![[ M_R_C_A_T ]](mrcat-s.gif)
The MR-CAT insertion device line is fully operational and has the following capabilities and instrumentation.
We currently have a Si (111) monochromator consisting of a cryo-cooled first crystal designed by the IIT Center for Synchrotron Radiation Research and Instrumentation (CSRRI) and a 250mm long second crystal which provides an energy range of 4.8keV to 30keV from the fundamental reflection. Both crystals have been chemically polished and have been measured to deliver the theoretical photon flux to the experimental station. The second crystal has a piezoelectric tuning actuator with a.c. feedback and a Bragg-normal motion which permits some degree of fixed-offset operation. In combination with the multichannel scaler electronics described below, we are able to take complete EXAFS scans of 1000eV in under 10s.
The MR-CAT beamline has a 60cm long flat harmonic rejection mirror with Pt and Rh coatings. This mirror resides in the experimental station and may be moved vertically in or out of the beam as the experiment requires. A second float glass mirror is available for use as a steering mirror for liquid scattering experiments.
This part of the beamline gives us the ability to position large sample chambers and detectors to the beam with maximum flexibility for the wide range of experiments required by MR-CAT scientists. The goniometer has been mounted to a lift table of our own design which permits the two vertical axes of the goniometer to be positioned perpendicular to the beam direction as it is deflected by the mirror system or truly vertical as required by the individual experiment. Given the requirement for maximum flexibility, we have been forced to think of how we may most effectively reconfigure the beamline for a new experiment in a short time. In particular, the presence of a vertically deflecting mirror at the front of the experimental station, requires us to place all optical components on an incline to be parallel to the x-ray beam. We have developed an X95 rail system which performs this function and standardizes all component mounts to one of two rail-to-beam distances. Therefore, as a new experiment begins and beam position, sample holders and detectors are repositioned, rough alignment of the entire optical system can be recovered quickly by moving the goniometer center into alignment with the beam. Two of the 8 circles which control the detector position have encoded motors which permit continuous scanning and data acquisition using the multichannel scaler described below.
Basic microfocusing capability is now available. our system consists of a separate kinematically mounted table of out own design with a vibration isolation breadboard and positioning systems for sample, microscope and Kirkpatrick-Baez mirrors. The minimum spot size for the current mirrors is approximately 5m×5m. The system has been used for fluorescence mapping and spectroscopy experiments.
The MR-CAT sector is currently equipped with two Daresbury design spectroscopy ion chambers for use on the main X95 spectroscopy rail and 6 smaller Cornell-type ion chambers which may be mounted on the spectroscopy rail or on the Huber goniometer detector arm. Three Lytle-type fluorescence detectors are also available. Data collection is through a standard instrument chain of Keithley electrometers, V-F converters and a 32 channel multichannel scaler. The multichannel scaler permits continuous of the energy and the goniometer detector motors.
The goniometer detector arm can be fitted with one of two flat Si analyzer crystals and NaI scintillation detectors for high resolution diffraction experiments.
The MR-CAT instrumentation also includes a single-element solid state detector and a 13-element solid state detector for dilute XAFS and Fluorescence measurements. At the present time, we are limited to approximately collection times of greater than 6s per data point but we expect that XIA (the electronics vendor) will be implementing a quick-scan capability in their firmware over the next 6 months and we will be using this to substantially speed up the data collection times with this detector.
We have also begun a project to fabricate a bent Laue fluorescence analyzer. Over the past year, we have successfully built and demonstrated a prototype with a single element and limited solid angle. This detector will be capable of easily separating close-lying fluorescence lines and will not be as count rate limited as a solid state detector. We built and tested an initial production model of the bent Laue fluorescence analyzer. The second revision of this design will be fabricated for the 2002-1 run and can been made available to all users with advance notice.
Data acquisition is handled by the MX system, written by William Lavender. A preliminary manual as well as source code is available at http://www.imca.aps.anl.gov/mx/
Development of experimental capabilities in the bending
magnet First optical Enclusure is ongoing. This station is not expected
to be in operation for at least 18 months.