Beam-induced Effects Research Articles

Beam-induced atomic migration at Ag-containing nanofacets at an asymmetric Cu grain boundary

Abstract

Intense heavy ion beam-induced temperature effects in carbon-based stripper foils

At the future FAIR facility, reliably working solid carbon stripper foils are desired for providing intermediate charge states to SIS18. With the expected high beam intensities, the foils experience enhanced degradation and limited lifetime due to severe radiation damage, stress waves, and thermal effects. This work presents systematic measurements of the temperature of different carbon-based stripper foils (amorphous, diamond-like, and carbon-nanotube based) exposed to 4.8 MeV/u U, Bi, and Au beams of different pulse intensities. Thermal and spectroscopic analyses were performed by means of infrared thermography and Fourier transform infrared spectroscopy. The resulting temperature depends on the foil thickness and strongly increases with increasing pulse intensity and repetition rate.

Analysis of electron beam-induced effect on electrical switching properties of glass chalcogenide GeTe thin films through Raman spectroscopy

The electrical switching behavior of amorphous GeTe thin films deposited by thermal evaporation technique and exposed to different doses of electron irradiation has been investigated. All the glasses subjected to electron irradiation below 8 kGy have been found to exhibit memory-type electrical switching behavior whereas irradiation at 8 kGy led to electrical breakdown of the device. It has been observed that the threshold switching value decreases initially and then rises again with increasing doses which may be due to structural rearrangement upon irradiation. Raman study has been performed to get greater insight on the irradiation-induced structural modification in the sample. The study exhibited remarkable change in the relative intensity, along with significant band shift with increasing irradiation dose which is in consistent with threshold field for switching.

Beam-induced effects and radiological issues in high-intensity high-energy fixed target experiments

The next generation of accelerators for Megawatt beams moves us into a completely new domain of extreme specific energies of up to 0.1 MJ/g (Megajoule/gram) and specific power up to 1 TW/g (Terawatt/gram) in interactions with matter. The paper is focused on deleterious effects of controlled and uncontrolled impacts of such beams on components of beam-lines, target stations, beam absorbers, shielding and environment. Two new experiments at Fermilab are taken as an example. The Long-Baseline Neutrino Experiment (LBNE) will explore the interactions of the world's highest-intensity neutrino beam by sending it from Fermilab more than 1,000 kilometers through the Earth's mantle to a large liquid argon detector. The Mu2e experiment is devoted to studies of the conversion of a negative muon to electron in the field of a nucleus without emission of neutrinos.

Luminosity measurement at ILC

In this paper we describe a method of luminosity measurement at the future linear collider ILC that estimates and corrects for the impact of the dominant sources of systematic uncertainty originating from the beam-induced effects and the background from physics processes. Based on the relativistic kinematics of the collision frame of the Bhabha process, the beam-beam related uncertainty is reduced to a permille independently of the precision with which the beam parameters are known. With the specific event selection, different from the isolation cuts based on topology of the signal used at LEP, combined with the corrective methods we introduce, the overall systematic uncertainty in the peak region above 80% of the nominal center-of-mass energy meets the physics requirements to be at the few permille level at all ILC energies.

Studies of Corrosion of Al Thin Films using Liquid Cell Transmission Electron Microscopy

ABSTRACTA fundamental understanding of the processes that occur during early stages of corrosion is traditionally limited by the dearth of techniques that probe the liquid-solid interface with both high spatial resolution and microstructural detail such as grain size and orientation. Here, we demonstrate that with a microfluidic liquid flow cell holder, we can track the progress of corrosion in situ in Al thin films with transmission electron microscopy (TEM). To mitigate the loss of resolution caused by imaging through liquid, we developed a method in which the liquid is temporarily de-wetted from the entire windowed area by switching the liquid stream from pure water to a mixture of ethanol and water. In the de-wetted region, we then collected images of the film microstructure with high spatial resolution over regular intervals while maintaining a low electron flux over the imaged area to minimize beam-induced effects. For as-deposited films, we find that the corrosion progresses in a fractal manner, consistent with reported behavior for films studied in water with low iron and chloride concentrations. For films that were subjected to rapid thermal annealing, we observe a higher density of pitting events, which we attribute to defects created by thermal stress in the oxide film. Furthermore, we observe that the pits can form at multiple locations in a single grain and are not confined to grain boundaries.

