Slow Ion Beams Research Articles

Guiding a 7.5 keV Ar3+ ion beam using a cylindrical glass channel

Although guiding slow multi-charge ion beams using insulator capillaries has been vigorously studied for the last two decades, controlling the shape and surface condition of the inner wall of the capillary has been an issue. We attempted to guide 7.5 keV Ar3+ ion beams using a channel formed by a pair of cylindrical convex glass and a cylindrical concave glass to resolve this issue. We measured both the charge state and the kinetic energy of the exiting ions from the cylindrical glass channel. The ions kept both their initial charge state and initial kinetic energy during transportation in the channel, even at tilt angles from ‒3° to +3°. Guiding using a pair of curved glass surfaces has the advantage of more easily controlling the shape and surface condition of the capillary. This technique can make it easy to precisely adjust the incident angle of the ion beam onto various targets.

Excitation of Ion Cyclotron Waves by Ion and Electron Beams in Compensated-current System

Abstract Ion cyclotron waves (ICWs) can play important roles in the energization of plasma particles. Charged particle beams are ubiquitous in space, and astrophysical plasmas and can effectively lead to the generation of ICWs. Based on linear kinetic theory, we consider the excitation of ICWs by ion and electron beams in a compensated-current system. We also investigate the competition between reactive and kinetic instabilities. The results show that ion and electron beams both are capable of generating ICWs. For ICWs driven by ion beams, there is a critical beam velocity, v bi c , and critical wavenumber, k z c , for a fixed beam density; the reactive instability dominates the growth of ICWs when the ion-beam velocity and the wavenumber , and the maximal growth rate is reached at for a given . For the slow ion beams with , the kinetic instability can provide important growth rates of ICWs. On the other hand, ICWs driven by electron beams are excited only by the reactive instability, but require a critical velocity, (the Alfvén velocity). In addition, the comparison between the approximate analytical results based on the kinetic theory and the exact numerical calculation based on the fluid model demonstrates that the reactive instabilities can well agree quantitatively with the numerical results by the fluid model. Finally, some possible applications of the present results to ICWs observed in the solar wind are briefly discussed.

Electrical characterization of molybdenum oxide lamellar crystals irradiated with UV light and proton beams

MoO3 lamellar single crystals were processed into planar metal-semiconductor-metal devices and subjected to irradiation cycles with ultraviolet light and 2 MeV protons in vacuum. In-situ electrical characterization demonstrates that these sensor devices respond well to the radiation with a gain of ~30% upon proton irradiation. However, response times are slow and strong persistent photoconductivity and ion beam induced conductivity are observed when the excitation source is switched off. The current decay is strongly increased when the irradiation chamber is vented with air suggesting that surface processes are at the origin of persistent conductivity. The observed conductivity changes are explained based on a model considering the creation of electron-hole pairs as well as adsorption and desorption processes of oxygen molecules at the surface of the samples.

Numerical simulations of purification and final charge state analysis of the slow ion beam for the FISIC project

SynopsisThe Fast Ion–Slow Ion Collisions (FISIC) project consists of a crossed-beam arrangement to study ion-ion collisions in the intermediate velocity regime. For the low energy channel, ion trajectory simulations has been used to develop a complete beam line that includes a new Omega type purification system located just before the collision point and a charge state analyzer after interaction.

Study of the slow ion beam penetrating the low density plasma target

Energy loss of the slow ion beam impacting on a low density hydrogen gas target was measured. A good agreement between the experimental and theoretical results is found. The result of the ion beam passing through a fully ionized hydrogen plasma target is shown too.

Optimization of a charge-state analyzer for electron cyclotron resonance ion source beams

A detailed experimental and simulation study of the extraction of a 24 keV He(+) beam from an ECR ion source and the subsequent beam transport through an analyzing magnet is presented. We find that such a slow ion beam is very sensitive to space-charge forces, but also that the neutralization of the beam's space charge by secondary electrons is virtually complete for beam currents up to at least 0.5 mA. The beam emittance directly behind the extraction system is 65 π mm mrad and is determined by the fact that the ion beam is extracted in the strong magnetic fringe field of the ion source. The relatively large emittance of the beam and its non-paraxiality lead, in combination with a relatively small magnet gap, to significant beam losses and a five-fold increase of the effective beam emittance during its transport through the analyzing magnet. The calculated beam profile and phase-space distributions in the image plane of the analyzing magnet agree well with measurements. The kinematic and magnet aberrations have been studied using the calculated second-order transfer map of the analyzing magnet, with which we can reproduce the phase-space distributions of the ion beam behind the analyzing magnet. Using the transfer map and trajectory calculations we have worked out an aberration compensation scheme based on the addition of compensating hexapole components to the main dipole field by modifying the shape of the poles. The simulations predict that by compensating the kinematic and geometric aberrations in this way and enlarging the pole gap the overall beam transport efficiency can be increased from 16% to 45%.

