Source Chamber Research Articles

Numerical Simulation of a Multi-Cusp Ion Source for High Current H- Cyclotron at RISP

The rare isotope science project (RISP) has been launched in 2011 to support a wide range science program in nuclear, material, and bio-medical sciences as well as interdisciplinary programs. The production of rare isotope beams at RISP is currently configured to include facilities for both an In-flight Fragmentation (IF) system and an Isotope Separator On-Line (ISOL) system, which will utilize a 70 MeV H− cyclotron. The cyclotron will deliver 70kW proton beam power to ISOL targets, where rare isotopes are generated and re-accelerated by a linear accelerator.A multi-cusp ion source used widely in H− cyclotrons is designed to have cusp geometries of magnetic field inside the ion source chamber, where ions are confined and enhanced plasma densities. Therefore the magnetic confinement fields produced by a number of permanent magnetic poles help to increase H− beam currents. In this work a numerical simulation is performed to understand the effect of multi-cusp magnetic fields when the number of magnetic poles is varied from 6 to 14. It is found that the larger number of magnetic poles provides a stronger ion confinement yielding higher extracted H− ion currents while the extracted electron current becomes lower.

Modeling of silicon nanoparticle formation in inductively coupled plasma using a modified collision frequency function

A model is presented to describe particle growth in inductively coupled plasma. The model consists of plasma chemistry and a coagulation module that adopts a modified collision frequency function. The modified collision frequency function is modified by a collision correlation factor that reflects the repulsive force of the particle charge in plasma in order to describe the reduction of coagulation among medium size particles (around 100 nm). In this model, plasma state and concentration of nuclei are determined by a spatially averaged global model in the plasma chemistry module. Particle growth is calculated by a coagulation module. To verify the validity of the model, comparison analysis is performed between experimental data obtained with PBMS and models, some of which are modified by a collision correlation factor. The analysis is performed with respect to dependencies on synthesis time, plasma source power and chamber pressure. From the analysis, we confirm the validity of the model that adopts a modified collision frequency function for the plasma condition.

Diffusion of phenolic compounds through polyethylene films

ABSTRACT: This paper presents experimental results of the diffusion of phenolic compounds through virgin and aged polyethylene (PE) films. The study considers five chlorophenols contaminants (4-chlorophenol, 2,4-dichlorophenol, 2,4,6-tricholophenol, 2,3,5,6-tetrachlorophenol, and pentachlorophenol) that are known to be toxic even at very low concentrations. The concentration dynamics in the source and receptor chambers of the diffusion cells is interpreted using the numerical code Pollute. For virgin PE film, partition coefficients ranged from 0.68 to 278, which corresponded to 4-chlorophenol and pentachlorophenol, respectively. Diffusion coefficients ranged from 1.0 × 10−14 to 2.7 × 10−13 m2/s, which corresponded to pentachlorophenol and 2,4-dichlorophenol, respectively. The study also looked at how the partition and diffusion coefficients were affected by the aqueous solubility, n-octanol–water partition coefficient, molecular diameter, and molecular weight. The trends observed in this study are similar to those found for diffusion of phenolic compounds through PE geomembranes. The results also revealed trends that differ from those previously reported for diffusion of volatile organic compounds (VOCs) through geomembranes. The existing empirical relationships for VOCs are not applicable except for calculating how the diffusion coefficient evolves as a function of solubility in water. Increasing the number of chlorine atoms on the phenolic nucleus causes an increase in the partition coefficient, which is tentatively attributed to the polarity of the molecules under study.

ANALYSIS OF FUEL CONSUMPTION AND OXIDES OF NITROGEN USING OXYGEN ENRICHED AIR IN COMPRESSION IGNITION ENGINE

Pollution is one major factor which affects the environment nowadays, resulting in green house effect and global warming. Suitable methods are introduced to increase the engine fuel economy and bring down the emissions within the tolerable limit. One way of doing it is by inducting oxygen into the combustion chamber since oxygen is a combustion enhancer the amount of oxygen entering into the combustion chamber if increased it would result in better engine performance and lower emissions. Oxygen can be inducted in the intake stroke by the help of an external source and mixing chamber is provided so that it helps in better mixing of air and supplementary oxygen. This additional increase of air will affects all parameters of the engine like operating temperature, fuel consumption, Brake power, emissions, and heat release but only fuel consumption and Oxides of Nitrogen (NOx) alone is analyzed. Load test was conducted on a compression Ignition engine for various concentration of oxygen from (21% to 27%) with an interval of 2%. This experimental study shows better fuel economy and better brake specific fuel consumption but led to a very high percentage of Oxides of Nitrogen (NOx) emission and lower carbon monoxide (CO), hydro carbon (HC) emission.

