Direct cooling is adopted for most high heat load components in SPring-8 beamlines. On the other hand, contact cooling
is employed for some components such as a graphite filter, aluminum filter, mirror, and cryogenic monochromator
silicon crystal. For the thermal design of the contact cooling components, it is important to obtain reliable thermal
contact conductance value. The conductance depends on many parameters such as the surface materials, surface
roughness, flatness of the surface, interstitial materials, temperature of the contact surface, and contact pressure. An
experimental setup is fablicated to measure the conductance at liquid nitrogen temperature and room temperature. The
thermal contact conductance of a Si-Cu interface and that of a Si-In-Cu interface are measured at cryogenic temperature
at contact pressures ranging from 0.1-1.1 MPa. The conductance of an Al-Cu interface and that of a graphite-Cu interface
are measured using gold and silver foils as interstitial materials. The measurements are performed at room temperature
and at pressures ranging from 0.5-4 MPa. The experimental setup and the results obtained are presented.
The performance of the SPring-8 cryogenic cooling system was examined extensively, especially, on the features closely related to the actual experimental situations. The cryogenic cooling system has sufficient cooling capability to handle the permitted highest heat load of 478 W at BL29XUL which equips the SPring-8 standard in-vacuum undulator. The effect of the heat load on the beam profile and the rocking curve width was reasonably small. The rocking curve width with Si 333 diffraction at 18.7 keV was close to the theoretical width 0.86”. Thus the monochromator conserves the good spatial coherence originating from the small source size of the undulator. Mechanical vibrations at frequencies of 30-100 Hz degraded the parallelism between the two monochromator crystals. The angular width of the mechanical vibration was measured to be 0.2” independent of the heat load and the flow rate of the circulating liquid nitrogen. The output intensity was stable and had no drift under any heat load. On the other hand, it took a few hours before the output energy stabilized, when the heat load was increased from 0.135 to 112 W.
Most SPring-8 x-ray beamlines are installed double-crystal monochromators that are standardized. For x-ray undulator beamlines where power density of the beam are quite high, rotated-inclined double-crystal geometry is usually adopted, which enlarges the footprint of the incident beam on the crystal surface to reduce the power density. On the other hand, adjustable-inclined double-crystal geometry is adopted for bending-magnet beamlines to extend the available energy range with a limited Bragg angle range. The standardized monochromator mechanism is compatible to both of the geometries, only by changing crystal mounts. Detailed description of the monochromator mechanism is presented.