Showing papers on "Synchrotron published in 2006"

Three-dimensional mapping of a deformation field inside a nanocrystal

Abstract: Synchrotron X-ray radiation, produced by electron accelerators at central facilities, can now be produced in extremely narrow coherent beams. When these X-rays illuminate a crystal of nanometre dimensions a diffraction pattern emerges that is highly resolved. This provides a powerful new tool for structural analysis, as the fine features of the diffraction pattern can be interpreted in terms of sub-atomic distortions within the crystal attributable to its contact with an external support. Coherent X-ray diffraction patterns derived from third-generation synchrotron radiation sources can lead to quantitative three-dimensional imaging of lattice strain on the nanometre scale. Coherent X-ray diffraction imaging is a rapidly advancing form of microscopy: diffraction patterns, measured using the latest third-generation synchrotron radiation sources, can be inverted to obtain full three-dimensional images of the interior density within nanocrystals1,2,3. Diffraction from an ideal crystal lattice results in an identical copy of this continuous diffraction pattern at every Bragg peak. This symmetry is broken by the presence of strain fields, which arise from the epitaxial contact forces that are inevitable whenever nanocrystals are prepared on a substrate4. When strain is present, the diffraction copies at different Bragg peaks are no longer identical and contain additional information, appearing as broken local inversion symmetry about each Bragg point. Here we show that one such pattern can nevertheless be inverted to obtain a ‘complex’ crystal density, whose phase encodes a projection of the lattice deformation. A lead nanocrystal was crystallized in ultrahigh vacuum from a droplet on a silica substrate and equilibrated close to its melting point. A three-dimensional image of the density, obtained by inversion of the coherent X-ray diffraction, shows the expected facetted morphology, but in addition reveals a real-space phase that is consistent with the three-dimensional evolution of a deformation field arising from interfacial contact forces. Quantitative three-dimensional imaging of lattice strain on the nanometre scale will have profound consequences for our fundamental understanding of grain interactions and defects in crystalline materials4. Our method of measuring and inverting diffraction patterns from nanocrystals represents a vital step towards the ultimate goal of atomic resolution single-molecule imaging that is a prominent justification for development of X-ray free-electron lasers5,6,7.

Trends in synchrotron-based tomographic imaging: the SLS experience

Abstract: Synchrotron-based X-ray Tomographic Microscopy (SRXTM) is nowadays a powerful technique for non-destructive, high-resolution investigations of a broad kind of materials. High-brilliance and high-coherence third generation synchrotron radiation facilities allow micrometer and sub-micrometer, quantitative, three-dimensional imaging within very short time and extend the traditional absorption imaging technique to edge-enhanced and phase-sensitive measurements. At the Swiss Light Source TOMCAT, a new beamline for TOmographic Microscopy and Coherent rAdiology experimenTs, has been recently built and started regular user operation in June 2006. The new beamline get photons from a 2.9 T superbend with a critical energy of 11.1 keV. This makes energies above 20 keV easily accessible. To guarantee the best beam quality (stability and homogeneity), the number of optical elements has been kept to a minimum. A Double Crystal Multilayer Monochromator (DCMM) covers an energy range between 8 and 45 keV with a bandwidth of a few percent down to 10-4. The beamline can also be operated in white-beam mode, providing the ideal conditions for real-time coherent radiology. This article presents the beamline design, its optical components and the endstation. It further illustrates two recently developed phase contrast techniques and finally gives an overview of recent research topics which make intense use of SRXTM.

Log-parabolic spectra and particle acceleration in blazars. III. SSC emission in the TeV band from Mkn 501

Abstract: Curved broad-band spectral distributions of non-thermal sources like blazars are described well by a log-parabolic law where the second degree term measures the curvature. Log-parabolic energy spectra can be obtained for relativistic electrons by means of a statistical acceleration mechanism whose probability of acceleration depends on energy. In this paper we compute the spectra radiated by an electron population via synchrotron and Synchro-Self Compton processes to derive the relations between the log-parabolic parameters. These spectra were obtained by means of an accurate numerical code that takes the proper spectral distributions for single particle emission into account. We found that the ratio between the curvature parameters of the synchrotron spectrum to that of the electrons is equal to ∼0.2 instead of 0.25, the value foreseen in the δ-approximation. Inverse Compton spectra are also intrinsically curved and can be approximated by a log-parabola only in limited ranges. The curvature parameter, estimated around the SED peak, may vary from a lower value than that of the synchrotron spectrum up to that of emitting electrons depending on whether the scattering is in the Thomson or in the Klein-Nishina regime. We applied this analysis to computing the synchro-self Compton emission from the BL Lac object Mkn 501 during the large flare of April 1997. We fit simultaneous BeppoSAX and CAT data and reproduced intensities and spectral curvatures of both components with good accuracy. The large curvature observed in the TeV range was found to be mainly intrinsic, and therefore did not require a large pair production absorption against the extragalactic background. We regard this finding as an indication that the Universe is more transparent at these energies than previously assumed by several models found in the literature. This conclusion is supported by recent detection of two relatively high redshift blazars with HESS.

