Design of the Nb/sub 3/Sn dipole D20

The design of a 55-mm bore superconducting Nb/sub 3/Sn dipole with a short sample field of 13 T at 4.3 K and a current of 5500 A/turn is presented. The superconducting dipole has two layers of Nb/sub 3/Sn coils, each wound in a double pancake. The inner cable has 37 strands with a strand diameter of 0.75 mm and a Cu/Sc ratio of 0.4; the outer cable has 47 strands with a diameter of 0.48 mm and a Cu/Sc ratio of 1.15. To obtain a high transfer function and low saturation effects on the multipoles, the stainless steel collar is elliptical and the iron yoke is close in. The thin collar itself provides only a minimum prestress and the full prestress of 100 MPa is given by a 25-mm welded stainless steel shell or by winding a wire around the yoke. Aluminium spacers are used as assembly tools and as a means to control the gap size in the vertically split iron yoke. The authors present the magnetic design and the calculated stress and strain distribution in structure and coils. A 1-m model called D20 is to be built and tested at LBL.>