Positive Hydrogen Ions Research Articles

First Principles Calculations Study of Lithium-Montmorillonite for Humidity Sensor Application

In this study, we performed calculations on the water molecule adsorbed on lithium montmorillonite using first principles-calculation by means of electronic-structure calculation, with emphasis on approaches based on Density Functional Theory (DFT). The mechanism of water molecule adsorption on the surface of lithium-montmorillonite was investigated from the electronic structure point of view to seek the possibility of using montmorillonite as humidity sensor. The effects of the Van der Waals force to the electronic properties of water molecule on the surface of montmorillonite was also considered and obtained that the structure is more stable energetically. The interaction of water molecule with surface of montmorillonite yields the rotation of the hydrogen atoms of water molecule due to the occurrence of repulsive interaction between two positive ions of hydrogen of water molecule and lithium. From the calculations, lithium-montmorillonite can be considered as a good material for humidity sensor application since there is an electrical change observed even though it is a relatively small that is 0.657 eV.

Negative ion production and beam extraction processes in a large ion source (invited).

Recent research results on negative-ion-rich plasmas in a large negative ion source have been reviewed. Spatial density and flow distributions of negative hydrogen ions (H(-)) and positive hydrogen ions together with those of electrons are investigated with a 4-pin probe and a photodetachment (PD) signal of a Langmuir probe. The PD signal is converted to local H(-) density from signal calibration to a scanning cavity ring down PD measurement. Introduction of Cs changes the slope of plasma potential local distribution depending upon the plasma grid bias. A higher electron density H2 plasma locally shields the bias potential and behaves like a metallic free electron gas. On the other hand, the bias and extraction electric fields penetrate in a Cs-seeded electronegative plasma even when the electron density is similar. Electrons are transported by the penetrated electric fields from the driver region along and across the filter and electron deflection magnetic fields. Plasma ions exhibited a completely different response against the penetration of electric fields.

A collisional radiative model of hydrogen plasmas developed for diagnostic purposes of negative ion sources.

A collisional radiative model of low-pressure hydrogen plasmas is elaborated and applied in optical emission spectroscopy diagnostics of a single element of a matrix source of negative hydrogen ions. The model accounts for the main processes determining both the population densities of the first ten states of the hydrogen atom and the densities of the positive hydrogen ions H(+), H2 (+), and H3 (+). In the calculations, the electron density and electron temperature are varied whereas the atomic and molecular temperatures are included as experimentally obtained external parameters. The ratio of the Hα to Hβ line intensities is calculated from the numerical results for the excited state population densities, obtained as a solution of the set of the steady-state rate balance equations. The comparison of measured and theoretically obtained ratios of line intensities yields the values of the electron density and temperature as well as of the degree of dissociation, i.e., of the parameters which have a crucial role for the volume production of the negative ions.

Adjustable ECR Ion Source Control System: Ion Source Hydrogen Positive Project

ISHP (Ion Source Hydrogen Positive) project consists of a highly versatile ECR type ion source. It has been built for several purposes, on the one hand, to serve as a workbench to test accelerator related technologies and validate in-house made developments, at the first stages. On the other hand, to design an ion source valid as the first step in an actual LINAC. Since this paper is focused on the control system of ISHP, besides the ion source, all the hardware and its control architecture is presented. Nowadays the ion source is able to generate a pulse of positive ions of Hydrogen from $2~\mu\hbox{s}$ to a few $ms$ range with a repetition rate ranging from $1~Hz$ to $50~Hz$ with a maximum of $45~mA$ of current. Furthermore, the first experiments with White Rabbit (WR) synchronization system are presented.

The role of emulsion properties and stability in vegetable oil uptake by regranulated cork sorbents

BACKGROUND This work presents a novel approach to the understanding of electrostatic phenomena and sorbate–sorbent interactions in oil sorption. The study focuses on sorption of sunflower oil onto regranulated cork granules as promising natural sorbents. RESULTS It was shown that lowering the pH caused neutralization of negative surface charge by the positive hydrogen ions, leading to a reduction in the negative value of ζ-potential, and further destabilization of the emulsion, and an increase in oil and grease (O&G) uptake by cork granules. The effect of ionic strength was studied using a 3-level, 2-factor (32) full factorial design with O&G removal efficiency as the response variable. Linear effects of NaCl concentration, pH, and their interaction were found to be statistically significant (P < 0.05). Higher salt concentrations enhanced O&G removal due to double layer compression. Kinetic and equilibrium studies showed that the sorption process could be well described by a mechanism of partitioning governed by the external film fluid resistance. CONCLUSION In the conditions of 0.2 mol L−1 NaCl and pH 6, a mass transfer model adequately predicted oil removal of emulsions with approximately 140 mg L−1 O&G to values below discharge limits using 1.6 g L−1 of cork granules. © 2015 Society of Chemical Industry

