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wiki:design_construction [2022/02/02 17:14]
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 "inserts" in a liquid helium dewar . Due to their small size, the heat exchangers have a small total area, and heat leaks make it difficult to reach temperatures below 10 mK.    * 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 "inserts" in a liquid helium dewar . Due to their small size, the heat exchangers have a small total area, and heat leaks make it difficult to reach temperatures below 10 mK.
  
-   * Larger refrigerators with heat exchangers of typical diameters larger than 10 cm ("Grenoble design") can reach temperatures on the order of 2 mK, with flow rates of 100 *mol/s. They can also provide large cooling power, with flow rates up to 10 mmol/s, obviously at higher working temperatures. +   * Larger refrigerators with heat exchangers of typical diameters larger than 10 cm ("Grenoble design") can reach temperatures on the order of 2 mK, with flow rates of 100 µmol/s. They can also provide large cooling power, with flow rates up to 10 mmol/s, obviously at higher working temperatures. 
    * 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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   * The still plays an important role: the **3He flow rate** of the dilution refrigerator, and hence the cooling power available at the level of the mixing chamber, **is mainly determined by the power applied to the still**.      * The still plays an important role: the **3He flow rate** of the dilution refrigerator, and hence the cooling power available at the level of the mixing chamber, **is mainly determined by the power applied to the still**.   
 +
 +===== The Continuous heat exchanger  =====
 +
 +===== The Step ("discrete") heat exchangers =====
  
 ===== The Mixing Chamber  ===== ===== The Mixing Chamber  =====
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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.
 +
  
wiki/design_construction.1643822097.txt.gz · Last modified: 2022/02/02 17:14 by henri.godfrin@neel.cnrs.fr

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