Particle beam irradiation apparatus, treatment planning unit, and particle beam irradiation method

Abstract: A particle beam irradiation apparatus includes a synchrotron, two scanning electromagnets, an beam delivery apparatus for outputting an ion beam extracted from the synchrotron, and an accelerator and transport system controller, and a scanning controller. These controllers stop the output of the ion beam from the beam delivery apparatus; in a state where the output of the ion beam is stopped, change the irradiation position of the ion beam by controlling the scanning electromagnets; and after this change, control the scanning electromagnets to start the output of the ion beam from the beam delivery apparatus and to perform irradiations of the ion beam to at least one irradiation position a plurality of times based on treatment planning information.

The Bonn Electron Stretcher Accelerator ELSA: Past and future

Abstract: In 1953, it was decided to build a 500MeV electron synchrotron in Bonn. It came into operation 1958, being the first alternating gradient synchrotron in Europe. After five years of performing photoproduction experiments at this accelerator, a larger 2.5GeV electron synchrotron was built and set into operation in 1967. Both synchrotrons were running for particle physics experiments, until from 1982 to 1987 a third accelerator, the electron stretcher ring ELSA, was constructed and set up in a separate ring tunnel below the physics institute. ELSA came into operation in 1987, using the pulsed 2.5GeV synchrotron as pre-accelerator. ELSA serves either as storage ring producing synchrotron radiation, or as post-accelerator and pulse stretcher. Applying a slow extraction close to a third integer resonance, external electron beams with energies up to 3.5GeV and high duty factors are delivered to hadron physics experiments. Various photo- and electroproduction experiments, utilising the experimental set-ups PHOENICS, ELAN, SAPHIR, GDH and Crystal Barrel have been carried out. During the late 90's, a pulsed GaAs source of polarised electrons was constructed and set up at the accelerator. ELSA was upgraded in order to accelerate polarised electrons, compensating for depolarising resonances by applying the methods of fast tune jumping and harmonic closed orbit correction. With the experimental investigation of the GDH sum rule, the first experiment requiring a polarised beam and a polarised target was successfully performed at the accelerator. In the near future, the stretcher ring will be further upgraded to increase polarisation and current of the external electron beams. In addition, the aspects of an increase of the maximum energy to 5GeV using superconducting resonators will be investigated.

Stochastic particle acceleration and synchrotron self-Compton radiation in TeV blazars.

Abstract: Aims. We analyse the influence of the stochastic particle accelera tion for the evolution of the electron spectrum. We assume that all investigated spectra are generated inside a spherical, homogeneous source and also analyse the synchrotron and inverse Compton emission generated by such an object. Methods. The stochastic acceleration is treated as the diffusion of the particle momentum and is described by the momentum‐diffusion equation. We investigate the stationary and time dependent solutions of the equation for several different evolutionary scenarios. The scenarios are divided into two general classes. First, we analyse a few cases without injection or escape of the particles during th e evolution. Then we investigate the scenarios where we assume continuous injection and simultaneous escape of the particles. Results. In the case of no injection and escape the acceleration process, competing with the radiative cooling, only modifies the i nitial particle spectrum. The competition leads to a thermal or quasi‐thermal distribution of the particle energy. In the case of the inj ection and simultaneous escape the resulting spectra depend mostly on the energy distribution of the injected particles. In the simplest case, w here the particles are injected at the lowest possible energies, the competition b etween the acceleration and the escape forms a power‐law energy distribution. We apply our modeling to the high energy activity of the blazar Mrk 501 observed in April 1997. Calculating the evolution of the electron spectrum self‐consistently we can reproduce the observed spectra well with a number of free parameters that is comparable to or less than in the “classic stationary” one‐zone synchrotron self‐Compton scenario.

