ScholarBank@NUShttps://scholarbank.nus.edu.sgThe DSpace digital repository system captures, stores, indexes, preserves, and distributes digital research material.Sat, 19 Oct 2019 00:42:47 GMT2019-10-19T00:42:47Z50181- Velocity distribution functions of Na+ ions drifting in helium, neon and argonhttps://scholarbank.nus.edu.sg/handle/10635/98551Title: Velocity distribution functions of Na+ ions drifting in helium, neon and argon
Authors: Hogan, M.J.; Ong, P.P.
Abstract: Measurements are reported of the velocity distribution functions of room-temperature Na+ ions drifting in helium, neon and argon gas under the influence of an electric field at E/n in the range 16-261 Td. The distributions were found to become wider, have larger RMS velocities and become more skewed toward higher velocities as E/n was increased. They also were shifted increasingly further from the velocity space origin with increasing E/n. The ion-to-neutral-mass ratio was found to be an important parameter in determining the properties of the distributions. The experimental results were used to evaluate the accuracy of theoretical analytic expressions for the velocity distributions.
Fri, 01 Jan 1988 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/985511988-01-01T00:00:00Z
- Transport properties of Na+ ions in Kr gashttps://scholarbank.nus.edu.sg/handle/10635/98450Title: Transport properties of Na+ ions in Kr gas
Authors: Tan, T.L.; Ong, P.P.; Hogan, M.J.
Abstract: The transverse-diffusion coefficients for Na+ ions drifting in Kr gas have been experimentally measured with estimated accuracies of better than 3% at E/N values ranging from 5 to 500 Td (1 Td=10-21 V m2) at about 303 K. In addition, elaborate calculations of the transport properties for the Na+-Kr system have been made by using Monte Carlo simulations (MCSs) and the generalized Einstein-relation techniques. The experimental results are compared with values obtained from MCSs using the interaction potential of Koutselos, Mason, and Viehland [J. Chem. Phys. 93, 7125 (1990)] as input. Agreement within 3% for the entire range of E/N is observed in the comparisons. MCS-calculated values of longitudinal-diffusion coefficients are also compared with those determined experimentally by Thackston et al. [J. Chem. Phys. 73, 2012 (1980)]. © 1993 The American Physical Society.
Fri, 01 Jan 1993 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/984501993-01-01T00:00:00Z
- An appraisal of the three-temperature theory and the interaction potentials of K +-He and K +-Kr by Monte Carlo Simulationhttps://scholarbank.nus.edu.sg/handle/10635/95757Title: An appraisal of the three-temperature theory and the interaction potentials of K +-He and K +-Kr by Monte Carlo Simulation
Authors: Ong, P.P.; Hogan, M.J.
Abstract: Monte Carlo simulation calculations on a supercomputer have been made of the mobility of K + ions drifting in pure He and Kr gases respectively under the action of a uniform electric field. Typical errors of 1% or less are achieved. By making direct comparisons with other theoretical and experimental data, these calculations have helped to verify both the three-temperature theory used to derive the theoretical mobility as well as the validity of various interaction potentials proposed. Results of these comparisons together with an earlier one for the K +-Ar system provide evidence that the three-temperature theory is generally applicable for the three different ion-neutral mass ratios studied, but yields a slight overestimation of the mobility around the peak mobility region. © 1991 IOP Publishing Ltd.
Sun, 28 Jul 1991 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/957571991-07-28T00:00:00Z
- Reexamination of the Li+-He interaction potentialhttps://scholarbank.nus.edu.sg/handle/10635/97787Title: Reexamination of the Li+-He interaction potential
Authors: Ong, P.P.; Hogan, M.J.; Tan, T.L.
