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
One of the challenges of fourth-generation synchrotron light sources as Sirius at the Brazilian Synchrotron Light Laboratory (LNLS) is the high power density that may affect the beamline optical elements by causing figure deformations that deteriorate the quality of the beam. Indeed, surface specifications for height errors of X-ray mirrors are often within a few nanometers. To deal with these thermal management challenges, thermo-mechanical designs based on cryogenic silicon have been developed, taking advantage of its high thermal conductance and low thermal expansion in temperatures of about 125 K. A liquid nitrogen (LN2) cryostat connected to the optics by copper braids has been used to handle moderate power loads, reducing costs when compared to closed-circuit LN2 cryocoolers and mechanically decoupling flow-induced vibrations from the optics. To guarantee the functionality of such systems, lumped mass thermal models were implemented together with auxiliary finite elements analyses. With the first systems in operation, it has been possible to compare and validate the developed models, and to carry out optimizations to improve them for future projects, by adjusting parameters such as emissivity, thermal contact resistance, and copper braid conductance. This work presents the updated models for CARNAÚBA and CATERETÊ beamlines as reference cases.