Atomic Beam Source Research Articles

原子状酸素照射に対する木質炭素/シリコン材料の抵抗性

An analysis of the erosional properties of carbonized lignin with a Si content of 0 to 40% under the simulated atomic oxygen (AO) conditions found in low earth orbit was carried out. The AO environment was produced using a laser detonation atomic oxygen beam source. X-ray photoelectron spectroscopy revealed an increase in the atomic concentration of oxygen-related groups on the surface of the carbonized lignin with and without Si. The erosion rate was found to be low for the case of carbonized lignin with>20% Si. The Si-free sample exhibited a resistance to oxidation due to the formation of an oxide area that protected it from further AO effects on chemical bonds such as C=C bonds. The surface chemistry of the Si-free samples was similar to that of diamond-like carbon (DLC). These experimental results suggest that carbonized lignin derived from Sugi wood has the potential to be used in materials for space applications.

High-flux two-dimensional magneto-optical-trap source for cold lithium atoms

We demonstrate a novel 2D MOT beam source for cold 6Li atoms. The source is side-loaded from an oven operated at temperatures in the range 600<T<700 K. The performance is analyzed by loading the atoms into a 3D MOT located 220 mm downstream from the source. The maximum recapture rate of ~10^9 /s is obtained for T=700 K and results in a total of up to 10^10 trapped atoms. The recaptured fraction is estimated to be 30(10)% and limited by beam divergence. The most-probable velocity in the beam (alpha_z) is varied from 18 to 70 m/s by increasing the intensity of a push beam. The source is quite monochromatic with a full-width at half maximum velocity spread of 11 m/s at alpha_z=36 m/s, demonstrating that side-loading completely eliminates beam contamination by hot vapor from the oven. We identify depletion of the low-velocity tail of the oven flux as the limiting loss mechanism. Our approach is suitable for other atomic species.

An improved high intensity recycling helium-3 beam source

We describe an improved high intensity, recycling, supersonic atomic beam source. Changes address several issues previously limiting performance and reliability of the apparatus, including the use of newly available vacuum pumps and modifications to the recycling system. We achieve a source intensity of 2.5 x 10(19) atoms/s/sr, almost twice that previously achievable during recycling. Current limits on intensity are discussed.

Broad beam source of fast atoms produced as a result of charge exchange collisions of ions accelerated between two plasmas

Experimental study of a fast argon atom beam source is carried out and the study results are presented. The source comprises a 90-mm deep and 210-mm in diameter hollow cathode as well as a flat emission grid, both electrodes made of titanium. The study revealed main factors, which influence the zone diameter of homogeneous substrate etching by a broad beam of fast argon atoms, produced as a result of charge exchange collisions of ions, accelerated between a plasma emitter inside the hollow cathode and a secondary plasma in the working vacuum chamber, the plasmas being separated from each other with the grid. It is shown that at a distance from the grid, exceeding the resonant charge exchange length up to 4 times, elastic collisions have no appreciable impact on the spatial distribution of the etching rate in the vacuum chamber. The homogeneous etching zone diameter is mainly influenced by angular characteristics of accelerated particles in the grid plane. At a constant beam power up to 3–5 kW the diameter is rising with a decrease of their energy and with a corresponding increase of the beam current.

Intense atomic and molecular beams via neon buffer-gas cooling

We realize a continuous, intense, cold molecular and atomic beam source based on buffer-gas cooling. Hot vapor (up to 600 K) from an oven is mixed with cold (15 K) neon buffer gas, and then emitted into a high-flux beam. The novel use of cold neon as a buffer gas produces a forward velocity distribution and low-energy tail that is comparable to much colder helium-based sources. We expect this source to be trivially generalizable to a very wide range of atomic and molecular species with significant vapor pressure below 1000 K. The source has properties that make it a good starting point for laser cooling of molecules or atoms, cold collision studies, trapping, or nonlinear optics in buffer-gas-cooled atomic or molecular gases. A continuous guided beam of cold deuterated ammonia with a flux of 3×1011 ND3 molecules s−1 and a continuous free-space beam of cold potassium with a flux of 1×1016 K atoms s−1 are realized.

