Suppression of vibration induced by reciprocal motion of displacer in cryopump with an active dynamic vibration absorber

An active dynamic vibration absorber is introduced to a cyropump system achieving ultra-high vacuum and extremely low temperature environments for fine observation and high-accuracy measurement. In a cryopump, a so-called displacer moves reciprocally for alternative adiabatic expansion and exhaust of helium gas. Such a motion induces vibration in the vacuum chamber on which the pump is fixed. It may negatively affect observation and measurement performed in the chamber. To remove this vibration effectively, an active dynamic vibration absorber is designed, fabricated and installed in the system. Both empirical and model-based approaches are applied in reducing vibration at multiple specified frequencies. Finally, the vibration is almost eliminated at five specified frequencies.