Ion Beam Axis Research Articles

Three-dimensional analysis of RF-biased ion optics with misalignments of apertures

Accelerator grid hole shift is a critical reason for erosion failure of optic systems in ion thrusters, which may also cause an unexpected roll torque about the ion beam axis. A three-dimensional (3D) model of ion optics is developed based on a particle-in-cell Monte Carlo collision method to investigate the plasma dynamics and performance of radio frequency (RF) grid systems with misalignments of apertures, which are compared with those in the direct current (DC) grid system. For the benchmark case, the 3D model gives a better agreement with the experiments in the ion energy distribution function (IEDF) compared with the two-dimensional model from a previous publication, with 36.4% and 47.9% relative error reduction of the peak position and full width at half maximum (FWHM), respectively, indicating the effectiveness of the developed 3D model. Simulations show that in the RF grid system the ion beamlet is deflected in the direction opposite to the shift of the accelerator grid hole, while electrons move first in the hole shift direction, and then deflect in the opposite direction. The average ion beamlet deflection angle calculated is consistent with the predictions from linear optical theory in both the RF and DC grid system. The amplitude of beamlet deflection angle fluctuation with time decreases with the increase of RF frequency. When the grid holes shift, the ion beamlet will deflect with the divergence angle almost unchanged in the DC grid system, while the beamlet divergence angle increases in the RF grid system. When RF frequency is low, the big vortex-like structure in the electron velocity phase diagram breaks into small vortices, showing a reduced oscillation intensity. The hole shift also causes high-frequency oscillation in the shift direction. In terms of performance, the RF grid system is more sensitive to grid hole shift than the DC grid system.

Active space debris removal by ion multi-beam shepherd spacecraft

Contactless transportation of a passive object by an ion beam generated by an active spacecraft's thruster is a promising way of space debris removal. The study proposes a modification of the ion beam shepherd concept using an array of impulse transfer thrusters. The multi-beam scheme provides significant increase the generated ion force, which reduces a space debris object deorbit time, thereby reducing the probability of its collision with other orbital objects. The aim of the work is to study the possibility of using several ion beams for effective contactless transportation of a space debris object. Controlling the angular motion of the object permits orientation of the object to maximize the generated ion force. The article proposes a control law for impulse transfer thrusters, which is based on the calculation of the energy of the object's unperturbed motion, and two control schemes that implement this law: (1) relay control, which implies turning the thruster on and off, and (2) ion beam axis direction control for one of the thrusters. For a space debris object of a cylindrical shape, a comparison of the time and fuel costs required for deorbiting the object using one, two, and three impulse transfer thrusters is made. It is shown that the addition of thrusters significantly reduces the descent time, but has little effect on the mass of required fuel. For the case of two engines, the best angle of ion beams axes direction and the most preferable angular motion mode are determined. Numerical simulation of space debris removal is carried out for the case when the space debris object is in the least favorable mode of angular motion and the proposed control schemes are used. The ion beam direction control scheme showed better results than the relay scheme. The use of multiple ion beams opens up new possibilities for creating new ion beam shepherd spacecraft design and developing new control methods and laws.

Towards an Intrinsic Doppler Correction for X-ray Spectroscopy of Stored Ions at CRYRING@ESR

We report on a new experimental approach for the Doppler correction of X-rays emitted by heavy ions, using novel metallic magnetic calorimeter detectors which uniquely combine a high spectral resolution with a broad bandwidth acceptance. The measurement was carried out at the electron cooler of CRYRING@ESR at GSI, Darmstadt, Germany. The X-ray emission associated with the radiative recombination of cooler electrons and stored hydrogen-like uranium ions was investigated using two novel microcalorimeter detectors positioned under 0∘ and 180∘ with respect to the ion beam axis. This new experimental setup allowed the investigation of the region of the N, M → L transitions in helium-like uranium with a spectral resolution unmatched by previous studies using conventional semiconductor X-ray detectors. When assuming that the rest-frame energy of at least a few of the recorded transitions is well-known from theory or experiments, a precise measurement of the Doppler shifted line positions in the laboratory system can be used to determine the ion beam velocity using only spectral information. The spectral resolution achievable with microcalorimeter detectors should, for the first time, allow intrinsic Doppler correction to be performed for the precision X-ray spectroscopy of stored heavy ions. A comparison with data from a previous experiment at the ESR electron cooler, as well as the conventional method of conducting Doppler correction using electron cooler parameters, will be discussed.

