the variational method to the reflectometry problem is shown to yield results that are similar to those obtained via the analytic signal. The difference is not significant, especially if detailed measurements are not required, but only averaged ones.
In search of bare ions
Authors: Fehrenbach C. W.
Published: July 2002

Recent beam requests for the CryEBIS facility in the J. R. Macdonald Laboratory at Kansas State University have asked for bare ions for experiments on charge exchange processes. One of these experiments has minimum beam current limitations. In this article I explore how the output current of the EBIS will depend on the charge when bare ions are being produced. Also, practical considerations are discussed both in tuning the ion source, and in separating heavy ions from background light ions with charge-to-mass ratios of 1/2.
High intensity metallic ion beams from an ECR ion source at GANIL
Authors: Lehérissier P. , Barué C. , Canet C. , Dupuis M. , Flambard J. L. , Gaubert G. , Gibouin S. , Huguet Y. , Jaffres P. A. , Jardin P. , Lecesne N. , Lemagnen F. , Leroy R. , Pacquet J. Y. , Pellemoine-Landré F. , Rataud J. P.
Published: July 2002

In recent years, progress concerning the production of high intensity of metallic ion beams (58Ni, 48Ca, 76Ge) at GANIL have been performed. The metallic ion from volatile compound method has been successfully used to produce a high intensity nickel beam with the ECR4 ion source: 20 e μA of Ni11+58 at 24 kV extraction voltage. This beam has been maintained for 8 days and accelerated up to 74.5 MeV/u by our cyclotrons with a mean intensity of 0.13 pμA on target. This high intensity, required for experiment, led to the discovery of the doubly magic Ni48 isotope. The oven method has been first tested with natural metallic calcium on the ECR4 ion source, then used to produce a high power beam (740 W on target, i.e., 0.13 pμA accelerated up to 60 meV/u) of Ca48 still keeping a low consumption (0.09 mg/h). A germanium beam is now under development, using the oven method with germanium oxide. The ionization efficiencies have been measured and compared.
Design and construction of four-hole ECR ion source
Authors: Kashiwagi H. , Hattori T. , Okamura M. , Takahashi Y. , Hata T. , Yamamoto K. , Okada S. , Sugita T.
Published: July 2002

When a large current is accelerated, many radio frequency quadrupole (RFQ) LINAC are needed, because the acceleration limit of a RFQ LINAC is 20 mA–30 mA. Therefore the same number of ion source are needed. But the limit is not the current limit of ion source. If the RFQ LINAC has many RFQ channels, it can accelerate large currents. We designed an accelerator with four RFQ channels to prove this principle. An ion source which extracts four equal beams from one chamber is needed for this RFQ LINAC. A four-hole ECR ion source was designed and manufactured after calculating the magnetic fields by OPERA, and simulating beam trajectory using the program FUGUN. In this ion source, since four extraction holes are located off axis by about 50 mm, the beam is deflected. We calculated this deviation.
Angular distribution of ions emitted from Nd:YAG laser-produced plasma
Authors: Láska L. , Krása J. , Pfeifer M. , Rohlena K. , Gammino S. , Torrisi L. , Andò L. , Ciavola G.
Published: July 2002

Angular distribution of ion currents emitted from laser-produced plasmas are reported for a Nd:YAG laser with intensities lower than 1×1010 W/cm2. This distributions are strongly peaked along the normal to the target surface for Cu, Sn, Ta, W, Au, and Pb ion streams, independent of the incidence angle of the irradiated target. For Al, Ni, and Nb the main axis tends to decline to about −10°. The comparison of fits of Gaussian function and cosP(α−α0)+y0 to the experimental data verified the formal equivalency of both the functions. Fitted values of the FWHM and of the exponent P are compared for all the elements used. The angular distribution of mean ion velocity 〈v〉 and ion kinetic energy 〈E〉 are presented.
Computational design studies for an ion extraction system for a “volume-type” ECR ion source
Authors: Zaim H. , Alton G. D.
Published: July 2002

Numerical studies have been performed for optimally extracting high-intensity, space-charged-limited multicharged ion beams from an all-permanent-magnet, “volume-type” electron cyclotron resonance ion source, equipped with a three-electrode extraction system. These studies clearly demonstrate the importance of being able to adjust the extraction gap in order to ensure high quality, minimum divergence (highly transportable) ion beams. Optimum extraction conditions are reached whenever the plasma meniscus has an optimum curvature for a given current density. Optimum perveance (optimum current) values are found to closely agree with those derived from elementary analytical theory for extraction of space-charge-dominated beams. Details of the electrode system design as well as angular divergence and root-mean-square (rms) emittance versus extraction parameter data (e.g., perveance and extraction gap) are provided for ion beams of varying charge-state and mass, extracted under the influence of a mirror-geometry plasma confinement magnetic field.
Laser absorption spectroscopy with a blue diode laser in an aluminum hollow cathode discharge
Authors: Scheibner H. , Franke St. , Solyman Samir , Behnke J. F. , Wilke C. , Dinklage A.
Published: July 2002

