Ion Collection Research Articles

Online analysis of gas-phase radical reactions using vacuum ultraviolet lamp photoionization and time-of-flight mass spectrometry

A home-made vacuum ultraviolet photoionization time-of-flight mass spectrometer has been developed and coupled to an atmospheric simulation chamber operated at atmospheric pressure and to a fast flow tube at low pressure (1-10 Torr). Gas sampling from the simulation chamber is realized directly via a capillary effusive beam, and sampling from the flow tube is via a continuous molecular beam inlet. Both devices are connected simultaneously to the ionization chamber of the mass spectrometer and can be switched in-between within minutes to study gas-phase radical reactions of atmospheric interest in a large range of reaction conditions and reaction times (from milliseconds in the flow tube to hours in the simulation chamber). A cage-shaped photoionization source combined with a commercial 10.6 eV krypton lamp has been developed to provide a high ion collection efficiency along the long light path in the cage. This way, a multiplexed detection with high sensitivity down to the sub-parts per billion volume concentration range, e.g., a limit of detection of 0.3 ppbv with an accumulation time of 60 s for benzene and 1.3 ppbv for the methyl radical, is obtained. The performance and suitability of the setup are illustrated by the study of the chlorine-initiated oxidation reaction of toluene in the atmospheric simulation chamber and in the fast flow tube. Stable products and reactive intermediates have been well-determined and their reaction dynamics are discussed.

Target normal sheath ion acceleration by fs laser irradiating metal/reduced graphene oxide targets

Target normal sheath ion acceleration is applied with a high contrast fs laser irradiating advanced targets based on thin metallic films (Al, Cu, Ag and Au) covering micrometric foils of reduced graphene oxide (rGO). The laser intensity is of about 1018 W/cm2 and the laser focal position with respect to the target surface is optimized to have the maximum proton acceleration. Plasma diagnostics are investigated using time-of-flight technique employing SiC detectors, ion collectors, and gaf-chromic films. Micrometric aluminum absorbers were employed to separate the faster proton detection by other accelerated ions. At the optimized laser focal position, the maximum proton acceleration of 2.5 MeV and 3.0 MeV energy was obtained using Ag(200 nm) and Au(200 nm) covering rGO(7 μm) targets, respectively. The high proton energy is due to the high electrical and thermal conductivity and high mechanical resistance of the used rGO foils and to the high plasma electron density of the target.

Characterization of an extrapolation chamber in beta radiation beams and Monte Carlo modelling

At the Calibration Laboratory (LCI) of the IPEN/CNEN, studies are in development on the establishment of a standard composed by the beta radiation sources for the dosimetry and calibration for personal monitoring in Brazil. For this purpose is used the Böhm extrapolation chamber (PTW model 23392). This chamber was already characterized at LCI in 90Sr/90Y beams using two different entrance windows: one of aluminized Mylar and another of PET (polyethylene terephthalate) known as Hostaphan. In this work, this extrapolation chamber was characterized in 85Kr and 147Pm beams. All tests were carried out with the reference 90Sr /90Y source, for comparison purposes. The Monte Carlo code MCNP5 code was used to obtain an extrapolation chamber and the BSS2 system sources computational model, based on the determination of the absorbed dose rate. Saturation curves, ion collection efficiency, ion recombination, polarity effect, stability of response, null depth, linearity of response, variation of response as a function of source-detector distance, extrapolation curves, correction factors and absorbed dose rates were obtained. The difference between the experimental absorbed dose rates and those obtained using the Monte Carlo model, compared to those from the calibration certificates, was less than 1.9% for the 108 histories for each BSS2 system source. All results of the performed tests are within the limits of the international recommendations. The results for the 90Sr/90Y source were in good agreement with previous works performed at LCI. These results are suitable for the establishment of a standard instrument for the dosimetry and calibration of beta radiation sources and detectors in the LCI/IPEN. This standard will allow the calibration of detectors in beta radiation beams in dosimetry services in Brazil.

