Bubble-Induced Vibration in Liquid Nitrogen Cryopump

Abstract

Gravitational Waves (GW) predicted by Einstein in 1915 were detected by LIGO (Laser Interferometer Gravitational-Wave Observatory) on September 14, 2015. This is the first direct detection of GW and the first observation of a binary black hole merger. The comparative low signal of the GW makes the observation very challenging; however, continuous improvement in detection equipment will open to observe more phenomenon of the universe. Liquid Nitrogen Cryopump is one of the key components of LIGO system to maintain the UHV and also the main source of noise due to bubbles. The bubble induced noise is one of the noises that could distort the signal. Cryogenic fluids are always in the boiling modes and inducing the bubble noise continuously. The present work is an attempt to theoretically investigate bubble induced vibration and noise with the help of bubble dynamics. The configuration of LN2 cryopump as circular concentric shell makes the investigation more challenging. The departure force on the liquid nitrogen bubble is of the order of 10-5 N, which provides the initial acceleration of ~2g. The bubble moves through the liquid nitrogen and impacts the surface, which produces the vibration and noise. The noise is analyzed in terms of force, acceleration, velocity and the displacement. The induced noises are in the range -16 dB to - 146 dB. This work will open the new window for the cryogenic fluid usability for the vibration-free environment. Hence it is a new emerging area of investigation.