Closing and pumping

In this section, it is assumed that all work is finished, and you just need to close the vessel.

You will have to be two persons or more, with at least the following equipment:

• A selection of mm-size hex-keys.
• A hoist or other lifting device.
• Heat-insulating gloves.
• An oven. Even better: A vacuum-oven and a bottle of dry air.
• A vacuum pump with appropriate hose and fittings.

In order to achieve a good vacuum, a large molecular sieve, containing 140 g activated charcoal, is installed. For the sieve to function properly, it should be cleaned whenever warm. Charcoal outgasses relatively well at room temperature, but still better at higher temperatures. Therefore, the getter should be removed from NOTCam and baked at 100 to 150 deg Celsius. For the best result, bake the getter in a vacuum oven, and when the baking is complete, fill the oven with dry air. As the getter will be inefficient when very warm, the idea is to only expose it to atmospheric air for a brief period where is is very warm. For this reason, speed is important for the procedure, and it should be rehearsed before it is performed.

The procedure is:

1. Remove the getter from NOTCam and place it in a vacuum chamber with a baking facility. Bake the oven at 150C for several hours until the pressure is below mBar. You may choose to start baking the day before the instrument is to be closed. Optionally, you may try to use an ordinary clean oven - but it is uncertain how well this will work. Do not stop baking until you are completely prepared to close NOTCam.

2. Stop baking by letting dry synthetic air or Nitrogen into the oven until ambient pressure is reached. Make certain that your oven can handle accidental over-pressure in a safe way. Leave it for a few minutes to let the getter absorb as much of the gas as it can. Open the oven and, using gloves, mount the getter on the cold table.

3. Mount the upper radiation shield. Take special care not to tear off the temperature sensor that may be mounted on the back of the detector flange, and to align all electrical wires of the three bundles (motor control, detector and temperature sensors) with the cut-outs in the radiation shield. When the shield is in place, secure it by tightening the eight screws at the edge.

4. Push the two halves of the super insulation blanket properly into place, and secure it by tightening a Teflon wire around the intersection.

5. Mount the upper half of the vacuum vessel, using a hoist. Take care not to damage the super insulation. Make sure that the O-ring and the flange in contact with it are clean.

6. Mount the entrance baffle: First mount the gold plated spherical reflector, then the painted baffle on top of it. Last, place the super insulation cap over the baffle.

7. Next item to mount is the entrance window flange. The O-ring with it's two steering rings must be held in place while the window flange is mounted. It can be difficult to keep the O-ring in the correct position, and a leak may result. Preferably, the O-ring still sticks to the vessel from the previous mounting, making things a lot easier.

8. Connect the controller box so that pressure can be monitored.

9. Connect a vacuum pump to NOTCam and start pumping.

10. When the pressure is 1 mBar or less, tighten the nuts holding the two halves of the vessel together. It should take no more than half an hour to get below 1 mBar.