Bakeout of YIN
1. First bakeout
The bakeout was performed in a part of the heating tent of the vacuum group (Lothar Schulz, Theo Bieri). Only sections 1 and 2 have been used (4 heaters) and the rest of the tent heaters were disconnected. The magnet was hanging on chains on a crane and later placed onto the bottom plate of the tent.
Fig. 1: Bakeout tent for SLS vacuum sections
During the backout the pressure at the turbo molecular pump and the temperature of the chamber has been recorded.
Fig.2: Temperature during 1st bakeout run
Fig. 3: Pressure at the turbo pump during bakeout
The pressure during the bakeout let one assume that a seal of the chamber has been damaged by the high temperature. However, the leak test showed no leaks of the vacuum tank. It is very probably that the sheet metal of the core (about 1000 pieces of 0.2mm thickness transformer core) started heavy outgassing. Unfortunately this outgassing exceeded the threshold of the pump stand and the pump was switched off automatically. By connecting a second pump in series was it possible to continue the bakeout while pumping without the need to close the valve inside the bakeout oven.
2. Second bakeout
In a second bakeout run the threshold values of the turbo pump have been deactivated in order to avoid automatic switch-off. Obviously was the first bakeout run not enough to get rid of the water and gas between the sheet metal of the septum core. The chamber was now placed on the bottom of the bakeout tent in order to release the crane to other users.
Fig. 4: Temperature during the 2nd bakeout
Fig. 5: Pressure during 2nd bakeout
The results of the 2nd bakeout as well as another leak test confirmed the assumption that the YIN tank is tight and the heavy outgassing was very probably caused only by the large surface of the sheet metal. The end pressure of the vacuum was almost similar to the starting pressure and the leak test showed again no leak. The tank was moved back to the Pulsed Magnets Area and the ion-getter pump was started. The current pressure (reading of the getter pump front panel) is in the 2E-9 mBar region (as of 6.12.1999).
