Pulsed Ion Research Articles

Production of low-Z ions in the Dresden superconducting electron ion beam source for medical particle therapy

We report on experiments with a new superconducting electron beam ion source (EBIS-SC), the Dresden EBIS-SC, with the objective to meet the main requirements for their application in particle-therapy facilities. Synchrotrons as well as innovative accelerator concepts, such as high-gradient linacs which are driven by a large-current cyclotron (CYCLINACS) and direct drive RF linear accelerators may benefit from the advantages of EBISs in regard to their functional principle. First experimental studies of the production of low-Z ions such as H(+), H(2)(+), H(3)(+), C(4+), and C(6+) are presented. Particular attention is paid to the ion output, i.e., the number of ions per pulse and per second, respectively. Important beam parameters in this context are, among others, ion pulse shaping, pulse repetition rates, beam emittance, and ion energy spread.

Investigation of ion–ion-recombination at atmospheric pressure with a pulsed electron gun

For future development of simple miniaturized sensors based on pulsed atmospheric pressure ionization as known from ion mobility spectrometry, we investigated the reaction kinetics of ion-ion-recombination to establish selective ion suppression as an easy to apply separation technique for otherwise non-selective ion detectors. Therefore, the recombination rates of different positive ion species, such as protonated water clusters H(+)(H(2)O)(n) (positive reactant ions), acetone, ammonia and dimethyl-methylphosphonate ions, all recombining with negative oxygen clusters O(2)(-)(H(2)O)(n) (negative reactant ions) in a field-free reaction region, are measured and compared. For all experiments, we use a drift tube ion mobility spectrometer equipped with a non-radioactive electron gun for pulsed atmospheric pressure ionization of the analytes. Both, ionization and recombination times are controlled by the duty cycle and repetition rate of the electron emission from the electron gun. Thus, it is possible to investigate the ion loss caused by ion-ion-recombination depending on the recombination time defined as the time delay between the end of the electron emission and the ion injection into the drift tube. Furthermore, the effect of the initial total ion density in the reaction region on the ion-ion-recombination rate is investigated by varying the density of the emitted electrons.

Simultaneous and sensitive analysis of inorganic and organic gaseous compounds by pulsed discharge helium ionization detector (PDHID)

A simple gas chromatographic method has been developed for the simultaneous and sensitive analysis of inorganic (H2, CO, and CO2) and organic gaseous compounds (CH4, C2H4, C2H6, C3H6, C3H8, iso-C4H10, and n-C4H10). The analysis of these gases generally requires multi-columns and/or multi-detectors, whereas the proposed method uses a single micropacked column and a single pulsed discharge helium ionization detector (PDHID). All of the investigated peaks (except for the N2 and O2 peaks, which are the major components of air) show good separation when using an oven temperature program from 40°C to 300°C. This gas chromatography‐PDHID system yielded good linearity and a relative standard deviation of less than 5%. This sensitive and convenient method shows great potential in analyses of various types of gaseous compounds.

Survivability of First-Wall Materials in Fusion Devices: An Experimental Study of Material Exposure to Pulsed Energetic Ions

The confining walls in future fusion power plants will be subjected to an intense energetic bombardment from X-rays, ions, and neutrons. This is true for both direct-drive inertial fusion energy (IFE) and magnetic fusion energy (MFE) designs. We focus in this paper on the threat spectra presented by energetic ions. X-rays are predicted to present a less significant threat in direct-drive IFE, and neutron effects cannot be readily simulated in current experimental facilities. For the experimental results presented herein, the energetic ions are generated in the Repetitive High-Energy Pulsed Power 1 (RHEPP-1) facility at Sandia National Laboratories. Depending upon whether the ion pulses are of nitrogen (previous database) or helium (this paper), the pulse width varies from 100 ns to as much as 500 ns, respectively. While this is short compared to ˜500-μs transient events anticipated in MFE operation, data from both IFE and MFE experiments for tungsten exposure are shown to exhibit similar fluence thresholds when thermal diffusion is taken into account by use of the heat flux parameter H = Power density × t1/2, where t is the characteristic event time duration.Long-term exposure of tungsten to RHEPP-1 nitrogen pulses indicates that above a level of ˜1 J · cm−2 /pulse, polycrystalline tungsten roughens severely, the cause of which appears to be thermomechanical distress, with loosening of grains near the surface the primary result. This roughening is correlated with unacceptable mass loss. While this occurs below melting temperatures, allowing the surface to melt by raising the per-pulse fluence does not appear to be a viable approach to smoothing the surface. Oriented grain material such as ITER-specified tungsten performs significantly better than polycrystalline tungsten, but under helium exposure it appears to suffer additional surface deterioration that appears to be connected to helium pore and bubble formation at absorbed implantation levels of mid-1015 He/cm2. This level is below previously reported levels of concern for helium retention effects and well short of required survival duration. Experiments with three-dimensional "needle" geometries, designed to increase the effective surface area for heat absorption and reduce helium implantation in depth, show promising results that need further investigation to confirm long-term survival.

