MiniGRAIL progress report 2001: the first cooldown

The results of the first cooldown of MiniGRAIL are presented. MiniGRAIL is a 65 cm diameter spherical gravitational wave detector made of CuA16%, having a mass of 1150 kg. The sphere is suspended from a seven-stage vibration isolation system with a total weight of about 950 kg. The sphere should be cooled to below 20 mK. During the first run the sphere was cooled down to 1.8 K. A forced helium flow was used to cool the sphere down to 4 K, which took only two days. Further cooling to 1.8 K was done using a I K pot. We measured the temperature dependence of the mechanical quality factor and made an evaluation of the heat leaks (for more details see www.minigrail.nl).