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Free keywords:
NbTi; fusion; critical current
Abstract:
While the International Thermonuclear Experimental Reactor
(ITER) conceptual design retained the Nb3Sn for toroidal field
(TF) and central solenoid (CS) coils, the low working field
(around 6 T) promoted the choice of NbTi for the poloidal field
(PF) coils. EU has carried out the experimental study of
industrial NbTi strands and cables with different internal
structures in order to choose the one which generate the lowest
losses when used in the PF operating conditions (i.e. pulsed
field). CEA has contributed to this project through the
experimental study of the transport properties variations with
respect to magnetic field and temperature of two candidate
strands. One of them contains an internal CuNi barrier and the
other is Ni-plated. A homemade cryostat is used to control the
temperature of the sample which is wound on a VAMAS-like
mandrel. J(c) measurements are presented here and subsequently
the parameters deduced from scaling laws and their variation
with temperature between 4.2 and 7 K and with field up to I 1
T. A comparison between the two strands characteristics and
ITER PF coils criteria is also discussed. The results are in
good agreement with literature and lie inside an acceptable
range in spite of some discrepancy with the ITER PF criteria: a
recent thermo-hydraulic simulation confirmed it. In the future,
this study, completed by AC losses measurements on cabled
strands, should help to optimise the strands performances below
the ITER PF security margins. (C) 2002 Published by Elsevier
Science B.V.
