Wilfried Schildkamp

An ultrafast mechanical shutter for X-rays

Abstract A new shutter which can open and close in 2 μs is presented. The shutter can stop hard X-rays and is suitable for use with pinhole camera systems. This paper describes its design and presents preliminary data from its first use at the CESR storage ring to isolate 120 ps X-ray pulses.

Quantitive analysis of Laue diffraction patterns recorded with a 120 ps exposure from an X-ray undulator

X-ray Laue diffraction patterns with an exposure time of 120 ps have been obtained from single crystals of an indole alkaloid and of the enzyme lysozyme using the X-rays emitted as a single bunch of electrons traverses a hard X-ray undulator inserted in CESR, the Cornell Electron–Positron Storage Ring. The patterns were recorded on a sensitive storage-phosphor detector. Despite complexities posed by the sharp variation of the incident X-ray spectrum with wavelength and the weakness of the diffraction patterns, accurate crystallographic structure amplitudes were extracted from the Laue intensities by the generalized scale-factor approach to the determination of the wavelength- and position-dependent correction factors. The results show that crystallography is feasible on the 100 ps time scale and open up the prospect of time-resolved measurements of ultra-rapid changes in molecular structure.

Performance of a hard x-ray undulator at CHESS (invited)

A 3.3‐cm period Nd‐Fe‐B hybrid undulator has been designed and successfully operated in the Cornell Electron Storage Ring (CESR). This 2‐m‐long, 123‐pole insertion device is a prototype of one of the undulators planned for the Advanced Photon Source. In dedicated operation, the undulator produced the expected brightness at 5.437 GeV with the fundamental x‐ray energy ranging from 4.3 to 7.9 keV corresponding to a change in gap from 1.5 to 2.8 cm.

Laue diffraction from biological samples

Abstract Various aspects of the Laue technique, largely as applied to protein crystals, are considered: the principles of static and time-resolved experiments, and their advantages and disadvantages; its experimental application to strongly diffracting crystals to yield exposures as low as 4ms, and to time-resolved studies of thermal unfolding; and quantitation of diffraction using monochromatic or polychromatic X-rays from tiny or weakly diffracting crystals.

Protein crystallographic data acquisition and preliminary analysis using kodak storage phosphor plates

Abstract X-ray diffraction data from single crystals of typical proteins are very weak, numerous, and subject to systematic errors arising from radiation damage at long exposure times. Compared with films, the Kodak storage phosphor technology described in the accompanying paper [1] offers the prospect of greatly improved signal-to-noise, increased sensitivity particularly at shorter wavelengths, and wide dynamic range, though with more modest spatial resolution. To assess the suitability of this technology for protein crystallographic data collection, we have collected both monochromatic oscillation and wide bandpass Laue data at CHESS on crystals ranging in unit cell size from ∼ 50 A (lysozyme) to ∼ 300 A (viruses). A direct comparison of the Kodak storage phosphor with conventional Kodak Direct Exposure Film (DEF-5) was obtained by making immediately sequential exposures on the same crystal with the two detector systems. Even with an exposure time one order of magnitude less than with the corresponding film, the storage phosphor yielded data with improved signal-to-noise. Thus, storage phosphors enable more data to be acquired per crystal, with less radiation damage, and with better precision. Such detectors appear extremely well suited to protein crystallographic applications, both static and time-resolved, with both monochromatic and polychromatic X-ray sources.

Design of a tunable and focusing single crystal monochromator for powerful X-ray sources

Abstract A new design of a focusing monochromator is presented which overcomes both the drastic change in energy resolution when a cylindrically bent crystal is tuned to different energies and the thermal problems that arise with intense wiggler sources. A bi-triangular crystal is asymmetrically cut for the lowest desired energy and pressed to a curved cooling plate which corresponds to the focusing radius at the lowest energy. When tuning to a higher energy the most effective asymmetric cut is re-established by a rotation around the scattering vector. This rotation also changes the effective radius of bend and the position of the focal spot. The focal spots lie on approximately a straight line at a convenient angle to the secondary monochromatic beam.

Helium cooling of X-ray optics during synchrotron heating

Abstract A cooling scheme for focussing monochromator crystals is presented, which is capable of handling the heat load produced by wiggler radiation.

A heat transfer study for beamline components in high‐power wiggler and undulator beamlines. Part II. Beryllium windows (invited)

The designs for heat transfer capabilities of beryllium windows and prefilters at Cornell High Energy Synchrotron Source (CHESS) high power wiggler and undulator beamlines are discussed, based on experimental test results and finite element analysis calculations for determining temperature and thermal stress values and distributions.

Laue Photography from Protein Crystals

The recent advent of intense, polychromatic, pulsed synchrotron x-ray sources has prompted a re-examination of the Laue diffraction technique, particularly as applied to crystals of proteins and other macromolecules. This article reviews briefly the main aspects of the Laue technique, and how it may be applied to the general area of time-resolved crystallography. Applications have as their goal the elucidation of the structure of short-lived intermediates in such processes as enzymatic catalysis, ligand binding and release, and protein folding and unfolding. Knowledge of the structure of such intermediates is critical to a full understanding of molecular mechanisms of action, yet they are inaccessible to conventional x-ray techniques since their lifetimes are typically very much less than one second.

Nondestructive position monitor for synchrotron radiation

Abstract In order to measure the vertical beam position in the wiggler beam line at CHESS (Cornell High Energy Synchrotron Source) a position monitor was constructed which measures the vertical beam positions of two beams passing through it, one from the 6-pole wiggler and one from the following dipole. The position monitor is a split ionization chamber with a resolution better than 10 μm and a bandwidth of greater than 100 Hz over a linear range of 5 mm.