12 December, 2000

Finishing little bits at AST/RO

Today we finished a few small projects that have been ongoing at AST/RO for the last week. Two weeks ago, Chris noted a small leak in one of the hoses that runs helium from a compressor to the dewars. This helium acts as a refrigerant, and with the small leak, the dewars were not remaining as cold as they need to be. Although we knew this leak existed, it could have been in one of 10 places. Finding a small leak is tricky. Ordinarily, one would hope to hear the sound of gas escaping. However, the room where the dewars are is fairly noisy so this was not an option. There are also devices called helium sniffers which would be able to detect a small amount of helium escaping from the line somewhere. However, we didn’t have a helium sniffer. So, we decided to put a soap solution around the possible leak locations and see if bubbles form. If there is air escaping from the tubing, it should continue to escape and blow a bubble in the soap. However, we had problems with the soap solution staying where we wanted it to be, and we were unable to locate the leak. There is commercial liquid available that works on the same principle as the soap, and we located a bottle of it over the weekend, and yesterday we finally isolated the location using this liquid. When placed over the leaky joint, bubbles started to form. With the location of the leak finally known, we could replace the faulty hose. While taking off the old one, we noticed the o-ring in the junction between the hose and the pipe was malformed. So, this pesky leak turned out to be an easy fix- replace the o-ring. We reattached the hose, and the system was once again working properly. Yeah!

The other ongoing project has been finishing the various parts of the PoleSTAR installation. The PoleSTAR receiver had been successfully installed ahead of schedule and was up and running when I arrived. But the computers that keep the system in check were still being tested to make sure that they are working properly. The final stage of this was to run water through the system to keep it a constant temperature. Yesterday we connected the water hoses, and today were able to run water through it for the first time. Soon the water will be replaced with antifreeze if the system continues to run properly.