DC Ion Beam Research Articles

Conceptual Design of an Electrostatic Trap for High-Intensity Highly Charged Pulsed Beam

Highly charged ion sources play an important role in the advancement of heavy-ion accelerators worldwide. Demands of highly charged heavy ions for new and existing accelerators have driven the performance of ion sources to their limits. A new high charge state ion accumulating trap concept is proposed that converts a dc ion beam from an electron cyclotron resonance (ECR) ion source into a short-pulsed ion beam with suitable compression ratios. With a simple trap composed of an electron gun, a solenoid, and a set of drift tubes (DTs), the injected ions from a dc operation ECR ion source will be trapped radially and axially. By manipulating the potential of the DT, highly charged ions can be accumulated with multiple injections and extracted with augmentation of ion intensity in pulses of tens of μs. This article presents the simulations and design features of the envisioned ion trap.

Ion sputtering for preparation of thin MAX and MXene phases

Thin films of MAX and MXene phases were prepared by ion beam sputtering followed by thermal annealing in vacuum. For this purpose, a Low Energy Ion Facility (LEIF) using heavy ions for target irradiation was developed, and the DC ion beam sputtering method was implemented. The process for preparing MAX and MXene thin composites consists of two steps. First step: bombarding the elemental targets with low-energy ions (either all targets together, each with the corresponding size, or each target separately and repeatedly); it results in synthesis of either homogeneous layers of mixed phases or multilayer arrays of individual phases. Second step: thermal annealing under vacuum with a suitable temperature and time to induce a diffusion process, mutual phase interaction and finally the formation of MAX or MXene composites with the desired structure. After installation of the LEIF system and the introduction of the two-step method, i.e. DC ion sputtering with subsequent thermal processing, the first Ti-based MAX and MXene carbides, Ti2SnC and Ti2C, in thin films of composites were prepared and analyzed.

Direct-current current transformer for the measurement of an electric propulsion ion beam.

An important task in the development of electric propulsion devices is ground-based testing. In order to characterize electric thrusters, their generated ion beams are regarded as figures of merit and have to be well-known and understood. We present an approach to measure DC ion beam currents generated by electric thrusters by means of an inductive direct-current current transformer. In contrast to commonly used devices like Faraday cups, this device can measure the beam current non-intrusively by means of magnetic field coupling rather than charge collection. This paper shows the development of a prototype sensor which can measure currents in the typical range for electric thrusters with high resolution and satisfactory accuracy. A detailed SPICE model to assist during hardware development is also introduced and verified by test case measurements. The prototype has been tested and validated with a radio-frequency ion thruster. Its readout shows very good agreement with the output of an analytical model which computes a Gaussian-shaped ion beam in the far-field based on experimental input data.

Four-harmonic buncher for radioactive and stable beams switching at the ATLAS facility

The Argonne Tandem Linac Accelerator System (ATLAS) is planning an upgrade to a multi-user facility to simultaneously accelerate both stable beams from an ECR ion source and radioactive beams from an Electron Beam Ion Source charge breeder. The ATLAS Multi-User Upgrade will need to provide high transmission of ion beams with a mass-to-charge ratio up to 7 as it enables more options to alternate radioactive and stable beams. Currently, the bunching is provided with a lumped circuit multi-harmonic buncher, which cannot effectively operate at the required amplitude of the saw-tooth voltage for ions with mass-to-charge ratio of 7 due to thermal issues.RadiaBeam Systems in collaboration with Argonne National Laboratory has designed a four-harmonic coaxial resonator buncher with the ATLAS fundamental frequency of 12.125 MHz, and a compact, less than 2-m-long, footprint, capable of providing the required voltage of 6.2 kV. This device allows fast and reliable pre-bunching of DC ion beams with the capability of fast switching of heavy-ion radioactive and stable beams for delivery to multiple users. In this paper, we will discuss the RF and engineering design considerations of this buncher.

Integrated Linear-processing Ion-beam Sputtering System Using a Meter-scale Ribbon-beam

We present a system capable of performing linear PVD processing by DC ion beam sputtering, suitable for reactive or high-vacuum deposition of dielectrics, metals, or magnetic materials onto conductive, insulating, or magnetic substrates. This equipment can be installed on a single vacuum flange for mounting on a variety of vacuum systems, but linear flow systems are preferred. Our recently developed ion source can generate ribbon ion beams of high current and low divergence over a wide range of energies, but is optimized for about 1 to 5 keV, and high ion currents of up to 1A per meter breadth; breadths of several meters are possible. The current density is an order of magnitude higher than existing systems. Uniformity is intrinsically good and can be controlled in real-time. The ion source and the sputter target are mounted close to each other and to the target; the cross section of the equipment does not change as the equipment is scaled up to large dimensions. The ion beam impinges on the sputter target at the optimum angle and energy, in a field-free region, and in high vacuum. This combination of conditions is unique, and dramatically raises the sputter yield. Free choice of beam energy permits higher thermal efficiency. High vacuum means that the deposited atoms comprising the film retain the full energy of several eV that was produced in the sputtering process. The geometry further permits extremely simple and efficient jetting of reactive gases such as oxygen for the production of oxide films. The single broad-beam source has far higher current density and a far more compact layout than existing ion-beam sputtering systems, and can be installed in linear processing systems in a similar manner to linear magnetrons.

