Vacuum system cost savings and design of production facility and installation scenario
Development of a cost-effective production and underground installation strategy for Einstein Telescope's Ultra High Vacuum (UHV) system; in particular, the arm vacuum system comprising approximately 120 km of 1 m diameter UHV tubes. The system must operate for a minimum of 50 years and be low maintenance.
In order not to disturb the laser beams repeatedly reflecting between the test masses (mirrors used to detect the passage of a gravitational wave), the laser beams must be in a UHV (Ultra High Vacuum) system.
Current detectors use standard stainless steel (AISl304L) and 3-4 km long, 0.7-0.9 m diameter and 3-4 mm wall thickness long UHV tubes for the arms of the interferometer (= 'arm vacuum system') with a volume of several 1000 m3, set at 1.E-8 mbar. If we apply this technology to the Einstein Telescope (ET) - which requires about a hundred times larger volume and a much lower residual vacuum pressure of 1.E-10 mbar - it will result in an expensive arm vacuum system.
In view of these potentially high costs and also in an effort to avoid - or at least simplify - in-situ burnout operations, alternative - particularly more cost-effective - concepts for ET's arm vacuum system should be studied.
Examples:
- Easier to process and cheaper low-carbon steel has better properties for hydrogen outgassing than standard stainless steel, eliminating the need for firing (baking out at high temperature).
- Ribbed tubes allow a significant reduction in the required wall thickness and do not require additional precautions (such as bellows) to accommodate length variations.
Nested tubes with a UHV-capable inner liner and a low-cost strong outer layer could be more economical to implement.
Given the huge system, an on-site production plant, also minimizing logistics, seems desirable. Similarly, the production and underground installation scheme should be optimized together.
Finally, the arm vacuum system requires numerous other components and services, such as: vacuum pumps; bellows to accommodate (thermally induced) longitudinal variations; baffles to limit scattered light; Cranes and partitions to compartmentalize the arm vacuum system during interventions; diagnostic equipment (RGAs, vacuum, pressure, etc. sensors); cryotraps to prevent water vapor in particular from the towers from reaching the arm vacuum system; bake-out facilities if needed; etc. Overall system integration is crucial, not only in view of the high cost, but also in view of the required long service life of at least 50 years with ideally low maintenance, i.e., the arm vacuum system must be very robust.
Key challenges in a nutshell:
refers only to the arm vacuum system, i.e. not to the much smaller vacuum towers that house the main instruments
- Large UHV system: about 120 km of pipes with a diameter of 1 m, i.e. a volume of about 100,000 m3;
- 10. E-10 mbar vacuum pressure;
- Expected lifespan of at least 50 years, i.e. it must be robust;
- Cost-effective production and underground installation strategy;
- Research alternative materials/layouts for the "simple UHV standard"-but expensive-thick-walled stainless steel tube: Low carbon steel or aluminum; thin-walled ribbed tube; nested tubes, etc.;
- System optimization: vacuum vessels, pumps, valves, bellows, baffles, cryotraps, diagnostic instruments (for instance RGAs), etc.
Goals
Engineering goal | Pipe design, optimize design choices, topics:
- Material selection (low carbon steel?);
- Wall concept (solid versus corrugated versus nested tubes (inner liner));
- Production concept (external versus on-site production): assembly technology (welding technology);
- Compartmentalize the arm vacuum system/maintenance;
- Component choices: vacuum vessels, pumps, valves, bellows, baffles;
- Diagnostic equipment (RGAs, vacuum, pressure sensors, etc.);
- Cryotraps to prevent particularly water vapor from the towers from reaching the arm vacuum system;
- Baking out facilities if needed;
- Variables to optimize: material costs, out tray requirements, length variations and stray light management.
Total (all detectors):
- 120 km of 1 m diameter UHV pipes;
- 50 years with low maintenance life;
- Safe design (to produce/use/maintain).
Arm vacuum system (1 detector):
- 10 km of pipe length (diameter 1 m);
- 10,000 m3 capacity;
- 1.E-10 mbar.
Overall system integration is crucial, not only in terms of cost, but also in terms of the required long service life of at least 50 years with ideally low maintenance, i.e., the arm vacuum system must be very robust.
More information
Einstein Telescope for Business - Vacuum information session (pdf)
Status of the beampipe activities (pdf)
Einstein Telescope - beampipe requirements (pdf)
Openstellingstekst voor de R&D-regeling Vacuümtechnologie (in Dutch)