The PF system consists of 6 independent coils (PF1 to PF6) with different dimensions, but all pancake-wound using two-in-hand NbTi-based cable-in-conduit conductors (CICCs). The coils are composed of stacks of double pancakes (DPs). Each DP is wound with two-in-hand CICC and consists of a top and bottom layer. Each continuous section of CICC used in the two-in-hand winding is referred to as a unit length (UL). The CICC for the PF coils of ITER relies on twisted, multifilament, nickel-plated, NbTi-based composite strands. The strands are cabled and the cable is jacketed to become a CICC. This notice refers only to the strands for PF6 coil. The multifilament composite strand is made up of NbTi filaments embedded in a high purity Cu matrix. The last stage of strand fabrication starts from the assembly of a final composite billet, consisting of NbTi rods wrapped with Nb foils in a Cu matrix. The billet is drawn down in multiple passes to the final strand diameter.

The drawing passes are interleaved with high temperature heat treatments to favour the production of a-Ti precipitates and achieve high pinning forces. At the end of the process the strand shall include a few thousand NbTi filaments (~7μm in diameter). The strand is then nickel plated with a thickness of 1–2μm. As part of the acceptance process of the strand, the suppliers are required to perform room temperature and 4,2 K measurements on the manufactured strand lengths in order to ensure that the chemical, metallurgical, electrical, mechanical, dimensional and surface conditions of the strands conform to the quality requirements specified in the technical specification of the PF conductor procurement arrangement (1.1.P6C.EU.01.0). In addition F4E is required to verify on a regular basis the measurements carried out by the strand suppliers. The verifications shall be performed by a company or institute acting as the reference laboratory on the strand verification samples, adjacent to the samples used by the strand suppliers for critical current measurements. The verification characterisation shall include: diameter, nickel-plating thickness and adhesion, twist pitch direction and length, copper-to-non-copper volume ratio, RRR, critical current and resistive transition index, and hysteresis loss; they shall also include additional extended characterisation tests i.e. critical current as a function of temperature and magnetic field.