LNLS, Campinas, Brazil
CNPEM, Campinas, SP, Brazil
Sirius, the Brazilian 4th-generation light source at the Brazilian Synchrotron Light Laboratory (LNLS), presents high-performance requirements in terms of preserving photon-beam quality, particularly regarding wavefront integrity and position stability. In this context, it is imperative that many silicon optical elements* be effectively cooled, such that temperatures and their control-related parameters can be precisely handled to the point in which thermal effects are acceptable concerning figure distortions and drifts at different timescales. For this class of precision equipment, the required performance can only be achieved with robust thermal management.** For this, relevant aspects related to the implementation of liquid nitrogen cooling systems need to be emphasized. Currently, two solutions are present at the first-phase beamlines, according to the component thermal load: (1) an in-house low-cost system for components under moderate loads (< 50 W), such as the mirror systems and the four-bounce monochromators, comprising a commercial cryostat connected to an instrumented vessel, whose level and pressure are controlled by the standard beamline automation system that can automatically feed it from a secondary service unit or a dedicated transfer line; (2) a commercial cryocooler for high-heat-load applications (50 - 3000 W), such as the double-crystal monochromators. This work presents the in-house solution: requirements, design aspects, operation range, as well as several discoveries and improvements deployed during the commissioning of the CATERETÊ and the CARNAÚBA beamlines, such as the prevention of ice formation, stabilization of both thermal load and flow-rate, and auto-filling parameters, among others.
*TOLENTINO. Innovative instruments (…) for the CARNAÚBA beamline at Sirius-LNLS. SRI (2018).
**VOLPE. Performance validation of the thermal model for optical components. Submit to MEDSI (2020)
LNLS, Campinas, Brazil
CNPEM, Campinas, SP, Brazil
Beamlines of new 4th-generation machines present high-performance requirements in terms of preserving beam quality, in particular wavefront integrity and position stability at micro and nanoprobe stations. It brings about numerous efforts to cope with engineering challenges comprehending high thermal load, cooling strategy, crystal manufacturing, vibration sources, alignment and coupled motion control. This contribution presents the design and performance of a four-bounce silicon-crystal monochromator for the Sirius beamlines at the Brazilian Synchrotron Light Source (LNLS), which is basically composed of two channel-cut crystals mounted on two goniometers that counter-rotate synchronously. The mechanical design ascertained the demands for the nanoprobe and coherent scattering beamlines - namely, CARNAÚBA and CATERETÊ - focusing on solutions to minimize misalignments among the parts, to grant high stiffness and to ensure that the thermal performance would not impair beam characteristics. Hence, all parts were carefully simulated, machined, and measured before assembling. This work details mechanical, thermal, diagnostics, and dynamic aspects of the instruments, from the design phase to their installation and initial commissioning at the beamlines.