The Laser Interferometer Gravitational-Wave Observatory (LIGO) was designed to detect gravitational waves predicted by Einstein’s General Theory of Relativity over 100 years ago: “The discovery of gravitational waves was not merely another obscure milestone in theoretical physics, but a totally new way of seeing the universe,” explains Rainer Weiss, professor of physics at MIT and inventor of the laser interferometers that LIGO is based on.
On Sept. 14, 2015, the LIGO system detected a very slight disruption – the first direct detection of gravitational waves. Researchers confirmed the disruption was a signal of gravitational waves that originated from a pair of violently colliding massive black holes 1.3 billion light years from Earth.
Joshua LeBeau, VAT Regional Sales Manager, is a big fan: “This discovery was a historic moment in science – and proved that Einstein’s prediction of the existence of gravitational waves, very fine ripples in the fabric of space-time, was correct. The project's founders—Barry Barish and Kip Thorne of Caltech, and Rainer Weiss of MIT — all shared the 2017 Nobel Prize in Physics for their work. Well deserved!”
The LIGO system is based on two identical – and enormous – detectors located 1,865 miles apart, in Livingston, Louisiana and in Hanford, Washington. Each detector consists of two stainless steel vacuum tubes (covered by protective concrete pipes) about twelve feet tall and 4-km (2½-miles) long and arranged in an L-shape. Because of their extreme length, the pipes are raised from the ground by about a yard at each end, to keep them absolutely flat, due to the Earth’s curvature.
Each L-shaped detector is essentially a huge vacuum chamber traversed by laser beams. These lasers are bounced down each pipe with mirrors at each end. A passing gravitational wave stretches space in one tube while contracting space in the other tube by an infinitesimal amount, resulting in tiny changes in the time it takes a beam to traverse the tunnels. This lag sets off an alarm in LIGO’s detectors.
Before LIGO went online, the enormous stainless steel vacuum chambers needed to be evacuated. After 40 days of pumping, LIGO achieved one of the purest vacuums ever created on Earth, a trillionth as dense as the atmosphere at sea level, or 10-9 mbar, a typical pressure in UHV applications.
“Unfortunately, we bought the large valves – 48” and 44” – for the main ports from an inferior source and installed VAT vacuum valves (10”) on the smaller ports of LIGO’s tubes,” explains Rainer Weiss, a physicist at MIT. “The VAT valves perform flawlessly, while the large valves have caused us unending problems – we learned our lesson!”
LIGO ordered 86 VAT UHV gate valves, which were assembled in an ISO 6 clean room, as specified by the client. Widely used in R&D for UHV isolation applications, the Series 10.8 UHV gate valves are equipped with VATLOCK technology, which provides reliable sealing without any friction at the gate seal. A key feature of the VATLOCK is that it is locked in the closed position, eliminating any risk of vacuum loss due to pneumatic failure.
Dr. Markus Poppeller, VAT Product Manager adds: “The field proven Series 10.8 UHV gate valves feature a number of technical innovations to help maintain a clean vacuum environment: ‘grease free’ mechanics, ‘vulcanized gates,’ VATSEAL metal seals, and edge-welded bellows. In a final step, our high purity cleaning process guarantees that VAT vacuum valves are best in class.”
“These valve features and the VATLOCK technology guarantee the lowest possible outgassing and permeation rates, which support the priority of a clean UHV vacuum environment for LIGO,” adds Wolfgang Niessner, VAT Product Manager.
LIGO's engineers continue to improve the sensitivity of the detectors. The upgrades will significantly increase LIGO's capabilities and multiply the volume of space that can now be observed by the detectors. The success of these improvements is evidenced by the number of gravitational wave detections made since the initial discovery in 2015 – LIGO has gone on to identify over 30 additional detections of gravitational waves, mostly from colliding black holes.