Newtonian noise introduced by impellers in LIGO Voyager and Cosmic Explorer gravitational wave observatories

Abstract

Third generation ground-based gravitational wave detectors are proposing the use of cryogenics. The low-temperature regime will require a cooling-down system capable of removing heat from test masses and maintaining its low temperature. The present study analyzes the Newtonian noise introduced by rotating impellers used in a cooling-down system with sub-cooled nitrogen circulating in a loop. In order to calculate this noise, a computational model was developed and the results were compared to the LIGO Voyager and Cosmic Explorer design sensitivity curves. For a system using two impellers having three blades each, the model shows that this Newtonian noise is always below the sensitivity curve if their distance to the test mass center is greater than 2.3 m for LIGO Voyager and 2.4 m for Cosmic Explorer. In addition, our calculations showed zero noise values for specific impeller’s locations, depending on the blade number. This revealed a new region where it is possible to minimize the noise.