Multi-Stage Dilution Refrigerator with Active Second-Stage Cooling
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Solution Overview
Problem
Existing cryogenic cooling systems face challenges in achieving low temperatures due to parasitic heat loads on the cold plate, which increases helium-3 circulation rates and requires more cooling power, leading to inefficiencies and high costs, especially in large-scale applications like quantum information processing.
Innovation Solution
A cryogenic cooling system with a second dilution unit that applies active cooling directly to the second stage, reducing reliance on neighboring stages and incorporating a continuous heat exchanger to minimize helium-3 requirements, allowing for lower temperatures and increased cooling capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a cold plate is arranged between the still and mixing chamber to provide passive cooling, then the cold plate can serve as a mounting point for experimental services, but any heat load applied to the cold plate becomes parasitic and directly impacts the base temperature of the mixing chamber
Solution Approach 1:
The system divides the cooling function into separate stages: the cold plate handles experimental service mounting and intermediate cooling, while the second mixing chamber provides dedicated active cooling to the third stage. This segmentation prevents heat loads from experimental services from directly impacting the base temperature of the mixing chamber.
Solution Approach 2:
The second mixing chamber acts as an intermediary active cooling source between the cold plate and the third stage. It absorbs heat loads from the cold plate before they can reach the third stage, protecting the base temperature while allowing the cold plate to serve its mounting function.
2Reliability
If additional dissipative elements are installed to ensure adequate thermalisation of experimental wiring, then thermalisation is improved, but the heat load on the dilution refrigerator increases requiring more cooling power
Solution Approach 1:
The system applies cooling locally at different stages: the second mixing chamber provides local active cooling at the third stage to handle dissipation from experimental wiring, while the first mixing chamber provides cooling at the second stage. This local cooling approach maintains reliable thermalisation without requiring excessive total cooling power.
3Power
If the circulation rate of helium-3 is increased to compensate for additional dissipation at the still, then more cooling power is available, but the optimum flow rate cannot be attained and helium-3 consumption increases
Solution Approach 1:
The second mixing chamber provides self-service active cooling at the third stage, generating cooling power locally through the dilution of helium-3 into helium-4. This eliminates the need to increase the overall circulation rate to compensate for dissipation, maintaining optimum flow rates and reducing helium-3 consumption.
4Power
If more step heat exchangers are provided to increase cooling power at the third stage, then cooling capacity increases, but the helium-3 requirement increases significantly
Solution Approach 1:
The system changes the cooling mechanism at the third stage from passive conduction through heat exchangers to active cooling through the phase change and mixing process in the second mixing chamber. This parameter change provides increased cooling power while reducing helium-3 requirements, as the mixing process is more efficient than conventional heat exchanger-based cooling.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration enables lower base temperatures, improved heat load tolerance, and reduced helium-3 consumption, effectively addressing the inefficiencies and cost issues of prior systems by providing active cooling at the second stage, thereby maintaining lower temperatures across the system.
Implementation Method 1
Cooling is obtained at the mixing chamber from the enthalpy of mixing as helium-3 is diluted into helium-4
Implementation Method 2
Helium-3 is boiled at the still, which removes energy due to the latent heat of vaporisation
Implementation Method 3
The heat exchanging unit comprises a continuous heat exchanger arranged between the still and a cold plate
Data Source
AI summary
A cryogenic cooling system is provided comprising a first stage 6, a second stage 7, and a third stage 8, wherein the second stage 7 is arranged between the first stage 6 and the third stage 8. A first dilution unit 12 is provided comprising a first still 11 and a first mixing chamber 13, wherein the first still 11 is thermally coupled to the first stage 6 and the first mixing chamber 13 is thermally coupled to the third stage 8. A second dilution unit 32 is further provided comprising a second still 31 and a second mixing chamber 33, wherein the second still 31 is thermally coupled to the first stage 6 and the second mixing chamber 33 is thermally coupled to the second stage 7.