Abstract: Using various recently proposed interaction potentials for the Li+-He system, elaborate calculations of the mobility, longitudinal, and transverse diffusion coefficients of Li+ swarms in helium have been made by high-speed Monte Carlo simulations (MCS's). In addition, the transverse diffusion coefficients for this ion-neutral-atom pair have been experimentally measured with total errors of ±3%. The close agreement of the present experimental results with those of Skullerud, Eide, and Stefansson [J. Phys. D 19, 197 (1986)] as well as the faithful MCS reproduction of all three transport coefficients using the interaction potential proposed by Larsen et al. [J. Phys. B 21, 2519 (1988)] over the entire range of E/N (electric field to neutral-particle number density ratio) studied not only provides confirmation of their transport coefficient values, but also lends strong support for their proposed interaction potential. In comparison, the more recent potentials of Ahlrichs et al. [J. Chem. Phys. 88, 6290 (1988)] and of Koutselos, Mason, and Viehland [J. Chem. Phys. 93, 7125 (1990)] did not reproduce the experimental data quite as well. As a benchmark the MCS calculations have also provided evidence of the accuracy of the Kramers-Moyal expansion method in calculating the transport coefficients. © 1992 The American Physical Society.
Wed, 01 Jan 1992 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/977871992-01-01T00:00:00Z
- Measurements of DT/μ of Na+ ions in argon and neonhttps://scholarbank.nus.edu.sg/handle/10635/97160Title: Measurements of DT/μ of Na+ ions in argon and neon
Authors: Hogan, M.J.; Ong, P.P.
Abstract: Room temperature measurements of the ratio DT/μ between the transverse diffusion coefficient and the mobility of mass-identified ions in a neutral gas are reported for Na+ ions in argon and neon. A new apparatus was used which, in contrast to previous methods, does not involve mechanical movement which alters the geometry of the drift tube assembly during a measurement scan, or variation of the experimental conditions inside it. Results with an estimated accuracy of better than 3% were obtained at E/N values ranging from 10 to 260 Td with argon and 10 to 200 Td with neon.
Mon, 01 Jan 1990 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/971601990-01-01T00:00:00Z
- Interaction potential of K+ in Ar: A Monte Carlo simulation mobility-comparison testhttps://scholarbank.nus.edu.sg/handle/10635/96951Title: Interaction potential of K+ in Ar: A Monte Carlo simulation mobility-comparison test
Authors: Hogan, M.J.; Ong, P.P.
Abstract: A standardized Monte Carlo simulation (MCS) procedure is used as a routine test of the accuracy of any interaction potential of an ion-atom binary pair. By capitalizing on the performance of a supercomputer, the procedure achieves a highly realistic simulation of the ionic motion and calculates the resulting mobilities of the ions in the neutral gas. These values are then compared against accurate experimental values, assumed available. For cases where the same interaction potential has also been used as input for kinetic-theory calculations of mobilities, the procedure may be extended to check the accuracy of the theory itself. The interaction potentials of Lamm et al. [J. Chem. Phys. 74, 3042 (1981)]; Budenholzer, Gislason, and Jorgensen [J. Chem. Phys. 78, 5279 (1983)]; and Koutselos, Mason, and Viehland [J. Chem. Phys. 93, 7125 (1990)] for the K+-Ar pair as an illustrative case study are examined. The calculations indicate that the potential of Koutselos, Mason, and Viehland is the most accurate currently available. Furthermore, a comparison of the MCS calculations with the two-temperature theoretical mobilities of Lamm et al. and the three-temperature mobilities of Koutselos, Mason, and Viehland suggests that both theories are quite accurate at both the low- and high-ionic-drift-energy regions, but are up to about 2% too high at the intermediate-energy region. © 1991 The American Physical Society.
Tue, 01 Jan 1991 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/969511991-01-01T00:00:00Z
- Velocity distributions of He+, Ne+ and Ar+ in parent gaseshttps://scholarbank.nus.edu.sg/handle/10635/98552Title: Velocity distributions of He+, Ne+ and Ar+ in parent gases
Authors: Ong, P.P.; Hogan, M.J.
