  The ITER cable-in-conduit conductors (CICCs) are built up from sub-cable
bundles, wound in different stages, which are twisted to counter coupling loss
caused by time-changing external magnet fields. The selection of the twist
pitch lengths has major implications for the performance of the cable in the
case of strain sensitive superconductors, i.e. Nb3Sn, as the electromagnetic
and thermal contraction loads are large but also for the heat load from the AC
coupling loss. Reduction of the transverse load and warm-up cool-down
degradation can be reached by applying longer twist pitches in a particular
sequence for the sub-stages, offering a large cable transverse stiffness,
adequate axial flexibility and maximum allowed lateral strand support. Analysis
of short sample (TF conductor) data reveals that increasing the twist pitch can
lead to a gain of the effective axial compressive strain of more than 0.3 %
with practically no degradation from bending. For reduction of the coupling
loss, specific choices of the cabling twist sequence are needed with the aim to
minimize the area of linked strands and bundles that are coupled and form loops
with the applied changing magnetic field, instead of simply avoiding longer
pitches. In addition we recommend increasing the wrap coverage of the CS
conductor from 50 % to at least 70 %. The models predict significant
improvement against strain sensitivity and substantial decrease of the AC
coupling loss in Nb3Sn CICCs, but also for NbTi CICCs minimization of the
coupling loss can be achieved. Although the success of long pitches to
transverse load degradation was already demonstrated, the prediction of the
combination with low coupling loss needs to be validated by a short sample
test.
