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Softening The Vacuum with N$ _2$


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\begin{itemize}
\item {\bf How Long:} $\sim$16 Hours.
\item {\bf Thermal Shock:} Very High.
\end{itemize}\end{shaded}

Softening the vacuum will add gas to the OVC to allow conduction from the room directly to the cold mass. Depending on what is in the cryostat this may or may not be possible, as the accelerated warm up will result in thermal gradients across the cold mass.

To soften the vaccum:

  1. Attach one end of a vacuum line to the OVC valve and place the other end submerged in LN$ _2$ . Use a dewar that is open to atmosphere, this will ensure that the OVC doesn't overpressure. Wait about 5 minutes before proceding. This will allow the moisture in the lines to condense into the LN$ _2$ .


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{\bf DO NOT VENT FROM A PRESSURIZED DEWAR.}
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  2. Crack the OVC valve open just enough to hear a faint hissing. You should see the OVC pressure jump to $ \sim 2$ mBar. After about 5 to 10 minutes the OVC pressure will climb to 1 bar. Once the hissing fully stops, open the OVC valve completely.


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{\bf Do not close the OVC valve until you have reached room temperature.}
\end{shaded}

  3. Make sure that the LN$ _2$ does not run dry to ensure that no moisture gets into the OVC.

This faster process will allow conduction from the environment to warm the fridge up in about 16 hours. The fridge will collect a lot of condensation in this process, and will drip lots of water. Remove all electronics from the area.


next up previous contents
Next: Softening the Vacuum with Up: Speeding Up The Warm Previous: Speeding Up The Warm   Contents
Jonathan Ouellet 2014-08-26