Pulsed Ion Research Articles

Measurement of the Spatial Distribution of Ultracold Cesium Rydberg Atoms by Time-of-Flight Spectroscopy

We prepare nS (n = 49) cesium Rydberg atoms by two-photon excitation in a standard magnetooptical trap to obtain the spatial distribution of the Rydberg atoms by measuring the time-of-flight (TOF) spectra in the case of a low Rydberg density. We analyze the time evolution of the ultracold nS Rydberg atoms distribution by changing the delay time of the pulsed ionization field, defined as the duration from the moment of switching off the excitation lasers to the time of switching on the ionization field. TOF spectra of Rydberg atoms are observed as a function of the delay time and initial Rydberg atomic density. The corresponding full widths at half maximum (FWHMs) are obtained by fitting the spectra with a Gaussian profile. The FWHM decreases with increasing delay time at a relatively high Rydberg atom density (>5 × 107/cm3) because of the decreasing Coulomb interaction between released charges during their flight to the detector. The temperature of the cold atoms is deduced from the dependence of the TOF ...

Development and application of a gas chromatography method for simultaneously measuring H2 and CH4 in hydrothermal plume samples

AbstractA robust, simple and efficient gas chromatography (GC) method is presented for determining H2 and CH4 concentrations simultaneously in water samples. The GC system consists of one detector (pulsed discharge helium ionization detector—PDHID), two columns in two ovens, respectively, and two 2‐position‐6‐port purge valves. In this method, H2 and CH4 in water samples were first extracted into the headspace of syringes, then injected into the GC system. Both H2 and CH4 were detected by a PDHID. The separation of CH4 from O2 and N2 in seawater is achieved by switching the O2 and N2 out of the carrier gas flow at the appropriate time window. H2 and CH4 concentrations in water samples collected from hydrothermal plumes at the Southwest Indian Ridge were determined successfully using this method.

High-resolution ion pulse ionization chamber with air filling for the 222Rn decays detection

The construction and characteristics of the cylindrical ion pulse ionization chamber (CIPIC) with a working volume of 3.2L are described. The chamber is intended to register α-particles from the 222Rn and its daughter׳s decays in the filled air sample. The detector is less sensitive to electromagnetic pick-ups and mechanical noises. The digital pulse processing method is proposed to improve the energy resolution of the ion pulse ionization chamber. An energy resolution of 1.6% has been achieved for the 5.49MeV α-line. The dependence of the energy resolution on high voltage and working media pressure has been investigated and the results are presented.

Effective doping of low energy ions into superfluid helium droplets.

We report a facile method of doping cations from an electrospray ionization (ESI) source into superfluid helium droplets. By decelerating and stopping the ion pulse of reserpine and substance P from an ESI source in the path of the droplet beam, about 10(4) ion-doped droplets (one ion per droplet) can be recorded, corresponding to a pickup efficiency of nearly 1 out of 1000 ions. We attribute the success of this simple approach to the long residence time of the cations in the droplet beam. The resulting size of the doped droplets, on the order of 10(5)/droplet, is measured using deflection and retardation methods. Our method does not require an ion trap in the doping region, which significantly simplifies the experimental setup and procedure for future spectroscopic and diffraction studies.

Short intense ion pulses for materials and warm dense matter research

We have commenced experiments with intense short pulses of ion beams on the Neutralized Drift Compression Experiment-II at Lawrence Berkeley National Laboratory, by generating beam spots size with radius r<1mm within 2ns FWHM and approximately 1010 ions/pulse. To enable the short pulse durations and mm-scale focal spot radii, the 1.2MeV Li+ ion beam is neutralized in a 1.6-meter drift compression section located after the last accelerator magnet. An 8-Tesla short focal length solenoid compresses the beam in the presence of the large volume plasma near the end of this section before the target. The scientific topics to be explored are warm dense matter, the dynamics of radiation damage in materials, and intense beam and beam-plasma physics including selected topics of relevance to the development of heavy-ion drivers for inertial fusion energy. Here we describe the accelerator commissioning and time-resolved ionoluminescence measurements of yttrium aluminum perovskite using the fully integrated accelerator and neutralized drift compression components.