Whole-Cell Imaging at Nanometer Resolutions Using Fast and Slow Focused Helium Ions

Observations of the interior structure of cells and subcellular organelles are important steps in unraveling organelle functions. Microscopy using helium ions can play a major role in both surface and subcellular imaging because it can provide subnanometer resolutions at the cell surface for slow helium ions, and fast helium ions can penetrate cells without a significant loss of resolution. Slow (e.g., 10–50 keV) helium ion beams can now be focused to subnanometer dimensions (∼0.25 nm), and keV helium ion microscopy can be used to image the surfaces of cells at high resolutions. Because of the ease of neutralizing the sample charge using a flood electron beam, surface charging effects are minimal and therefore cell surfaces can be imaged without the need for a conducting metallic coating. Fast (MeV) helium ions maintain a straight path as they pass through a cell. Along the ion trajectory, the helium ion undergoes multiple electron collisions, and for each collision a small amount of energy is lost to the scattered electron. By measuring the total energy loss of each MeV helium ion as it passes through the cell, we can construct an energy-loss image that is representative of the mass distribution of the cell. This work paves the way to use ions for whole-cell investigations at nanometer resolutions through structural, elemental (via nuclear elastic backscattering), and fluorescence (via ion induced fluorescence) imaging.

PRECISE NUCLEAR PHYSICS MEASUREMENTS WITH ION TRAPS

Ion traps are well suited for precision measurements also with exotic and rare species as radioactive nuclei. They provide a well controlled storage volume, stable fields and the means to handle the ion sample. The applications are first of all precise mass measurements and the therewith connected physics questions. Furthermore, ion traps are used to manipulate slow ion beams, to purify samples for decay spectroscopy or to observe the decay itself to measure for instance the β - ν correlation. An overview of the existing ion trap facilities for radioactive nuclei is given.

High Yield and High Throughput Reactive IBAD MgO Process for Long-length, HTS Wire Production at SuperPower

AbstractSuperPower's IBAD (ion beam assisted deposition) MgO process has been changed to reactive ion beam sputtering of Mg metal target instead of MgO ceramic target, which gives ∼ 60 % increase in deposition rate. The process speed was increased from 195 m/h to 360 m/h. Texture of IBAD MgO tapes by this reactive process was found to degrade faster during long length run. This uniform issue was resolved with feedback control during long run and from run to run. The bottleneck of alumina layer process due to slow ion beam sputtering deposition was removed by new high rate reactive magnetron sputtering at transition mode. The new alumina process speed can be as high as 3,000 m/h in our Pilot Buffer system. The yttria layer process was also changed to high rate reactive magnetron sputtering at transition mode with achievable speed as high as 10,000 m/h in our Pilot Buffer system. The routine production speed of alumina and yttria is 750 m/h due to limitation of tape driving system. The high rate magnetron-sputtered alumina/yttria yields the same texture of IBAD MgO as ion beam sputtered alumina/yttria. Now we are routinely producing IBAD MgO template tapes of ∼ 1.4 km with a uniform in-plane texture ∼ 6-7 degrees. Record high critical current of 813 A/cm over a one meter length and a world record critical current times length value of > 233,8100A-m was obtained with our routinely-produced high throughput IBAD MgO buffers. The requirements for a better IBAD texturing layer than IBAD MgO are also suggested.

Highly-charged ion induced surface nano-modification

Nano-modification of highly-oriented pyrolytic graphite (HOPG) surfaces using slow highly-charged ion (HCI) beam irradiation has been demonstrated. Single HCI impact creates nanoscale protrusions in which the electronic structure is different from that formed by singly-charged ion impact. By combining slow HCI irradiation with electron injection onto the impact region, a transition of sp 2 to sp 3 hybridization is obtained, resulting in I– V characteristics of the impact region showing non-conductive properties with ∼ 6 eV band gap. The size of the features created by Ar 8+-impact on HOPG are about ∼ 1 nm in diameter at 400 eV kinetic energy, which corresponds with a region where electron emission occurs by the Coulomb potential of the HCI. Assuming that 20 carbon atoms are contained in the structure formed, we discuss plausible sp 3 carbon structures by means of Raman spectroscopic measurements and DV-Xα molecular orbital calculations. The energy level structure of the non-spherically symmetric sp 3 structure of 20 carbon atoms shows values of energy gap corresponding to those obtained in the experiment. The results presented suggest that single impact of HCI on solid surfaces creates new nanostructure features, and HCI would be a good tool for collective material-modification-processing with nanoscale controllability.