Swift heavy ion-induced effects in Ce-doped nickel ferrite nanoparticles

Swift heavy ions of various energies are being used for material modifications. The induced modifications depend on the kind of defects produced during interaction of ions with the target material. In the present work, irradiation of 200 MeV Ag beam-induced effects in NiFe2O4 and NiCe0.04Fe1.96O4 nanoparticles are studied at two different fluences, 2×1012 and 1×1013 ions/cm2. Nanoparticles of nickel ferrite and Ce-doped nickel ferrite were prepared by chemical route. X-ray diffraction pattern shows peaks corresponding to pure spinel structure in both the systems, NiFe2O4 and NiCe0.04Fe1.96O4. The pristine as well as irradiated nanoparticles were characterized by high-resolution transmission electron microscopy (HRTEM), Raman spectroscopy, electron paramagnetic resonance spectroscopy (EPR) and vibrating sample magnetometer (VSM). Raman spectra show bands corresponding to spinel structure. After irradiation, the position of the bands does not change significantly for both samples. The widths corresponding to the same band in both the systems show opposite trend with fluence. VSM results show that after irradiation, the magnetization decreases from 40 to 32 A m2/kg for NiFe2O4 and from 39 to 31 A m2/kg for NiCe0.04Fe1.96O4. EPR results show that after doping with Ce as well as irradiation, the EPR line width is reduced, making samples important for applications.

In situ imaging of orthoclase–aqueous solution interfaces with x-ray reflection interface microscopy

The use of x-ray reflection interface microscopy (XRIM) to image molecular-scale topography at the aqueous–solid interface, in situ, is described. Specifically, we image interfacial topography of the orthoclase-(001)–aqueous solution interface at room temperature and describe the challenges associated with in situ XRIM imaging. The measurements show that the reflectivity signal for in situ XRIM measurements is substantially smaller than that for ex situ measurements, because of both intrinsic and extrinsic factors. There is also a systematic temporal reduction in the image intensity with increasing x-ray dose, revealing that interaction of the focused x-ray beam with the orthoclase interfaces leads to interfacial perturbations, presumably in the form of surface roughening. This image fading is localized to the x-ray beam footprint, suggesting that the primary damage mechanism is initiated by photoelectrons produced by x-ray beam absorption near the substrate–electrolyte interface. Finally, the role of aqueous solution composition in controlling the sensitivity of the orthoclase surface to x-ray beam-induced effects is explored. A substantial increase in the orthoclase (001) surface stability was observed in solutions having elevated ionic strength, apparently as a result of the reduced lifetime of radiation chemistry products at these conditions.

Beam-induced effects in soft X-ray photoelectron emission microscopy experiments

The beam-induced effects, a consequence of the high photon flux density used in soft X-ray photoelectron emission microscopes in operation at the 3rd generation synchrotron sources, are discussed and illustrated using some representative results obtained with the microscopes at the laboratory Elettra. The focus is on the photon-induced charge potential and chemical degradation, which might be a severe problem for photon-sensible specimens. The possible steps to avoid, reduce or even make use of the beam-induced effects are outlined.

Electron beam-induced thickening of the protective oxide layer around Fe nanoparticles

There are many circumstances in science where the process of measuring the properties of a system alters the system. An imaging process can exert an inadvertent effect on the object being observed. Consequently, what we observe does not necessarily represent what had been present before the observation. Normally, this effect can be ignored if the consequence of such a change is believed not to be significant. The expansion of nanostructured materials has made high-resolution transmission electron microscopy one of the indispensable tools for probing the characteristics of nanomaterials. Modification of nanoparticles by the electron beam during their imaging has been widely noticed and this is generally believed to be due to electron beam-induced heating effect, defect formation in the particles, charging of the particle, or excitation of surrounding gases. However, an explicit experimental identification of which process dominates is often very hard to establish. We report the thickening of native oxide layer on iron nanoparticle under electron beam irradiation. Based on atomic level imaging, electron diffraction, and computer simulation, we have direct evidence that the protecting oxide layer formed on Fe nanoparticle at room temperature in air or oxygen continues to grow during an electron beam bombardment in the vacuum system typical of most TEM systems. Typically, the oxide layer increases from ∼3 to ∼6 nm following ∼1 h electron beam exposure typically with an electron flux of 7×10 5 nm −2 s −1 and an vacuum of ∼3×10 −5 Pa. Partial illumination of a nanoparticle and observation of the shell thickening conclusively demonstrates that many of the mechanisms postulated to explain such processes are not occurring to a significant extent. The observed growth is not related to the electron beam-induced heating of the nanoparticle, or residual oxygen ionization, or establishment of an electrical field, rather it is related to electron beam-facilitated mass transport across the oxide layer (a defect-related process). The growth follows a parabolic growth law.

