Improvements made on infrared detectors such as pixel pitch reduction, detector resolution increase, and functions directly integrated at sensor level have impact on the required cryogenic cooling power. Next to that the cryogenic operating temperature of the detector is determined by the used detector technology, required bandwidth and performance and may vary between 60K to 170K. That’s why today, it is important that developed cryogenic coolers are able to address a wide range of cold temperature and cryogenic power, and to be able to predict cryocooler performances at sensor engine level in order to select the best product for a specific IR application. Undeniably the cooler size, weight and consumption are important parameters for the system design but next to that coolers shall be flexible, optimized and efficient to avoid very specific definitions or developments for each type of detector. The paper presents the work made at Thales in order to determine performance models for the legacy products in function of the cold temperature, the dewar characteristics and the ambient temperature. These models are based on a performance mapping. The presentation answers questions such as how to choose a cooler, or how to optimize a cooler in function of the system characteristics. Finally, a new cooler with a larger cooling power as todays series of RM coolers is presented in order to extend the range that can be covered by Thales Rotary products.
The RMs1 is the new SWaP rotary cooler qualified by Thales in 2018. The architecture and the building blocks used to design that cooler have led to significant improved efficiency. The paper will describe the performances of the product, especially its thermal efficiency. An updated presentation of the reliability figures will also be done. The current available cryogenics power and the thermal efficiency allow RMs1 to be used for a wide range of applications. Either large detector arrays could be cooled by an RMs1 at High Operating Temperature, either smaller dies could be cooled down to lower temperature. The presentation will focus on the associated tuning of some parameters like the filling pressure to find the best trade-off adapted to the application. For instance, 24/7 applications will focus on reliability while HHTI may be more concerned by the power consumption. Also a first reflection will be presented on the potential definition and performance of a splitted RMs1 cooler where the cold fingers is detached from the compressor enabling a more flexible integration with a significantly reduced length in the axis of the cold finger. As a result, a mapping of cryogenics performances will be presented.
The cooler reliability is a major performance requested by the customers, especially for 24h/24h applications, which are a growing market. Thales has built a reliability policy based on accelerate ageing and tests to establish a robust knowledge on acceleration factors. The current trend seems to prove that the RM2 mean time to failure is now higher than 30,000hr. Even with accelerate ageing; the reliability growth becomes hardly manageable for such large figures. The paper focuses on these figures and comments the robustness of such a method when projections over 30,000hr of MTTF are needed.
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