Rapid cycling medical synchrotron and beam delivery system

Abstract: A medical synchrotron which cycles rapidly in order to accelerate particles for delivery in a beam therapy system. The synchrotron generally includes a radiofrequency (RF) cavity for accelerating the particles as a beam and a plurality of combined function magnets arranged in a ring. Each of the combined function magnets performs two functions. The first function of the combined function magnet is to bend the particle beam along an orbital path around the ring. The second function of the combined function magnet is to focus or defocus the particle beam as it travels around the path. The radiofrequency (RF) cavity is a ferrite loaded cavity adapted for high speed frequency swings for rapid cycling acceleration of the particles.

Heating and Non-thermal Particle Acceleration in Relativistic, Transverse Magnetosonic Shock Waves in Proton-Electron-Positron Plasmas

Abstract: We report the results of 1D particle-in-cell simulations of ultrarelativistic shock waves in proton-electron-positron plasmas. We consider magnetized shock waves, in which the upstream medium carries a large scale magnetic field, directed transverse to the flow. Relativistic cyclotron instability of each species as the incoming particles encounter the increasing magnetic field within the shock front provides the basic plasma heating mechanism. The most significant new results come from simulations with mass ratio $m_p/m_\pm = 100$. We show that if the protons provide a sufficiently large fraction of the upstream flow energy density (including particle kinetic energy and Poynting flux), a substantial fraction of the shock heating goes into the formation of suprathermal power-law spectra of pairs. Cyclotron absorption by the pairs of the high harmonic ion cyclotron waves, emitted by the protons, provides the non-thermal acceleration mechanism. As the proton fraction increases, the non-thermal efficiency increases and the pairs' power-law spectra harden. We suggest that the varying power law spectra observed in synchrotron sources powered by magnetized winds and jets might reflect the correlation of the proton to pair content enforced by the underlying electrodynamics of these sources' outflows, and that the observed correlation between the X-ray spectra of rotation powered pulsars with the X-ray spectra of their nebulae might reflect the same correlation.

Synchrotron emission in small scale magnetic field as possible explanation for prompt emission spectra of gamma-ray bursts

Abstract: Synchrotron emission is believed to be a major radiation mechanism during gamma-ray bursts' (GRBs) prompt emission phase. A significant drawback of this assumption is that the theoretical predicted spectrum, calculated within the framework of the ``internal shocks'' scenario using the standard assumption that the magnetic field maintains a steady value throughout the shocked region, leads to a slope F_ u \propto u^{-1/2} below 100 keV, which is in contradiction to the much harder spectra observed. This is due to the electrons cooling time being much shorter than the dynamical time. In order to overcome this problem, we propose here that the magnetic field created by the internal shocks decays on a length scale much shorter than the comoving width of the plasma. We show that under this assumption synchrotron radiation can reproduce the observed prompt emission spectra of the majority of the bursts. We calculate the required decay length of the magnetic field, and find it to be \~10^4 - 10^5 cm (equivalent to 10^5 - 10^6 skin depths), much shorter than the characteristic comoving width of the plasma, ~3*10^{9} cm. We implement our model to the case of GRB050820A, where a break at <~ 4 keV was observed, and show that this break can be explained by synchrotron self absorption. We discuss the consequences of the small scale magnetic field scenario on current models of magnetic field generation in shock waves.

Synchrotron Emission in Small-Scale Magnetic Fields as a Possible Explanation for Prompt Emission Spectra of Gamma-Ray Bursts

Abstract: Synchrotron emission is believed to be a major radiation mechanism during gamma-ray bursts' (GRBs) prompt emission phase. A significant drawback of this assumption is that the theoretical predicted spectrum, calculated within the framework of the "internal shocks" scenario using the standard assumption that the magnetic field maintains a steady value throughout the shocked region, leads to a slope Fν ∝ ν-1/2 below 100 keV, which is in contradiction to the much harder spectra observed. This is due to the electron cooling time being much shorter than the dynamical time. In order to overcome this problem, we propose here that the magnetic field created by the internal shocks decays on a length scale much shorter than the comoving width of the plasma. We show that under this assumption synchrotron radiation can reproduce the observed prompt emission spectra of the majority of the bursts. We calculate the required decay length of the magnetic field, and find it to be ~104-105 cm (equivalent to 105-106 skin depths), much shorter than the characteristic comoving width of the plasma, ~3 × 109 cm. We implement our model to the case of GRB 050820A, where a break at 4 keV was observed, and show that this break can be explained by synchrotron self-absorption. We discuss the consequences of the small-scale magnetic field scenario on current models of magnetic field generation in shock waves.