Evaluation of the applicability of four different radon measurement techniques for monitoring CO2 storage sites

Four different techniques for measuring radon activity in soil gases were analyzed in the natural analogue of Campo de Calatrava, Spain, to study its application in superficial monitoring of CO2 storage sites. The following methods were applied: (i) alpha spectroscopy monitors (SARAD, model RTM-2100), (ii) pulse ionization chamber detector (RADON v.o.s. model RM-2), (iii) solid-state nuclear track (CR-39) detectors and (iv) Lucas cell detectors (EDA model RD-200). Measurement protocols and selection criteria were defined according to the different phases of a CCS project, i.e., pre-injection, injection and post-injection.Radon measurements and CO2 fluxes were determined at 36 points around a natural CO2 leak. The concentrations of 222Rn in the soil gases by ionization chamber detectors (RM-2) and alpha spectrometry monitors (SARAD RTM-2100) showed consistent data, whereas passive detectors (CR-39) did not produce realistic 222Rn activity values although anomalous concentrations related to the CO2 leak were recognized. This implies that the latter can be used to create a control grid to estimate whether an increase of radon concentration due to a possible CO2 leak occurs. The Lucas cell (EDA RD-200) produced the greatest analytical uncertainty and, in the present configuration, this method appears the least appropriate for monitoring CO2 storage sites.

SU‐E‐J‐138: On the Ion Beam Range and Dose Verification in Hadron Therapy Using Sound Waves

Purpose:Accurate range verification is of great importance to fully exploit the potential benefits of ion beam therapies. Current research efforts on this topic include the use of PET imaging of induced activity, detection of emerging prompt gamma rays or secondary particles. It has also been suggested recently to detect the ultrasound waves emitted through the ion energy absorption process. The energy absorbed in a medium is dissipated as heat, followed by thermal expansion that leads to generation of acoustic waves. By using an array of ultrasound transducers the precise spatial location of the Bragg peak can be obtained. The shape and intensity of the emitted ultrasound pulse depend on several variables including the absorbed energy and the pulse length. The main objective of this work is to understand how the ultrasound wave amplitude and shape depend on the initial ion energy and intensity. This would help guide future experiments in ionoacoustic imaging.Methods:The absorbed energy density for protons and carbon ions of different energy and field sizes were obtained using Fluka Monte Carlo code. Subsequently, the system of coupled equations for temperature and pressure is solved for different ion pulse intensities and lengths to obtain the pressure wave shape, amplitude and spectral distribution.Results:The proposed calculations show that the excited pressure wave amplitude is proportional to the absorbed energy density and for longer ion pulses inversely proportional to the ion pulse duration. It is also shown that the resulting ionoacoustic pressure distribution depends on both ion pulse duration and time between the pulses.Conclusion:The Bragg peak localization using ionoacoustic signal may eventually lead to the development of an alternative imaging method with sub‐millimeter resolution. It may also open a way for in‐vivo dose verification from the measured acoustic signal.

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.

Effects of Layer Thickness on the Microstructures of TiN/AlTiN Multilayer Coatings

TiN/AlTiN multilayer coatings were deposited on tungsten carbide cutting tool by applying a direct current on a pulsed bias arc ion plating system. The effect of pulsed bias layer thickness on sample properties was investigated. The amount of grain size decreased with increasing layer thickness. The crystal structure of the coatings was determined using a D8 Advance Bruker X-ray diffractometer with CuKa (λ = 1.5405 Å) radiation. TiN/AlTiN multilayer coatings were crystallized with orientations in the (111), (200), (222), and (311) crystallographic planes, and the microstructure was enhanced with preferred orientation in the (111) plane. Compared with the substrate, all the specimens coated with TiN/AlTiN multilayer coatings exhibited better X-ray diffraction properties.

Development of a sequential data correction method for isotope ratio analysis by resonance ionization mass spectrometry

A sequential data correction method using several experimental parameters of pulsed resonance ionization mass spectrometry was developed to reduce mass discrimination effects for isotope ratio analysis as well as fluctuations in the ion count rate. This correction method was applied to isotope ratio determination of stable titanium isotopes using a two-step, single color ionization scheme. A significant improvement of the precision of the measured isotopic ratio of stable titanium isotopes was demonstrated after correction with a parameter set consisting of laser power, atmospheric pressure, and laser frequency.

Modification of the surface properties of highly dispersed AlB12 by a high-power carbon ion beam

Modifications in the morphology, elemental composition, and microstructure of aluminum dodecaboride (AlB12) surface layers exposed to a high-power ion beam are studied using scanning electron microscopy, X-ray microanalysis, and optical metallography. It is demonstrated that the topography of the ion-modified aluminum dodecaboride surface is determined by the dose and power density of the carbon ion beam. It is established that the effect of the high-power pulsed carbon ion beam on the AlB12-based material fabricated by self-propagating high-temperature synthesis leads to the formation of boron carbide on the surface of the latter.