Transport Properties of YBa2Cu3O7 Josephson Junctions at THz Frequencies

Abstract For application in a THz scanning microscope we employ Josephson junctions from the high-temperature superconductor YBa2Cu3O7 on a so called Josephson cantilever to measure the local microwave power density in the half space above a device under test. The Josephson junctions are prepared by pulsed laser deposition and argon ion etching on symmetric LaAlO3 30 ∘ -bicrystal substrates. To achieve high sensitivity at THz frequencies, a high I c R n product is required. Therefore, the Josephson junctions are operated on a cryo-cooler at low temperature of about 36 K under vacuum conditions. The high frequency characterization is accomplished in the near field of a Gaussian far infrared gas laser beam optically pumped by a CO2 laser. We use strong emission lines of formic acid at 762 GHz and 1.2 THz for the investigations and report on the electrical transport properties determined from the current-voltage characteristics of the Josephson junctions under influence of external magnetic field and far-infrared radiation.

MICROSTRUCTURE AND MECHANICAL PROPERTIES OF DLC FILMS DOPED WITH HIGH CRYSTALLINITY CrN NANOPARTICLES

DLC films with dispersed high crystallinity CrN nanoparticles were prepared by high power pulsed magnetron discharge plasma ion implantation deposition(HPPMS-PIID) combined with DC magnetron sputtering(DCMS).The surface morphology,structure and properties of CrN-DLC films with the different currents of C target were studied.The results show that the C content increases as the raise of the current of the C target and clear characteristics of DLC films are found at a higher C content.CrN doped in DLC exists as nanoparticles with highly 200 preferred orientation, and the smallest size of the CrN grains is 42.39 nm.The C1s peak primarily consists of the three peaks that correspond to C-sp~2,C-sp~3 and CN-sp~3,and the ratio of total sp~3 to sp~2 is 44.8%.Excellent adhesion between film and substrate with critical load of 66.8 N and high nanohardness up to 24.3 GPa are achieved due to highly energetic ion bombardment and implantation in HPPMS-PIID.

Effect of Air Condition on Alpha-radioactivity Measurement by Airflow Pulse Ionization Chamber

Effect of Air Condition on Alpha-radioactivity Measurement by Airflow Pulse Ionization Chamber

Investigation of the Utility of Laser-Secondary Neutral Mass Spectrometry for the Detection of Polyaromatic Hydrocarbons in Individual Atmospheric Aerosol Particles

The distribution of polyaromatic hydrocarbons (PAHs) in ambient aerosol particles is of importance to both human health and climate forcing. Although time-of-flight secondary ion mass spectrometry (ToF-SIMS) has proven useful for studying the distribution of organic compounds in individual aerosol particles, it is difficult to detect PAHs at relevant concentrations in individual aerosol particles because of their low ion yield. In this study, we explore the potential of using laser secondary neutral mass spectrometry (Laser-SNMS) to study three PAHs: pyrene, anthracene, and naphthalene. Because of the high volatility of PAHs, a cryostage was required for the analysis to prevent sublimation of the molecules into the vacuum chamber. We studied two laser systems, a 157 nm excimer laser, which is capable of single-photon ionization of the PAHs, and a 193 nm laser, which requires multiphoton ionization. Under optimized conditions for laser power density and primary ion pulse length, 193 nm postionization resulted in a 2-50-fold increase in ion yield over ToF-SIMS. Using the 157 nm laser, the yield was increased by more than 3 orders of magnitude for all 3 PAHs studied. The single-photon postionization process proved superior in terms of both yield enhancement and reduced fragmentation. By using the optimized 157 nm laser system and a cryostage, we were able to detect PAHs on the surface of 2 μm diameter ambient aerosol particles.