The JLab high power ERL light source

Abstract: A new THz/IR/UV photon source at Jefferson Lab is the first of a new generation of light sources based on an Energy-Recovered, (superconducting) Linac (ERL). The machine has a 160 MeV electron beam and an average current of 10 mA in 75 MHz repetition rate hundred femtosecond bunches. These electron bunches pass through a magnetic chicane and therefore emit synchrotron radiation. For wavelengths longer than the electron bunch the electrons radiate coherently a broadband THz ∼ half cycle pulse whose average brightness is >5 orders of magnitude higher than synchrotron IR sources. Previous measurements showed 20 W of average power extracted [Carr, et al., Nature 420 (2002) 153]. The new facility offers simultaneous synchrotron light from the visible through the FIR along with broadband THz production of 100 fs pulses with >200 W of average power. The FELs also provide record-breaking laser power [Neil, et al., Phys. Rev. Lett. 84 (2000) 662]: up to 10 kW of average power in the IR from 1 to 14 μm in 400 fs pulses at up to 74.85 MHz repetition rates and soon will produce similar pulses of 300–1000 nm light at up to 3 kW of average power from the UV FEL. These ultrashort pulses are ideal for maximizing the interaction with material surfaces. The optical beams are Gaussian with nearly perfect beam quality. See www.jlab.org/FEL for details of the operating characteristics; a wide variety of pulse train configurations are feasible from 10 ms long at high repetition rates to continuous operation. The THz and IR system has been commissioned. The UV system is to follow in 2005. The light is transported to user laboratories for basic and applied research. Additional lasers synchronized to the FEL are also available. Past activities have included production of carbon nanotubes, studies of vibrational relaxation of interstitial hydrogen in silicon, pulsed laser deposition and ablation, nitriding of metals, and energy flow in proteins. This paper will present the status of the system and discuss some of the discoveries we have made concerning the physics performance, design optimization, and operational limitations of such a first generation high power ERL light source.

Tune-stabilized linear-field ffag for carbon therapy*

Abstract: A hybrid design for a Fixed-Field Alternating-Gradient (FFAG) accelerator has been invented which uses edge and alternating-gradient focusing principles applied in a specific configuration to a combined-function magnet to stabilize tunes through an acceleration cycle which extends over a factor of 2-6 in momentum. Using normal conducting magnets, the final, extracted energy from this machine attains 400 MeV/nucleon and thus supports a carbon ion beam in the energy range of interest for cancer therapy. Competing machines for this application include superconducting cyclotrons[1], synchrotrons[2], and, more recently, scaling FFAGs. The machine proposed here has the high average current advantage of the cyclotron with smaller radial aperture requirements that are more typical of the synchrotron; and as such represents a desirable innovation for therapy machines.

Stochastic particle acceleration and synchrotron self--Compton radiation in TeV blazars

Abstract: We analyse the influence of the stochastic particle acceleration for the evolution of the electron spectrum. We assume that all investigated spectra are generated inside a spherical, homogeneous source and also analyse the synchrotron and inverse Compton emission generated by such an object. The stochastic acceleration is treated as the diffusion of the particle momentum and is described by the momentum-diffusion equation. We investigate the stationary and time dependent solutions of the equation for several different evolutionary scenarios. The scenarios are divided into two general classes. First, we analyse a few cases without injection or escape of the particles during the evolution. Then we investigate the scenarios where we assume continuous injection and simultaneous escape of the particles. In the case of no injection and escape the acceleration process, competing with the radiative cooling, only modifies the initial particle spectrum. The competition leads to a thermal or quasi-thermal distribution of the particle energy. In the case of the injection and simultaneous escape the resulting spectra depend mostly on the energy distribution of the injected particles. In the simplest case, where the particles are injected at the lowest possible energies, the competition between the acceleration and the escape forms a power-law energy distribution. We apply our modeling to the high energy activity of the blazar Mrk 501 observed in April 1997. Calculating the evolution of the electron spectrum self-consistently we can reproduce the observed spectra well with a number of free parameters that is comparable to or less than in the "classic stationary" one--zone synchrotron self-Compton scenario.

In situ synthesis of mixed-valent manganese oxide nanocrystals: an in situ synchrotron X-ray diffraction study.