A space charge compensation model for positive DC ion beams

In this paper, we revisit and extend a formula to predict the compensation of space charge in positive DC ion beams of non-relativistic energy, as they are for example found in the injector beam lines of heavy ion accelerator facilities.The original formula was presented in 1975 by Igor Gabovich et al. and takes into account the de-compensation through Coulomb collisions of the primary beam ions and the compensating electrons. We extend its usability to arbitrary (positive) charge states of the ions and non-quasineutral beams.The resulting formula compares well with measurements using a retarding field analyzer and a multi-species generalization of it was incorporated into beam transport simulations using the particle-in-cell code WARP.

Performance characteristics of HBC stripper foils irradiated by 650 keV H− and high intensity DC ion beams

Newly developed Hybrid type Boron mixed Carbon (HBC) stripper foils are extensively used not only for the RCS of J-PARC and PSR of LANL, but also for other low energy, high intensity proton accelerators in medical applications. We had before tested HBC stripper foils with 3.2MeV Ne+ and DC heavy ion beams.In order to further understand characteristics of HBC stripper foils, we measured the following parameters using the KEK-650keV H− and light ion Cockcroft Walton DC accelerator: foil lifetime, thickness reduction, uniformity before and after beam irradiation, and foil deformation. Energy deposition in the present experiment was adjusted to a similar level to that of the HBC foil used in the RCS of J-PARC’. In addition, to understand the reason why the HBC stripper foils have high durability against high intensity beam irradiation, we investigated various physical properties, and compared them between the HBC foils and other tested carbon stripper foils.The sizes of the carbon particles in the HBC foil were found to play a vital role in the lifetime.

The decay of ion bunches in the self-bunching mode

The properties of ion bunches stored in an electrostatic ion beam trap (EIBT) have been investigated using the Cryogenic Trap for Fast ion beams (CTF). The extremely high vacuum used rendered the main ion loss mechanism, namely collisions with the rest gas, negligible. Aluminum dimer anions were photo-detached by a pulsed laser to measure the longitudinal ion distribution in the bunch, which for the first time revealed the presence of a dc ion beam component co-existing with the oscillating ion bunch after several hundreds of revolutions. Bunches stabilized by the so-called self-bunching mode of operation have been observed for times as long as 12 s (a factor of 100 longer than previous room-temperature experiments) using N+2 and Al−2 bunches at 6–7.1 keV beam energies after which the bunch abruptly decayed. The decay of the bunch was observed to be intensity dependent and is well reproduced by a model that includes the expansion of the bunch along the beam axis, intrabeam scattering and collisional losses between the bunch and the dc component. Radio-frequency bunching of the ions resulted in the extension of the bunch observation time to 600 s, placing upper limits on all other EIBT ion bunch and trap losses as well as supporting the newly developed decay model and EIBT-adapted bunch dynamics.

Lithium diffusion in sputter-deposited Li4Ti5O12 thin films

Li4Ti5O12 (LTO) thin films are deposited by dc-ion beam sputtering at different oxygen partial pressures and different substrate temperatures. In order to investigate, how these two parameters influence the atomic structure, the specimens are characterized by X-ray diffraction and transmission electron microscopy. Electrochemical characterization of the films is done by cyclic voltammetry and chrono-potentiometry. To determine an averaged chemical diffusion coefficient of lithium, a method is developed, evaluating c-rate tests. The results obtained by this method are compared to results obtained by the well established galvanostatic intermittent titration technique (GITT), which is used to determine a concentration dependent diffusion coefficient of lithium in LTO.

Dual-plasma ion process for surface treatment of insulators

Surface treatment of insulator materials has growing needs recently. However, accumulation of charges on the insulator surface limits the applicability of plasma methods for the insulator processing. A radio-frequency-bias method is a good choice but it still has a problem coming from the oscillating sheath potential. In the present study, we are proposing the dual-plasma ion process, a new plasma process that enables for insulator samples to be treated by an energy-controlled, dc ion beam without surface charging. The concept and results of the proof-of-principle experiment are given.