(py)LIon: A package for simulating trapped ion trajectories

The (py)LIon package is a set of tools to simulate the classical trajectories of ensembles of ions in electrodynamic traps. Molecular dynamics simulations are performed using LAMMPS, an efficient and feature-rich program. (py)LIon has been validated by comparison with the analytic theory describing ion trap dynamics. Notable features include GPU-accelerated force calculations, and treating collections of ions as rigid bodies to enable investigations of the rotational dynamics of large, mesoscopic charged particles. Programme summaryProgram Title: (py)LIonProgram Files doi:http://dx.doi.org/10.17632/ywwd9nnxjh.1Licencing provisions: MITProgramming language: Matlab, PythonSubprograms used: LAMMPSNature of problem: Simulating the dynamics of ions and mesoscopic charged particles confined in an electrodynamic trap using molecular dynamics methodsSolution method: Provide a tested, feature-rich API to configure molecular dynamics calculations in LAMMPSUnusual features: (py)LIon can treat collections of ions as rigid bodies to simulate larger objects confined in electrodynamic traps. GPU acceleration is provided through the LAMMPS ▪ package.

D2EHPA is a potential extractant for extraction of europium and samarium from chloride medium

Europium and samarium, the most valuable rare earth metals are broadly used in different areas such as fluorescent, medical materials and samarium-cobalt permanent magnet in the industrial community. Solvent extraction is an extensively applied separation process for collection of high purity rare earth metal ions. Due to the congruent physical and chemical properties of rare earth metal ions, the separation of specific elements from the mixture is ambiguous. In such places solvent extraction process is most efficient because of their ease in terms of the equipment and conditions associated with them. Solvent extraction, using di-2-ethylhexylphosphoric acid (D2EHPA) is the most frequently used industrial extractant for the extraction and separation of rare earth metal ions compared with other extractants. Present report deal with the studies on solvent extraction of europium (III) and samarium (III) from chloride medium using D2EHPA diluted in kerosene. Utmost extraction such as 96.65% Eu(III) and 86% Sm(III) happened at 0.001 mol/L hydrogen ion concentration in the aqueous medium. 100% extraction of Eu (III) and Sm(III) has been noticed with 0.07 mol/L and 0.08 mol/L D2EHPA, respectively. The separation factors of Eu/Co and Sm/Co are 1844.44 and 1556, respectively.

Beam energy recovery for fusion and collector design for tests on compact sources

The next fusion project DEMO, which will be the evolution of the experimental fusion reactor [International Tokamak Experimental Reactor (ITER)], would require a high efficient energy production. As in ITER, DEMO will use fast Neutral Beam (NB) injectors to increase the plasma temperature needed for the fusion reaction. A way to recover the electric energy production efficiency in DEMO could be the beam energy recovery in the NB production, which is produced by a D- beam, neutralized by a gas cell with 60% efficiency. A compact energy recovery device with an axisymmetric cylindrical ion collector that uses only decelerating electric fields combined with the beam space charge effect has been recently proposed. It can be used for a test on the beam of the NIO1 (Negative Ion Optimization 1) source, a compact ion source (scaled down from ITER size sources) that has been developed at INFN-LNL and Consorzio RFX (Padua). The detailed collector design to be used on one of the beamlets of the NIO1 source within typical space limitation is presented and discussed here. Furthermore, a preliminary trajectory simulation for a beam with a rectangular geometry similar to the beam used in ITER to verify the beam recovery for a nonaxial symmetric geometry is also shown.

Satellite formation flying control using an innovative technique subject to electromagnetic acceleration

The electrostatic charge became a possible method to control both orbital and attitude motion without fuel consumption or reduce the fuel cost. This study needs to install an ion collector on the satellite to increase the level of charging as artificial charging. In this paper, we developed a linearised satellite relative motion and a combination of Lorentz forces provided by modulating spacecraft's electrostatic charge (magnetic and electric fields) that can be used to keep the desired relative distances and orientations considering J2 perturbation. The proposed controller contains a feedback control using a real-time fuel-optimal control approach is considered for satellite formation control in eccentric orbits based on the developed linear J2 dynamic model. Comprehensive simulation numerical results confirmed the capability of Lorentz force to correct the drift in the relative position of formation flying due to the effect of J2, these corrections depend on the value of charge to mass ratio and magnitude of the relative position.

