Lower the Dewar

The dewar is the blue cylindrical shell that surrounds the IVC. We also refer to the dewar as the “main bath”, which will be used throughout the manual. Lowering the main bath is necessary if you are starting a run and the detector needs to be replaced for a different one. If the MB is not already lowered for your benefit, then you must take care of this. If you’re in the middle of circulation and/or the main bath is still cold, please read the entire last chapter ’Warm Up’ to properly end the run so that you may follow the procedures below to drop the dewar. Lowering the MB is better accomplished with two people because the MB needs to be guided as it lowers such that it doesn’t get caught or hit the lines, IVC, or polyethylene.

1. The MB is lifted and lowered by two metal cords that are commanded by a hand crank. Attach these two metal cords to the sides of the MB through two loops located near the top of the MB. Steel pins are used to attach the cords to the loops.
2. You will now remove the screws securing the MB to the platform.
   1. Remove the M5 O-ring screws circularly patterned on top of the MB (these are the smallest set of fridge screws). Place these into the plastic fridge screws box.
   2. Remove the M8 screws on the bottom side of the top flange of the MB (these are the middle-sized set of screws for securing the fridge). Place these into the plastic box.
   3. Remove the two M12 screws that secure the MB to the platform from above (these are the largest screws out of the bunch). Place these into the plastic box.
3. The MB is no longer secured to the platform and is being held by the two metal wires. Remove the wooden doors beneath the MB because the next step is to lower the MB into the pit.
4. One person will turn the hand crank to lower the MB while another stands on the ladder to keep eye level with the top of the MB so it doesn’t sway and lowers evenly. Keep an eye on the polyethylene as the MB lowers because it may catch. Note that the following instructions are not yet applicable if the MB and IVC are cold. Follow the instructions to wrap the IVC and partially lower the dewar from the ’Warm Up’ chapter. Once the IVC has warmed up, then you may proceed with the next steps.
5. When the dewar lowers to the bottom of the pit and is resting on the ground, remove the pins that keep the metal cords attached. Lift the cords and hang them on the ledges of the platform’s pillars.
6. Cover the top of the MB with the fan attached to the cardboard and turn the fan on. This is to warm up the dewar (if it is cold) and to protect it from objects accidentally falling inside.
7. Cover the pit with the wooden doors.