Vacuum beampipes
The vacuum system lies at the core of the ET. It will contain 120 Km of 1-m diameter steel pipes tubes, equipped with baffles to mitigate light scattering, through which laser beams propagate in ultrahigh vacuum (UHV) between the input and end mirrors of the interferometers. Other elements across the vacuum tubes are the pumping stations, bake-out systems and valves.
CERN is leading the design of the vacuum pipes, aiming to produce a two arm, 40 m pilot sector which will lead to the final design of the vacuum pipes. At present, two options for the pipes are considered. The first one requires the fabrication of 1 m diameter tubes (up to 20 m long), potentially to a large spectrum of manufacturing industries that are generally involved in the production of boilers or pipes for gas and oil transport. The minimum requirement would be the quality of the welding, particularly for AISI 441 stainless steel grade, and the respect of a given geometrical tolerance. The additional UHV and dust conditioning would be performed in another facility, possibly near the installation site. The conditioning encompasses UHV-compatible cleaning and treatment in a dust-controlled area, possibly ISO6 compatible.
In the other option, the vacuum tubes would be manufactured and conditioned by suppliers that have demonstrated capability and experience in the construction of large UHV systems in defined dust-controlled environments. The delivered product would be ready for installation without additional conditioning.
Aimed companies:
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For the first option, producers of tubes, gas pipelines, or boilers with certain tolerance requirements and demonstrated capability in UHV-compatible welding. Automatised continuous laser welding would be an asset.
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Considering the second option for tube fabrication, the aimed companies are those that are involved in the production of large UHV systems and that include in their portfolio cleaning capabilities and dust-controlled procedures.
Vacuum Towers
The vacuum system of the towers consists of the chambers that host the critical parts of the interferometer: the optics, the anti-seismic suspensions and the test-masses in particular. They are vertical chambers, with cylindrical or conical geometry, exceeding 10 m in height, with volumes of tens of cubic meters and mass over 20 tons each. They operate at vacuum levels ranging from HV to UHV, often separated by large valves and operated also in-air when accessed by personnel for tunings and maintenance. A key feature of these systems is the direct interface with the many subsystems of the interferometer, imposing stringent specific features, e.g. stiff mechanical structure and extremely clean surfaces free from chemical residues and particulates.
Between 80 and 120 towers are foreseen for ET, depending on the finally chosen configuration, together with interconnecting pipes (links) and auxiliary chambers (‘mini-towers’). The system is completed by large gate valves (up to 1 m in size) and by vacuum-compatible materials used to realize the internal electromechanical assemblies, which must also comply with strict vacuum-compatibility and contamination-control requirements.
Aimed companies:
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Large-scale mechanical industries capable of manufacturing and handling stainless-steel structures up to 4 m in diameter and 15 tons.
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Suppliers of high-technology sealing systems.
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Manufacturers of UHV components such as large gate valves and viewports.
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Companies providing qualified cleanroom-grade cleaning and surface preparation for large assemblies.
Cryogenics
The Einstein Telescope's design includes a "xylophone" configuration, where the low-frequency detector (ET-LF) uses cryogenics, while a separate high-frequency detector (ET-HF) operates at room temperature. This dual design optimizes the observatory's sensitivity across a broad range of gravitational wave frequencies. Although the temperature goal of the ET-LF mirror, ranging between 10 and 20 K seems easily achievable by the present cryogenic technologies, lowering the mirror temperature without injecting noise from the cooling system is a technical challenge, as well as deploying cryotransfer lines hundreds of meters long.
The sensitivity of the gravitational wave detectors is limited by the thermal noise of the suspended mirrors, which depends upon the dissipation coefficients of the system (for which the choice of the material is critical) and its temperature.
Aimed companies:
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Manufacturers with proven expertise in the construction of large helium refrigeration systems, including compressor stations on surface and cryogenic coldbox underground. The ET cryoplants must provide cooling to the cryopumps and the cryostats of ET-LF and the cryopumps of ET-HF. It requires helium to cool part of the interferometer at different temperatures as 80 K, 10K, 5K and 1.9 K.
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Suppliers of high reliability actuators and sensors operating at low temperature. These are crucial elements to monitor and control the suspended mirror keeping the detector running.
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Companies providing solutions to monitor and control the thermal status of the ET cryogenic parts.
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Industry with expertise in the production of superinsulation materials.