Abstract: Phase transformations of materials can be studied by in situ synchrotron X-ray diffraction. However, most reported in situ synchrotron XRD studies focus on solid state/gel systems by measuring phase/structure changes during application of pressure or heat. Phase transformations during material synthesis and their applications, especially in wet chemistry processes with different media, have not drawn much attention. Here, using manganese oxides as examples, we report the successful characterization of phase transformations in in situ hydrothermal synthesis conditions by the in situ synchrotron XRD method using a quartz/sapphire capillary tube as the synthesis reactor. The results were used for better design of materials with controlled structures and properties. This method can be generally used for synthesis of manganese oxides as well as for in situ characterization of other material syntheses using hydrothermal, sol-gel, and other methods. In addition, catalytic processes in liquid-solid, gas-solid, and solid-solid systems can also be studied in such an in situ way so that catalytic mechanisms can be better understood and catalyst synthesis and catalytic processes can be optimized.

XAFS experiments at beamline I811, MAX-lab synchrotron source, Sweden

Abstract: A description of a new facility for X-ray absorption spectroscopy at the materials science beamline, I811, at MAX-lab synchrotron source, Lund, Sweden, is given. The beamline is based on a superconducting multipole wiggler source inserted in a straight section of the 1.5 GeV MAX-II ring. X-rays in the energy range 2.4–12 keV are extracted by a standard optical scheme consisting of a vertical collimating first mirror, double-crystal monochromator, and a second vertically focusing mirror. The second monochromator crystal provides sagittal focusing. The total flux impinging on the sample at 9 keV is 5 × 1011 photons s−1, for a minimum beam spot of 0.5 mm × 0.5 mm. The beamline has facilities for experiments in transmission, fluorescence and total-electron-yield mode and experiments have been performed by international research groups on a wide range of materials, such as dilute systems with metal concentrations below 10 p.p.m.

Radio emission models of colliding-wind binary systems. Inclusion of IC cooling

Abstract: Radio emission models of colliding wind binaries (CWBs) have been discussed by Dougherty et al. (2003). We extend these models by considering the temporal and spatial evolution of the energy distribution of relativistic electrons as they advect downstream from their shock acceleration site. The energy spectrum evolves significantly due to the strength of inverse-Compton (IC) cooling in these systems, and a full numerical evaluation of the synchrotron emission and absorption coefficients is made. We have demonstrated that the geometry of the WCR and the streamlines of the flow within it lead to a spatially dependent break frequency in the synchrotron emission. We therefore do not observe a single, sharp break in the synchrotron spectrum integrated over the WCR, but rather a steepening of the synchrotron spectrum towards higher frequencies. We also observe that emission from the wind-collision region (WCR) may appear brightest near the shocks, since the impact of IC cooling on the non-thermal electron distribution is greatest near the contact discontinuity (CD), and demonstrate that the impact of IC cooling on the observed radio emission increases significantly with decreasing binary separation. We study how the synchrotron emission changes in response to departures from equipartition, and investigate how the thermal flux from the WCR varies with binary separation. Since the emission from the WCR is optically thin, we see a substantial fraction of this emission at certain viewing angles, and we show that the thermal emission from a CWB can mimic a thermal plus non-thermal composite spectrum if the thermal emission from the WCR becomes comparable to that from the unshocked winds. We demonstrate that the observed synchrotron emission depends upon the viewing angle and the wind-momentum ratio, and find that the observed synchrotron emission decreases as the viewing angle moves through the WCR from the WR shock to the O shock. We obtain a number of insights relevant to models of closer systems such as WR 140. Finally, we apply our new models to the very wide system WR 147. The acceleration of non-thermal electrons appears to be very efficient in our models of WR 147, and we suggest that the shock structure may be modified by feedback from the accelerated particles.

Single-bounce monocapillaries for focusing synchrotron radiation: modeling, measurements and theoretical limits

Abstract: Single-bounce hollow glass capillaries with ellipsoidal shapes have been used at the Cornell High Energy Synchrotron Source recently for various microbeam experiments, with focal spot sizes from 12 to 23 µm, divergences from 2 to 8 mrad, intensities up to 450 times the intensities of incident X-rays, and working distances up to 55 mm. Simple formulae are developed in this paper to explain capillary performance given the X-ray source size, capillary dimensions and slope errors. Capillary length is optimized for best focusing performance. Capillary fabrication accuracy is reported and capillary X-ray tests confirm the focusing properties expected from formulae. The application of capillaries to third-generation X-ray sources and future energy-recovery linac X-ray sources are discussed.

