MiniGRAIL

Gravitational Radiation Antenna In Leiden

Kamerlingh Onnes Laboratory, Leiden University, The Netherlands

Suspension

The MiniGRAIL attenuation system consists of a room temperature part and a cryogenic part. The cryostat is suspended from a concrete support, which is built on specially designed low vibration islands. The concrete platform, which holds the dewar rests on a stack of rubber and wooden rings that works as a low frequency absorber. The low pass mechanical filter, consisting of a stack of masses and springs, is mounted inside of the cryostat. Seven masses and springs are suspended from the top flange of the cryostat with three stainless steel cables, hanging from three helical springs meant to damp low frequency vibrations. The stack is inserted in the neck of the cryostat. The stainless steel cables hold the upper mass (number one), while the other masses hang from each other by means of stainless steel springs and copper rods. Ten radiation shields are mounted between the upper mass and the top flange. The fifth intermediate shield is thermally anchored to the nitrogen reservoir of the cryostat and the last shield is coupled to the helium reservoir. The stainless steel cables are thermally anchored to both shields with flexible copper braid. The stack begins with four CuAl6% masses followed by three copper masses, denoted as mass number one to seven in the figure.