Fluence enhancement of a 4 MeV-C4+ ion beam transmitted through a cylindrical glass channel after charging

We have developed a glass channel to guide ions heavier than protons and alpha particles with kinetic energies of several MeVs. The fluence of a 4 MeV-C4+ ion beam transmitted through the cylindrical glass channel (CGC) was measured by counting the number of etch pits using a CR39 solid-state nuclear track detector. After charge of the CGC using the incident ions with 31 nC, the fluence of the transmitted ions increased by 23%–26% at an angle of 0° with respect to the ion beam axis, compared to that before the charging process. In this case, the kinetic energy of the ions transmitted through the CGC maintained the incident kinetic energy of 4.0 MeV in absence of preceding charge up.

Fuel costs estimation for ion beam assisted space debris removal mission with and without attitude control

Contactless space debris removal systems are the promising direction for solving the space debris problem. An ion beam transportation method is based on blowing the space debris with a high-speed plasma flow generated by the engine of an active spacecraft. The aim of the work is to evaluate the effect of controlling the attitude motion of space debris on the amount of fuel consumption during the contactless transportation. Four control strategies for an active spacecraft are proposed and compared. The first strategy involves transporting the object without considering its attitude motion. The second strategy involves stabilizing the object in a stable angular equilibrium position. The third strategy assumes transportation the space debris in the oscillation mode with the maximum average force. The fourth strategy involves stabilizing the object in an angular position corresponding to the maximum ion force. The control laws for the spacecraft's thrusters and for the direction of the ion beam axis, implementing these strategies, are proposed. The simulation of the transportation of the rocket stage is carried out and the fuel costs for various strategies are calculated. The most preferable from the point of view of minimizing fuel consumption is the second strategy. The fourth strategy is ineffective. The results obtained in this work can be used in the preparation of contactless space debris removal missions.

Uniformity improvement of fuel target implosion by phase control in heavy ion inertial fusion

A dynamic smoothing method was proposed based on a phase control to stabilize plasma instabilities and smooth plasma non-uniformities. In this paper, the dynamic smoothing method is applied to a spherical fuel target implosion in heavy ion inertial fusion (HIF). We found that the wobbling motion of each heavy ion beam (HIB) axis induces a phase-controlled HIBs energy deposition, and consequently the phase-controlled implosion acceleration is realized, so that the HIBs illumination non-uniformity is successfully smoothed. HIB accelerators provide a well-established capability to oscillate the HIBs axes with a high frequency. In inertial confinement fusion, a fuel implosion uniformity is essentially important to compress the DT fuel and release the fusion energy, and the non-uniformity of the implosion acceleration should be less than a few %. The results in this paper also demonstrate that the wobbling HIBs would provide an improvement in the fusion energy output gain.

Study of leukosapphire surface morphology change by argon ion beam at small grazing angle

Subject of Research. The paper presents the results of experimental study on the specific features of argon ion beam effect on a sapphire surface at small grazing angles. Mechanically ground and defective epipolished leucosapphire plates with 20 × 20 × 1.2 mm in size were used as experimental samples. The initial surface roughness of the polished samples was 0.250–1 μm and of the epipolished ones was 5–10 nm. Method. The ion beam deposition setup was used for research. It includes the ion source of CLAN-53M type with ion neutralizer. The ion source generates ion flux with energies in the range of 150–1500 eV, with an output ion current density up to 4 mA/cm2, with ion current from 10 to 80 mA. The studies were carried out at different technological parameters of ion-beam polishing: the ion energy and the angle between the sapphire surface and the ion beam axis α. Main Results. We have determined effects of sapphire surface morphology change both with preservation and change in the overall roughness level, and the effect of surface structuring during processing in two projections with the formation of flat peaks with a diameter of 2 μm. The experiment results have shown that the maximum efficiency (the highest value is a change in the arithmetic average surface roughness) during ion-beam polishing is observed at α equal to 15° and the ion beam energy of 400 eV. When α value changes from 25 to 30°, an oriented change of the surface morphology from the symmetrically ordered surface microrelief to an asymmetric one occurs. At the same time, the flat sides do not bleed much, and the effect of steep shadow smoothing of the local microrelief is observed with retention of the same general roughness level. After the sample surface processing with ion beam at the first stage of the experiment, it was re-processed at 90° angle relative to the previous treatment, which led to cross-spraying of the shadow sections and the design of gentle peaks with a diameter of about 2 μm (effect of the substrate surface structuring). Practical Relevance. After the ion-beam polishing of epipolished sapphire substrate samples, smoothing of the highest surface irregularities is observed, and the average arithmetic value of surface roughness has decreased from 5.7 nm to 0.9 nm for the polished sample.