Ion beam sputter deposition of V 2O 5 thin films

V 2O 5 thin films were deposited by means of dc-ion beam sputtering. To determine the influence of various deposition parameters, samples were characterized by X-ray diffractometry and transmission electron microscopy. Using electron energy loss spectroscopy, the oxidation state of vanadium was quantified based on the chemical shift of absorption edges. Measurement of in-plane direct current showed that the electronic conductivity varies over several orders of magnitude depending on the preparation conditions. The desired structure suitable for battery applications is achieved by sputtering under partial pressure of oxygen and suitable post-annealing under ambient atmosphere. Reversible intercalation of Li into the produced thin films was demonstrated.

A new SIMS paradigm for 2D and 3D molecular imaging of bio-systems

With the implementation of focused primary ion beams, secondary ion mass spectrometry (SIMS) has become a significant technique in the rapidly emerging field of mass spectral imaging in the biological sciences. Liquid metal ion guns (LMIG) offered the prospect of sub-100 nm spatial resolution, however this aspiration has yet to be reached for molecular imaging. This brief review shows that using LMIG the limitations of the static limit and low ionization probability will restrict useful imaging to around 2 mum spatial resolution with high-yield molecules. The only prospect of going beyond this in the absence of factors of 100 increase in ionization probability is to use polyatomic ion beams such as C (60) (+) , for which bombardment induced damage is low. In these cases sub-micron imaging becomes possible, using voxels together with molecular depth profiling and 3D imaging. The discussion shows that conventional ToF-SIMS instrumentation then becomes a limitation in that the pulsed ion beam has a very low duty cycle which results in inordinately long analysis times, and pulsing the beam means that high-mass resolution and high spatial resolution are mutually incompatible. New instrumental configurations are described that allow the use of a dc ion beam and separate the mass spectrometry for the ion formation process. Early results from these instruments suggest that sub-micron analysis and imaging with high mass resolution and good ion yields are now realizable, although the low ion yield issue still needs to be solved.

Development of a pepper pot emittance probe and its application for ECR ion beam studies

A pepper pot–scintillator screen system has been developed and used to measure the emittance of DC ion beams extracted from a high-intensity permanent magnet ECR ion source. The system includes a fast beam shutter with a minimum dwell time of 18ms to reduce the degradation of the CsI(Tl) scintillator by DC ion beam irradiation and a CCD camera with a variable shutter speed in the range of 1μs–65s. On-line emittance measurements are performed by an application code developed on a LabVIEW platform. The sensitivity of the device is sufficient to measure the emittance of DC ion beams with current densities down to about 100nA/cm2. The emittance of all ion species extracted from the ECR ion source and post-accelerated to an energy of 75–90keV/charge have been measured downstream of the LEBT. As the mass-to-charge ratio of ion species increases, the normalized RMS emittances in both transverse phase planes decrease from 0.5–1.0πmmmrad for light ions to 0.05–0.09πmmmrad for highly charged 209Bi ions. The dependence of the emittance on ion's mass-to-charge ratio follows very well the dependence expected from beam rotation induced by decreasing ECR axial magnetic field. The measured emittance values cannot be explained by only ion beam rotation for all ion species and the contribution to emittance of ion temperature in plasma, non-linear electric fields and non-linear space charge is comparable or even higher than the contribution of ion beam rotation.

Synthesis of the silicon and silicon oxide doped a-C:H films from hexamethyldisiloxane vapor by DC ion beam

In this research silicon and silicon oxide doped hydrogenated amorphous carbon films have been synthesized by direct ion beam deposition from hexamethyldisiloxane (HMDSO) vapor mixture with hydrogen (H 2) or acetylene (C 2H 2) gas. Adherent and stable coatings of the thickness up to 0.8 μm were deposited onto the stainless steel and tooling steel. Presence of a few atomic percents of Si was enough to achieve stable coatings. In the HMDSO + C 2H 2 film silicon is found in the form of the SiC while in HMDSO + H 2 film Si presents as silicon oxide (SiO x ). Raman spectra of the deposited films were typical for diamond like carbon (DLC). Films deposited from mixture with hydrogen gas had higher optical transparency (E 04 bandgap 3.1 vs. 1.6 eV for film deposited from mixture with acetylene gas) and lower refractive index (1.7 vs. 2.1 at 632.8 nm wavelength). However, more transparent SiO x doped DLC films had more disordered structure as well.

