Design Approach and Analysis Results for Structure Feeders of ITER Magnets

Abstract

The superconducting magnet system of ITER has 5,000 tons of cold mass as steel structures to support the gravity and electromagnetic forces. These steel structures need to be maintained at 4.4 K during magnet operations. The magnet system has three STR (structure) feeders for distribution, monitoring and control of helium to remove heat loads from these large steel structures during cool down and normal operation. One SHe (supercritical helium) circulation pump for flow rate of 2.7 kg/s, in a closed loop is used only for cooling of structures, and these 3 STR feeders are part of this loop. Each STR feeder has 3 main components: SCVB (structure cooling valve box), CFT (cryostat feed through) and ICF (in-cryostat feeder). Unlike the coil feeders, STR feeders do not have bus bars, current leads & SBB ("S"-bend box), and present some difference in the design approach. The SCVB is placed outside the enclosure of the nuclear radiation shield and hence contains elements needing maintenance like valves and instruments required for diagnosis and operation of the cooling paths. Each SCVB has to accommodate about 20 valves within a limited available space. Some SHe lines will have running length of about 50 m from SCVB to coil structures, but the layout is such that the use of expansion joints can be avoided. The details of the design approach and analysis results will be presented in this paper.

Cryogenic Engineering Design of the ITER Superconducting Magnet Feeders

“…The same concept as for TFC is used for PFC and CS feeders, but here, each feeder connects to one coil or module. The STR feeders have one supply valve for each pair of TFC structures, but the return paths have 4 valves each [3]. For the thermal shield, there is a valve on each helium supply and return paths and this concept is same for all 29 feeders.…”

“…The return control valves for busbars will have a Table II gives the flow rates for different components and the pressure drops in these magnet components including the paths up to the feeder valves. Reference [3] gives the detailed flow rates for structure cooling paths.…”

“…Parallel cooling paths are considered on the panel to reduce the pressure drop. Reference [3] gives some analysis results.…”

“…For the convenience of design, assembly and functional needs, it has been planned to have 31 independent feeders distributed around the Tokamak cryostat at the top and bottom levels. The feeders are further classified into six functional groups: 1) Nine TFC (Toroidal Field Coil) feeders, 2) Six CS (Central Solenoid) feeders, 3 [4].…”

“…[7] and STR feeders [3] can be found in the references included here. The CS and PFC feeders have very similar PFDs.…”