Radiolytic Formation of Fe3O4 Nanoparticles: Influence of Radiation Dose on Structure and Magnetic Properties

Colloidal Fe3O4 nanoparticles were synthesized using a gamma-radiolysis method in an aqueous solution containing iron chloride in presence of polyvinyl alcohol and isopropanol as colloidal stabilizer and hydroxyl radical scavenger, respectively. Gamma irradiation was carried out in a 60Co gamma source chamber at different absorbed doses. Increasing the radiation dose above a certain critical dose (100 kGy) leads to particle agglomeration enhancement, and this can influence the structure and crystallinity, and consequently the magnetic properties of the resultant particles. The optimal condition for formation of Fe3O4 nanoparticles with a uniform and narrow size distribution occurred at a dose of 100 kGy, as confirmed by X-ray diffractometry and transmission electron microscopy. A vibrating sample magnetometry study showed that, when radiation dose increased, the saturation and remanence magnetization decreased, whereas the coercivity and the remanence ratio increased. This magnetic behavior results from variations in crystallinity, surface effects, and particle size effects, which are all dependent on the radiation dose. In addition, Fourier transform infrared spectroscopy was performed to investigate the nature of the bonds formed between the polymer chains and the metal surface at different radiation doses.

Experimental method development for estimating solid-phase diffusion coefficients and material/air partition coefficients of SVOCs

The solid-phase diffusion coefficient (Dm) and material/air partition coefficient (Kma) are key parameters for characterizing the sources and transport of semivolatile organic compounds (SVOCs) in the indoor environment. In this work, a new experimental method was developed to estimate parameters Dm and Kma. The SVOCs chosen for study were polychlorinated biphenyl (PCB) congeners, including PCB-52, PCB-66, PCB-101, PCB-110, and PCB-118. The test materials included polypropylene, high density polyethylene, low density polyethylene, polytetrafluoroethylene, polyether ether ketone, glass, stainless steel and concrete. Two 53-L environmental chambers were connected in series, with the relatively stable SVOCs source in the source chamber and the test materials, made as small “buttons”, in the test chamber. Prior to loading the test chamber with the test materials, the test chamber had been dosed with SVOCs for 12 days to “coat” the chamber walls. During the tests, the material buttons were removed from the test chamber at different exposure times to determine the amount of SVOC absorbed by the buttons. SVOC concentrations at the inlet and outlet of the test chamber were also monitored. The data were used to estimate the partition and diffusion coefficients by fitting a sink model to the experimental data. The parameters obtained were employed to predict the accumulation of SVOCs in the sink materials using an existing mass transfer model. The model prediction agreed reasonably well with the experimental data.

Numerical analysis of atomic density distribution in arc driven negative ion sources

The purpose of this study is to calculate atomic (H(0)) density distribution in JAEA 10 ampere negative ion source. A collisional radiative model is developed for the calculation of the H(0) density distribution. The non-equilibrium feature of the electron energy distribution function (EEDF), which mainly determines the H(0) production rate, is included by substituting the EEDF calculated from 3D electron transport analysis. In this paper, the H(0) production rate, the ionization rate, and the density distribution in the source chamber are calculated. In the region where high energy electrons exist, the H(0) production and the ionization are enhanced. The calculated H(0) density distribution without the effect of the H(0) transport is relatively small in the upper region. In the next step, the effect should be taken into account to obtain more realistic H(0) distribution.

Photocatalytic removal of cadmium (II) and lead (II) from simulated wastewater at continuous and batch system

Aims: The aim of this study was to evaluate the photocatalytic processes for cadmium (Cd 2+ ) and lead (Pb 2+ ) removal at continuous and batch system. Materials and Methods: This study was performed at laboratory scale. The reactors used in this study consisted of three parts: Ultraviolet (UV) source, reaction cell, and mixing chamber. The experiments were carried out in a batch and continuous reactor for synthetic wastewater. The concentration of Cd 2+ and Pb 2+ was constant (25 mg/L) in all experiments and effect of titanium dioxide (TiO 2 ) dose, pH, and air dispersion was investigated on the removal efficiency. Results: The results showed that with increasing TiO 2 dose and pH, the cadmium and lead removal increase. The maximum removal of cadmium and lead was obtained in TiO 2 dose 0.9 g/L and pH: 11 that were equal to 99.8 and 99.2% respectively. Furthermore, when air dispersion increased, the removal efficiency increased; while in the air dispersion 2 cm 3 /L the removal efficiency was maximum (88 and 93.2% at the contact time 56 min for Cd 2+ and Pb 2+ , respectively).Conclusion: According to these results the TiO 2 has been considered as photocatalyst is the separable and recyclable, so UV/TiO 2 process is an environment friendly process for toxic metal removal.