Comparison of femtosecond laser-driven proton acceleration using nanometer and micrometer thick target foils

AbstractAdvancement of ion acceleration by intense laser pulses is studied with ultra-thin nanometer-thick diamond like carbon and micrometer-thick Titanium target foils. Both investigations aim at optimizing the electron density distribution which is the key for efficient laser driven ion acceleration. While recently found maximum ion energies achieved with ultra-thin foils mark record values micrometer thick foils are flexible in terms of atomic constituents. Electron recirculation is one prerequisite for the validity of a very simple model that can approximate the dependence of ion energies of nanometer-thick targets when all electrons of the irradiated target area interact coherently with the laser pulse and Coherent Acceleration of Ions by Laser pulses (CAIL) becomes dominant. Complementary experiments, an analytical model and particle in cell computer simulations show, that with regard to ultra-short laser pulses (duration ~45 fs at intensities up to 5 × 1019 W/cm2) and a micrometer-thick target foil with higher atomic number a close to linear increase of ion energies manifests in a certain range of laser intensities.

Formation of surface structures on single-crystalline silicon under the action of nanosecond high-power ion beam pulses

We have studied the formation of surface structures on single-crystalline silicon surface under the action of a nanosecond pulsed high-power proton-carbon ion beam. Morphological features of the structures that appear as a result of this processing are described and possible mechanisms of their formation are considered.

Cold cesium molecules produced directly in a magneto—optical trap

We report on the observation of ultracold ground electric-state cesium molecules produced directly in a magneto—optical trap with a good signal-to-noise ratio. These molecules arise from the photoassociation of magneto—optical trap lasers and they are detected by resonantly enhanced multiphoton ionization technology. The production rate of ultracold cesium molecules is up to 4×104 s−1. We measure the characteristic time of the ground electric-state cesium molecules generated in the experiment and investigate the Cs2+ molecular ion intensity as a function of the trapping laser intensity and the ionization pulse laser energy. We conclude that the production of cold cesium molecules may be enhanced by using appropriate experimental parameters, which is useful for future experiments involving the production and trapping of ultracold ground electric-state molecules.

Test of pixel detectors for laser-driven accelerated particle beams

Laser-driven accelerated (LDA) particle beams have due to the unique acceleration process very special properties. In particular they are created in ultra-short bunches of high intensity exceeding more than 107 per bunch. Characterization of these beams is very limited with conventional particle detectors. Non-electronic detectors such as imaging plates or nuclear track detectors are, therefore, conventionally used at present. Moreover, all these detectors give only offline information about the particle pulse position and intensity as they require minutes to hours to be processed, calling for a new highly sensitive online device. Here, we present tests of different pixel detectors for real time detection of LDA ion pulses.Experiments have been performed at the Munich 14MV Tandem accelerator with 8–20 MeV protons in dc and pulsed beam, the latter producing comparable flux as a LDA ion pulse. For detection tests we chose the position-sensitive quantum-counting semiconductor pixel detector Timepix which also provides per-pixel energy- or time-sensitivity. Additionally other types of commercially available pixel detectors are being evaluated such as the RadEye™1, a large area (25 x 50 mm2) CMOS image sensor.All of these devices are able to resolve individual ions with high spatial- and energy-resolution down to the level of μm and tens of keV, respectively. Various beam delivering parameters of the accelerator were thus evaluated and verified. The different readout modes of the Timepix detector which is operated with an integrated USB-based readout interface allow online visualization of single and time-integrated events. Therefore Timepix offers the greatest potential in analyzing the beam parameters.

Regulated and unregulated emissions from a spark-ignition engine fuelled with low-blend ethanol–gasoline mixtures

The effects of ethanol addition to gasoline on the exhaust emissions (including regulated and unregulated emissions) and the conversion efficiencies of the three-way catalyst (TWC) were investigated in a three-cylinder spark-ignition (SI) gasoline engine. Three typical fuel blends – commercial 93# (Research Octane Number) gasoline (E0), E10, and E20 (with 0 per cent, 10 per cent, and 20 per cent ethanol in the blends by volume) – were used in the experiment. Unregulated emissions were measured by gas chromatography with a pulsed discharge helium ionization detector. Experimental results show that the regulated emissions of hydrocarbon, carbon monoxide, and nitrogen oxides decreased before and after the TWC with the increase of ethanol fraction in the fuel blends. However, the unregulated emissions of ethanol, acetaldehyde, and formaldehyde increased with the increase of ethanol fraction and decreased with increased engine speed and/or torque. Ethanol emission was not detected when fuelled with gasoline (E0). Ethanol emission was intensively influenced by the exhaust temperature and disappeared when the exhaust temperature was higher than 900 K for E10 and E20 operation. Acetaldehyde emission definitely comes from the oxidation of ethanol; the engine speed and load have opposite effects on acetaldehyde emission. Both ethanol and acetaldehyde can be converted effectively by the TWC. More formaldehyde was emitted at higher engine speed and lower load operating conditions.