Abstract: Measurements are made of the velocity distributions of He+, Ne+ and Ar+ ions drifting in their respective parent gas under the action of a uniform electric field at room temperature (297-300K). Considerable improvements have been implemented in the present apparatus in comparison with older systems. The drift tube is greatly enlarged and its pressure accurately controlled by a regulating servo-valve. A new ion optical system coupled with a wider quadrupole analyser head ensures a high collection efficiency of ions transmitted through the retarding potential grids. A novel in-drift obstacle and a 90 degrees off-axis detector effectively suppress interference from UV photons and metastable species. Experimental results for E/N ranging from 60 to 320 Td are compared with both the Wannier equation for the RMS ion velocity and the corresponding Maxwellian distribution. The typical experimental curve is found to possess only a single maximum with its peak displaced towards the low velocity end and an enhanced high velocity tail in comparison with the Maxwellian.
Tue, 01 Jan 1985 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/985521985-01-01T00:00:00Z
- Experimental study of longitudinal end effects in transverse diffusion measurements of Na+ ion swarms in He gashttps://scholarbank.nus.edu.sg/handle/10635/96569Title: Experimental study of longitudinal end effects in transverse diffusion measurements of Na+ ion swarms in He gas
Authors: Tan, T.L.; Ong, P.P.; Hogan, M.J.
Abstract: The inevitable presence of longitudinal end effects in drift-tube mass spectrometers, if not corrected for, can cause significant systematic errors in measurements of ion transport coefficients. In our transverse diffusion measurements of Na+ ions in He and several other ion-neutral pairs, appreciable longitudinal end effects were detected for sufficiently high values of E÷N, the ratio of electric field to neutral gas number density. Systematic measurements at various drift length and analysis reveal that these end effects are generally more pronounced for ion-neural pairs with very low or very high mass ratio. They can be either positive or negative and their magnitudes can be quantified by a simple linear relationship of the transverse ion current density profile with drift length.
Sat, 01 Jan 1994 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/965691994-01-01T00:00:00Z
- Interaction potential, transport properties, and velocity distributions of Na+ ions in Nehttps://scholarbank.nus.edu.sg/handle/10635/58415Title: Interaction potential, transport properties, and velocity distributions of Na+ ions in Ne
Authors: Ong, P.P.; Hogan, M.J.; Lam, K.Y.; Viehland, L.A.
Abstract: Comparisons of experimentally measured transport properties with values determined from calculations based on three-temperature-kinetic theory, on bi-Maxwellian kinetic theory, and on Monte Carlo simulations have established that the Na+-Ne interaction potential of Koutselos, Mason, and Viehland [J. Chem. Phys. 93, 7125 (1990)] is a close approximation to the true potential. (In the bi-Maxwellian approach, the ions are modeled in first-approximation as a large fraction that behaves according to a low-temperature Maxwell distribution and a small fraction that follows one of higher temperature; the true distribution is computed from these by a weighted-residual method.) This potential was then used to compute velocity distribution functions of Na+ ions in room-temperature Ne at widely different average ion energies. The skewness of the distributions in the direction of the electric field initially increased rapidly with increasing energy, and then slowly decreased, as did the excess kurtosis both parallel and perpendicular to the electric-field direction. It was clearly established that there is correlation between the perpendicular and parallel velocity-component distribution functions and that the correlation increases with increasing average ion energy. © 1992 The American Physical Society.
Wed, 01 Jan 1992 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/584151992-01-01T00:00:00Z
- An apparatus for measuring DT/K without in-vacuum mechanical motionhttps://scholarbank.nus.edu.sg/handle/10635/95756Title: An apparatus for measuring DT/K without in-vacuum mechanical motion
Authors: Ong, P.P.; Hogan, M.J.
Abstract: A new drift-tube apparatus has been developed for measuring D T/K, the ratio of the transverse diffusion coefficient to the mobility of ions in a neutral gas under the influence of an electric field. It harnesses existing technology in mechanical, electronic, materials, and computer engineering. The main features are the ion current detector, which comprises 65 parallel rods, and an external mechanical multiplexer, which was designed to have extremely low (fA order) leakage currents and noise levels. Unlike with other earlier systems, the need for precise mechanical motion or adjustments of experimental conditions inside the drift tube during data collection has been circumvented. Its design therefore simplifies construction and makes operation less error prone. Data collection is computer controlled. A value for D T/K can now typically be obtained in less than 20 min, which greatly increases the rate at which results can be obtained as well as reduces the chance of unwanted variations in experimental conditions occurring during data collection. Results are estimated to be accurate to within 3%.
