What type of system utilizes two or more refrigeration systems working simultaneously to achieve ultra-low temperatures?

A cascade system is designed to achieve ultra-low temperatures by employing two or more refrigeration cycles that work in tandem. In this setup, each refrigeration system operates at different temperature levels, allowing the first stage to cool the refrigerant to an intermediate temperature. This refrigerant is then passed to the second stage, which further reduces the temperature to extremely low levels. This method is effective because it optimizes efficiency and performance by ensuring that each stage operates within its optimal range, thereby enhancing the overall cooling effect.

In contrast, the other systems mentioned typically do not involve multiple stages with the same focus on achieving ultra-low temperatures. For example, a dual-stage system entails two stages but is often limited to not specifically targeting extremely low temperatures as efficiently as a cascade system. A combined system might suggest an integration of different types of systems but does not inherently imply operation at ultra-low temperatures like a cascade setup. Meanwhile, a multi-receiver system generally refers to a configuration with various storage capabilities and is not specifically designed for ultra-low temperature applications. Thus, the cascade system is distinctly suited for achieving the extremely low temperatures required in specific industrial and laboratory settings.