Production of a nm sized slow HCI beam with a guiding effect

We have developed a method to produce a nm sized slow highly-charged ion beam based on a self-organized charge up inside a single tapered-glass capillary. In order to investigate the characteristics of the obtained beams, the transmission of 8 keV Ar8+ beam through the capillary of 5-cm long with 800/24 μm inlet/outlet inner diameter was examined. The transmitted beam had the same size as the outlet with the beam-density enhancement of approximately 10. The initial beam was guided through a capillary tilted by as large as ±100 mrad and it still kept the incident charge. A focused ion beam of Ga+ was employed to manufacture the capillary outlet as small as several hundreds nm in diameter and fabricate a thin glass window at the capillary outlet for biological applications.

Laser spectroscopy of trapped 7Be and 10Be at a prototype slow RI-beam facility of RIKEN

A next-generation slow radioactive nuclear ion beam facility (SLOWRI) which provides slow, high-purity and small emittance ion beams of all elements is being build as one of the principal facilities at the RIKEN RI-beam factory (RIBF). High energy radioactive ion beams from the projectile fragment separator BigRIPS are thermalized in a large gas catcher cell The thermalized ions in the gas cell are guided and extracted to a vacuum environment by a combination of de electric fields and inhomogeneous rf fields (rf carpet ion guide). From there the slow ion beam is delivered via a mass separator and a switchyard to various devices: such as an ion trap, a collinear fast beam apparatus, and a multi-reflection time of flight mass spectrometer. In the R&D works at the present RIKEN facility, an overall efficiency of 5% for a 100A MeV 8Li ion beam from the present projectile fragment separator RIPS was achieved and the dependence of the efficiency on the ion beam intensity was investigated. Recently our first spectroscopy experiment at the prototype SLOWI was performed on Be isotopes. Energetic ions of 10Be and 7Be from the RIPS were trapped and laser cooled in a linear rf trap and the specific mass shifts of these isotopes were measured for the first time.

Current-Drive Efficiency in a Degenerate Plasma

In a degenerate plasma, the rates of electron processes are much smaller than the classical model would predict, affecting the efficiencies of current generation by external noninductive means, such as by electromagnetic radiation or intense ion beams. For electron-based mechanisms, the current-drive efficiency is higher than the classical prediction by more than a factor of 6 in a degenerate hydrogen plasma, mainly because the electron-electron collisions do not quickly slow down fast electrons. Moreover, electrons much faster than thermal speeds are more readily excited without exciting thermal electrons. In ion-based mechanisms of current drive, the efficiency is likewise enhanced due to the degeneracy effects, since the electron stopping power on slow ion beams is significantly reduced.

Space-charge effects in the catcher gas cell of a rf ion guide

Slow radioactive ion beams have been produced with an overall efficiency of 4% by thermalizing energetic ions produced by a projectile fragment separator in a He-gas cell and guiding them to a vacuum vessel by dc and rf fields. Space charge was observed to have a limiting effect. Since the ionization of He atoms by energetic ions creates a region of high space charge, many thermalized ions of interest are pushed toward the walls of the gas cell. Such losses have been investigated for different incoming ion intensities.

Nuclear polarization measurement of H/D atoms extracted from a storage cell with a Lamb-shift polarimeter

The occupation numbers of the individual hyperfine substates in a beam of hydrogen or deuterium atoms are measured with a Lamb-shift polarimeter. Therefore, the nuclear polarization of an atomic beam can be determined with high precision of about 0.5 % within 20 s. The measurements are carried out with the atomic beam source for the internal polarized storage-cell gas target of ANKE ( I ∼ 7 × 10 16 atoms/s). The polarization of a slow (500–2000 eV) ion beam with currents higher than 1 nA can be measured as well. When the intensity of the atomic beam is reduced by a factor of 100, the Lamb-shift polarimeter still provides a precise measurement with an error of about 2% within 30 s. Thus, it is thought possible to determine the nuclear polarization of the atomic gas inside the storage cell, when a sample of these atoms effuse into the Lamb-shift polarimeter through a sample tube. First, results obtained with a simple Teflon cell, a new ionizer with an internal getter pump, a newly designed Wien filter and a larger photomultiplier are presented. Planned studies to optimize the polarization measurement are discussed as well.

Effects of a slow ion beam on ion-acoustic waves

The influence of a slow ion beam on an ion-acoustic wave is studied theoretically and experimentally. A kinetic dispersion relation of an ion-beam–plasma system predicts a critical value of the ion-beam density above which the ion-acoustic wave is transformed into the fast mode of the ion beam. Below the critical value, the ion-acoustic wave propagates without transforming into the fast mode of space charge waves for any beam velocity. A dispersion relation based on a fluid model does not provide such a critical value for the ion-beam density. Experimentally, the ion-beam density is controlled carefully to test the presence of the critical density at which the change in topology of dispersion roots appears.