Tue, 01 Jan 1991 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/957561991-01-01T00:00:00Z
- Impurity ion production in alkali ion sourceshttps://scholarbank.nus.edu.sg/handle/10635/96888Title: Impurity ion production in alkali ion sources
Authors: Hogan, M.J.; Ong, P.P.
Abstract: It has long been known that new alkali ion sources utilizing thermionic emission from alkali aluminosilicates can achieve high percentages of the desired ion by a sufficiently long "burn-in." Observations are reported here of instances where increased impurity ion emission can reoccur and lead to possible measurement errors in experimental systems lacking mass spectrometers. The ratio of impurity K+ ions to Na+ ions from a burned-in Na2O·Al2O3· 2SiO2 source was measured to be 0.55.
Mon, 01 Jan 1990 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/968881990-01-01T00:00:00Z
- Transverse diffusion and interaction potential for K + drifting in Arhttps://scholarbank.nus.edu.sg/handle/10635/98452Title: Transverse diffusion and interaction potential for K + drifting in Ar
Authors: Ong, P.P.; Hogan, M.J.
Abstract: Experimentally measured values of the ratio, D T/K, of the transverse diffusion coefficient to the mobility for K + ions drifting in argon gas are reported. Results were obtained with estimated accuracies of ±3% at E/N values ranging from 10-600 Td (1 Td=10 -21 V m 2) and have been adjusted to 298 K. These experimental values are compared with values obtained from Monte Carlo simulations using several proposed interaction potentials as input. The comparisons suggest that none of the potentials examined is a totally accurate representation of the K +-Ar interaction potential. © 1991 IOP Publishing Ltd.
Thu, 14 Feb 1991 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/984521991-02-14T00:00:00Z
- Interpretation of measurements of ion energy distributions in drift tubeshttps://scholarbank.nus.edu.sg/handle/10635/96971Title: Interpretation of measurements of ion energy distributions in drift tubes
Authors: Hogan, M.J.; Ong, P.P.
Abstract: The interpretation of experimental measurements of the energy distributions of low-density, ion swarms drifting in an electric field is discussed. The ratio, R, of the mean energy of a measured energy distribution to that predicted by Wannier's equation is found to have an expected value greater than one at intermediate field strengths. Measurements of R for He+ and Ar+ ions in their respective parent gas are interpreted in terms of the analysis presented. © 1985.
Fri, 10 May 1985 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/969711985-05-10T00:00:00Z
- A study of K+-He and K+-Kr atomic interaction potentials based on transverse diffusion measurementshttps://scholarbank.nus.edu.sg/handle/10635/95689Title: A study of K+-He and K+-Kr atomic interaction potentials based on transverse diffusion measurements
Authors: Hogan, M.J.; Ong, P.P.
Abstract: The ratio of the transverse diffusion coefficient to the mobility, D T/K, has been measured for K+ ions drifting in helium and krypton in the presence of a uniform electric field. Results at 298 K are reported at E/N values ranging from 10 to 220 Td for K+-He and 5 to 420 Td for K+-Kr. Values of DT/K for these two systems were also calculated with a Monte Carlo simulation method which used a number of proposed potentials as input. The accuracy of these potentials has been evaluated by comparing the results to the experimentally determined values. For K+-He none of the available potentials seems to be completely accurate, but for K+-krypton the potential of Koutselos, Mason, and Viehland appears to be a very good representation of the actual potential. Within the ranges studied, the estimated accuracy of the experimental measurements is ± 2.5% and the accuracies for the Monte Carlo calculations are ± 1% for K+-He and ± 0.5% for K +-Kr. © 1991 American Institute of Physics.
Tue, 01 Jan 1991 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/956891991-01-01T00:00:00Z
- Transport properties and interaction potential for Na+ ions in Xe gashttps://scholarbank.nus.edu.sg/handle/10635/98446Title: Transport properties and interaction potential for Na+ ions in Xe gas
Authors: Tan, T.L.; Ong, P.P.; Hogan, M.J.
