AC loss, interstrand resistance and mechanical properties of prototype EU DEMO TF conductors up to 30 000 load cycles

Abstract

Two prototype Nb 3 Sn cable-in-conduit conductors conductors were designed and manufactured for the toroidal field (TF) magnet system of the envisaged European DEMO fusion reactor. The AC loss, contact resistance and mechanical properties of two sample conductors were tested in the Twente Cryogenic Cable Press under cyclic load up to 30 000 cycles. Though both conductors were designed to operate at 82 kA in a background magnetic field of 13.6 T, they reflect different approaches with respect to the magnet winding pack assembly. The first approach is based on react and wind technology while the second is the more common wind and react technology. Each conductor was tested first for AC loss in virgin condition without handling. The impact of Lorentz load during magnet operation was simulated using the cable press. In the press each conductor specimen was subjected to transverse cyclic load up to 30 000 cycles in liquid helium bath at 4.2 K. Here a summary of results for AC loss, contact resistance, conductor deformation, mechanical heat production and conductor stiffness evolution during cycling of the load is presented. Both conductors showed similar mechanical behaviour but quite different AC loss. In comparison with previously tested ITER TF conductors, both DEMO TF conductors possess very low contact resistance resulting in high coupling loss. At the same time, load cycling has limited impact on properties of DEMO TF conductors in comparison with ITER TF conductors.

Numerical Investigation on Induced Current Distribution and AC Losses in a Prototype Cable for the European DEMO TF Coils

“…As described in detail in [5], the DEMO W&R cable sample interstrand resistances have been measured by Twente University to get sets of contact resistance values corresponding to different cabling stages. The measurements corresponding to stages from 1 to 5 have been considered to determine the intra-petal contact resistance R cintra (Ωm), whereas those taken from stage 6, corresponding to the whole cable, have been considered for the inter-petal value R cinter (Ωm).…”

“…The measurements corresponding to stages from 1 to 5 have been considered to determine the intra-petal contact resistance R cintra (Ωm), whereas those taken from stage 6, corresponding to the whole cable, have been considered for the inter-petal value R cinter (Ωm). With a THELMA detailed geometrical cable model, representing all the strands, the topology of the test arrangement described in [5] could be reproduced exactly.…”

“…For both the contact resistance models, the parameters were determined with a statistical approach, considering a cable created with a random Θ Θ Θ array. A wide set of interstrand resistances R c = u i,j /i j,i were computed for many couples of strands and suitably classified according to the combinations R stk defined in [5]. From the statistical point of view, the obtained values cannot be thoroughly considered the results of independent outcomes, since the strand geometries of a given cable are not all independent.…”

“…of experimental results taken by Twente University from the W&R prototype conductor proposed by ENEA [5].…”

Progress in the design of the superconducting magnets for the EU DEMO

“…AC losses were measured by using both calorimetric and magnetization methods [16,21], with the magnetic field orientation either perpendicular or orthogonal to the wide conductor side. The energy deposited per cycle and per unit volume is rather high, with a pronounced difference depending on the orientation.…”