A GaN-based blue diode laser is employed for laser absorption spectroscopy in an aluminum hollow cathode glow discharge plasma. A Littrow grating stabilized external resonator is used for tuning the wavelength of laser emission. Scanning the wavelength of the laser probes the absorption profile of aluminum transitions yielding ground state aluminum densities. Hyperfine structure has to be taken into account in order to obtain correct temperatures. The diode laser is used to investigate both the temperature and the density of aluminum atoms sputtered from a cathode surface by ion bombardment from the cathode fall region. The blue diode laser allows quick and easy access to aluminum ground state atoms at low costs.
The development of a charge breeding system with ECR ion sources of permanent magnets
Authors: Oyaizu M. , Jeong S. C. , Tojyo E. , Kawakami H. , Ishiyama H. , Miyatake H. , Enomoto K. , Katayama I. , Nomura T.
Published: July 2002

For the construction of an electron cyclotron resonance (ECR) charge breeder at the KEK-JAERI radioactive nuclear beam facility, we have made and tested a pilot charge breeding system consisting of two compact-sized ECR ion sources. Using a simulation code, we have investigated the geometrical beam acceptance of the present system for the external injection of ions of interest into ECR plasma. Following discussions on the ECR plasma influenced by a deceleration potential for the external injection, the charge breeding efficiency for Ar ions is presented and discussed.
Inductively coupled plasmas sustained by an internal oscillating current
Authors: Tsakadze E. L. , Ostrikov K. N. , Xu S. , Storer R. , Sugai H.
Published: July 2002

A global electromagnetic model of an inductively coupled plasma sustained by an internal oscillating current sheet in a cylindrical metal vessel is developed. The electromagnetic field structure, profiles of the rf power transferred to the plasma electrons, electron/ion number density, and working points of the discharge are studied, by invoking particle and power balance. It is revealed that the internal rf current with spatially invariable phase significantly improves the radial uniformity of the electromagnetic fields and the power density in the chamber as compared with conventional plasma sources with external flat spiral inductive coils. This configuration offers the possibility of controlling the rf power deposition in the azimuthal direction.
Influence of filament materials on vacuum ultraviolet emission in H− ion source
Authors: Nishiura M. , Sasao M. , Matsumoto Y. , Hamabe M. , Wada M. , Yamaoka H. , Bacal M.
Published: July 2002

The increase of H− current is observed, when the tantalum filaments are used instead of the tungsten filaments. In terms of the production rate of vibrational populations of hydrogen molecules with tungsten and tantalum filaments, we measured the Werner and Lyman emission bands (90–170 nm) the vacuum ultraviolet region to obtain the spectra of molecular hydrogen in an ion source, and observed a significant difference of spectrum between the two cases. From the pressure dependence, it is found that the production rate of vibrationally excited hydrogen molecules is well correlated with the H− density measured by photodetachment in hydrogen plasmas.
Monte Carlo simulation of negative ion transport in the negative ion source (Camembert III)
Authors: Sakurabayashi T. , Hatayama A. , Miyamoto K. , Ogasawara M. , Bacal M.
Published: July 2002

Transport process of negative hydrogen ions (H−) in a large hybrid multicusp H− source, “Camembert III,” has been analyzed by a three-dimensional Monte Carlo simulation code. The realistic geometry and multicusp magnetic-field configuration are taken into account. Various important destruction processes of H− and Coulomb collision with background plasma are also included in the model. Both the volume- and surface-produced H− ion trajectories are followed. For volume-produced H− ions, most of the H− ions can reach the wall in the low-pressure case (1 mTorr), while in the high-pressure case (3 mTorr) most of the H− ions are destructed by volume loss reactions before reaching the wall. This shows that the wall loss is significant at low pressure as in the experiments. For surface-produced H− ions, the influence of its birthplace on the H− current is studied. Negative ions created on the sidewall hardly can reach the center of the source due to trapping by the multicusp magnetic field. As a result, H− ions created on the sidewall do not have a significant effect on the H− current.
Present status of the negative ion based neutral beam injector for JT-60U
Authors: Ohga T. , Umeda N. , Akino N. , Ebisawa N. , Grisham L. , Hikita S. , Honda A. , Itoh T. , Kawai M. , Kazawa M. , Kuriyama M. , Kusaka M. , Mogaki K. , Oohara H. , Pengyuan L. , Satoh F. , Seki H. , Tanai Y. , Toyokawa Y. , Usui K. , Yamamoto T. , Yamazaki H.
Published: July 2002

