Nano-modulated electron beams via electron diffraction and emittance exchange for coherent x-ray generation

We present a new method for generation of relativistic electron beams with current modulation on the nanometer scale and below. The current modulation is produced by diffracting relativistic electrons in single crystal Si, accelerating the diffracted beam and imaging the crystal structure, then transferring the image into the temporal dimension via emittance exchange. The modulation period can be tuned by adjusting electron optics after diffraction. This tunable longitudinal modulation can have a period as short as a few angstroms, enabling production of coherent hard x-rays from a source based on inverse Compton scattering with total accelerator length of approximately ten meters. Electron beam simulations from cathode emission through diffraction, acceleration and image formation with variable magnification are presented along with estimates of the coherent x-ray output properties

Nested Kirkpatrick–Baez (Montel) optics for hard X-rays

A comprehensive description and ray-tracing simulations are presented for symmetric nested Kirkpatrick-Baez (KB) mirrors, commonly used at synchrotrons and in commercial X-ray sources. This paper introduces an analytical procedure for determining the proper orientation between the two surfaces composing the nested KB optics. This procedure has been used to design and simulate collimating optics for a hard-X-ray inverse Compton scattering source. The resulting optical device is composed of two 12 cm-long parabolic surfaces coated with a laterally graded multilayer and is capable of collimating a 12 keV beam with a divergence of 5 mrad (FWHM) by a factor of ~250. A description of the ray-tracing software that was developed to simulate the graded multilayer mirrors is included

Novel neutron focusing mirrors for compact neutron sources

We demonstrated neutron beam focusing and neutron imaging using axisymmetric optics, based on pairs of confocal ellipsoid and hyperboloid mirrors. Such systems, known as Wolter mirrors, are commonly used in x-ray telescopes. A system containing four nested Ni mirror pairs was implemented and tested by focusing a polychromatic neutron beam at the MIT Reactor and conducting an imaging experiment at HFIR. The major advantage of the Wolter mirrors is the possibility of nesting for large angular collection. Using nesting, the relatively short optics can be made comparable to focusing guides in flux collection capabilities. We discuss how such optics can be used as polychromatic lenses to improve the performance of small-angle-scattering, imaging, and other instruments at compact neutron sources.United States. Dept. of Energy. Office of Basic Energy Sciences (Award DE-FG02-09ER46556)National Science Foundation (U.S.) (Award DMR-0526754)United States. Dept. of Energy. Office of Basic Energy Sciences (Award DE-FG02-09ER46557

From X-Ray Telescopes to Neutron Focusing

No abstract availabl

Commensurate-Incommensurate Transition in the Charge-Density-Wave State of K0.30moo3

The blue bronze K0.30MoO3 has a charge-density wave (CDW) which forms at T=181 K. At temperatures below 181 K, nonlinear conductivity due to charge transport by the CDW has been observed. We have performed x-ray and elastic-neutron-scattering experiments which show that at onset the CDW is incommensurate with a reduced wave vector of q=(0, 0.263, 0.5). The b* component of q is temperature dependent and the incommensurability =q-b*/4 decreases to zero near T=100 K. Measurements of the threshold electric field for nonlinear charge transport show a broad decrease as the temperature is lowered beginning near 100 K. No increase of the threshold field in the commensurate CDW phase is inconsistent with the depinning of a rigid CDW, but may be explained by the transport of CDW phase solitons or dislocations

MIT inverse Compton source concept

A compact X-ray source based on inverse Compton scattering of a high-power laser on a high-brightness linac beam is described. The facility can operate in two modes: at high (MHz) repetition rate with flux and brilliance similar to that of a beamline at a large 2nd generation synchrotron, but with short ∼1 ps pulses, or as a 10 Hz high flux-per-pulse single-shot machine. It has a small footprint and low cost appropriate for university or industry laboratories. The key enabling technologies are a high average power laser and a superconducting accelerator. The cryo-cooled Yb:YAG laser amplifier generates ∼1 kW average power at 1 μm wavelength that pumps a coherent cavity up to 1 MW stored power. The high-brightness electron beam is produced by a superconducting RF photoinjector and linac operating in CW mode with up to 1 mA current. The photocathode laser produces electron pulses at either 100 MHz with 10 pc per bunch, or at 10 Hz with 1 nC per bunch in the two operating modes. The design of the facility is presented, including optimization of the laser and electron beams, major technical choices, and the resulting X-ray performance with a focus on the 100 MHz mode

Structure of cholesterol helical ribbons and self-assembling biological springs

We report the results of x-ray-scattering studies of individual helical ribbons formed in multicomponent solutions of cholesterol solubilized by various surfactants. The solutions were chemically defined lipid concentrate (CDLC) and model bile. In these and many analogous multicomponent surfactant–cholesterol solutions, helical ribbons of two well defined pitch angles, namely 11° and 54°, are formed. We have suggested previously that this remarkable stability results from an underlying crystalline structure of the sterol ribbon strips. Using a synchrotron x-ray source, we have indeed observed Bragg reflections from individual ribbons having 11° pitch angle. We have been able to deduce the parameters of the unit cell. The crystal structure of these ribbons is similar to that of cholesterol monohydrate, with the important difference that the length of the unit cell perpendicular to the cholesterol layers is tripled. We discuss possible origins for this triplication as well as the connection between the crystalline structure and the geometrical form of the helical ribbons.United States. Dept. of Energy. Office of Basic Energy Sciences (Award No. DE-FG02-04ER46149

Report of the American Physical Society Study Group on Boost-Phase Intercept Systems for National Missile Defense: Scientific and Technical Issues

This issue of RMP has, as a special supplement, the report of an APS study group on the physics and engineering issues that must be addressed in designing a missile defense system capable of intercepting a hostile missile while it is still burning, the so-called “boost phase.” The challenges for boost-phase intercept are significant, chiefly because of the short time window during which detection, decision, launch, and interception must occur. Some aspects of the problem have not previously been analyzed in such depth in the public domain. This study was made on the basis of unclassified information and so is presented here in its entirety

Demonstration of achromatic cold-neutron microscope utilizing axisymmetric focusing mirrors

An achromatic cold-neutron microscope with magnification 4 is demonstrated. The image-forming optics is composed of nested coaxial mirrors of full figures of revolution, so-called Wolter optics. The spatial resolution, field of view, and depth of focus are measured and found consistent with ray-tracing simulations. Methods of increasing the resolution and magnification are discussed, as well as the scientific case for the neutron microscope. In contrast to traditional pinhole-camera neutron imaging, the resolution of the microscope is determined by the mirrors rather than by the collimation of the beam, leading to possible dramatic improvements in the signal rate and resolution.United States. Dept. of Energy (Office of Basic Energy Sciences, Materials Sciences and Engineering under Award No. DE-FG02-09ER46556)United States. Dept. of Energy (Office of Basic Energy Sciences, Materials Sciences and Engineering under Award No. DE-FG02-09ER46557)United States. Dept. of Energy (interagency Agreement No. DE_AI01-01EE50660)National Institute of Standards and Technology (U.S.). Center for Neutron ResearchNational Institute of Standards and Technology (U.S.). Director’s OfficeNational Institute of Standards and Technology (U.S.). Radiation and Biomolecular Physics Divisio