Modification of the properties of porous silicon for solar cells by hydrogenation

The prospects of creating a solar cell with antireflection coating on porous silicon were shown, for which the process of electrochemical hydrogenation of porous silicon on p-type silicon substrates with a resistivity of 0.1...10 Om×sm and substrates with the formed emitter junction n + -p was studied. For the process of electrochemical hydrogenation of porous silicon at its cathodic polarization, potentiostatic current-voltage curves of the system Pt (anode) - electrolyte - «porous silicon/silicon» (cathode) for electrolytes with different chemical composition were studied. A comparison of the photoluminescence spectra of as-grown, chemically processed and hydrogenated porous layers has shown that hydrogen saturation of the porous silicon surface during cathodic polarization increases photoluminescence intensity to a level typical for samples that previously have passed special chemical treatment. The research results of luminescent properties of hydrogenated porous silicon layers can be interpreted by an increase in photoluminescence intensity of hydrogenated porous silicon layers. These results are confirmed by experiments on the secondary ion mass spectrometer (SIMS), where, after hydrogenation, we can see a steady intensity (number of the read pulses) of secondary ions of the multicrystalline Baysix type silicon substrate surface in static mode with the presence of H 2 + ions. Through the model representation of the silicon PEC structure with the antireflection coating based on the porous silicon layer, the solar cell was developed and its parameters, which have shown that the conversion efficiency of the SC with hydrogenated porous silicon is by 1.28 times higher (16.1%) than without it (12 6%) were measured.

Wakefield and stopping power of a hydrogen ion beam pulse with low drift velocity in hydrogen plasmas

AbstractA two-dimensional particle-in-cell (PIC) simulation is carried out to study the wakefield and stopping power for a hydrogen ion beam pulse with low drift velocity propagation in hydrogen plasmas. The plasma is assumed to be collisionless, uniform, non-magnetized, and in a steady state. Both the pulse ions and plasma particles are treated by the PIC method. The effects of the beam density on the wakefield and stopping power are then obtained and discussed. It is found that as the beam densities increase, the oscillation wakefield induced by the beam become stronger. Besides, the first oscillation wakefield behind the bunch is particularly stronger than others. Moreover, it is found that the stationary stopping power increases linearly with the increase of the beam density in the linear/semilinear region.

Geochemical modeling of a sustained shallow aquifer CO2 leakage field study and implications for leakage and site monitoring

A geochemical numerical modeling study was conducted to constrain processes occurring in field and laboratory experiments, simulating CO2 leakage from geological storage on shallow potable aquifers. A leak was previously physically simulated in a shallow potable aquifer at Vrøgum plantation, Western Denmark by injection of 1600kg of gas phase CO2 over 72 days. Here, a 1-dimensional reactive transport model was constructed based on field and laboratory results and subsequently used to explore the contributions of various geochemical processes to explain observed results from the carbonate free system. Finite gibbsite derived Al3+ driven cation exchange is able to explain the majority of water chemistry change observed at Vrøgum including: a pulse like effect showing a fast peak and return toward background levels for alkalinity and dissolved ion concentrations; and increasing and persistent acidification via buffering exhaustion. Model processes were supported further by simulation of a batch experiment conducted on the Vrøgum glacial sand, employing the same processes and sediment parameters. The fitted reactive transport model was subsequently used to extend predictions and explore various scenarios. Extended predictions suggest the pulse of elevated ions travels with advective flow succeeded by a zone of increasing acidification. Model runs at higher PCO2 (implying greater depths) suggest amplification of effects, i.e., greater peaks and more rapid and severe acidification. Calcite limits acidification, however, induces additional Ca driven ion exchange giving rise to more significant chemistry change. Although a site specific model, results have significant implications for risks posed to water resources from CCS leakage and implementation of MMV programs.

Influence of Bias Parameters and Plasma Density on Vacuum Arc Macroparticle Accumulation

Several regularities of the accumulation of vacuum arc metal macroparticles (MP) on the sample on repetitively pulsed biasing (105 Hz, 7 µs, −0.5 kV to −3.5 kV) have been investigated. It has been shown that the substrate temperature plays a very important role in controlling the MP amounts on the sample. A possibility to change the metal particle number density on the substrate in the range from 105/cm2 to 107/cm2, depending on bias pulse parameters, sample temperature, and ion plasma saturation current density, has been demonstrated. The shape of MPs and their adhesion to the substrate surface depends strongly on the MP energy balance in a high-voltage space charge sheath.

Mass spectrometry imaging with laser-induced postionization.

Matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI) can simultaneously record the lateral distribution of numerous biomolecules in tissue slices, but its sensitivity is restricted by limited ionization. We used a wavelength-tunable postionization laser to initiate secondary MALDI-like ionization processes in the gas phase. In this way, we could increase the ion yields for numerous lipid classes, liposoluble vitamins, and saccharides, imaged in animal and plant tissue with a 5-micrometer-wide laser spot, by up to two orders of magnitude. Critical parameters for initiation of the secondary ionization processes are pressure of the cooling gas in the ion source, laser wavelength, pulse energy, and delay between the two laser pulses. The technology could enable sensitive MALDI-MS imaging with a lateral resolution in the low micrometer range.