THE BLAST EXPERIMENT: POLARIZED ELECTRON SCATTERING FROM HYDROGEN AND DEUTERIUM

At the MIT-Bates Linear Accelerator Center, the nucleon form factors have been measured by scattering polarized electrons from vector-polarized hydrogen and deuterium. The experiment used the longitudinally polarized electron beam stored in the MIT-Bates South Hall Ring along with an isotopically pure, highly vector-polarized internal atomic hydrogen and deuterium target provided by an atomic beam source. The measurements were carried out with the symmetric Bates Large Acceptance Spectrometer Toroid (BLAST). Results are presented for the proton form factor ratio, [Formula: see text], and for the charge form factor of the neutron, [Formula: see text]. Both results are more precise than previous data in the corresponding Q2 ranges.

The BLAST experiment

The Bates large acceptance spectrometer toroid (BLAST) experiment was operated at the MIT-Bates Linear Accelerator Center from 2003 until 2005. The detector and experimental program were designed to study, in a systematic manner, the spin-dependent electromagnetic interaction in few-nucleon systems. As such the data will provide improved measurements for neutron, proton, and deuteron form factors. The data will also allow details of the reaction mechanism, such as the role of final state interactions, pion production, and resonances to be studied. The experiment used: a longitudinally polarized electron beam stored in the South Hall Storage Ring; a highly polarized, isotopically pure, internal gas target of hydrogen or deuterium provided by an atomic beam source; and a symmetric, general purpose detector based on a toroidal spectrometer with tracking, time-of-flight, Cherenkov, and neutron detectors. Details of the experiment and operation are presented.

THE POLARIZED INTERNAL GAS TARGET OF ANKE AT COSY

A first storage cell for the Polarized Internal gas Target (PIT) of the ANKE facility at COSY was produced from a Teflon-coated pure Aluminum foil and successfully used in the double polarized experiment with a 1.2 GeV polarized deuteron beam carried out at the COSY accelerator in January 2007. Prior to this experiment, the minimum possible cross section of the storage-cell beam tube at the interaction point at ANKE was determined, based on the COSY beam profile at different beam formation stages. Electron cooling combined with stacking and stochastic cooling have been studied as well. Experiments with N2 gas in the storage cell to simulate the background produced by beam interaction with the aluminum cell walls were performed. The analysis of the [Formula: see text] and [Formula: see text] reactions showed that events from the extended target can be clearly identified in the ANKE detector system. Taking into account the known intensity of the Atomic Beam Source (ABS), the expected target density in the experiment with a storage-cell beam tube of 15hor × 20vert × 390long mm3 and a 130 mm long feeding tube with 15 mm diameter reach values of 3.2 × 1013 at/cm2. The polarization, measured by the np → dπ0 reaction with the storage-cell, was 0.75 ± 0.06.

Direct simulation of low-pressure supersonic gas expansions and its experimental verification

The use of gas expansions to generate atomic or molecular beams has become a standard technique in nuclear and hadron physics for the production of polarized ion beams and gas targets. A direct simulation Monte Carlo method was used to understand the processes occurring in an expansion of highly dissociated hydrogen or deuterium gas at low densities. The results were verified in several measurements including time-of-flight and beam-profile determinations which showed that the supersonic gas expansions can properly be described by the Monte Carlo calculations. Additionally a new method of beam formation, the hollow carrier jet, was tested under the conditions of the atomic beam source operation.

Surface modification of poly(tetrafluoroethylene) by saddle field fast atom beam source

The surface of poly(tetrafluoroethylene) (teflon, PTFE) was treated by saddle field fast atom beam (FAB) source in hydrogen, helium and nitrogen with about 1 kV accelerating voltage, up to an estimated particle fluence of 10 17 cm − 2 . The untreated and FAB-treated samples were characterised by XPS, Raman microspectroscopy, single pass topographic and multipass wear tests and water contact-angle measurements. According to XPS results, upon FAB-treatment the surface F/C value decreased drastically. Raman microspectroscopic measurements testified to the formation of a carbonised surface layer. The thickness of the graded, amorphous carbon-containing layer determined by in-depth Raman microspectroscopic analysis ranged between 5.5 ± 1 and 10.5 ± 1 μm. In addition to radiation damage, a decisive role of degradation induced by thermal effects and diffusion of reactive particles was suggested. The small scale wear resistance of the hydrogen and nitrogen FAB-treated samples improved in comparison with that of the untreated PTFE. The mean surface roughness increased for the treated samples in the order of N < He < H. Water contact-angle decreased upon FAB-treatment. The effect of increased wettability remained durable for at least three months.