Production of negative hydrogen ions on metal grids

Negative hydrogen ions are produced on a nickel grid with positive-ion irradiation. In order to investigate the production mechanism, a copper grid without the chemisorption of hydrogen atoms and positive helium ions without negative ionization are used for comparison. Positive hydrogen ions reflected on the metal surface obtain two electrons from the surface and become negatively ionized. It is found that the production yield of negative ions by desorption ionization of chemisorbed hydrogen atoms seems to be small, and the production is a minor mechanism.

Angle-resolved intensity and energy distributions of positive and negative hydrogen ions released from tungsten surface by molecular hydrogen ion impact

Hydrogen ion reflection properties have been investigated following the injection of H+, H2+ and H3+ ions onto a polycrystalline W surface. Angle- and energy-resolved intensity distributions of both scattered H+ and H− ions are measured by a magnetic momentum analyzer. We have detected atomic hydrogen ions reflected from the surface, while molecular hydrogen ions are unobserved within our detection limit. The reflected hydrogen ion energy is approximately less than one-third of the incident beam energy for H3+ ion injection and less than a half of that for H2+ ion injection. Other reflection properties are very similar to those of monoatomic H+ ion injection. Experimental results are compared to the classical trajectory simulations using the ACAT code based on the binary collision approximation.

A collisional radiative model for low-pressure hydrogen–caesium plasmas and its application to an RF source for negative hydrogen ions

A collisional radiative (CR) model for caesium in low-temperature, low-pressure hydrogen–caesium plasmas is introduced. This model includes the caesium ground state, 14 excited states, the singly charged caesium ion and the negative hydrogen ion. The reaction probabilities needed as an input are based on literature data, using some scaling and extrapolations. Additionally, new cross sections for electron collision ionization and three-body recombination have been calculated.The relevance of mutual neutralization of positive caesium ions and negative hydrogen ions is highlighted: depending on the densities of the involved particle species, this excitation channel can have a significant influence on the population densities of excited states in the caesium atom. This strong influence is successfully verified by optical emission spectroscopy measurements performed at the IPP prototype source for negative hydrogen ions.As a consequence, population models for caesium in electronegative low-temperature, low-pressure hydrogen–caesium plasmas need to take into account the mutual neutralization process. The present CR model is an example for such models and represents an important prerequisite for deducing the total caesium density in such plasmas.

Formation of anions and cations via a binary-encounter process inOH++ Ar collisions: The role of dissociative excitation and statistical aspects

Molecular fragmentation leading to the formation of negatively and positively charged hydrogen ions in 7-keV ${OH}^{+}$ + Ar collisions is investigated experimentally. The most striking finding is that negative and positive hydrogen ions are emitted with very similar angular dependences. Also, the kinetic energy distribution of the ${H}^{+}$ fragment shows strong similarities with that of the ejected ${H}^{\ensuremath{-}}$ ion. The kinematics of the emitted H core is found to be essentially driven by its scattering on the atomic target. However, in addition to this binary-encounter process, dissociative electronic excitation of the molecular projectile has to be invoked to explain the observed fragmentation patterns. Though the electron capture process is complex, it is shown that the relative population of the different final charge states of the outgoing fragments can be described by simple statistical laws.

Model of the behavior of MOS structures under ionizing irradiation

A quantitative model describing the behavior of MOS structures under ionizing irradiation is developed. The model is based on the capture of holes by hydrogen-containing traps. Some traps are charged and thus form a positive space charge in the insulator. The other traps decay to release positive hydrogen ions. These ions migrate in the insulator electric field to the insulator-semiconductor interface, where they depassivate surface states. The charging of surface states both under irradiation and during measurement of the threshold voltage is taken into account.