Intense ion beam generation in a diode with explosive emission cathode in self-magnetically insulated mode

This paper presents a review of experimental studies on pulsed intense ion beam generation in self-magnetically insulated diodes with an explosive emission cathode. The experiments were carried out with the TEMP-4M accelerator operating in double-pulse mode: the first pulse is of negative polarity (300–500 ns, 100–150 kV), and this is followed by a second pulse of positive polarity (150 ns, 250–300 kV). The ion beam energy density is 0.5–5 J/cm2 depending on the diode geometry. We have developed a new spiral geometry of the diode. In a spiral diode it is possible to increase the efficiency from 5–9% (previously studied diodes) up to 20–25%. We conducted a study on shot-to-shot variation in the ion beam parameters. It was found that the standard deviation of the energy density does not exceed 11%, whilst the same variation for ion current density was 20–30%. Focusing properties of an ion beam have been significantly improved by using a metal shield on the grounded electrode. Use of the shield on the grounded electrode provides decrease in the beam divergence from 11° to 7.5–8°.

Dynamics of N2 Dissociation upon Inner-Valence Ionization by Wavelength-Selected XUV Pulses.

Ionization of nitrogen by extreme ultraviolet (XUV) light from the Sun has recently been recognized as an important driver of chemical reactions in the atmosphere of Titan. XUV photons with energies of 24 eV and above convert inert nitrogen molecules into reactive neutral and ionic fragments that initiate chemical reactions. Understanding the XUV-induced fragmentation poses significant challenges to modern theory owing to its ultrafast time scales, complex electronic rearrangements, and strong dependence on the XUV photon energy. Here, we apply femtosecond time-resolved photoelectron and photoion spectroscopy to study dissociative ionization of nitrogen, the most abundant molecule in Titan's atmosphere, at selected XUV photon energies using a table-top XUV time-compensating monochromator. We probe the resulting dynamics using a time-delayed infrared (IR) ionization pulse. Coupled with ab initio calculations, the results allow us to assign the major dissociation channels resulting from production of an inner-valence hole, with important implications for models of Titan's XUV-driven atmospheric chemistry.

Structure and optical property of Cr-O films deposited by pulsed bias arc ion plating

A series of uniform and transparent Cr-O films were synthesized on the silicon and quartz glass substrates at different bias voltages by pulsed bias arc ion plating. Effects of bias voltage on surface morphology, phase structure, composition, chemical valence states, hardness and optical property of the films were investigated by field emission scanning electron microscopy, grazing incident X-ray diffraction, X-ray photoelectron spectroscopy, nanoindentation and ultraviolet-visible spectrophotometer, respectively. Results indicate that the bias voltage can improve the quality of the films significantly and plays an important role in the film properties. Macroparticles and holes are observed on the surface of the films if without application of bias voltage, while the films prepared with bias voltage are uniform and smooth. The crystalline phase of the film is of amorphous structure if without bias voltage. While the bias voltage applies and increases from -100 V to -500 V, the Cr2O3 phase appears and changes into CrO phase. The crystal plane (104), (116) of the Cr2O3 phase and (200) of the Cr phase are observed in the film at the bias voltage of -100 V. When the bias voltage is above -200 V, the crystal planes (311) and (400) of the CrO phase can be observed. In order to further obtain the structure information, a detailed XPS study is performed. Chromium in the films shows different valence states, namely metallic Cr, Cr2+, Cr3+ and Cr6+. Thereby, the main components of the polycrystalline films are Cr2O3 and CrO phases, meanwhile, and the films also contain a small amount of CrO3 and metal Cr phases. The films under different bias voltage show good mechanical properties and the hardness of all the films is above 19 GPa. With the increase of bias voltage the hardness first increases and then decreases, reaching a maximum value of 24.4 GPa at the bias voltage of -300 V. The films show good optical transmittance and its highest value can be up to 72%. As the bias voltage rises, it is observed first the red shift and then blue shift of the absorption edge. And the optical band gap reaches the maximum value of 1.88 eV when the bias voltage is -200 V. Therefore, Cr-O functional films can be synthesized by pulsed bias arc ion plating and the phase structure and properties can be effectively adjusted.

System for measuring temporal profiles of scintillation at high and different linear energy transfers by using pulsed ion beams.

We have developed a system for measuring the temporal profiles of scintillation at high linear energy transfer (LET) by using pulsed ion beams from a cyclotron. The half width at half maximum time resolution was estimated to be 1.5-2.2 ns, which we attributed mainly to the duration of the pulsed ion beam and timing jitter between the trigger signal and the arrival of the ion pulse. The temporal profiles of scintillation of BaF2 at different LETs were successfully observed. These results indicate that the proposed system is a powerful tool for analyzing the LET effects in temporal profiles of scintillation.