Effects of Mass Flow Rate Imbalance Among Petals During ${\rm T}_{\rm CS}$ Measurements of ITER TF Short Samples in SULTAN

Abstract

Since year 2009, the joint of the toroidal field (TF) conductor samples tested in the SULTAN facility at PSI Villigen, CH, is solder-filled, so that the helium coolant can only flow axially inside the central channel. The latter is however plugged starting 40-45 mm downstream of the joint. The helium has then to pass from the central channel into the annular cable region over such a short length that the desired homogeneity of the flow distribution among the petals in the high field region is not guaranteed a priori, since central helix and petal wrappings act as azimuthally non-uniform obstacles to the radial flow. In the paper we first present a geometrical model for estimating this interference to the radial flow, and combine it with a CFD (ANSYS-FLUENT) model of the hydraulic effect of the plug, in order to estimate the mass flow rate imbalance among the petals at the beginning of the plug. This is then used as boundary condition by the THELMA code, to parametrically assess the results of a TCS measurement.

Analysis of sudden quench of an ITER superconducting NbTi full-size short sample using the THELMA code

“…Such models are clearly restricted to timescales sufficiently long to guarantee temperature uniformity on the cross section of each CICC component. However, recent tests of short-length full-size samples of Nb3Sn ITER CICC have shown that, in some relevant situations, the temperature in the annular region is not uniform, with indirect evidence of temperature differences arising between the different last-but-one wrapped cabling stages (the so-called petals) [20][21][22]. Other applications of the THELMA code, see [23], also confirmed the role of the current distribution on the performance of this kind of sample.…”