Dear colleagues

Over Christmas we will be carrying out some essential maintenance to the MEG facilities. The most important job that we will be doing is warming the sensor dewar. During the past year the dewar will have slowly accumulated a small amount of solid oxygen, nitrogen and water in the bottom of the Helium reservoir and this affects the insulation properties of the system. By warming the system up we can remove all the frozen solids. The system will be cleaned out and then we will be cooling it down again to liquid Helium temperatures.

We will do the final Helium fill on the morning of the 18th of December. We lose 20% of the Helium a day so the dewar will effectively cease to be at liquid Helium temperatures from the 23rd. We would not advise anyone to carry out experiments from the 21st onwards as the characteristics of the system cannot be guaranteed once the Helium level goes below about 15%.

The system will be allowed to warm up over Christmas and we will start work on a number of maintenance jobs in the new year. These will culminate with the recooling of the MEG dewar starting on the 10th of January. This should take 5 days. We plan to allow MEG experiments to resume on the 17th.

I hope that you will be pleased to hear that a major quarterly maintenance of the MRI system on Friday went very smoothly. A new cooling system was installed and this should improve air flow through the bore of the magnet. There had also been a problem with some coherent noise being observed on some scans (not head scans) and the cause of this was located and removed.