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Just Arrived: New Vacuum Envelope for the MIT LIGO Advanced System Test Interferometer

Just Arrived: New Vacuum Envelope for the MIT LIGO Advanced System Test Interferometer

- Contributed by David Shoemaker

Earlier this year, the MIT test interferometer finished its work on Phase Noise sensing and digital servo tests. (See the February 1998 newsletter for the most recent report.) It was then disassembled along with the rest of the lab when we moved to our new surroundings in July (as described in the newsletters for Summer, April, and March 1998). Parts taken from the vacuum envelope are now being used at MIT for small-scale experiments in suspension development and compensation of thermal lensings--but more on those experiments in a later newsletter at another time. Other parts of the vacuum envelope were sent to Caltech to be part of the Thermal Noise Interferometer. (Click here for a Caltech site devoted to progress of the TNI), as well as for use by CEGG, the research lab of Caltech's Prof. Ron Drever.

A new vacuum envelope to upgrade the MIT facility and let it contribute to the next phase of LIGO R&D has been in fabrication at Process System International, the same manufacturer who made the vacuum system for the LIGO Observatories. The new vacuum system uses LIGO-like tanks and consists of a "BSC" or Beam Splitter Chamber, so-called because it was originally planned to house the beam splitter though it is now used for all the large suspended optics, and three "HAMs" or Horizontal Access Modules, which are general-purpose chambers allowing access through large openings next to the optics. This equipment is configured in an L-shape of 15 m length, with a "mid-station" in one arm to allow modulation frequency sidebands to fit comfortably. The vacuum system had been just recently completed, as was our new lab, and the time for the transport and installation of the one to the other was now upon us. A complete photographic slideshow awaits you below, but hold on! We're not finished with the set-up yet!

The system, which we have christened LASTI (for LIGO Advanced System Test Interferometer), will be used to develop and test components for future interferometers to be installed at the LIGO Observatories. Because the physical interfaces are identical to those at the Observatories, we can test isolation and suspension components as they will be installed at the Observatories, and this is in fact our principal target for this installation. The LIGO Scientific Collaboration Suspension Working Group is gearing this installation for the critical system tests and high-sensitivity characterization of the next generation of isolation and suspension systems. Of course, we will consider any other way this test interferometer can help make LIGO work, now or in the future.

And now for the fun part: photos of the installation! The only entrance to our new high bay that we could even come close to using was within one inch (!!!) of the size of the incoming chambers (and that was only after the main ports were taken off the chamber sides). The rigging devised to bring in the components was imaginative, and involved tipping and twisting the components (with all possibilities tried in 3-D CAD first, of course), and then transfer from crane to crane, as the chamber was literally inched in.

Figure 1 Figure 2 Figure 3 Figure 4


In Figure 1 (starting at left), one of the connecting tubes is lowered gingerly to earth. Figure 2: Here is a HAM, slipping comfortably in the door. Figure 3: One HAM in (at left in the photo), another coming in the door (at center right). In this shot notice also the remnants of the old vacuum system (the "tiny" chambers at far right and behind the middle HAM). And in Figure 4: A view from outside of the BSC's cap as it enters the door.


In Figure 5 at left we see a view of one of the two sides which just barely clear the door frame. Yes, the clearance is about an eighth of an inch. (Ok, it was a gaping half-inch on the other side!) Next in Figure 6, the BSC is seen on its way in the door. Will it flip...? Figure 7: Here the BSC is just coming down to the ground level...but not quite level... Lastly, Figure 8: Our once empty high bay is now stuffed. On the left in the shot is one of the connecting tubes, on the right are two HAM chambers.

Figure 5 Figure 6 Figure 7 Figure 8

Process System International will spend a number of months placing, installing, and testing the vacuum system, after which we will start installation of the isolation system components. While the real action right now is at the LIGO Observatories, it is great to have a mini-LIGO interferometer coming together in our own MIT backyard, getting prepared for our next research effort.