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wiki:design_construction [2022/02/02 16:52] henri.godfrin@neel.cnrs.fr |
wiki:design_construction [2022/12/15 17:46] (current) henri.godfrin@neel.cnrs.fr |
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* Small dilution refrigerators ("la Jolla" style) have diameters of a few cm, their 3He flow rate is ~10 to 50 µmol/sec. They are often used as " | * Small dilution refrigerators ("la Jolla" style) have diameters of a few cm, their 3He flow rate is ~10 to 50 µmol/sec. They are often used as " | ||
- | * Larger refrigerators with heat exchangers of typical diameters larger than 10 cm (" | + | * Larger refrigerators with heat exchangers of typical diameters larger than 10 cm (" |
* Cooling power at the MC is given by the simple expression | * Cooling power at the MC is given by the simple expression | ||
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**[[1k_pot|Link to Publications HERE]]** | **[[1k_pot|Link to Publications HERE]]** | ||
+ | |||
+ | ===== The 3He condensation line ===== | ||
+ | {{ wiki: | ||
===== The " | ===== The " | ||
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* The still plays an important role: the **3He flow rate** of the dilution refrigerator, | * The still plays an important role: the **3He flow rate** of the dilution refrigerator, | ||
+ | |||
+ | ===== The Continuous heat exchanger | ||
+ | |||
+ | ===== The Step (" | ||
===== The Mixing Chamber | ===== The Mixing Chamber | ||
- | {{ wiki: | + | {{ wiki: |
* The mixing chamber can be made out of copper, stainless steel, plastics, etc. Plastic MC are used in the presence of varying magnetic fields, to avoid eddy current heating. | * The mixing chamber can be made out of copper, stainless steel, plastics, etc. Plastic MC are used in the presence of varying magnetic fields, to avoid eddy current heating. | ||
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* The figure shows the cooling power of different types of dilution refrigerators. | * The figure shows the cooling power of different types of dilution refrigerators. | ||
- | * Cooling power = 82 dn3/dt T^2, for T>3 Tmin | + | * Cooling power = 82 dn3/dt T^2. This standard formula relates the cooling power in watts to the flow rate expressed in moles/sec (dn3/dt). |
+ | It is applicable | ||
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* Pumped 3He refrigerators have larger cooling powers that dilution refrigerators for T>0.35 K. The are also significantly more user friendly... | * Pumped 3He refrigerators have larger cooling powers that dilution refrigerators for T>0.35 K. The are also significantly more user friendly... | ||
+ | |||
+ | |||
+ | ===== Troubleshooting Dilution Refrigerators ===== | ||
+ | * 1 K pot hot, pressure is low. Filling capillary blocked. Remove LHe so that the bath level is below the intake, keep 4He pressure in Pot above bath pressure. Having a heater on the 1K pot capillary can help, applying heat pulses... | ||
+ | |||
+ | * High inlet pressure. Air? Hydrogen? Water? | ||
+ | |||
+ | * Low still pressure. Still empty? Check T_still vs. P_still ! If there is no liquid, the pressure j | ||
+ | * is low, but the temperature is high. | ||
+ | |||
+ | * No cooling power. Interface level in MC? Heat leak to MC? Apply heat and check cooling power at higher temperatures. 3He/4He ratio OK? | ||
+ | |||
+ | * Heating spikes, temperature oscillations. Superfluid leak to Vacuum can? Check for spikes in the vaucum can pressure. | ||
+ | |||