ИСТИНА

Experimental research of seismic and gravitational backgrounds was foreseen in the frame of ET_W2 program. Measurements of the seismic noise level were performed along the horizontal tunnel of the Baksan Neutrino Observatory (BNO) having 4 km length under the Andyrchi mount (3700 m). A simple estimate of correspondent spectral intensity of the Newtonian Gravitational Noise associated with the measured seismic background wase found using Saulson model. According to this model, stochastic displacements of the interferometer’s mirror under the action of the variable Newtonian gravity field induced by seismic perturbations at different deep level 300, 1500 and 3800 m in BNO are presented. The ET mirrors should operate at low temperature. Investigation of the of the substrate and mirror coating behaviors is important task in the frame of ET_W2 program. The direct measurement of the Finess characteristics of the Fabry-Perrot interferometer during cooling process was chosen in the cryogenic mirrors experiment in SAI MSU. At the first stage of this experiment the cryostat for the cooling of relatively large volume was elaborated. The temperature of 4K was achieved to the test body of ~10 kg. At the second stage, the Fabry-Perrot interferometer from the mirrors with CaF2 substrates was constructed, attached to this test body for the good thermal conductivity. The current process of this experiment is discussed.