Tuesday, May 17, 2011

A letter for a lot of money

Starting up a new experimental physics research group is again and again interesting. Last time I was really nervous was when I for the first time signed the paperwork to hire someone (in case you're from the US, in Germany and many other European countries PhD students are in the sciences paid employees). Today, another lengthy process came to its (momentary) conclusion; I'll have however to explain this a bit.
Our research is focussing on electronic and mechanical processes at extremely low temperatures. "Extremely low" means in that case something like 20mK, or 0.02 degrees above absolute zero, or -272.95°C. To reach such temperatures, several steps of cooling have to be employed. First, the entire experimental assembly is submerged in a dewar (something like a thermos flask) filled with liquid helium, boiling away at 4.2K. Then, inside another vacuum chamber, evaporation cooling with again liquid helium is used to lower the temperature even further to somewhere around 1.5K. Lastly a closed cooling cycle with a mixture of the two isotopes of helium, helium-3 and helium-4, is used to lower the temperature even further to the base temperature of 0.02K. This entire machinery is called a dilution refrigerator; it was invented in 1951, and is by now available commercially from several companies worldwide.
So what happened today? Well, after getting a grant for buying one of them beasties, writing up the specifications, starting the Europe-wide call for tenders, awaiting and carefully evaluating the quotes, finally I've sent off the decision letter. "Please buy this one." Phew. I hope all works out, this thing costs about as much as a top-range Ferrari...

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