Experimental Investigation on Plasma Plume Potential

An experimental investigation is carried out to quantify the potential of the plasma plume emitted by an ion thruster type plasma source. A capability for efficient 2-D measurements of the plume profile is developed. The effects of plume expansion, plume charge-exchange (CEX) plasma, and facility background plasma on plume potential are investigated. For plasma source and vacuum chamber operating conditions considered in this paper, we find that the propellant CEX plasma is the primary factor that terminates the plume expansion process, and thus largely controls the magnitude of the plume potential with respect to the ambient.

A multi purpose source chamber at the PLEIADES beamline at SOLEIL for spectroscopic studies of isolated species: Cold molecules, clusters, and nanoparticles

This paper describes the philosophy and design goals regarding the construction of a versatile sample environment: a source capable of producing beams of atoms, molecules, clusters, and nanoparticles in view of studying their interaction with short wavelength (vacuum ultraviolet and x-ray) synchrotron radiation. In the design, specific care has been taken of (a) the use standard components, (b) ensuring modularity, i.e., that swiftly switching between different experimental configurations was possible. To demonstrate the efficiency of the design, proof-of-principle experiments have been conducted by recording x-ray absorption and photoelectron spectra from isolated nanoparticles (SiO2) and free mixed clusters (Ar/Xe). The results from those experiments are showcased and briefly discussed.

Commissioning and operation of the deuteron injector for PKUNIFTY project

PKUNIFTY (PeKing University Neutron Imaging FaciliTY), a thermal neutron imaging facility based on a 2 MeV RFQ accelerator, has been constructed at Peking University. Its deuteron injector, which consists of a 2.45 GHz permanent magnet electron cyclotron resonance (PMECR) deuteron ion source and a two-solenoid low energy beam transport (LEBT), aims at producing and delivering 50 mA, 50 keV deuteron beam with a duty factor of 10% (1 ms, 100 Hz). In the preliminary tests of RFQ accelerator, the ECR ion source and LEBT are required to operate at various duty factors (from 1% to 10%). The deuteron ion source has been tested with different pulse widths for this reason. In order to optimize the transmission parameters, the beam current at the exit of RFQ as a function of solenoids tuning and steering magnets tuning are carefully studied. The beam emittance at the entrance of RFQ has been measured with space charge compensation by different argon gas (RG) pressure from 1.6 × 10(-4) Pa to 4.7 × 10(-3) Pa. The measuring results show the best compensating pressure is 3.5 × 10(-3) Pa with a minimal normalized rms emittance of 0.12 pi mm mrad. During the commissioning, we found the purity of deuteron gas is an important factor which severely affects ECR discharge and plasma intensity inside the ion source chamber. The detailed experimental results obtained during the commissioning are discussed in this paper.

Numerical study of atomic production rate in hydrogen negative ion sources with the effect of non-equilibrium electron energy distribution function

Spatial non-uniformity of the dissociative hydrogen atom (H0) production has been investigated in a large negative ion source (JAEA 10 A source) with the electron energy distribution function (EEDF) obtained by a Monte-Carlo simulation code for electron transport in 3D3V (three dimensional real and velocity) space. It has been shown that the H0 production rate becomes larger in the upper region (one side in the longitudinal direction) of the source chamber. This spatial non-uniformity of the H0 production profile is mainly explained by the non-equilibrium features of the EEDF in the upper region, i.e., the EEDF consists of thermal electron component with kinetic energy ε < 25 eV and fast electron component with energy ε > 25 eV in the upper region, while the EEDF mainly consists of only thermal electrons in the bottom region. These characteristics for the EEDF and the energy dependence of cross-sections for dissociation and dissociative ionization processes lead to the non-uniform profile of the H0 production. The above numerical results of the spatial H0 non-uniformity are validated and confirmed by comparisons with those by spectroscopic measurement. It has been clarified that the non-equilibrium (fast electron) component of the EEDF has a large contribution to the non-uniformity of the H0 production rate.