Calcium fluoride windows for high-energy chemical lasers

The development of high-energy lasers requires optical windows capable of handling megajoule beam energies without compromising the system’s performance. Calcium fluoride (CaF2) has been identified as a prime candidate for windows operating at chemical laser wavelengths due to very low bulk absorption and exceptionally small thermal lensing coefficients; it is, however, vulnerable to structural failure owing to poor mechanical strength characteristics and a large thermal stress factor. It is, therefore, essential to properly assess the ultimate potential of this material, which we attempt to do here in the following manner: (a) We assemble reliable numbers for all pertinent properties of (111)-oriented CaF2 single crystals and polycrystalline isotropic aggregates (PIAs), such as fusion-cast CaF2, which requires addressing issues relating to the elastic properties, the stress-optic coefficients, and the flexural strength. (b) We provide correct analytical expressions for evaluating the impact of pressure- and beam-induced effects on wave-front phase distortions and mechanical failure modes, taking advantage of a previous investigation [J. Appl. Phys. 98, 043103 (2005)]. (c) We perform detailed calculations on “model” windows made of either (111)CaF2 or (PIA)CaF2 that transmit optimally truncated Gaussian beams at wavelengths of 1.15 and 3.39μm, for run times such that lateral heat conduction and surface cooling can be ignored. Our main conlusions are as follows: (a) With CaF2 windows thermal lensing, as measured in terms of the Strehl ratio and on assuming coating absorptances of no more than 3×10−5, is of no consequence in the sense that catastrophic failure may occur at fluence levels way below the threshold for optical distortion. (b) Evidence of a poor Weibull shape factor (m≃3.5) degrades the design safety margins, which requires operating at peak intensities of no more than 100kW∕cm2 to achieve optimum on-target fluences. (c) Regarding the issue of (111)CaF2 vs (PIA)CaF2, we note that fusion-cast material outperforms single crystals based on the figure of merit for distortion, as well as fracture and yield strengths, but contrary to (111)-oriented material, it exhibits birefringence that may rule out its use if depolarization is of concern.

Three-dimensional calculation of high-power, annularly distributed, laser-beam-induced thermal effects on reflectors and windows

Based on the three-dimensional transient heat conduction equation and the elastic stress-strain equation, the temperature rise, distortion, and equivalent stress distributions of a high-reflectivity silicon reflector and a white bijou window irradiated by a high-power sloped annularly distributed laser beam are simulated using a three-dimensional finite element model (FEM). The effects of laser intensity, output duration, beam obscure ratio, and laser intensity spatial gradient on the results are especially investigated. The effects of mirror and window thermal distortion on laser beam phase aberrations are also evaluated. This noncylindrosymmetric three-dimensional FEM can be used to evaluate high-power, high-energy, laser beam-induced thermal effects on optical components.

Ion beam-induced erosion and humidity effect of MgO protective layer prepared by vacuum arc deposition

Ion beam-induced erosion and humidity effect of MgO protective layer prepared by vacuum arc deposition

Measurement of 100-nm polystyrene sphere by transmission electron microscope

The mean diameter of the 100-nm polystyrene sphere was measured with the transmission electron microscope (TEM) with a view to the development of the accurate and visual sizing technique for nm scale particles. To minimize the sizing error due to the inaccurate instrument-stated magnification and the edge location uncertainty, the 300-nm spheres were mixed with 100-nm spheres to provide an internal calibrator, whose diameter is accurately known. The diameters of 100-nm spheres were determined by comparing with that of 300-nm spheres in the same negatives (TEM pictures). For the correction of the electron beam-induced shrinkage effect, the dependence of the shrinkage on the accelerating voltage, beam intensity, and the exposure time was examined and analyzed. Based on such an investigation, and with the several data manipulation routines, the mean diameter was determined with the expanded uncertainty of approximately 2% at the 95% confidence level. The measured value is consistent with those obtained by other laboratories using different techniques for the same spheres.

Beam-induced radiation in a muon storage ring for a neutrino factory

Beam-induced radiation effects have been simulated for a 30-GeV and a 50-GeV muon storage ring designed for a neutrino factory. Calculations include power dissipation and residual dose rates on lattice components. It is shown that by appropriately shielding the superconducting magnets, quench stability can be achieved along with residual dose rates which allow hands-on maintenance. Studies on tunnel shielding further showed that unlimited-occupancy areas could be achieved during machine operation if such enclosures are placed to the inside of the ring. Finally, neutrino-induced radiation levels were computed to large distances for outside the arcs and downstream of the production straights.