Abstract: The ratio, DT/K, of the transverse diffusion coefficient to mobility for Na+ ions drifting in Xe gas has been experimentally measured. Inevitable longitudinal end effects present in the drift tube were duly corrected for. Results at ∼303 K are reported at electric field to neutral gas density ratios, E/N, ranging from 5 to 440 Td. Furthermore, elaborate calculations of the reduced mobility, K0, the ratio, D L/K, of the longitudinal diffusion coefficient to mobility, and DT/K were calculated with a Monte Carlo simulation (MCS) method which used the interaction potential of Koutselos, Mason, and Viehland [J. Chem. Phys. 93, 7125 (1990)] as input. The accuracy of this potential has been evaluated by comparing the results with the experimental data and those calculated using the generalized Einstein relations technique. Agreement within 3% between the experimental values of DT/K and those from MCS calculations for the whole range of E/N suggests that the interaction potential represents fairly well the true potential. The error of the experimental measurements of DT/K is estimated to be better than 3.5% and that of the MCS calculations is better than 1% for K0 and 2.5% for D T,L/K. © 1994 American Institute of Physics.
Sat, 01 Jan 1994 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/984461994-01-01T00:00:00Z
- SODIUM ION PRODUCTION IN A SIMPLE MICROWAVE DISCHARGE ION SOURCE.https://scholarbank.nus.edu.sg/handle/10635/97957Title: SODIUM ION PRODUCTION IN A SIMPLE MICROWAVE DISCHARGE ION SOURCE.
Authors: Hogan, M.J.; Ong, P.P.
Abstract: Microwave discharge ion sources have commonly been used to produce ions from gases. In this paper we report the extension of such a source to the production of ions from a non-gaseous material without the complication of a magnetic field. The source is simple in design and easily constructed. Discharges which were initiated in argon produce Na** plus ions from both sodium iodide and pure sodium. The absolute and relative rates of production of Na** plus ions were found to vary greatly with the discharge pressure and incident microwave power.
Mon, 01 Sep 1986 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/979571986-09-01T00:00:00Z
- Characteristics of aluminosilicates as thermionic sources of Na+ and K+ ionshttps://scholarbank.nus.edu.sg/handle/10635/95953Title: Characteristics of aluminosilicates as thermionic sources of Na+ and K+ ions
Authors: Hogan, M.J.; Ong, P.P.; Ang, J.L.; Cheang, K.K.
Abstract: A number of synthetic samples of sodium and potassium aluminosilicates with different compositions were prepared using an r.f.-induction furnace. Their characteristics as thermionic emission sources of alkali ions were studied and compared. Based on total emission current and its stability, and the purity of ion content, it was established that samples Na2O:Al2O3:2SiO2 and K2O:Al2O3:2SiO2 possess the best composition ratios to use as Na+ and K+ ion sources respectively. © 1992.
Mon, 17 Aug 1992 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/959531992-08-17T00:00:00Z
- COMPARISON OF THEORETICAL ANALYTIC ION VELOCITY DISTRIBUTION FUNCTIONS WITH EXPERIMENTAL MEASUREMENTS.https://scholarbank.nus.edu.sg/handle/10635/96035Title: COMPARISON OF THEORETICAL ANALYTIC ION VELOCITY DISTRIBUTION FUNCTIONS WITH EXPERIMENTAL MEASUREMENTS.
Authors: Hogan, M.J.; Ong, P.P.
Abstract: Analytic velocity distribution functions of ions drifting through a buffer gas under the influence of an electric field are compared with experimentally obtained measurements of velocity and energy distribution functions. Good matches are found for particular examples, but in general the analytic functions relative to the experimental functions are shifted to lower velocities when the ratio of the electric field to the neutral number density is low and to higher velocities when the ratio is high. The effect of using experimentally determined values of the drift velocity and diffusion coefficients in the analytic expressions is also investigated.
Wed, 01 Jan 1986 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/960351986-01-01T00:00:00Z