Enhancement of negative hydrogen ion production in an electron cyclotron resonance source

In this paper, we present a method for improving the negative hydrogen ion yield in the electron cyclotron resonance source with driven plasma rings where the negative ion production is realized in two stages. First, the hydrogen and deuterium molecules are excited in collisions with plasma electrons to high-laying Rydberg and high vibration levels in the plasma volume. The second stage leads to negative ion production through the process of repulsive attachment of low-energy electrons by the excited molecules. The low-energy electrons originate due to a bombardment of the plasma electrode surface by ions of a driven ring and the thermoelectrons produced by a rare earth ceramic electrode, which is appropriately installed in the source chamber. The experimental and calculation data on the negative hydrogen ion generation rate demonstrate that very low-energy thermoelectrons significantly enhance the negative-ion generation rate that occurs in the layer adjacent to the plasma electrode surface. It is found that heating of the tungsten filaments placed in the source chamber improves the discharge stability and extends the pressure operation range.

Laser Beam Filtration for High Spatial Resolution MALDI Imaging Mass Spectrometry

We describe an easy and inexpensive way to provide a highly defined Gaussian shaped laser spot on target of 5μm diameter for imaging mass spectrometry using a commercial MALDI TOF instrument that is designed to produce a 20μm diameter laser beam on target at its lowest setting. A 25μm pinhole filter on a swivel arm was installed in the laser beam optics outside the vacuum ion source chamber so it is easily flipped into or out of the beam as desired by the operator. The resulting ion images at 5μm spatial resolution are sharp since the satellite secondary laser beam maxima have been removed by the filter. Ion images are shown to demonstrate the performance and are compared with the method of oversampling to achieve higher spatial resolution when only a larger laser beam spot on target is available.

High pressure nanoelectrospray ionization mass spectrometry for analysis of aqueous solutions

Nanoelectrospray ionization (nanoESI) with a very fine emitter and nanoliter solution flow rate is known to be suitable for aqueous solutions. However, under atmospheric pressure, its stability with aqueous solutions is not always guaranteed particularly in the negative ion mode where corona and arc discharge tend to occur more easily. Electrical discharge can be quenched to a certain extent by adding electron scavenging gases like SF6 or CO2 to the ion source. The onset potential that is required to induce the discharge also increases with an increase of gas pressure. Recently, we have reported on a series of high pressure electrospray ion sources that were stable in both positive and negative ion modes using air or N2 as the working gas. In this paper, we compare the performance of nanoelectrospray under atmospheric pressure and super-atmospheric pressure for the analysis of samples in aqueous solution. The comparative study was performed using the same ion source chamber that could be pressurized up to 6 bar. The pressure in the first pumping stage of the mass spectrometer was kept constant when the ion source pressure was changed by using an additional pump with variable pumping speed. High pressure nanoESI optimized at 2-3 bar demonstrated a 3-5 times improvement in ion signal intensity compared to atmospheric pressure nanoESI, and the signal stability was significantly improved particularly in the negative mode.

Electron ionization of different large perfluoroethers embedded in ultracold helium droplets: effective freezing of short‐lived decomposition intermediates

Electron ionization of three perfluoroethers (PFEs), C(6)F(14)O(3), C(8)F(18)O(4), and C(10)F(20)O(5), is studied in the gas phase and when the molecules are embedded in ultracold helium (He) droplets. The molecules investigated are model compounds for perfluoropolyethers used as lubricants in technical applications. The present study gives insight into possible radiolysis pathways upon radiation exposure. The experiments utilized a crossed electron/droplet beam apparatus consisting of a He droplet source and pick-up chamber combined with a commercial time-of-flight mass spectrometer. The doped droplets were ionized by electron ionization at 70 eV. The He environment strongly affects the ionization patterns in the way that both the molecular ion M(+) and high-mass fragment ions formed by the loss of light neutral species such as F([M-F](+)), or CF(3)OCF(2) ([M-CF(3)OCF(2)](+)), etc., became strong signals in the mass spectrum. These signals were not or only barely visible in the gas-phase experiment and were identified as short lived (< µs) dissociation intermediates which in the gas phase immediately decomposed into lower-mass fragment ions. Ionic fragmentation intermediates are frozen and subsequently stabilized in the He environment. Helium droplets can hence be viewed as a cryogenic laboratory transforming short-lived decomposition intermediates into stable fragment ions appearing as strong signals in the mass spectrum.