Simulation of motion of many ions in a linear Paul trap

The quadrupole linear Paul trap is one of the key instruments in building highly stable atomic clocks. However, a frequency reference based on a single trapped ion is limited in stability due to the time needed for the interrogation cycle which cannot be further shortened. A promising strategy is the utilization of multiple trapped ions. The ions of the same kind then repulse each other with the Coulomb force, which is countered by the ponderomotive force of the time depended field in the trap. A few ions form a chain along the axis of a linear Paul trap. Adding more ions (a few tens or hundreds) gives rise to Coulomb crystals. We created an efficient simulation code which calculates the motion of such collections of ions in quasi-static radiofrequency fields of real linear quadrupole traps (including the micromotion). We include a model for laser cooling of the ions. The simulation tool can be used to study the formation and the dynamics of Coulomb crystals under conditions corresponding to various experimental setups.

Drones in Disaster Management and Humanitarian Action: A Case Study in The Aftermath of Nepal Earthquake 2015

Nepal ranks 6th, 11th and 30th in the list of countries vulnerable in terms of risk from climate change, earthquake and flood respectively. Frequent multi-disasters in a difficult terrain makes disaster management a challenge, and up-to-date geo-information plays a critical role in proper disaster management. Unmanned Aerial Vehicle (UAV) enables quicker geoinforma t ion collection compared to traditional surveying methods, hence leading to efficient disaster management. UAVs were introduced in Nepal in the aftermath of the April 2015 Earthquake. An unprecedented number of small and lightweight UAVs were flown over highly damaged areas and heritage sites by journalists and humanitarian responders to assist in immedia te rescue, relief, and reconstruction efforts. However, risks to national security by the unregula ted use of drones was realized by the Government of Nepal and the Ministry of Home Affairs, and hence they released a guideline that controlled the use of UAVs through a thoroughly difficult permission procedure. This vastly limited the use of drones in Nepal and increasing adoption of the technology for humanitarian causes also slowed down rapidly. However, increasing demand has recently led to a revised Drone Flight Guidelines 2075 that now provides authorit y to local governments to grant permissions through easier processes for lightweight drones thus encouraging good usages of drones. This paper attempts to identify, analyze and document the social applications of Drone technology in Nepal and highlights the specific use of Drones in post-earthquake reconstruction of damaged buildings, hydropower projects, landslide mapping, aerial surveillance during disasters, rescue efforts, delivery of medicines and health supplies in rural areas and many more. It also reflects the change in perception of the government towards drone technology.International Journal of Human and Health Sciences Supplementary Issue: 2019 Page: 19

Determination of the Average Energy of Iron Ions in the Axial Direction of a Micropinch Discharge Using an Ion Collector

The paper is devoted to determining the average ion energy for plasma propagating in the axial direction of a high-current low-inductance vacuum spark discharge in the Pion facility. The measurements have been carried out using an ion collector. The average energy of singly of singly charged iron ions depending on the voltage across the interelectrode gap is determined.

Efficient isotope-selective pulsed laser ablation loading of 174Yb+ ions in a surface electrode trap.

We report a highly efficient loading of 174Yb+ ions in a surface electrode ion trap by using single pulses from a Q-switched Nd:YAG laser to ablate neutral atoms, combined with a two-photon photo-ionization process. The method is three orders of magnitude faster to load a single ion as compared to traditional resistively heated sources and can load large collections of ions in seconds. The negligible thermal load of this method enables the use of this ablation-based loading scheme in ion traps operating under cryogenic conditions.

