A Set of H-S Windscreens and Test Results of it on the YNAO NVST

Solar Telescopes often work without domes, but are set up near large water surfaces such as those of seas or lakes. Such a strategy keeps good seeings at the sites, but on the other hand, the air flow between land and water may cause vibrations of telescopes. To reduce the negative effects,we have designed and installed a set of Hindering and Steering Windscreens for our NVST(New Vacuum Solar Telescope). We report in this paper key design points and encouraging results. Our H-S Windscreen consists of three parts: (1) The first is a wind deflector consisting of many rectangular lamellas. Long edges of a lamella are flatly set on the supporting frame, and the plane surface of the lamella has a specific angle from the horizontal level decided by numerical simulations. The material for lamella is of low thermal conductivity to avoid strong heat exchange. (2) The second is a curved wind baffle the height of which is adjustable according to the telescope pointing. (3) The third is a circular supporting frame, which turns around according to wind directions. The H-S Windscreens have been put into use with the NVST at the Fuxian Lake Solar Observing Station since August 2010. We give some test results. The H-S Windscreen can reduce the wind force by an order of magnitude and the wind-speed variation. The design of the NVST windscreen is thus successful in reducing the effect of wind force on the telescope and in increasing observation time.