Experimental set-ups for study of material properties at low temperatures

摘要

The Low Temperature Laboratory in IIT Madras was started in 1971. For nearly ten years prior to this I was doing theoretical work in lattice dynamics, non-linear elastic properties of crystals and in surface modes. Put I always believed that the bedrock of science is experiment. So when I got a chance to develop experimental activity in low temperature physics I grabbed the opportunity. It took us nearly two years to understand the working of the liquid nitrogen and helium plants and produce liquid helium reliably. The helium plant we had in the beginning was producing 1.5 liters per hour of liquid helium with liquid nitrogen precooling. We got initially a grant of Rupees Ten thousand per year which was just sufficient to import six cylinders of helium gas from UK. We could not buy equipment like temperature controllers, precision pressure gauges for vapor pressure measurement and calibrated thermometers. Prof. Klipping who was involved in the German Co-operative program with IIT, Madras, sent us some old discarded piece of equipment which we rectified and used for our measurement. Once we started producing liquid helium we set up some experiments in low temperature physics and offered cryogenics as an elective course in M.Sc. Physics. Later we were successful in getting projects from DST and we could build the facilities in the laboratory gradually. We increased the capacity of the liquid helium plant to 5 liters per hour using second hand compressor. Around 1985 we could get a new helium plant producing 10 liters/hour. We increased our liquid nitrogen capacity by adding one more philips liquefier in the eighties and a larger nitrogen liquefier in 1990. In IUC, Indore, all the nitrogen plants and the liquid helium plant were about twenty years old and obtained as gifts. We made the plants work and produce cryogen reliably. In this process we developed expertise in operating and maintaining these liquefiers. I believe such expertise is essential to keep low temperature activities going. But such experience is not easy to acquire.