Ion-beam Investigation in a 1.5-kJ Dense Plasma Focus Device

An investigation of energetic ion beam emission from a low-energy (1.5 kJ) Mather-type plasma focus (PF) device operating with argon gas is studied with an operating pressure ranging from 2 × 10−2 to 1 Torr. The device has been energized by 30.84-μF capacitors charged up to 10 kV, giving a peak discharge current up to 120 kA with a rise time of 3 μs. A Faraday cup (FC) and its operation has been studied. This device is utilized to perform time-of-flight (TOF) measurements in order to characterize the beams of charged particles. The FC is placed at 20 cm from the tip of anode electrode at 0° with respect to anode axis to detect the ions. The FC operating in bias ion collector mode has been developed for measuring and characterizing pulsed ion beam. Energy and velocity of ions are determined with the TOF method, taking into account distance from the center electrode to the detection plane. The surface morphology of the pristine and irradiated ZnOCo0.04 samples is investigated as imaged by scanning electron microscope (SEM). The untreated sample showed rather relatively smooth surface; meanwhile, the SEM micrographs of bombarded samples display numerous small voids on the surface of the ZnOCo0.04 samples as a result of ion beam emission from PF device. X-ray fluorescence analysis showed that there are some new elements appeared on the surface of the sample after exposed to the ion beam; these elements and their concentrations are recorded. The surface roughness values for the pristine and the irradiated ZnOCo0.04 sample with Ar ion beam at different plasma shots are measured. A Vickers microhardness tester is used to measure the surface hardness, and the results demonstrate a significant increase in the hardness depending on the ion dose and decreases by increasing the applied load at 0° angular position.

Energy-and-pitch-angle-resolved escaping beam ion measurements by Faraday-cup-based fast-ion loss detector in Wendelstein 7-X

With the objective of understanding the energetic-particle loss mechanism in three-dimensional plasmas, a Faraday-cup-based fast-ion loss detector (FILD) was developed and installed in OP1.2b in Wendelstein 7-X (W7-X) as a collaboration between the National Institute for Fusion Science and Max-Planck-Institute for Plasma Physics. The FILD, which consists of double apertures and thin aluminum foils, was based on a magnetic spectrometer using the magnetic field of the fusion device. The double aperture limits the thermal ion, but allows the energetic ion to enter the FILD box. The thin aluminum foils serve as the ion collector. Orbit-following calculations were performed in order to find a suitable position for the FILD. The results indicated that barely co- and counter-going transit ions reached the FILD position mounted on the multi-purpose manipulator installed on W7-X. Moreover, because the injection angle of neutral beams injector installed on W7-X was relatively perpendicular, the target range of pitch angle was set to from 91 degrees to 150 degrees. An energy-and-pitch-angle map was created using a grid calculation code in order to decide on the position/size of aperture and aluminum foil. The grid calculation code indicates the position where the energetic ion would strike on the aluminum foil. Here, the map was used as the basis for designing an aluminum foil pattern with two energies and four pitch angle ranges. Also, note that the lower energy range was designed so that it accommodates a neutral beam injection energy of 55 kV. Measurements of beam ion losses were performed in neutral beam (NB) blip experiments, where concurrent increases and decreases of barely co-going transit beam ion losses due to NB injections were observed. Furthermore, this study validated that the FILD installed on a midplane manipulator probe is capable of probing a range of radii spanning 1.0–1.5 cm, over which the beam ion loss current would vary significantly.