The negative ion based neutral beam injector heating system for JT-60U has contributed to core plasma heating and noninductive current drive experiments on JT-60U. For increasing further the beam power and beam pulse duration, the serious issue is improvement of source plasma nonuniformity in the ion source. Various countermeasures have been devised to solve the nonuniformity. The first is to adjust the spatial distribution of the arc discharge through regulating the arc current limiting resistors to be connected in series to each of the filament groups. The second is to change the arc discharge mode through controlling the filament temperature. These measures have been found to be very effective.
Development of a large volume negative-ion source for ITER neutral beam injector
Authors: Watanabe K. , Amemiya T. , Hanada M. , Iga T. , Imai T. , Inoue T. , Kashiwagi M. , Kuriyama M. , Morishita T. , Okumura Y. , Takayanagi T. , Yamamoto T.
Published: July 2002

Development of the negative-ion sources has been conducted to realize a high power neutral beam injector for International Thermonuclear Experimental Reactor (ITER). A high negative-ion current density of 31 mA/cm2 (H−) at a very low pressure of 0.1 Pa has been produced in a cesium seeded multicusp plasma generator which has the same concept of the ITER source. For a vacuum insulated accelerator, a voltage holding experiment of long distance vacuum gaps up to ∼1.8 m has been performed. It was clarified that the transition region of product pressure distance (pd) from the vacuum breakdown to the gas discharge is about 0.2 Pa m which is high enough from the operating region of the ITER source. A prototype vacuum insulated accelerator was fabricated based on the experiment and tested. A high-energy H− beam acceleration up to 970 keV, 37 mA, and 1 s has been successfully demonstrated.
Long pulse operation of the KAMABOKO III negative ion source
Authors: Boilson D. , de Esch H. P. L. , Hemsworth R. S. , Kashiwagi M. , Massmann P. , Svensson L.
Published: July 2002

The target performance for the KAMABOKO ion source on the MANTIS test bed in Cadarache is to accelerate a beam of D− with a current density of 200 A/m2 and <1 extracted electron per accelerated D− ion, at an injected power ranging between 1 and 2 kW per liter of source volume, at a source pressure of 0.3 Pa. For ITER, a continuous neutral beam must be assured for pulse lengths of 500 s, but beams of up to 3600 s are also envisaged. During the last campaign, continuous beam pulses of duration up to 1000 s were demonstrated both in hydrogen and in deuterium. In this article, the source performance, the effect of the plasma grid temperature for long pulse operation, and the limits of the present experimental setup are described. Additionally, the effect of changing the strength of the magnetic filter in the ion source on the extracted ion and electron currents and the beam transmission is reported.
Efficient negative-ion sources for radioactive ion beam applications (abstract)
Authors: Alton G. D. , Liu Y. , Murray S. N. , Mills G. D. , Zaim H.
Published: July 2002

Direct extraction, negative-surface ionization, and sputter-type sources have been designed to efficiently ionize specific members of the group VII A elements (F, Cl, Br, I, and At) for use in the nuclear structure physics and nuclear astrophysics research programs at the Holifield Radioactive Ion Beam Facility (HRIBF). A negative surface ionization source that utilizes a solid, spherical geometry, LaB6 ionizer (φ≅2.7 eV) for negatively ionizing Cl, Br, l, and At. During off-line evaluation, the ionization efficiency for Cl− generation ranged between 15% and 20% and for Br− generation, between 15% and 25%. Chemically active elements, such as fluorine, are often released from refractory host materials in a variety of molecular forms. Consequently, the LaB6 surface ionization source, described above, is ineffective for simultaneously dissociating and negatively ionizing this element. To overcome this problem, a new concept source, referred to as the kinetic ejection negative ion source (KENIS), was developed. The source utilizes the Cs-sputter technique to effectively dissociate molecular carriers and ionize F at efficiencies in excess of 7%. The source has been used on-line to inject >3×107 17F−/s into the tandem accelerator and deliver ∼3×106 17F9+/s (fully stripped) to the research station for completion of important nuclear-astrophysics experiments. In this article, emphasis will be placed on the design details, materials of construction, ion optics, operational parameters, thermal transport properties, emittances, and measured ionization efficiencies for these sources.
Recent advances in Veeco’s radio frequency ion sources for ion beam materials processing applications (abstract)
Authors: Hayes A. V. , Kanarov V. , Yevtukhov R. , Williams K. , Hines D. , Druz B. , Hegde H.
Published: July 2002

