WATER-COOLED QUASI-DOUBLY BENT CRYSTAL MONOCHROMATOR FOR COMPTON-SCATTERING EXPERIMENTS

Commissioning and performance of a water-cooled quasi doubly bent crystal monochromator for Compton scattering experiments are described. The monochromator consists of an array of twenty singly bent crystals. Each crystal is half immersed in liquid Ga-ln alloy contained in a water-cooled holder. This is necessary because the monochromator must be able to withstand heat load of 4 kW from synchrotron radiation from an ellipsoid multipole wiggler at the 6.5 GeV accumulation ring. The alignment procedure for twenty singly bent crystals is described in detail. Its performance is as follows; the focused beam size of 60 keV x rays is about 3 mm (vertical) and 8 mm (horizontal). The flux is 6 X 10(12) photons/s at stored currents of 30 mA and the energy resolution is 88 eV for 60 keV x rays. Heating of various adjusting mechanisms by Compton scattered x rays from both the absorber used to suppress low energy x rays and the monochromator crystals is found to be a very serious problem for designing a high energy x-ray beamline.