Effects of roughness and temperature on low-energy hydrogen positive and negative ion reflection from silicon and carbon surfaces

Angle-resolved energy distribution functions of positive and negative hydrogen ions produced from a rough-finished Si surface under 1 keV proton irradiation have been measured. The corresponding distribution from a crystalline surface and a carbon surface are also measured for comparison. Intensities of positive and negative ions from the rough-finished Si are substantially smaller than those from crystalline Si. The angular distributions of these species are broader for rough surface than the crystalline surface. No significant temperature dependence for positive and negative ion intensities is observed for all samples in the temperature range from 300 to 400 K.

Development progresses of radio frequency ion source for neutral beam injector in fusion devices

A large-area RF (radio frequency)-driven ion source is being developed in Germany for the heating and current drive of an ITER device. Negative hydrogen ion sources are the major components of neutral beam injection systems in future large-scale fusion experiments such as ITER and DEMO. RF ion sources for the production of positive hydrogen (deuterium) ions have been successfully developed for the neutral beam heating systems at IPP (Max-Planck-Institute for Plasma Physics) in Germany. The first long-pulse ion source has been developed successfully with a magnetic bucket plasma generator including a filament heating structure for the first NBI system of the KSTAR tokamak. There is a development plan for an RF ion source at KAERI to extract the positive ions, which can be applied for the KSTAR NBI system and to extract the negative ions for future fusion devices such as the Fusion Neutron Source and Korea-DEMO. The characteristics of RF-driven plasmas and the uniformity of the plasma parameters in the test-RF ion source were investigated initially using an electrostatic probe.

Thermal distribution of a carbon foil used to extract a 30-MeV proton beam

Modern cyclotron technology employs negative hydrogen (H−) ion acceleration and positive hydrogen (H+) ion (proton) extraction using a carbon foil, which strips two electrons. The stripping efficiency depends on the thickness of the carbon foils. Typically, a 100-µg/cm2 carbon foil extracting 30-MeV protons at beam currents up to 250 µ A has a lifetime of ∼120 h (∼30,000 µAh accumulated current). However, the lifetime was found to be short when the cooling was poor during beam irradiation. Therefore, the high thermal power dissipated in the foil by charged particles (both protons and electrons) will be a serious problem for high current extractions during long-run operation. In this research, the thermal distribution of carbon foils for both protons and electrons is analyzed for extracting proton currents up to 1 mA. An optimized carbon foil will be discussed for the sake of extending lifetime expected ∼100 hours or longer at a 1-mA extraction. Thickness ranges of the strippers from 10 to 1,000 µg/cm2 are investigated by estimating the peak temperatures reached on the foils during proton-beam extraction. Reducing the peak temperatures calculated by modeling may be possible by decreasing the foil thickness, enlarging the beam size, and effectively reducing the ion-induced heat.

Identification of the extraction structure of H− ions by Hα imaging spectroscopy

Extraction structure of negative hydrogen ions (H−) (i.e. the regions where H− ions are effectively extracted from the plasma) was obtained using hydrogen Balmer-α (Hα) imaging spectroscopy and cavity ring-down spectroscopy. The H− ion density increases after caesium (Cs) seeding through a surface conversion process on a Cs-covered plasma-grid (PG) surface. We found a reduction in the H− density during beam extraction after Cs conditioning, and the same signal reduction appeared in the Hα intensity caused by the reduction in the excited hydrogen (n = 3) population, which in turn is caused by the decrease in the mutual neutralization process between positive and negative hydrogen ions. We clearly observed the reduction structure of the Hα emissions in the extraction region; the structure expands at optimal Cs conditioning. From this result, the H− ions, which are produced at the PG surface, release to the extraction region and widely distribute during arc discharge. We conclude that the reduction of the H− density is caused by the particle loss due to beam extraction from the PG apertures.

Hydrogen ions produced by plasma-assisted catalytic ionization using nickel grid

Positive and negative hydrogen ions are produced by plasma-assisted catalytic ionization using a nickel grid, where the irradiation current density of positive ions onto the grid can be controlled by the discharge power. The irradiation energy can be controlled by both the grid potential and the discharge plasma potential. Extraction properties and energy distributions of positive and negative ions produced in the cases of using the grid and a porous nickel plate are compared. Two production mechanisms of negative ions are found in the process of plasma-assisted catalytic ionization.

