BEAMLINE DESCRIPTION
Beamline Configuration
The main components of beamline X28C are shown in Fig.1. X28C is a white light beamline that accepts 6 milliradians of the horizontal radiation from the X-ray source. The beamline is compartmentalized with beampipes that are capped by Be windows. Each compartment is under ultra high vacuum system. Immediately downstream of the first vacuum-isolation beryllium window is a focusing mirror located at a distance of 9.7m away from the source. The mirror is made of single Si crystal coated with Pd and resides in a vacuum chamber on a mechanical support. The mirror, which has a cylindrical cut, is bendable to a toridial shape that allows both horizontal and vertical focusing of the X-ray beam. The reflected beam is passed through a 3.25 meter section of the vacuum beampipe until a second beryllium window, which terminates the beamline vacuum. The second Be window has BN3 coating on the downstream surface and is connected to the beampipe, which is filled with helium atmosphere. A water-cooled third Be window, coated with BN3 is installed downstream of the beampipe to form an exit window inside the hutch. A ~50mm air gap containing the secondary safety shutter (pre-shutter) separates the exit window from the flight tube, which is used for passing the X-ray upto the sample exposure chamber. The extendable flight tube is sealed with a pair of coated Be windows and also contains a pressurized helium atmosphere. Focusing the X-ray beam increases the flux density by > 120 fold. Mirror controls facilitate independent choice of mirror angle and mirror focus to avail variable beam intensities on the sample chamber. The motor control unit sets the different motor parameters like lift table, heavy jack, mirror angle, bender value, multiple sample holder position, KinTekl® control etc. through Labview software.
X28C Hutch Components and Apparatus
Computer controlled Pre-shutter, Helium flight tube, XZ transition table (lift table), Millisecond (unibilitz®) shutter with or without Aluminum plate for dose adjustment, Kintek® stop flow apparatus for time-resolved experiments, single stand set-up or computer controlled multiple sample holder (with temperature regulation) for sample exposures, photo diode/sensor to monitor beam profile, beam alignment, sample temperature monitoring device, dark room facility for photosensitive samples and laboratory-bench for sample distribution and preparation.
Computer System, Hardware and Software
Motor control unit, 1 GHz PIII with XP for motor control unit interface, KinTek® controller, Uniblitz shutter controller, NSLS data acquisition software with CAMAC interface, 1GHz PIII user computer with DVD-CD-Zip-Floppy drives and Printers.
Experiments and Scope
Steady state and time-resolved synchrotron footprinting, exposure of photosensitive molecules, temperature-controlled sample exposure (-37º-42ºC), membrane protein radiolysis, exposure of cell samples in frozen or liquid states.
Updated 28 January 2008
