On September 14, 2015, both the scientific and physical worlds were shaken - literally! Did you also feel torn? Probably not, because that would be like being able to feel someone on the other side of the world stomping their foot on the ground. What had happened? Due to the merger of two black holes at a distance of 1.3 billion light years a gravitational wave captured our Earth for 0.2 seconds. And for the first time, such a wave - predicted by Einstein's general theory of relativity - was experimentally detected on Earth by Project LIGO (Laser Interferometer for Gravitational Wave Observation). The Nobel Prize in Physics was awarded for this achievement in 2017.
For the elaborate detection of such large-scale extraterrestrial events, the signals must always be detected by two detectors simultaneously. Localization actually requires detection at three locations. In fact, four detectors are needed to cover all points of the compass. Therefore, work is being done worldwide to build up a network of detectors to detect even more of these events and to be able to make a more precise statement about their causes and origin. The latest child of this scientific effort is the LIGO India detector, the fifth in the world.
The first gravitational wave has led to a short distortion of the earth by about one trillionth in its extension. This unimaginably small change in length corresponds to a change in the Earth-Sun distance of 150 million kilometers by an atomic diameter of about 100 picometers. To measure such small changes in length, very sensitive interferometers are used. These measure the superposition of two crossed laser beams, each of which is reflected by a mirror at a distance of up to 4 kilometers. Even the smallest fluctuations in the mirror positions can thus be detected. To achieve the required sensitivity, these beams must be guided in a vacuum, because only here is the speed of light constant enough without the disturbing influence of thermal and atmospheric fluctuations.
Scientists at the Indian Institute for Plasma Research (IPR) designed LIGO's vacuum system. The challenges are great: the laser beams must be guided in ultrahigh vacuum (UHV) tubes of 1.2 meters in diameter. This is roughly equivalent to a vacuum volume of three competition swimming pools, making it one of the largest vacuum systems in the world. Nevertheless, operation should require only short maintenance intervals and pump-down times in order to always have as many detectors as possible ready for use worldwide at the same time.
VAT has already accompanied the development of the first LIGO in the USA in the design of the vacuum system. With large vacuum systems, segmentation into smaller separable volumes is essential. Only then can maintenance and repairs be carried out in a targeted manner in the affected areas, while keeping the rest of the system clean in the UHV.
"Based on the positive experience of US colleagues with VAT valves, the IPR contacted me back in early 2021," recalls Suman Kundu of Lawrence & Mayo, VAT's sales representative for vacuum components in India. "I knew that only VAT could supply such large valves with the desired quality and purity."
"It quickly became clear that the large DN 1250 HV gate valve of the 19.2 series best met the requirements set," explains Jürg Öhri, Sales Manager at VAT. "It is specified for the UHV range and the patented VATLOCK technology allows reliable closing with low force. This makes the high opening diameters of 1250mm or even more possible in the first place."
But LIGO India's requirements went beyond this. "In order to be able to use the valve in ultra-high vacuum, we wanted to ensure that no residual gases from the elastomer seals contaminated our system and that all components could be baked out to at least 150°C," clarify the vacuum specialists from IPR. But VAT was able to help here as well: Through an explicit residual gas analysis of all delivered valves, their purity could be proven beyond doubt, even up to 170°C bakeout temperature. The bakeout substantially shortens the pump-down times to UHV. In addition, the valve actuator was modified to meet customer requirements.
The LIGO India is currently under construction and the first VAT valves are already being delivered for it.
"We are very grateful to VAT for their technical know-how and flexibility in responding to customer-specific requests," says Suman Kundu, summarizing the experience gained from the project. "Through Lawrence & Mayo as a local partner on site, we were able to place our requirements in the right places at VAT at an early stage."
"The cooperation with IPR and Lawrence & Mayo was excellent and very efficient from the beginning. This way, it is easier for us to find a good solution for each specific requirement," Jürg Öhri sums up. "In the end, it's these passionate projects from the international research community that drive us. Because we, too, want to know what makes our world go round."
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