Fabrication and testing of Rutherford-type cables for react and wind accelerator magnets

LBNL#45189 SC-MAG 708 Fabrication and Testing of Rutherford-type Cables for React and Wind Accelerator Magnets P. Bauer, G. Ambrosio, N. Andreev, E. Barzi, D. Dietderich, K. Ewald, M. Fratini, A.K. Ghosh, H.C. Higley, S.W. Kim, G. Miller, J. Miller, J. Ozelis, R.M. Scanlan Abslract- A common coil design for a high-field accelerator dipole magnet using a Nb~n cable with the React-aDd-Wind approach is pursued by a collaboration between Fermilab and LBNL. The design requirements for the cable include a high operating current so that a field of 10-11 T can be produced, together with a low critical current degradation due to bending around a 90 mm radius. A program, using ITER strands of the internal tin type, was launched to develop the optimal cable design for React-aDd-Wind common coil magnets. Three prototype cable designs, all 15 mill wide, were fabric. ltcd: a 41- strand cable with 0.7 mm diameter strands; a 57~stralld cable with 0.5 mm diameter strands; and a 259~strand multi·level cable with a 6·around-l sub-element using 0.3 mm diameter wire. Two versions of these cables were fabricated: one with no core and one with a stainless steel core. Additionally, the possibility of a wide (22 rom) cable made from 0.7 mOl strand was explored. This paper describes the first results of the cable program including reports on cable fabrication and reaction, first winding tests and first results of the measurement of the critical current degradation due to cabling and bending. magnets is the cable, which must be designed to bend around a 90 mm radius with a low degradation of tile critical current «15%). If the wire is reacted on a spool with twice tile minimum coil bending radius, the maximum bending strain in the conductor will be equal in the straight section and in the ends of the magnet. The bending strain depends on the strand diameter used for the cable. In addition, the bending strain can be smaller or larger, depending on whether the layers of strands in the cable stick together or slide during cable bending. A R&D program [4] was launched to develop the optimal cable design for a react and wind common coil dipole. The strand chosen for the program was left-over ITER type wire manufactured by IOC. To keep bending strain below acceptable levels the strand diameter was restricted to '.5.0,7 mm. The material was drawn to the nominal wire sizes and sent to LBNL for cabling. Witi, tile high current requirement for the magnet (15-20 kA) ·a high aspect ratio cable design was pursued. The cables produced for the test program are described next. II. PROTOTYPE CABLE FABRICA nON AND REACTION Index Terms-Accelerator, superconducting cable, Nb 3 Sn. superconducting magnet, l. INTRODUCTION ECENlLY, a number of Nb,Sn dipole magnets have been built and tested in order to demonstrate the feasibility of using a brittle superconductor with a cosine theta winding approach [I]. The small bending diameters associated with the poles of cosine theta cross section dipoles require that the cable be wound in the unreacted condition in order to prevent damage to the Nb,Sn superconductor. An alternative design concept, the common coil design [2], utilizes flat pancake coils with large bending radii, and allows tile consideration of a react and wind technique for fabrication of coils [rom Nb,Sn or other brittle superconductors. Several designs for II T common coil dipoles were developed at FNAL in the past year [3]. All designs utilize Nb,Sn wire, with a J, (12 T, 4.2 K)=2000 Almm'. The key feature of these R Three cables with width 15 mm were chosen [or evaluation: (I) a 41 strand cable with 0.7 mm diameter strands, (2) a 57 strand cable with 0.5 mm strands, and (3) a 259 strand cable with 0.3 mm strands. The 259 strand cable is made in two steps--a first stage 6-around-1 cable and a seeond stage conSisting of 37 first stage elements cabled into the standard flat Rutherford-type cable (Fig. I). Manuscript received Sept 17, 2000. This work was supported by the U.S. Department of Energy. - -' P. Bauer, G. Ambrosio, N. Andreev E. Bani, K. Ewald, M. Fratini, S.W. Kim are with Fennilab, Batavia, IL 60510 USA (telephone: 630-840-5409, e-mail: pbauer@fnal.gov). D. Dietderich, H. C Higley, R. Scanlan are with Lawrence Berkeley Lab, Berkeley, CA 94720 USA. G. Miller, J. Miller are wi th the National High Magnetic Field L1.b, Tallahassee, FL 323 10 USA. A.K. Ghosh is with Brookhav