Non-uniformity smoothing of direct-driven fuel target implosion by phase control in heavy ion inertial fusion

We have proposed a dynamic smoothing method based on a phase control to smooth plasma non-uniformities in perturbed plasma systems. In this paper, the dynamic smoothing method is applied to a spherical direct-driven fuel target implosion in heavy ion inertial confinement fusion. We found that the wobbling motion of each heavy ion beam (HIB) axis induces a phase-controlled HIBs energy deposition, and consequently the phase-controlled implosion acceleration is realized, so that the HIBs irradiation non-uniformity is successfully smoothed. HIB accelerators provide a well-established performance to oscillate a HIB axis at a high frequency. In inertial confinement fusion, a fuel implosion uniformity is essentially significant for achieving the DT fuel compression and for releasing the fusion energy, and the non-uniformity of the implosion acceleration should be less than a few %. The results in this paper demonstrate that the wobbling HIBs would provide an improvement in the fuel target implosion uniformity.

Features of Ion-Beam Polishing of the Surface of Sapphire

The effect of an argon ion beam on the surface of sapphire is studied at different technological parameters: the ion energy, and the angle α between the sapphire surface and the ion-beam axis. The roughness of the sapphire surface is analyzed before and after ion polishing. The optimum ion-beam parameters are determined, at which the surface roughness after polishing decreases to 0.8 nm. At angles α = 20°–30°, the relief of the sapphire surface is found to become wavy. The study of the impact of the ion energy on the roughness of the sapphire surface in the 400–1200-eV range reveals that an increase in the energy of the ion beam to 1200 eV is accompanied with a decrease by 8.8 times in the roughness which falls below the level of 3 nm.

Azimuthal velocity measurement in the ion beam of a gridded ion thruster using laser-induced fluorescence spectroscopy

This paper presents the first laboratory-based study to measure the azimuthal velocities of ions in the beam of a gridded ion thruster. Through the operation of gridded ion thrusters in space, it has been confirmed that these thrusters cause an unexpected roll torque about the ion beam axis. To reveal the physical mechanism that produces this torque, laser-induced fluorescence spectroscopy has been applied to a microwave ion thruster that was installed in Japanese asteroid probes. This technique can be used to measure the azimuthal velocity by estimating the Doppler shift of the Xe II 5p4()6p 5/2 to Xe II 5p4()6s 3/2 transition at 834.659 nm. The measurement was conducted without a neutralizer cathode to avoid the possibility of the cathode affecting the trajectory of the ion beam. The measured velocity functions are the sum of the spectra of the high velocity beam ions and those of charge exchange ions. By deconvolving these spectra, the azimuthal velocities were successfully measured and were found to range from −700 to 620 m s−1 with an accuracy of ±25%. The measured azimuthal velocity profile was accurately reproduced by the simulated velocity profile obtained using a model, which includes the effects of the maximum possible misalignment of the accelerator grid with respect to the screen grid and the Lorentz force produced by the magnetic field leaked from the discharge chamber. A roll torque of 0.5 ± 0.1 μN m about the thrust axis was calculated from the velocity profile, which is lower than that reported in flight data, but additional mechanisms are suggested to explain this discrepancy.

Orthogonal time-of-flight mass spectrometry of an ion beam with a broad kinetic energy profile.

