ID29 - Multiple-wavelength Anomalous Diffraction (MAD)
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Conceptual design of the beamline
ID29 is intended for high intensity, high energy resolution MAD and SAD measurements over a wide range of X-ray wavelengths. It uses two complementary undulator sources - a standard U35 and an in vacuum U21. The beamline is automated so that users can select an absorption edge and the software will move the undulator gaps and monochromator angle to the X-ray wavelength required. The beam is conditioned by various sets of slits and attenuators, and monitored by a series of viewers and beam position monitors. The use of these devices aides the automated routines to check the beam characteristics. The main optical elements are a liquid nitrogen cooled channel-cut silicon monochromator and a cylindrical grazing incidence mirror, the latter which is bent to approximate to a toroidal curvature. The toroidal mirror is curved by a pneumatically operated bending mechanism and focusses the beam in both the horizontal and vertical. The nominal FWHM spot size at the sample is roughly 50*60 microns (H*V).
Two monochromator crystals are available, a high resolution Si(311) cut and a lower resolution Si(111) cut. The former is recommended for precise "white line" measurements. Due to geometry of the channel-cut crystal, the Si(311) monochromator can only be used at energies higher than 9.6 keV.
Since January 2009, ID29 is equipped with a microdiffractometer which allows to tailor the beam sizes down to 30, 20 and 10 microns in diameter. An additional beam cleaning aperture at the end of the collimator reduces the noise level on the detector. Due to the small beam sizes routinely available,
ID29 is no longer equipped by default with a minikappa device.
Nevertheless, this device can be mounted rapidly upon request but please note that the sphere of confusion with the kappa angle open is approximately 5 microns.
Available Wavelength Range
The above undulator sources give an almost continually tunable wavelength with high intensity over this wavelength range : 0.7 - 2.1 Å (20 - 6 keV) for the Si(111) and 0.7 - 1.3 Å (20 - 9.6 keV) for the Si (311) monochromator, respectively.
Detector
ID29 is equipped with an ADSC Q315R detector which has an active area of 315 x 315 mm2 (3072 x 3072 pixels, which are 102.6 microns in size for the default binned mode). The readout time is typically 1s in unbinned mode or 0.3s in binned mode.
The X-ray fluorescence detector for automatic absorption edge scanning is a Rontec Silicon drift diode which has an energy resolution of less than 250 eV at 5.9 keV and a maximum count rate of 1 MHz. Coupled with the a series of attenuators on actuators, this detector allows absorption spectra to be automatically recorded on the smallest of crystals as well as concentrated solutions of mother liquor.
Preparation laboratory and Data Processing
A small prep lab is available to users and this contains much of the basic material to prepare samples. Computing facilities are available to process diffraction images, solve crystal structres at the beamline and visualise electron density maps.
Complementary Information
As all other MX-beamlines, ID29 is also equipped with an automated sample changer.