Inverse Compton Scenarios for the TeV Gamma-Ray Emission of the Galactic Centre

Abstract: The intense Compton cooling of ultra-relativistic electrons in the Klein-Nishina regime in radiation dominated environments, such as that found in the Galactic Centre, may result in radically different electron spectra than those produced by Synchrotron cooling. We explore these effects and their impact on the X-ray and gamma-ray spectra produced in electron accelerators in this region in comparison to elsewhere in our galaxy. We discuss the broad-band emission expected from the newly discovered pulsar wind nebula G 359.95-0.04 and the possible relationship of this X-ray source to the central TeV gamma-ray source HESS J1745-290. Finally we discuss the possible relationship of the Galactic Centre INTEGRAL source IGR J1745.6-2901 to the TeV emission.

Quasar X-Ray Jets: Gamma-Ray Diagnostics of the Synchrotron and Inverse Compton Hypotheses: The Case of 3C 273

Abstract: The process responsible for the Chandra-detected X-ray emission from the large-scale jets of powerful quasars is a matter of ongoing debate. The two main contenders are external Compton scattering off the cosmic microwave background photons (EC/CMB) and synchrotron emission from a population of electrons separate from those producing the radio-IR emission. So far, no clear diagnostics have been presented to distinguish which of the two, if any, is the actual X-ray emission mechanism. Here we present such diagnostics based on a fundamental difference between these two models: the production of synchrotron X-rays requires multi-TeV electrons, while the EC/CMB model requires a cutoff in the electron energy distribution below TeV energies. This has significant implications for the γ-ray emission predicted by these two models, which can be tested through GeV and TeV observations of the nearby bright quasar 3C 273. We show how existing and future GeV and TeV observations can confirm or refute one or both of the above hypotheses.

X-Ray microanalytical techniques based on synchrotron radiation

Abstract: The development of 3rd generation synchrotron radiation sources like European Synchrotron Radiation Facility (ESRF) in parallel with recent advances in the technology of X-ray microfocusing elements like Kirkpatrick–Baez (KB) mirrors, diffractive (Fresnel zone plates, FZP) and refractive (compound refractive lenses, CRL) optics, makes it possible to use X-ray microscopy techniques with high energy X-rays (energy superior to 4 keV). Spectroscopy, imaging, tomography and diffraction studies of samples with hard X-rays at micrometre and sub-micrometre spatial resolutions are now possible. The concept of combining these techniques as a high-energy microscopy has been proposed and successfully realized at the ESRF beamlines. Therefore a short summary of X-ray microscopy techniques is presented first. The main emphasis will be put on those methods which aim to produce sub-micron and nanometre resolution. These methods fall into three broad categories: reflective, refractive and diffractive optics. The basic principles and recent achievements will be discussed for all optical devices. Recent applications of synchrotron based microanalytical techniques to characterise radioactive fuel particles (UO2) released from the Chernobyl reactor are reported.

Development of FFAG accelerators and their applications for intense secondary particle production

Abstract: Fixed Field Alternating Gradient (FFAG) synchrotron was revived recently with modern accelerator technologies Quite a few projects using FFAG synchrotrons have been proposed and some of them are under construction One of the most interesting applications with FFAG synchrotron is an intense neutron source with emittance recovery internal target

Brillouin spectrometer interfaced with synchrotron radiation for simultaneous x-ray density and acoustic velocity measurements

Abstract: We describe a new Brillouin spectrometer that has been installed on a synchrotron x-ray beamline for simultaneous measurements of sound velocities (by Brillouin scattering) and density (by x-ray diffraction). The spectrometer was installed at the 13-BM-D station (GSECARS) of the Advanced Photon Source. This unique facility has been tested in studies of transparent single crystal and polycrystalline materials at high pressure and temperature. The equation of state, acoustic velocities, and, hence, elastic moduli of materials as a function of pressure and temperature can now be determined without resort to a secondary pressure standard, such as the ruby fluorescence scale, or the equation of state of standard materials such as Au, Pt, or MgO, thus offering the potential to determine an absolute pressure scale. This article describes the design of the combined Brillouin-x-ray system and the first experimental results obtained. As a general-user facility, the system was designed to require minimal setup time ...