A combined experimental and modeling effort is undertaken to assess a detection system composed of an orthogonal extraction time-of-flight (TOF) mass spectrometer coupled to a continuous ion source emitting an ion beam with kinetic energy of several hundred eV. The continuous ion source comprises an electrospray capillary system employing an undiluted ionic liquid emitting directly into vacuum. The resulting ion beam consists of ions with kinetic energy distributions of width greater than a hundred of eV and mass-to-charge (m/q) ratios ranging from 111 to 500 000 amu/q. In particular, the investigation aims to demonstrate the kinetic energy resolution along the ion beam axis (axial) of orthogonally extracted ions in measurements of the axial kinetic energy-specific mass spectrum, mass flow rate, and total ion current. The described instrument is capable of simultaneous measurement of a broad m/q range in a single acquisition cycle with approximately 25 eV/q axial kinetic energy resolution. Mass resolutions of ∼340 (M/ΔM, FWHM) were obtained for ions at m/q = 1974. Comparison of the orthogonally extracted TOF mass spectrum to mass flow and ion current measurements obtained with a quartz-crystal microbalance and Faraday cup, respectively, shows reasonable numeric agreement and qualitative agreement in the trend as a function of energy defect.

Determination of the force transmitted by an ion thruster plasma plume to an orbital object

An approach to determine the force transmitted by the plasma plume of an ion thruster to an orbital object immersed in it using its central projection on a selected plane is proposed. A photo camera is used to obtain the image of the object central projection. The algorithms for the calculation of the transmission of momentum by the impacting ion beam are developed including the determination of the object contour and the correction of the error due to a camera offset from the ion beam axis, and the computation of the fraction of the ion beam that impinges on the object surface.

Cross-Linked Carbon Nanotube Heat Spreader

ABSTRACTAmong the exceptional properties of isolated individual carbon nanotubes (CNTs), exceptional thermal conductivity along their axis has been demonstrated, However they have also shown poor thermal transfer between adjacent CNTs. Thick bundles of aligned CNTs have been used as heat pipes, but the thermal input and output power densities are the same, providing no heat spreading effect. We demonstrate the use of energetic argon ion beams to join overlapping CNTs in a thin film to form an interpenetrating network with an isotropic thermal conductivity of 2150 W/m K. Such thin films may be used as heat spreaders to enlarge the thermal footprint of laser diodes and CPU chips, for example, for enhanced cooling. At higher ion energies and fluence, the CNTs appear to collapse and reform, aligned parallel to the ion beam axis, and form dense high aspect ratio tapered structures. The high surface area of these structures lends themselves to applications in energy storage, for example. We consider the mechanisms of energetic ion interaction with CNTs and junction formation of two overlapping CNTs during the subsequent self-healing process, as well as the formation of high aspect ratio structures under more extreme conditions

A new MOTRIMS apparatus for high resolution measurements in ion-atom collisions and trapped atoms studies

A new MOTRIMS (magneto-optical trap-target recoil ion momentum spectroscopy) apparatus has been built at the LPC-CAEN, and recently tested with a beam of 2 keV Na+ projectiles colliding on a trapped Rb target. In this work, we demonstrate the capability of the setup to provide, with a very high signal over background ratio, fully differential cross sections in scattering angle, initial state, and final state of the system. The fine control of the trapping lasers, the extraction of the recoil ions transverse to the ion beam axis, and the fast switching for the MOT magnetic field, are three characteristics promising for new studies including collisions with oriented targets or requiring electron detection.

A new magneto-optical trap-target recoil ion momentum spectroscopy apparatus for ion-atom collisions and trapped atom studies

A new magneto-optical trap-target recoil ion momentum spectroscopy apparatus has been built and tested at the LPC-CAEN. Dedicated to ion-atom collisions studies and excited fraction measurements, the setup combines a projectile ion beam line, a target of cold rubidium atoms provided by a magneto-optical trap (MOT), and a recoil ion momentum spectrometer. In a test experiment using a beam of Na(+) projectiles, we demonstrate its capability to measure, with a very high signal over background ratio, fully differential cross sections in scattering angle, initial state, and final state of the system. We detail, in this work, features that had not been described previously in the literature: an extraction of the recoil ions transverse to the ion beam axis, and a fast switch for the MOT magnetic field. Advantages of transverse versus longitudinal extraction are discussed, and future possibilities for the setup are presented.