Laser ablation-miniature mass spectrometer for elemental and isotopic analysis of rocks

A laser ablation-miniature mass spectrometer (LA-MMS) for the chemical and isotopic measurement of rocks and minerals is described. In the LA-MMS method, neutral atoms ablated by a pulsed laser are led into an electron impact ionization source, where they are ionized by a 70 eV electron beam. This results in a secondary ion pulse typically 10-100 μs wide, compared to the original 5-10 ns laser pulse duration. Ions of different masses are then spatially dispersed along the focal plane of the magnetic sector of the miniature mass spectrometer (MMS) and measured in parallel by a modified CCD array detector capable of detecting ions directly. Compared to conventional scanning techniques, simultaneous measurement of the ion pulse along the focal plane effectively offers a 100% duty cycle over a wide mass range. LA-MMS offers a more quantitative assessment of elemental composition than techniques that detect ions directly generated by the ablation process because the latter can be strongly influenced by matrix effects that vary with the structure and geometry of the surface, the wavelength of the laser beam, and the not well characterized ionization efficiencies of the elements in the process. The above problems attendant to the direct ion analysis has been minimized in the LA-MMS by analyzing the ablated neutral species after their post-ionization by electron impaction. These neutral species are much more abundant than the directly ablated ions in the ablated vapor plume and are, therefore, expected to be characteristic of the chemical composition of the solid. Also, the electron impact ionization of elements is well studied and their ionization cross sections are known and easy to find in databases. Currently, the LA-MMS limit of detection is 0.4 wt.%. Here we describe LA-MMS elemental composition measurements of various minerals including microcline, lepidolite, anorthoclase, and USGS BCR-2G samples. The measurements of high precision isotopic ratios including (41)K/(39)K (0.077 ± 0.004) and (29)Si/(28)Si (0.052 ± 0.006) in these minerals by LA-MMS are also described. The LA-MMS has been developed as a prototype instrument system for space applications for geochemical and geochronological measurements on the surface of extraterrestrial bodies.

Investigation on the regulated and unregulated emissions of a DME engine under different injection timing

In this study, a two-cylinder, direct injection compression ignition engine was retrofitted to run on dimethyl ether (DME) fuel. Under different fuel delivery timing, total hydrocarbon (THC), carbon monoxide (CO), nitrogen oxides (NOx), smoke, DME and formaldehyde (CH2O) emission characteristics of DME engine were investigated and compared with diesel engine. A gas chromatograph with pulsed discharge helium ionization detector (PDHID) was applied to measure the exhausted DME and CH2O, and the regulated emissions were detected with MEXA 7100 DEGR, Horiba. The measurement proved that DME and CH2O are the main components of THC emission from DME engine. And, for the reason that these two emissions are normally less responded by flame ionization detector (FID), the DME engine THC emission of FID should be corrected. Compared with diesel engine, DME engine can achieve smoke-free and significant lower THC and NOx emissions. CO emission of DME engine is decreased at low and middle engine speed conditions as well. CH2O emissions for both fuels are approximately equal. Retarding DME injection timing, NOx emission can be further reduced, while the increase of CO, THC, DME and CH2O emission are observed.

Time profiles of ions produced in a hot-cavity resonant ionization laser ion source

The time profiles of Cu, Sn, and Ni ions extracted from a hot-cavity resonant ionization laser ion source are investigated. The ions are produced in the ion source by three-photon resonant ionization with pulsed Ti:Sapphire lasers. Measurements show that the time spread of these ions generated within laser pulses of about 30 ns duration could be larger than 100 μs when the ions are extracted from the ion source. A one-dimensional ion-transport model using the Monte Carlo method is developed to simulate the time dependence of the ion pulses. The prediction of the model agrees reasonably well with the experimental data. To reproduce the observed ion time profiles, we find it necessary to postulate that ion-wall collisions are suppressed inside the ion source by an undetermined ion confinement mechanism and that a substantial fraction of the extracted ions are generated in the vapor-transfer tube rather than the hot cavity. Three-dimensional modeling will be necessary to understand the strong reduction in losses expected from ion-wall collisions which we interpret as evidence for confinement.

