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--- wiki:design_construction [2022/02/02 16:56]
henri.godfrin@neel.cnrs.fr
+++ wiki:design_construction [2022/12/15 17:46] (current)
henri.godfrin@neel.cnrs.fr
@@ Line 9: / Line 9: @@
    * 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
@@ Line 36: / Line 36: @@
 ===== The 3He condensation line  =====
-{{wiki:3He-condensation_HG.JPG?350|3He-condensation_®HG}}
+{{ wiki:3He-condensation_HG.JPG?400 |3He-condensation_®HG}}
 ===== The "still"  =====
@@ Line 49: / Line 49: @@
   * 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  =====
-{{ wiki:mixingchamber_hg.jpg?150|Mixing chamber_®HG}}
+{{ wiki:mixing_chamber_hg.jpg?170|Mixing chamber_®HG}} {{ wiki:mixingchamber_hg.jpg?150|Mixing chamber_®HG}}
   * 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.
@@ Line 62: / Line 66: @@
   * 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 for temperature T>3 Tmin, where Tmin is the base temperature of the dilution refrigerator (no applied external power).
@@ Line 70: / Line 75: @@
   * 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.

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