Bubble Induced Vibration in Liquid Nitrogen Cryopump

Abstract

Gravitational Waves (GW) predicted by Einstein in 1915 were detected by newlineLIGO (Laser Interferometer Gravitational-Wave Observatory) on September newline14, 2015. This is the first direct detection of GW and the first observation of a newlinebinary black hole merger. The comparative low signal of the GW makes the newlineobservation very challenging; however, continuous improvement in detection newlineequipment will open to observe more phenomenon of the universe. newlineLiquid Nitrogen Cryopump is one of the key components of LIGO system to newlinemaintain the UHV and also the main source of noise due to bubbles. The newlinebubble induced noise is one of the noises that could distort the signal. newlineCryogenic fluids are always in the boiling modes and inducing the bubble newlinenoise continuously. newlineThe present work is an attempt to theoretically inv estigate bubble induced newlinevibration and noise with the help of bubble dynamics. The configuration of newlineLN2 cryopump as circular concentric shell makes the investigation more newlinechallenging. The departure force on the liquid nitrogen bubble is of the order newlineof 10-5 N, which provides the initial acceleration of ~2g. The bubble moves newlinethrough the liquid nitrogen and impacts the surface, which produces the newlinevibration and noise. The noise is analyzed in terms of force, acceleration, newlinevelocity and the displacement. The induced noises are in the range -16 dB to - newline146 dB. This work will open the new window for th e cryogenic fluid usability newlinefor the vibration free environment. Hence it is a new emerging area of newlineinvestigation. newline