A modification of the laser detonation-type hyperthermal oxygen atom beam source for a long-term operation

It has been an impedimental problem, for the laser detonation-type atom beam generator, that a poppet in the pulsed supersonic valve is rapidly eroded by the irradiation of powerful laser light and high temperature plasma. In order to operate the atom beam source for a long duration, a modification was made to hide the poppet from direct irradiation of laser and plasma. The alteration of device configuration resulted in great improvement in endurance of poppet more than 300,000 repetitions. Morphology of a polyimide film exposed to approximately 200,000 pulses of hyperthermal oxygen atom beam showed a shaglike carpet structure, which is a characteristic to that exposed to energetic oxygen atoms. A flux of the oxygen atom beam was estimated to be 5x10(14) atoms/cm2/pulse at a location of 30 cm away from the nozzle throat.

Low conductance injection tubes for storage cell targets

The effect of adding internal fins to the injection tube of a storage cell target filled with a polarized atomic beam source has been studied. The tube conductance and the atomic beam intensity at the exit of the injection tube have been measured, observing an unexpectedly large beam loss. Simulations of the atomic beam reproduce the observed attenuation only when the non-zero azimuthal component of the atom's velocity is taken into account.

Investigating the wear characteristics of engineered surfaces: low-temperature plasma nitriding and TiN + MoSx hard-solid lubricant coating

Significant progress has been made in the past decade in plasma nitriding with a majority of the research work focusing on improving hardness and wear resistance of the nitrided surface through the reduction of nitriding temperature, pressure or time. Hard-solid lubricating coatings have also been extensively studied for lowering the wear rate and coefficient of friction of traditional hard coatings such as TiN by the combined effect of hardness and solid lubrication. In this study, the wear characteristics of low-temperature plasma-nitrided steel substrate performed using a Saddle-field fast atom beam source and TiN + MoSx hard-solid lubricant coating deposited by a closed-field magnetron-sputtering technique have been investigated. The thin hard layer in plasma-nitrided substrates exhibited much higher hardness and lower wear compared to the untreated substrate in pin-on-disc wear testing. In addition, the study of the wear track morphology of the nitrided samples evidenced significant reduction of deeper ploughing and plastic deformation due to higher hardness and load supporting of the nitrided layer. On the other hand, due to the incorporation of MoS2 in TiN coating, the wear resistance and coefficient of friction were greatly improved in TiN + MoSx coating compared to pure TiN coating. In contrast to TiN coating, a relatively smoother wear track with less abrasive wear also supported the beneficial effects of adding MoS2 in TiN coating.

Enhancement of the adhesive force of metal films on PTFE surface achieved by fast-atom-beam surface modification

We tried the method to increase the peel strength between thin film metals and various substrate materials using saddle field fast atom beam (FAB) sources. It is notable that the peel strength was increased more than several times for all substrates than those who were not modified by surface activation using FAB irradiation. Highest peel strength was observed at the coupling of Si and metals in both case of Ar irradiation and SF6 reactive etching by FAB. This surface activation technique was applied to the fabrication of microelectrodes for the detection of mouse nerve signals. The process is expected as one of the available techniques for pre-treatment of the film deposition for several electrical devices.

Application of Atomic Beams in Combination with Spectroscopic Observation for Plasma Diagnostic

Plasma can be studied and characterised by the analysis of its radiation. Signals obtained by passive spectroscopy contain much information about temperature, density and flux of the main species and impurities. The interpretation of measured line intensities requires the knowledge of atomic physics describing the specific radiation from the plasma. Tomographic methods are applied but they need symmetries for the calculation of local parameters. Additionally in magnetic confined plasmas the interpretation might be more difficult due to the Zeeman splitting.Asymmetries and steep gradients of plasma parameters as it appears in the plasma boundary of a tokamak or stellarator require the direct local measurement of these quantities. There are two methods to probe the plasma locally, by a laser or an atomic beam. In both cases, elastic collisions lead to scattering of light (Thomson scattering), respectively atoms (Rutherford scattering) and inelastic collisions cause the emission of light that is analysed (laser induced fluorescence, atomic beam diagnostics).In this article we will concentrate on the interaction of beam atoms with plasma, yielding to optical emission, which is observed with spectroscopic methods. After interaction with the bulk plasma the beam atoms or deuterons and impurity ions can be investigated. The first method is called beam emission spectroscopy (BES), the second charge exchange recombination spectroscopy (CXRS).Both techniques need two ports, one for the injection and a second for observation, which should be nearly perpendicular in order to get the best spatial resolution. The location of the measurement is determined by the intersection of the beam with the (perpendicular) line of sight of the detection systemThis paper is structured in four chapters. After this introduction the basic properties of atomic beam injection used for BES and CXRS are described in chapter II. The collisional-radiative model necessary for the interpretation of the measured line intensities is presented in the third part. Examples of atomic beam sources applied in tokamaks and evaluated signals are given in the last chapter.