Electron capture dissociation in a linear radiofrequency‐free magnetic cell

Electron capture dissociation in a linear radiofrequency‐free magnetic cell

Nano-Structure Controlled Polymer Electrolyte Membranes for Fuel Cell Applications Prepared by Ion Beam Irradiation

Fluoropolymer-based electrolyte membranes for fuel cells were prepared by using heavy ion beams from the cyclotron accelerator of the Takasaki Ion Accelerators for Advanced Radiation Application (TIARA), Japan Atomic Energy Agency (JAEA). The preparation method for these so-called nano-scale structure-controlled membranes involves (i) the swift heavy ion irradiation of polyvinylidene fluoride (PVDF) films and subsequent chemical etching to obtain cylindrical pores with a diameter of 100 nm, and (ii) the filling of proton-conducting polymer chains into the etched pores by gamma-ray-induced graft polymerization. The proton transport only in the thickness direction was observed for the resulting membranes with controlled ion exchange capacities, indicating the formation of one-dimensional straight proton-conducting pathways parallel to the ion-beam incident axis. The membranes exhibited a lower water uptake and reduced methanol permeability compared to commercially-available Nafion probably due to the restricted structures.

Nitride Formation on Titanium under Irradiation of Intense Pulsed Ion Beam

Nitriding of titanium was achieved in a vacuum of ~2×10-2 Pa by applying intense pulsed ion beam (IPIB) irradiation. Various phases including ‘pure’ nitrides (e.g. Ti2N, TiN) as well as carbonitrides (e.g. TiC0.3N0.7) were found on the IPIB-irradiated surfaces that depended on the ion beam intensity, shot number, and sample position with respect to the ion beam axis. It was found that the nitrides were preferably produced at moderate beam intensity by which the nitriding depth increased greatly with multi-shot irradiation. No or less nitrides were produced under irradiation of very high intensity or less number of shots. It is demonstrated that the IPIB nitriding process is very efficient even in vacuum where the residual N2 can readily react with melted Ti surfaces under IPIB irradiation. The origin of incorporated C in the nitrides is mainly attributed to the anode material of ion diode used in the IPIB apparatus.

Nanopantography: A New Method for Massively Parallel Nanopatterning over Large Areas

We report a radically different approach to the versatile fabrication of nanometer-scale preselected patterns over large areas. Standard lithography, thin film deposition, and etching are used to fabricate arrays of ion-focusing microlenses (e.g., small round holes through a metal/insulator structure) on a substrate such as a silicon wafer. The substrate is then placed in a vacuum chamber, a broad-area collimated beam of ions is directed at the substrate, and electric potentials are applied to the lens arrays such that the ions focus at the bottoms of the holes (e.g., on the wafer surface). When the wafer is tilted off normal (with respect to the ion beam axis), the focal points in each hole are laterally displaced, allowing the focused beamlets to be rastered across the hole bottoms. In this "nanopantography" process, the desired pattern is replicated simultaneously in many closely spaced holes over an area limited only by the size of the broad-area ion beam. With the proper choice of ions and downstream gaseous ambient, the method can be used to deposit or etch materials. Data show that simultaneous impingement of an Ar(+) beam and a Cl(2) effusive beam on an array of 950-nm-diam lenses can be used to etch 10-nm-diam features into a Si substrate, a reduction of 95x. Simulations indicate that the focused "beamlet" diameters scale directly with lens diameter, thus a minimum feature size of approximately 1 nm should be possible with 90-nm-diam lenses that are at the limit of current photolithography. We expect nanopantography to become a viable method for overcoming one of the main obstacles in practical nanoscale fabrication: rapid, large-scale fabrication of virtually any shape and material nanostructure. Unlike all other focused ion or electron beam writing techniques, this self-aligned method is virtually unaffected by vibrations, thermal expansion, and other alignment problems that usually plague standard nanofabrication methods. This is because the ion focusing optics are built on the wafer.

A FIB Micro-Sampling Technique for Three-Dimensional Characterization of a Site-Specific Defect

Abstract In characterization or failure analysis of new materials and semiconductor devices, the requirements for three dimensional observation and analysis are rapidly increasing. We discuss techniques for specimen preparation, three-dimensional observation, and elemental analysis of semiconductor devices that we developed using a system consisting of a dedicated focused ion beam (FIB) instrument and a scanning transmission electron microscope (STEM). The system utilizes a FIB-STEM compatible specimen holder with a specially designed rotation mechanism, which allows 360° rotation of a specimen on a conical stage (needle stub) around the ion beam axis of the FIB system and 360° rotation perpendicular to the electron beam in the STEM. A piece of sample (micro sample) is extracted from a specific-site by the micro-sampling technique and mounted on the needle stub. Instruments used in the study are the Hitachi FB-2100 FIB system with a micro-sampling attachment and the HD-2300 field emission 200kV STEM.