Coupling a versatile aerosol apparatus to a synchrotron: Vacuum ultraviolet light scattering, photoelectron imaging, and fragment free mass spectrometry

Abstract: An aerosol apparatus has been coupled to the Chemical Dynamics Beamline of the Advanced Light Source at Lawrence Berkeley National Laboratory. This apparatus has multiple capabilities for aerosol studies, including vacuum ultraviolet (VUV) light scattering, photoelectron imaging, and mass spectroscopy of aerosols. By utilizing an inlet system consisting of a 200μm orifice nozzle and aerodynamic lenses, aerosol particles of ∼50nm–∼1μm in diameter can be sampled directly from atmospheric pressure. The machine is versatile and can probe carbonaceous aerosols generated by a laboratory flame, nebulized solutions of biological molecules, hydrocarbon aerosol reaction products, and synthesized inorganic nanoparticles. The sensitivity of this apparatus is demonstrated by the detection of nanoparticles with VUV light scattering, photoelectron imaging, and charged particle detection. In addition to the detection of nanoparticles, the thermal vaporization of aerosols on a heater tip leads to the generation of intact gas phase molecules. This phenomenon coupled to threshold single photon ionization, accessible with tunable VUV light, allows for fragment-free mass spectrometry of complex molecules. The initial experiments with light scattering, photoelectron imaging, and aerosol mass spectrometry reported here serve as a demonstration of the design philosophy and multiple capabilities of the apparatus.

A Testable Stochastic Acceleration Model for Flares in Sagittarius A

Abstract: The near-IR and X-ray flares in Sagittarius A* are believed to be produced by relativistic electrons via synchrotron and synchrotron self-Comptonization, respectively. These electrons are likely energized by turbulent plasma waves through second-order Fermi acceleration that, in combination with the radiative cooling processes, produces a relativistic Maxwellian distribution in the steady state. This model has four principal parameters, namely the magnetic field B, the electron density n and temperature ?cmec2, and the size of the flare region R. In the context of stochastic acceleration, the quantities Rn1/2B and ?cRn should remain nearly constant in time. Therefore, simultaneous spectroscopic observations in the NIR and X-ray bands can readily test the model, which, if proven to be valid, may be used to determine the evolution of the plasma properties during an eruptive event with spectroscopic observations in either band or simultaneous flux density measurements in both bands. The formulae can be applied to other isolated or confined systems, where electrons are accelerated to relativistic energies by plasma wave turbulence and produce most of the emission via synchrotron processes.

Synchrotron x-ray powder diffraction studies in pulsed magnetic fields

Abstract: X-ray powder diffraction experiments under pulsed magnetic fields were carried out at the DUBBLE beamline (BM26B) at the ESRF. A mobile generator delivered 110kJ to the magnet coil, which was sufficient to generate peak fields of 30T. A liquid He flow cryostat allowed us to vary the sample temperature accurately between 8 and 300K. Powder diffraction patterns of several samples were recorded using 21keV monochromatic x-rays and an on-line image plate detector. Here we present the first results on the suppression of the Jahn-Teller structural distortion in TbVO4 by magnetic field. These data clearly demonstrate the feasibility of x-ray powder diffraction experiments under pulsed magnetic fields with relatively inexpensive instrumentation.

Use of neutron and synchrotron X-ray diffraction for evaluation of residual stresses in a 2024-T351 aluminum alloy variable-polarity plasma-arc weld

Abstract: The residual stress fields associated with variable-polarity plasma-arc (VPPA) welds in 2024-T351 aluminum alloy plates have been measured nondestructively using neutron and synchrotron X-ray diffraction. Neutron diffraction allows in-depth measurements of the full strain tensor to be made in thick components; synchrotron X-rays allow for rapid measurements of strains inside components, although their penetration is less than that of the neutrons and constraints arising from the diffraction geometry generally lead to only two strain components being easily measurable. Hence, a combination of the two techniques, applied as described herein, is ideal for a detailed nondestructive evaluation of residual stresses in plates. The residual stresses in a 12-mm-thick VPPA-welded aluminum 2024-T351 alloy plate have been measured using neutron diffraction. The stresses were then remeasured by a combination of neutron and synchrotron X-ray diffraction after the plate had been reduced in thickness (or, skimmed) to 7 mm by machining both sides of the weld, mimicking the likely manufacturing operation, should such welds be used in aerospace structures. A strong tensile residual stress field was measured in the longitudinal direction, parallel to the weld, in both the as-welded and skimmed specimens. There was only a slight modification of the residual stress state on skimming.