In this article we describe an advanced inductively coupled plasma ion source being developed at Veeco for applications in data storage and active optical device fabrication. The new source design minimizes rf capacitive coupling. Capacitive coupling is responsible for erosion of the quartz discharge chamber and high transverse ion energies. Suppression of capacitive coupling, however, can be problematic for some applications due to the fact that, without it, conductive coatings that shield the transfer of inductive power to the plasma can accumulate inside the source. The authors have developed a simple and unique protective device that when installed on the quartz hardware effectively inhibits rf losses in the deposited films, greatly extending the quartz maintenance cycle and overcoming the above problem. Reduction of capacitive coupling is achieved using a slotted Faraday shield inserted between the low-frequency 1.8 MHz rf antenna and the plasma. It is found that the rf power loss to this shield is extremely low, yet it is very effective, essentially eliminating signs of discharge chamber sputtering. Further advantages of these new design features and application to special controlled etching processes are described. Also, new performance and reliability data for Veeco’s recently developed “flangeless” self-aligned ion optics grid assembly, implemented on the RIM-210 focused beam deposition ion source is shown, demonstrating the advantages of this design.
Free excitons in cubic CdS films
Authors: Kanemitsu Yoshihiko , Nagai Takehiko , Kushida Takashi , Nakamura Seiji , Yamada Yoichi , Taguchi Tsunemasa
Published: July 2002

Cubic CdS layers have been epitaxially grown on (001) GaAs substrates by a low-pressure metalorganic chemical vapor deposition technique, and their free exciton states have been studied by means of modulated reflectance spectroscopy. Light-hole and heavy-hole excitons are split by biaxial compressive strains in the 2 μm CdS films. It has been found that a sharp photoluminescence (PL) appears at low temperatures and the PL energy coincides with the light-hole exciton energy. Two peaks in the PL excitation spectrum agree well with the light-hole and heavy-hole exciton energies. The free exciton energy has been determined for cubic CdS films on GaAs substrates.
Beam measurements on the H− source and low energy beam transport system for the Spallation Neutron Source (abstract)
Authors: Thomae R. , Gough R. , Keller R. , Leung K. N. , Schenkel T. , Aleksandrov A. , Stoeckli M. , Welton R.
Published: July 2002

The ion source and low energy beam transport section of the front-end systems presently being built by Lawrence Berkeley National Laboratory are required to provide 50 mA of H− beam current at 6% duty factor (1 ms pulses at 60 Hz) with a normalized rms emittance of less than 0.20 π-mm-mrad. Experimental results, including emittance, chopping, and steering measurements, on the performance of the ion source and LEBT system operated at the demanded beam parameters will be discussed.
Cooling effect of hydrogen negative ions in argon gas mixture
Authors: Nishiura M. , Sasao M. , Matsumoto Y. , Hamabe M. , Wada M. , Yamaoka H. , Bacal M.
Published: July 2002

The gas mixture effect upon the negative ion temperature in negative ion sources has been studied by the laser photodetachment technique. The ion source is operated at hydrogen pressure from 0.05 to 2.0 Pa. Then argon gas is added up to 100% of the hydrogen pressure. Maximum enhancement of the negative ion density is observed at around a 20%–40% argon to hydrogen mixture in the low hydrogen pressure region. The recovery time for the electron current signal after photodetachment becomes longer when more argon is added to hydrogen plasmas, indicating a lower negative ion temperature.
Brillouin and dielectric studies of the phase transition in the relaxor ferroelectric Pb(Ni1/3Nb2/3)O3
Authors: Fan H. J. , Kuok M. H. , Ng S. C. , Yasuda N. , Ohwa H. , Iwata M. , Orihara H. , Ishibashi Y.
Published: July 2002

Brillouin scattering has been performed on the relaxor ferroelectric Pb(Ni1/3Nb2/3)O3 (PNN) from 80 to 450 K across its Curie temperature. A diffuse phase transition from the paraelectric to ferroelectric phase, associated with a broad phonon frequency dip and a damping maximum, is observed around 200 K. A relaxation mode in the form of a broad Rayleigh wing, whose frequency is strongly temperature dependent above 190 K, is observed and analyzed based on a modified superparaelectric model. Dielectric studies of PNN have also been carried out at several measurement frequencies. The relation between the measurement frequency and the dielectric maximum temperature was analyzed on a modified Vogel–Fulcher model.
Boost–rotation symmetric vacuum space–times with spinning sources
Authors: Pravdová A. , Pravda V.
Published: July 2002

Boost–rotation symmetric vacuum space–times with spinning sources which correspond to gravitational field of uniformly accelerated spinning “particles” are studied. Regularity conditions and asymptotic properties are analyzed. News functions are derived by transforming the general spinning boost–rotation symmetric vacuum metric to Bondi–Sachs coordinates.
Stable orbits in a Higgs-Monopole field
Authors: Azizi Azizollah
Published: July 2002

Motion of Yang–Mills particles in Yang–Mills–Higgs fields are studied. By regarding the Higgs field contribution on the particle’s motion, a complete set of equations is worked out for the particle and fields. The planar motions as well as three-dimensional bounded motions are studied. Stable orbits are allowed in this scenario.