Room Temperature Radiolytic Synthesized Cu@CuAlO2-Al2O3 Nanoparticles

Colloidal Cu@CuAlO2-Al2O3 bimetallic nanoparticles were prepared by a gamma irradiation method in an aqueous system in the presence of polyvinyl pyrrolidone (PVP) and isopropanol respectively as a colloidal stabilizer and scavenger of hydrogen and hydroxyl radicals. The gamma irradiation was carried out in a 60Co gamma source chamber with different doses up to 120 kGy. The formation of Cu@CuAlO2-Al2O3 nanoparticles was observed initially by the change in color of the colloidal samples from colorless to brown. Fourier transform infrared spectroscopy (FTIR) confirmed the presence of bonds between polymer chains and the metal surface at all radiation doses. Results of transmission electron microscopy (TEM), energy dispersive X-ray spectrometry (EDX), and X-ray diffraction (XRD) showed that Cu@CuAlO2-Al2O3 nanoparticles are in a core-shell structure. By controlling the absorbed dose and precursor concentration, nanoclusters with different particle sizes were obtained. The average particle diameter increased with increased precursor concentration and decreased with increased dose. This is due to the competition between nucleation, growth, and aggregation processes in the formation of nanoclusters during irradiation.

Fractionation and incipient self-granulitization during deep-crust emplacement of Lower Ordovician Valle Fértil batholith at the Gondwana active margin of South America

Large granite batholiths were emplaced at the Gondwana active margin during Lower Ordovician in South America. These have contributed to crustal growth by net addition of silicic rocks to the continental crust. New U–Pb SHRIMP zircon age determinations, together with thermobarometric and geochemical data, yield that batholith magma intrusion is the responsible of heating and self-granulitization of early gabbro pulses. Partially molten granulitic gabbros, which appear as either early intruded into the metasedimentary host or as large inclusions within the batholith-forming Qtz-diorites, contain Opx-bearing, trondhjemitic leucosomes surrounding Hbl+Opx+Pl mafic mesosomes forming typical agmatitic structures. Hornblende–Plagioclase equilibria, applied to mineral pairs of granoblastic aggregates in textural equilibrium of metagabbro mesosomes, yield temperatures in the range 850–910°C for core-to-core pairs and in the range 1000–1075°C for rim-to rim pairs, at pressures of about 0.7GPa. SHRIMP zircon age revealed that the whole batholith was emplaced over a narrow time interval of 20Ma from 465 to 485Ma, with most ages clustered at about 470Ma. The age of metagabbros is 473±7Ma for older zircons and 454±4 for younger zircons. These ages are almost coincident within error with the age of host migmatites (477±5Ma) and those of batholith intrusion of 476±9Ma and 475±3Ma for Qtz-diorites and 475±5Ma for granites. Zircon overgrowths of these intrusive rocks yield sages clustered around 450Ma, revealing a protracted thermal history, more complex than previously believed. The geochemical study reveals that Qtz-diorites, tonalites and granodiorites form a continuous trend produced by magmatic fractionation from a parental dioritic magma. A weak adakitic tendency, with Sr/Y>15 in several samples, implies the presence of Grt in the source or magma chamber at a minimum pressure of 1.0GPa, higher than the depth of emplacement at 0.7GPa. The high temperature of magma emplacement, which induced the incipient self-granulitization of early magmatic pulses, together with the cotectic-like fractionation linking coeval Qtz-diorites, tonalites and granodiorites, is compatible with fractionation at the lower crust of a deep-generated, infracrustal, (sublithospheric?) intermediate magma.

Design and Construction of a Slow Positron Beam for Solid and Surface Investigations

On the basis of the design and construction of the slow positron beam SPONSOR at the Helmholtz-Centre Dresden-Rossendorf an example is given how to build-up a simple slow positron beam for solid surface investigations within a short time and without high financial costs. The system uses a 22Na source and consists of three main parts: (1) the source chamber with a thin film tungsten moderator used in transmission, and a pre-accelerator stage, (2) the vacuum system with magnetic transport, a bent tube for energy selection and an accelerator, (3) the sample chamber with a sample holder, Ge detectors and (4) facilities for remote control and data acquisition. These parts are described in detail. The paper is preferentially addressed to beginners in the field of slow positron beam techniques and other readers being generally interested in positron annihilation spectroscopy.

Influence of dose and ion concentration on formation of binary Al–Ni alloy nanoclusters

Colloidal Al–Ni nanoclusters were prepared in an aqueous polyvinyl alcohol solution containing aluminum chloride and nickel chloride as metal precursors, polyvinyl alcohol as a capping agent, isopropanol as a scavenger of hydroxyl radicals, and distilled water as a solvent. Gamma irradiations were carried out in a 60Co gamma source chamber at doses up to 100kGy. The nanocluster properties were characterized by transmission electron microscopy (TEM), UV–visible spectrophotometry, and X-ray diffraction (XRD). By controlling the dose and precursor concentration, nanoclusters with different particle sizes were obtained. The average particle diameter increased with increase of precursor concentration and decreased with increase of dose. This is owing to the competition between nucleation, growth, and aggregation processes in the formation of nanoclusters during irradiation.