A reflection lithography using multicharged ions

A new approach is proposed for lithography with an objective of high throughput and minimum feature size 50 nm and below — the Ion Reflection Lithography (IRL) using multicharged ions. The concept is based on a recent fundamental discovery of a special characteristic of multicharged ion interaction with solid surface: Very Slow Multicharged Ion (VSMCI) beams, i.e. in the eV/q energy range, can be selectively reflected on a nanometric scale from semiconductor and metal substrates. We present in this paper the basic processes of the interaction between a VSMCI and surfaces, and discuss the property of VSMCI to be reflected selectively in dependence on the conductive character of the substrate. The patterned ion beam formation which relies on an innovating reflective reticle is described and a first outline of an IRL system is presented.

Time-of-flight secondary ion mass spectrometry of matrix-diluted oligo- and polypeptides bombarded with slow and fast projectiles: positive and negative matrix and analyte ion yields, background signals, and sample aging.

Human angiotensin II, chain B of bovine insulin, and porcine insulin were determined by time-of-flight secondary ion mass spectrometry under impact of approximately 25 keV Xe+ and SF5+ ion beams and approximately 100 MeV 252Cf fission fragments. Matrix-embedded samples, dissolved in a large surplus of alpha-cyano-4-hydroxycinnamic acid, were prepared by nebulizer spray deposition, neat samples by the droplet technique. It is shown that the status of the sample can be assessed by evaluating the matrix-specific features of the mass spectra. The beneficial effect of matrix isolation was small for angiotensin but large for the insulin samples, which did not show parent peaks from neat material. Negative ion yields under SF5+ impact were up to a factor of 50 higher than with Xe+. For positive secondary ions, the enhancement was much smaller. The mass spectra produced by slow ion beams or fast fission fragments were qualitatively similar. Quantitative differences include the following: with fast projectiles the yields were about 10-30 times higher than with slow ions, but similar for negative ion emission under SF5+ bombardment; the analyte-to-matrix yield ratios were higher with slow ions and up to 250 times higher than the molar analyte concentration; for analyte ions the peak-to-background ratios were higher using slow projectiles; the fraction of carbon-rich collisionally formed molecular ions was much higher with fast projectiles. Sample aging in vacuum for up to five weeks strongly reduced the yield of protonated analyte molecules ejected by slow ion impact, but not of deprotonated species. Hence protonation seems to correlate with sample "wetness" or the presence of volatile proton-donating additives.

Thiosulfoxides (X 2SS) and disulfanes (XSSX): : first observation of organic thiosulfoxides

Using a combination of tandem mass spectrometry methodologies, collisional activation of fast (8 keV) or slow (20–30 eV) ion beams, neutralization–reionization and ion–molecule reactions, it is shown that thiosulfoxides X 2SS (X = H, CH 3, C 2H 5) are stable in the gas phase as radical cations as well as neutral molecules. The absence of isomerization into the more conventional disulfane structure, XSSX, is firmly demonstrated by ion-molecule reactions of the isomeric ions with methyl isocyanide and by collisional activation of “survivor” ions generated in neutralization–reionization experiments. All the mass spectral data have been recorded with a single hybrid mass spectrometer of sectors-quadrupole-sectors configuration. Molecular orbital calculations demonstrate that ionized thiosulfoxides and disulfanes are local minima on the MP2/6-31G∗ potential energy surface. The disulfane structures are found to be the most stable species by 91, 65 and 59 kJ/mol for X = H, CH 3 and C 2H 5, respectively. Heat of formation values of 1000, 810 and 760 kJ/mol are estimated for X 2SS ·+ ions (X = H, CH 3 and C 2H 5, respectively).

Spectroscopic Data for the 6it s6it p 3 P 1 level of Lu + for the Determination of the Solar Lutetium Abundance

We report spectroscopic measurements on the 6s6p 3P1 level of Lu+ at 28503.16 cm-1. The radiative lifetime of this level was measured to be 37.4 ± 1.9 ns using time-resolved laser-induced fluorescence of a slow ion beam. Branching fractions were determined from Lu spectra recorded using the 1.0 m Fourier transform spectrometer at the National Solar Observatory. Thelog(gf) values determined by combining the radiative lifetime and branching fractions for the λ3507.39,λ 5983.90, and λ6221.87 (air wavelengths) lines are - 1.16 ± 0.03, - 1.16 ± 0.06, and -0.76 ± 0.04, respectively. Theλ 6221.87 line has been identified by Bord, Cowley, and Mirijanian (1997) as the best candidate for the determination of the solar lutetium abundance because it is only slightly blended in the solar spectrum. The present λ6221.87 transition probability measurement brings their solar lutetium abundance into good agreement with the CI chondrite abundance.