Takeshi Uchiyama

Vacuum-compatible vibration isolation stack for an interferometric gravitational wave detector TAMA300

Interferometric gravitational wave detectors require a large degree of vibration isolation. For this purpose, a multilayer stack constructed of rubber and metal blocks is suitable, because it provides isolation in all degrees of freedom at once. In TAMA300, a 300 m interferometer in Japan, long-term dimensional stability and compatibility with an ultrahigh vacuum environment of about 10−6 Pa are also required. To keep the interferometer at its operating point despite ground strain and thermal drift of the isolation system, a thermal actuator was introduced. To prevent the high outgassing rate of the rubber from spoiling the vacuum, the rubber blocks were enclosed by gas-tight bellows. Using these techniques, we have successfully developed a three-layer stack which has a vibration isolation ratio of more than 103 at 300 Hz with control of drift and enough vacuum compatibility.

Two-dimensional X pendulum vibration isolation table

We have extended to two dimensions a previously developed vibration isolation table using crossed wire suspensions (X mechanisms). A load table is suspended using a combination of normal and upside-down X mechanisms so that it moves freely with a very long period in both horizontal directions but is moderately stiff in all other degrees of freedom. Periods of 5 s are easily achievable. The transfer function of the prototype reported here contains a number of elastic mode resonance peaks, but it is shown by analysis how to reduce or eliminate nearly all of these.

Two-dimensional low-frequency vibration attenuator using X pendulums

We have designed and constructed an improved two-dimensional X pendulum vibration–isolation table. It achieved a lower resonant frequency (7 s) than previous prototypes, and the effects of many parasitic elastic resonances have been reduced by careful balancing, leading to much improved vibration isolation around a few hertz.