Structural dynamics and energy flow in Rydberg-excited clusters of N,N-dimethylisopropylamine

In molecular beams, the tertiary amine N,N-dimethylisopropyl amine can form molecular clusters that are evident in photoelectron and mass spectra obtained upon resonant multiphoton ionization via the 3p and 3s Rydberg states. By delaying the ionization pulse from the excitation pulse we follow, in time, the ultrafast energy relaxation dynamics of the 3p to 3s internal conversion and the ensuing cluster evaporation, proton transfer, and structural dynamics. While evaporation of the cluster occurs in the 3s Rydberg state, proton transfer dominates on the ion surface. The mass-spectrum shows protonated species that arise from a proton transfer from the alpha-carbon of the neutral parent molecule to the N-atom of its ionized partner in the dimer. DFT calculations support the proton transfer mechanism between tightly bonded cluster components. The photoelectron spectrum shows broad peaks, ascribed to molecular clusters, which have an instantaneous shift of about 0.5 eV toward lower binding energies. That shift is attributed to the charge redistribution associated with the induced dipoles in surrounding cluster molecules. A time-dependent shift that decreases the Rydberg electron binding energy by a further 0.4 eV arises from the structural reorganization of the cluster solvent molecules as they react to the sudden creation of a charge.

Measurement of the temperature of an ultracold ion source using time-dependent electric fields

We report on a measurement of the characteristic temperature of an ultracold rubidium ion source, in which a cloud of laser-cooled atoms is converted to ions by photo-ionization. Extracted ion pulses are focused on a detector with a pulsed-field technique. The resulting experimental spot sizes are compared to particle-tracking simulations, from which an effective source temperature T = (3 ± 2) mK and the corresponding transversal reduced emittance εr = 1.4 × 10−8 m rad eV are determined. Space charge effects that may affect the measurement are also discussed.

Benchmark of Fluid and Kinetic Simulations of Type III Elming H-Mode on TCV

Although the most complex currently available fluid-neutral Monte-Carlo plasma boundary code package, SOLPS, has been a major player in the ITER divertor design, it has not yet been systematically used for the study of kinetic phenomena such as ELM transients. This paper investigates the relevance of fluid code results for transients, in particular at the targets where kinetic effects are most manifest, by comparing power and particle fluxes at the targets from SOLPS5 time-dependent simulations of TCV Type III ELMs with those obtained from dedicated Particle-in-Cell (PiC) kinetic transport code (BIT1) simulations. Although reasonable agreement is found in terms of the absolute magnitude of total heat fluxes, the arrival of the ion pulse at the target from upstream is significantly faster in SOLPS than expected on the basis of sonic transit times (as also seen in PiC). Adjustments of kinetic heat flux limiters to render the heat fluxes more convective in SOLPS are necessary in order to correct for this discrepancy. Moreover, because SOLPS does not account for the transfer of heat from electrons to ions inside the sheath, correction terms to the electron and ion power fluxes at the targets are required in SOLPS in order to better match PiC results. However, it does not appear possible within the scope of these sensitivity studies to simultaneously achieve expected delays and ion-electron power sharing in the fluid simulations.

Formation of Nano-Crystalline Phase in Hydrogenated Amorphous Silicon Thin Film by Plasma Focus Ion Beam Irradiation

A 3.3 kJ Mather type dense plasma focus device is used to generate a pulsed argon ion beam of 100 KeV in this work. Hydrogenated amorphous silicon (a-Si:H) film prepared by plasma enhanced chemical vapor deposition (PECVD) on c-Si substrate was irradiated with the argon ion beam produced by this dense plasma focus device. The effects of exposure to a single, 5 and 10 shots of dense plasma focus argon ion beam irradiation on the surface morphology, crystallinity and chemical bonding properties of the a-Si:H films were studied using Field Emission Scanning Electron Microscope (FESEM), X-ray Diffraction (XRD), Raman scattering and Fourier Transform Infrared (FTIR) spectroscopy, respectively. Formation of nano-crystalline silicon phase along with increase in structural order and hydrogen content in the film structure has been observed when the a-Si:H film was irradiated with a single shot of dense plasma focus argon ion beam. Exposure to 5 and 10 shots of the dense plasma focus argon ion beam irradiation reduced the hydrogen content resulting in a decrease in crystallinity and structural order in the film structure.