(Invited) Particle Formation Mechanisms in Low Temperature Plasmas

Low temperature plasmas, in particular when they are operated in molecular (organic) gases, are rather complex systems. Their distinct non equilibrium nature, characterized by low neutral gas temperatures (close to room temperature) and relatively high electron temperatures (easily reaching values up to several eV) make them a breeding place for a great variety of different species and depending on the precursor gas and the process conditions even a source for nanoparticles. The formation of nanoparticles has been observed in various discharge types operated in different kinds of gases or gas mixture as e.g.in silane, in fluorocarbons such as CF4 or C2F6 or in hydrocarbons as e.g. acetylene. The formation of nanoparticles in a plasma is either an unwanted side effect, occurring for example during the plasma based deposition of thin films (or the etching of microstructures) or it is the deliberate result of a process used e.g. for the production of nanoparticle deposits. In either way the understanding of the underlying mechanisms which are eventually responsible for the nanoparticle formation in low temperature plasmas is indispensable for the control of the whole process. However, the plasma based formation of nanoparticles is a rather complex procedure, which involves different plasma species, various timescales and several physical and chemical processes. The process starts with the dissociation of the original parent molecule due to electron impact reactions. These reactions are responsible for the initial formation of molecular fragments which can induce subsequent polymerization reactions leading by and by to the formation of larger and larger molecules and eventually to the formation of nanometer sized clusters. These initial protoparticles can further grow due to coagulation and/or accretion processes till they reach a size of some 10 nanometer. Once the particles have reached this size they become rapidly negatively charged and their further growth is mainly governed by the collection of positive ions and neutral radicals. In contrast to CVD processes which are mainly driven by neutral molecules and radicals plasma based processes involve also charged species, namely electrons and different kinds of ions. Depending on the precursor gas used for the given process this ionic component can include positive as well as negative ions. This contribution will focus on the nanoparticle formation in two exemplary systems: discharges operated in argon/acetylene and argon/aniline mixtures. While acetylene plasma are frequently used for the production of DLC films, the use of aniline discharges has been intensively studied for the (conformal) deposition of (ultra) thin polyaniline films or the production of polyaniline nanoparticle deposits. In particular the latter material class possess interesting potential applications in the field of biosensors and for the production of supercapacitors. Based on various in-situ plasma diagnostics (plasma ion mass spectroscopy, in-situ multi-pass FTIR spectroscopy, microvawe interferometry, laser light scattering and optical emission spectroscopy) and different discharge designs the particle formation in both systems is studied aiming to understand the underlying formation mechanisms in order to either promote or prevent the generation of nanoparticles. Special emphasis is paid to the role of the negative ion component. In non-pulsed discharges (low energy) negative ions are trapped in the positive plasma potential inside the plasma bulk and while not contributing to the flux of species reaching the wall of the plasma chamber they can be a dominant species inside the plasma volume. They may play therefore an important role in the initial formation of protoparticles i.e. in the early nucleation phase. Acknowledgments The authors would like to acknowledge the support obtained by the French National Research Agency via the project PlasmaBond. This work has received also funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 730872 (CALYPSO plus for the work at the HZB BESSY II synchrotron, Berlin) and under grant agreement No766894 FETOPEN project PEGASUS.

Application of Ion Sensitive Probe to High Density Plasmas in Magnum-PSI

Feasibility of an ion sensitive probe was evaluated in high electron density (> 5 × 1019 m−3) helium plasmas produced in the Magnum-PSI device. The ion sensitive probe showed that the ion temperature was ∼ 1 eV and almost equal to the electron temperature. Increasing the neutral pressure to efficiently lead to the electron-ion recombination processes, the electron currents were collected at the ion collector. A secondary electron emission in the guard electrode might have an effect on the ion current

Comparison of Langmuir probe and laser Thomson scattering for electron property measurements in magnetron discharges

Electron property measurements made by Langmuir probes and laser Thomson scattering have been compared in weakly magnetized plasma conditions using a planar unbalanced magnetron with the aim of assessing the accuracy of the probe diagnostic. The measurements were performed at several locations within the magnetic field configuration, the magnetic null region (≲1 mT) on the discharge axis and inside the last closed flux surface boundary with fields up to 33 mT. There was good diagnostic agreement during High Power Impulse Magnetron Sputtering, but significant discrepancies were observed for DC magnetron operation, even at the magnetic null. For some discharge conditions, the electron density determined by Thomson scattering was over an order of magnitude greater than the plasma density obtained from the Langmuir probe, using both ion and electron collection theories. In addition, the low energy part of the electron energy distribution function determined by the probe was depleted. The possible reasons for the discrepancies are discussed, with the conclusion being that the plasma was significantly perturbed by the probe stem. The range of plasma densities and electron temperatures measured in this study were 0.4–54 × 1017 m−3 and 0.2–5.9 eV, respectively.

