Helium Leak Check

Your pressure needs to be in a good enough range to use your mass spec (~10^-6 torr).

1. Turn on your mass spec.
2. Enter leak check mode.
3. Start He gas flow. You want to use a small tube or even a syringe needle to leak a gas flow just above ambient (when you can barely hear gas hissing out).
4. Leak He gas into possible areas of leaking in your chamber (flanges, bellows, valves, ceramic feedthroughs, water cooling lines, etc...). If your chamber pressure was better before, you should concentrate your leak check to areas that have been added or changed. Watch for the Helium signal to increase. When the signal increases, this corrolates to a leak being at the location you are leaking you are leaking He at. Possibly, if your system is large, there may be a delay. Because of this, leave enough time leaking at a particular location to identify if there is a delayed He signal increase.
5. If this fails, but you are sure there is a leak, try using the balloon method: using plastic bags (grocery, trash, etc), section off all areas of your chamber into different bags using tape to complete the seal. Poke your He leak into the bag and balloon the gas into the bag. If there is no mass spec signal increase, move on to the next balloon. If you see a signal increase with a particular balloon, then you have narrowed down your area of search. You know the leak is contained somewhere in there.

More detailed explanation here.

Mass Spec Procedure

Inficon Mass Spec (from Cindy Merida):

1. To begin, open TWare32 program. Make sure power supply for actual mass spectrometer is connected, and the RS232 cable is connected as well.
2. When program is opened, Sensor1_P1TSP2 will appear green if everything is connected properly, if not, it will appear blue.
3. Click on the Sensor icon, and monitor, to monitor the full mass spectrum.
4. The defaults on the mass spectrum are set at MaxAMU of 70, which can be changed to 100.
5. Make sure both the Emission and Multiplier icons are clicked to have the mass spectrum running properly. If pressure is bad, turn off the multiplier.
6. Also, the range can be changed, to give bigger peaks, adjust to a smaller range and vice versa.
7. When finished running, click stop on the software, and close the window. Unplug or switch off the power supply