Page 155 - Fundamentals of Magnetic Thermonuclear Reactor Design

136 Fundamentals of Magnetic Thermonuclear Reactor Design

TABLE 5.7 Parameters of Superconducting Strands Designed for ITER
Magnets

Coils
Parameters PFCs, CCs CS, TFCs
Nb 3 Sn Nb 3 Sn
‘Bronze’ ‘Internal tin’
Superconductor NbTi process process
2
Current critical density (A/mm ) 2900 (5 T) 850 (12 T) 1000 (12 T)
Hysteresis energy losses (±3 T), — <1000 <1000
3
(mJ/cm )
Filament diameter (µm) 6–8 — —
Strand diameter (mm) 0.73 0.82–0.83
Copper/non-copper ratio 1.6–2.3 1
Unit length (m) >1500 >1500
Electrical resistivity ratio at 273 >100 >100
and 4.2 K (RRR, residual resis-
tance ratio)
Coating thickness (µm) 2 (Ni) 2 (Cr)

l Manufacturing of the winding turns using a roller-type guide to ensure ac-
curacy of the turn diameter and absence of internal mechanical stresses.
l ‘Winding–heat treatment–insulation rewinding (insertion into the grooves
of a mechanical structure)’ procedure for Nb Sn coils.
3
The development of SC technologies and industrial equipment for super-
conducting coil manufacture, as well as experience gained during ITER model
coils manufacturing and testing, has brought applied superconductivity to a new
practical level.

5.4.3 Basic Superconducting Strands
The basic elements of superconducting cables are composite strands. Every
strand consists of a great number of thin SCF encased in a normally con-
ducting matrix. The strand manufacturing process depends on the super-
conducting parent material and process route whereby a superconducting
microstructure is formed. For example, Nb Sn SCs can be manufactured
3
either by the ‘bronze’ or the ‘internal tin’ process. Three out of six strand
suppliers for ITER employ the bronze process, and the other three prefer the
‘internal tin’ route.