Characterization of neutral beam source using dc cold cathode discharge and its application processes

Fast atom beam (FAB) sources using dc cold cathode discharge, comprising parallel plate electrodes and thick carbon plate cathodes with multiple beam extracting apertures, were developed to generate parallel and straight energetic neutral beams for precise etching of three-dimensional microstructures consisting of insulating materials. Conventional FAB sources and their applications are briefly reviewed, and the advantages of newly developed FAB sources and new applications are introduced. By using SF6 gas, a precise etching of quartz glass with an etch rate of 30 nm min−1, a uniformity of within 4% (P–V) in Ø76 mm, vertical etch profile, smooth etch surface and long-term etch rate stability over 250 min were realized. The neutralization coefficient and the beam current density were also measured using a secondary electron method and a pulse-counting method, making it possible to measure the neutralization coefficient without referring to databases for secondary electron yields. A neutralization coefficient of 98% was obtained at maximum, although, under practical etching conditions, the neutralization coefficient is less than 70%. By comparing the results of the simple model calculation with the experimental data, it was determined that the neutralization mechanism was dominated by charge transfer. The importance of neutralization in a process chamber is also discussed.

Development of atomic-beam resonance method to measure the nuclear moments of unstable nuclei

We have been working on the development of a new technique of atomic-beam resonance method to measure the nuclear moments of unstable nuclei. In the present study, an ion-guiding system to be used as an atomic-beam source have been developed.

Measurement of photoionization cross section from the 3s3p 1P1 excited state of magnesium

The photoionization cross section from the 3s3p 1P1 excited state has been measured in the energy region from the first ionization threshold up to 1.4 eV excess energy using a two-step photoionization and saturated ionization technique in conjunction with an atomic beam source and a time-of-flight mass spectrometer that enables the separation of the three stable isotopes of magnesium on the time axis. The absolute value of the photoionization cross sections from the 3s3p 1P1 excited state near the 3s ionization threshold has been measured as 90 ± 16 Mb (at 354.5 nm ionizing wavelength) for the dominating isotope (24Mg) whereas the value at the peak of the 3p2 1S0 auto-ionizing resonance has been determined as 785 ± 141 Mb. The present experimentally measured photoionization cross sections are compared with the existing experimental and theoretical work, showing excellent agreement.

Nucleon form factors and the BLAST experiment

Measurements of the charge and magnetic form factors of the nucleon present a sensitive test of nucleon models and QCD-inspired theories. A precise knowledge of the neutron form factors at low Q 2 is also essential to reduce the systematic errors of parity-violation experiments. At the MIT-Bates Linear Accelerator Center, the nucleon form factors have been measured by means of scattering of polarized electrons from vector-polarized hydrogen and deuterium. The experiment used the longitudinally polarized stored electron beam of the MIT-Bates South Hall Ring along with an isotopically pure, highly vector-polarized internal atomic hydrogen and deuterium target provided by an atomic beam source. The measurements have been carried out with the symmetric Bates Large-Acceptance Spectrometer Toroid (BLAST) with enhanced neutron detection capability.

Effective Rate Constants for the Surface Reaction between Solid Methanol and Deuterium Atoms at 10 K

The surface reactions of CH3OH, CH2DOH, and CHD2OH with cold D atoms at 10 K were investigated using an atomic beam source and FTIR. Methyl-deuterated isotopologues CH2DOH, CHD2OH, and CD3OH were produced by exposure of amorphous solid CH3OH to D atoms at 10 K, and the pseudo-first-order rates for the reactions CH3OH + D --> CH2OH + HD, CH2DOH + D --> CHDOH + HD, and CHD2OH + D --> CD2OH + HD were estimated. The ratios of the reaction rates of the second and third reactions to the first reaction were 0.69 +/- 0.11 and 0.52 +/- 0.14, respectively. The difference in reaction rates is thought to be due to a secondary kinetic isotope effect on the H-abstraction reaction from the methyl side by D atoms.