Beam loss studies in high-intensity heavy-ion linacs

The proposed Rare Isotope Accelerator (RIA) Facility, an innovative exotic-beam facility for the production of high-quality beams of short-lived isotopes, consists of a fully superconducting 1.4 GV driver linac and a 140 MV postaccelerator. To produce sufficient intensities of secondary beams the driver linac will provide 400 kW primary beams of any ion from hydrogen to uranium. Because of the high intensity of the primary beams the beam losses must be minimized to avoid radioactivation of the accelerator equipment. To keep the power deposited by the particles lost on the accelerator structures below $1\text{ }\mathrm{W}/\mathrm{m}$, the relative beam losses per unit length should be less than ${10}^{\ensuremath{-}5}$, especially along the high-energy section of the linac. A new beam dynamics simulation code TRACK has been developed and used for beam loss studies in the RIA driver linac. In the TRACK code, ions are tracked through the three-dimensional electromagnetic fields of every element of the linac starting from the electron cyclotron resonance (ECR) ion source to the production target. The simulation starts with a multicomponent dc ion beam extracted from the ECR. The space charge forces are included in the simulations. They are especially important in the front end of the driver linac. Beam losses are studied by tracking a large number of particles (up to ${10}^{6}$) through the whole linac considering all sources of error such us element misalignments, rf field errors, and stripper thickness fluctuations. For each configuration of the linac, multiple sets of error values have been randomly generated and used in the calculations. The results are then combined to calculate important beam parameters, estimate beam losses, and characterize the corresponding linac configuration. To track a large number of particles for a comprehensive number of error sets (up to 500), the code TRACK was parallelized and run on the Jazz computer cluster at ANL.

Compact surface plasma sources for heavy negative ion production

Features of a compact surface plasma source designed for heavy negative ion beam production are considered. Discharges in crossed E×B fields with hollow cathodes were used for efficient plasma generation. Production of heavy negative ion beams by plasma interaction with the surface of spherical focusing emitters made of different materials, such as copper and lanthanum hexaboride, with cesium catalysis are presented. The dynamics of emitter activation is discussed. dc ion beams with current up 0.9 mA have been extracted from the compact surface plasma sources with a 12-mm-diam LaB6 emitter and a emission aperture of 3 mm diam. Minimizing plasma and gas thickness between emitter and emission aperture is essential for minimizing negative ion destruction and maximizing high intensity beam production. A small mass analyzer and secondary ion mass spectroscopy were used to quantify boron ion yield. Presence of atomic and molecular boron negative ions is confirmed. The estimated emittance of the 0.5 mA heavy negative ion beam is ε=13 π mm mrad(MeV)1/2.

A prototype of a highly sensitive cryogenic current comparator with a HTS SQUID andHTS magnetic shield

A highly sensitive cryogenic current comparator (CCC) for the measurement of theintensity of faint beams, such as a radioisotope beam, was developed for the RIKEN RIbeam factory project. This monitor is composed of a high-temperature superconducting(HTS) magnetic shield and an HTS current sensor including an HTS superconductingquantum interference device (SQUID), which are cooled by a low-vibration pulse-tuberefrigerator. Both the HTS magnetic shield and the HTS current sensor based onBi2–Sr2–Ca2–Cu3–Ox (Bi-2223) were fabricated by dip-coating on a 99.9% MgO ceramic substrate.Recently, a prototype of the HTS SQUID CCC system was completed and wecarried out the first measurements using DC ion beams in the current range of0.5–20 µA, which were produced by the ECR (electron cyclotron resonance) ion source in the CNSexperimental hall. After the measurement was successfully carried out in the CNS, weinstalled the system into the beam transport line of the RIKEN Ring Cyclotron (RRC) tomeasure the current of the high-energy heavy-ion beam which has a bunchedmicrostructure. In this paper, we describe the performance and the present status of theprototype of the HTS SQUID CCC system and the results of the ion beam measurement.

Preparation of giant magnetostrictive thin film by magnetron and ion beam sputtering processes

Thin films of giant magnetostrictive materials were formed by dc magnetron sputtering and ion beam sputtering processes. A systematic investigation was made to examine the effect of these deposition processes on the magnetic properties and magnetostriction of TbFe2 and (Tb, Dy)Fe2 thin films. The magnetostriction of the films formed by dc sputtering was in the range from 200 to 400 ppm at a magnetic field H=15 kOe, whereas the films formed by the ion beam sputtering exhibited a slightly higher magnetostriction. For both processes, the increase in Ar partial pressure in the deposition processes strongly changed magnetic anisotropy from perpendicular to in plane, and increased magnetostriction and magnetostrictive response at low magnetic fields. However, the mixture of Xe gas into Ar gas in the dc sputtering lowered magnetization and gave almost no effect on magnetic anisotropy.

Ultrathin protective overcoats on magnetic hard disks

Composition, structure and protective properties of 50-100 /spl Aring/ thick hard disk overcoats prepared by DC magnetron sputtering and ion beam deposition were examined. Ion beam coatings were shown to possess superior properties as compared to the sputtered carbon films by nanoscale scratching and electrochemical corrosion techniques.

Design and Fabrication of DC Ion Beam for Heating of Plasma

DC type ion beam is produced by using different percentages of argon gas content. In this manner, about 90% of argon gas was ionized, and the ion beam diameter is controllable by the extractor in 10−3torr. The density of charged particles was measured by Faraday cup. In this paper, some recent findings are presented dealing with the analysis of the production of ion beam with different energy levels. Result of measurements compare with that of other sources.