Low-level RF systems for synchrotrons. Part II: High intensity. Compensation of beam-induced effects

The high intensity regime is reached when the voltage induced by the beam in the RF cavities is of an amplitude comparable to the desired accelerating voltage. In steady state this beam loadingcan be compensated by providing extra RF power. Transient beam loading occurs at injection or in the presence of a beam intensity that is not uniform around the ring. The transients are periodic at the revolution frequency. Without correction transient beam loading can be very harmful: The stable phase and bucket area will not be equal for all bunches. Strong beam loading often goes in pair with longitudinal instabilities because the RF cavities are a large contributor to the total ring impedance. The low level systems that reduce the effect of the transient beam loading will also increase the threshold intensity of the longitudinal instability caused by the cavity impedance at the fundamental RF frequency. Four classic methods are presented here: Feedforward, RF feedback, long delay feedback and bunch by bunch feedback. The first three fight against both effects: Transient beam loading and longitudinal instability, if caused by the cavity impedance (at the fundamental). The last one cures longitudinal instability (dipole mode) caused by any impedance in the machine but has no effect on the beam loading. These techniques have been made possible by the recent advent of fast digital circuitry and an emphasis will be put on the implementations.

Elastic recoil detection analysis with heavy ion beams

Elastic recoil detection analysis (ERDA) with very heavy ion beams such as 197Au or 209Bi has evolved into a universal IBA technique for simultaneous analysis of almost all elements, with essentially constant detection sensitivity. The characteristics of heavy-ion ERDA (HIERDA) are briefly outlined and illustrated using recent examples of data obtained with a 2-d position-sensitive ΔE- E detector system. Due to the strong Z 1 dependence of ERDA cross sections and our use of a large-solid-angle (∼5 msr) detector, extremely small beam doses are required — typically less than 10 11 ions per analysis. Hence, beam-induced damage effects are usually not serious. To confirm this, a series of HIERDA studies have recently been carried out on various targets, using 1.1 MeV/amu beams of 79Br, 127I, 197Au and 209Bi. Comparative measurements show that the loss of volatile low- Z elements (H, N, O, etc.) is often smaller for 230 MeV 209Bi than for 87 MeV 79Br. An account of these damage studies is presented separately (S.R. Walker, J.A. Davies, J.S. Forster, A.C. Kockelkoren, S.G. Wallace, these proceedings).

Excitation of Kinetic Alfvén Waves in a Flaring Loop

At the onset of a solar flare, initiated by magnetic reconnection high in the corona, reconnection outflow sets up warm proton beams (PBs), streaming down along just-reconnected field lines through steady underlying plasma. Incorporating this scenario, we study excitation of kinetic Alfven waves (KAWs) by PBs, keeping the effects of a beam-induced electric field and thermal effects. Taking into account the high growth rate (∼105 s−1), short relaxation distance (∼106 cm), and energy flux partition between the waves and the beam after relaxation (PKAW/PPB∼1), we conclude that PB-driven KAW instability is an efficient energy conversion mechanism in flaring loops. The quasilinear spectral energy concentration at the largest wavenumbers indicates the possibility of nonlinear spectral modification. We suggest that the resulting turbulence of KAWs plays an important role in the flare plasma energization.

Mimicking the Real World and Exploring New Ones with In-Situ Electron Microscopy

AbstractRecent progress with in-situ observations by electron microscopy is briefly surveyed by referring to developments in instrumentation for reflection and low energy electron imaging as well as for high resolution transmission imaging and spectroscopy. New opportunities have been opened up by environmental microscopy. With increased levels of illumination intensity, the ever present question of beam-induced effects is of mounting concern particularly in studies of non-metallic materials.

High-energy-ion-induced damages at metal-silicon interfaces during channeling measurements

The beam-induced damage near metal-silicon interfaces of Cu, Al, Ta, Ti and W deposited on Si(111) crystal substrates has been investigated using a MeV He ion scattering/channeling technique. Measurements have been performed on beam-induced changes in the Si interface peak (IP) under irradiation with MeV He ions. The results show that the induced changes can be classified into two categories; in the Ta, Ti and W cases, the effect attributable to the deposited metal was small while in the Cu and Al cases, an appreciable enhancement of the beam irradiation sensitivity was observed. The observed difference cannot be explained only by the differences in mass and atomic number of the overlayer. It seems that the chemical bond nature near the interface can be correlated with the beam-induced damage observed. The possibility is discussed that the beam-induced effect can be useful in detecting the chemical nature at metal-semiconductor junctions.