Separation of ion components produced by plasma-assisted catalytic ionization

Positive and negative hydrogen ions are produced by plasma-assisted catalytic ionization using a porous nickel plate, where the irradiation current density and energy of positive ions produced by discharge to the porous plate are controlled. The ion energy distributions are analyzed from the properties of current densities of positive and negative ions extracted from the porous surface. Positive ions passing through fine pores of the porous plate and positive and negative ions produced on the porous surface are observed. It is clarified that the produced fluxes of positive and negative ions and the flux balance between them are controlled by the irradiation current density and energy, respectively.

PIC code for the plasma sheath in large caesiated RF sources for negative hydrogen ions

Powerful negative hydrogen ion sources are required for heating and current drive at ITER. The physics of the production and extraction of high negative ion currents is much more complex than that for positive ions. One of the most relevant parameters is the shape of the plasma sheath, which determines the velocity of surface produced negative ions and thus the probability of the ions to reach the extraction system. In order to investigate the influence of hydrogen atoms, positive and negative hydrogen ions and positive caesium ions on the plasma sheath, a 1d3v particle in cell code (PIC) code for the plasma close to the extraction system has been developed. For typical plasma parameters of such ion sources, surface conversion of impinging atoms is the main negative ion production channel, while conversion of positive ions plays a minor role. Due to the formation of a potential minimum close to the surface, the emission of negative ions into the plasma is space charge limited. As a consequence, the flux of negative ions can be increased only by increasing the density of positive hydrogen ions. At identical plasma parameters, an isotope effect is determined by the mass of the particles only, resulting in lower fluxes of negative deuterium ions compared with hydrogen. A small amount of positive Cs does not change the plasma sheath and the H− flux significantly.

Design of an ion extractor system for a prototype ion source experiment for SST-1 neutral beam injector

An ion extractor system has been designed for the steady state superconducting tokamak (SST-1) neutral beam injector (NBI) for an experiment using a prototype ion source with fully integrated regulated high voltage power supply (RHVPS) and data acquisition and control system (DACS) developed at Institute for Plasma Research (IPR) to obtain experience of NB operation. The extractor system is capable of extracting positive hydrogen ion beam of ∼10 A current at ∼20 kV. This paper presents the beam optics study for detailed design of an ion extraction system which could meet this requirement. It consists of 3 grid accel– decel system, each of the grid has 217 straight cylindrical holes of 8 mm diameter. Grids are placed on a specially designed G-10 block; a fiber reinforc plastic (FRP) isolator of outer diameter of 820 mm and 50 mm thickness. Provisions are made for supplying high voltage to the grid system through the embedded feed-throughs. Extractor system has been fabricated, mounted on the SST-1 neutral beam injector and has extracted positive hydrogen ion beam of 4 A at 20 kV till now.

Hydrogen distribution in titanium materials with low outgassing property

This paper addresses a hydrogen outgassing mechanism in titanium materials with extremely low outgassing property by investigating hydrogen atoms distribution in depth around the surface in a titanium material and stainless steel. The evacuation time dependence of depth profiles of positive hydrogen ions was measured by time-of-flight secondary ion mass spectrometry (TOF-SIMS). In the stainless steel, concentration of hydrogen atoms decreases slowly at the surface oxide layer, while it decreases rapidly in the bulk by vacuum evacuation. Thus, the surface oxide layer is considered to prevent hydrogen diffusions in the bulk. On the other hand, in the titanium material, hydrogen atoms show maximum concentration at the boundary between the surface oxide layer and the bulk titanium. Moreover, concentration of hydrogen atoms decreases rapidly at the surface oxide layer, while those decrease slowly in the deep region below the surface-bulk boundary by vacuum evacuation. It is suggested that the boundary between the surface oxide layer and bulk titanium plays a role of a barrier for bulk hydrogen diffusions. These facts give very low hydrogen concentration near the surface, which results in an extremely low outgassing rate in titanium materials.

Scattering of light molecules from thin Al 2O 3 films

Molecular oxygen and hydrogen ions were scattered at grazing incidence from various thin Al 2O 3 films. The energy of incident particles was varied from 390 to 1000 eV. For scattered positive oxygen ions, negative ion fractions of up to 17% were recorded. For scattered positive hydrogen ions, the negative ion fractions reached up to 2%. These findings qualify thin films of Al 2O 3 as possible candidates for use as charge state conversion surfaces in neutral particle sensing instruments, which will work in space.