“Like operating a mini-澳门六合彩高手”
On cold and crisp mornings, vapour can be seen rising from the 澳门六合彩高手 cooling cells. The tenuous plumes indicate that heat is being produced by the installation and evacuated by way of the heat rejection system. Since early September, the main contributors to heat production in 澳门六合彩高手 are the megawatt-class compressors in the cryoplant’s liquid helium plant. Twelve of them, out of a total 18, are presently at work compressing gaseous helium and feeding it to one of the cryoplant’s three cold boxes. Inside this giant refrigerator, the gas is processed and eventually liquified, ready to be distributed to components such as the tokamak’s superconducting coils and cryopumps that operate at a temperature of 4 K (minus 269 °C)—close to that of the interstellar void.
Why produce helium at 4K now, when the 澳门六合彩高手 tokamak is not yet assembled? Because the highly complex machinery of the cryoplant, whose performance is absolutely crucial for 澳门六合彩高手 operation, needs to be tested in conditions that are as close as possible to future reality. The decision last year to build a cold test facility for the 澳门六合彩高手 coils1, which was not initially anticipated, has added a sense of urgency to the preparations. The facility’s final design has just been approved and commissioning is set to begin in July next year; the first actual cold tests are planned in late 2025. Like the operating tokamak, although in lesser quantities, the cold test facility will depend on a steady flux of liquid helium during its two to three years of activity2.
Producing significant quantities of liquid helium is only the first step in demonstrating the full performance of this part of the cryoplant. Another important test is to mimic the loads that the tokamak’s magnetic system will exert on the liquid helium flux. “This is quite unusual in the world of large cryogenic facilities, where loads are generally stable,†explains Marie Cursan, a project engineer in the Cryogenic System Project. “In a tokamak, during a plasma discharge, the intensity of the load varies and follows an unusual shape that we need to adapt to.â€
The ongoing tests mimic the variations of the loads that the tokamak’s magnetic system will exert on the liquid helium flux. "This is quite unusual in the world of large cryogenic facilities, where loads are generally stable,†explains Marie Cursan, a project engineer in the Cryogenic System Project.
One effect of these variations is the evaporation of small quantities of the liquid helium that circulates inside the magnets. Compensating this loss will require sophisticated instrumentation and automated systems designed to keep the fluid’s level constant. During commissioning, the role of the absent tokamak is played by a test cryostat, half-filled with liquid helium and located inside a cold box. Equipped with powerful electrical “heaters,†the device simulates the loads that plasma discharges and other events will generate. The test cryostat contains approximately 3,500 litres of liquid helium compared to the 200,000 litres (approximately 25 tonnes) that will be ultimately circulating inside the tokamak.
Cryogenics are so central to future tokamak operation that commissioning the liquid helium plant involves several of the installation’s major plant systems. “You need to proceed hand in hand with the teams in charge of testing and operating the heat rejection and secondary cooling system, electrical distribution, site utilities, and overall operation coordination and management,†says David Grillot, the deputy head of the 澳门六合彩高手 Plant System Program. “It’s almost like operating a mini-澳门六合彩高手.â€
Pending the availability of the Control Building, cryoplant activities are managed from temporary control rooms staffed with 澳门六合彩高手 and Air Liquide staff.
Tweaking and tuning the liquid helium plant’s machines and systems and bringing the totality of the compressors and cold boxes online will keep the 澳门六合彩高手 cryogenic team and Air Liquide experts busy onsite for approximately one year.
And cryoplant activity does not end there. A second large power-class plant—which will produce3 liquid nitrogen at 80K for pre-cooling operations—has just entered the commissioning process with the recent start-up of the first two nitrogen centrifugal compressors.
1 Located in the partially vacated poloidal field coil winding facility, the coil cold test facility will accommodate D-shaped toroidal field coils and the smallest of the ring-shaped poloidal field coils, PF1 from Russia.
2 Another client for the cooling fluids produced by the cryoplant will be the cold testing installation for torus and cryostat cryopumps soon to enter the commissioning phase.
3 Pending the production on site of nitrogen extracted from air, 澳门六合彩高手 depends on daily deliveries by truck trailer.