Improving and optimizing the structure of a cylindrical ionization chamber for radiation protection dosimetry: Guard electrode and chamber wall

Due to relative ease, high accuracy, high sensitivity, appropriate response, and other properties of ionization chambers, they are usually employed as reference instruments in dosimetry and quality assurance programs. Therefore, any improvement and optimization in the structure of these dosimeters can lead to accurate measurements of the absorbed dose. In the present study, the structure of a specific cylindrical ionization chamber (PTW, model 23361, Freiburg, Germany) was improved and optimized. After the design and construction of the new cylindrical ionization chamber, the performance of this dosimeter was investigated by saturation, ion collection efficiency, polarization, leakage current, stability, and linearity of response tests. The findings of performance tests showed that the response of the introduced dosimeter agrees with the recommended standards. The new design and construction of the guard electrode, both in length and arrangement of the dosimeter structure, can improve the electric field and decrease the leakage current. Moreover, the use of pure graphite in the chamber's wall can result to improve in the electric field of the chamber's sensitive volume, thereby improving the performance of the dosimeter.

3D-Simulation of a Bayard Alpert ionisation gauge using SIMION program

Numerical simulation of a Bayard-Alpert ionisation gauge using SIMION 8.1 software is presented. Gauge sensitivity, being the most important parameter of an ionisation gauge, has been derived using two different approaches. In the first one, SIMION is used to determine mean length of electron trajectories, and ion collection efficiency. From these values, known ionisation cross sections and the gas temperature, the sensitivity can be readily calculated. In the second and more detailed approach, a Monte Carlo method was implemented in the Lua programming language to simulate electron impact ionisation of the gas. The Lua code is incorporated in the SIMION trajectory simulations, in which the ionisation event is modelled by transforming a primary electron into an ion. This approach evaluates the contribution of each trajectory to the gas ionisation. It considers energy dependence of the ionisation probability and the contribution of the electrons backscattered from the grid to the sensitivity. The simulation approaches were tested on the gauge geometry, recently modelled by the CERN group. Very good quantitative agreement with the CERN simulations was obtained using both approaches. Monte Carlo simulations reveal that the relative contribution of electrons backscattered from molybdenum grid to the sensitivity is about 14%.

Investigation of Coatings for Langmuir Probes: Effect of Surface Oxidation on Photoemission Characteristics

AbstractSurface oxidation of Langmuir probes is an important issue for probe measurements in space environments. Followed by our previous work about the oxidation effect on the collection of ambient plasma electrons and ions, here we present its effect on photoemission from the probe surface of various materials. Photoemission is either a contamination for traditional Langmuir probes or a necessity for electric field probes in low‐density plasma. Our results show that all materials after oxidation have a varying degree of reduction in photoemission. The photoemission of copper, gold, and niobium drops most significantly followed by DAG213 (a resin‐based graphite coating), TiN (titanium nitride), and rhenium. Iridium, DAG213, and AquaDAG (graphite coating) have the largest photoemission after oxidation, making them appropriate coating candidates for electric field probes. Both DAG materials show a large photoemission enhancement after the oxidation products are cleaned off the surface. A long exposure test shows that the photoemission from iridium slowly degrades. Due to the high surface conductivity of oxidized iridium shown in previous work, it is suggested that iridium can be oxidized before flight to minimize the photoemission when being used as a coating for Langmuir probes. Overall, iridium is found to be a coating material appropriate for both electric field probes and Langmuir probes.

Improved gating device of time-of-flight ion mass analyzer for ion sources.

A gating device is a critical component in a time-of-flight (TOF) ion mass analyzer for identifying ion species extracted from ion sources according to their mass-to-charge ratio. It consists of several concentric ring electrodes to deflect as many ions as possible within a very short gate time, thus increasing the ion current collected in a Faraday cup. In this study, we further improve the ion collection efficiency of the gating device by minimizing potential distortion along the paths of ions, by modifying the structure of gate electrodes and applying a bipolar gate pulse on them. Using the improved gating device, we find that the ion beam current increased by nearly 50% compared to the conventional one without changing the noise level. The improved TOF system is well applied to identify the spectrum of ion species extracted from a cold cathode Penning ion source, depending on the operating conditions.