Critical Current of Superconducting Rutherford Cable in High Magnetic Fields with Transverse Pressure - eScholarship

TLDR: Dietderich and Scanlan as mentioned in this paper used a loading fixture capable of applying loads of up to 700kN in a split-pair solenoid in field s up to 12 T at 4.2 K. The results showed that very little if any permanent degradation occurred up to 185 to 210 MPa.

Abstract: ASC'98 Palm September 14- 18, 1998 D~~!i11JG L8/11- Jt: fj.:2/hF be:;}'! Critical Current of Superconducting Rutherford Cable in High Magnetic Fields with Transverse Pressure Daniel R. Dietderich and Ronald M. Scanlan, Lawrence Berkeley National Laboratory, Berkeley, CA 94720 Robert P. Walsh and John R. Miller National High Magneti c Field Laboratory, Tallahassee, FL 32706 Abstract-For high energy physics appli cations supereon· dueting cables are subjected to large stresses and high magnetic fields during service. It is essential to know how these cables perform in these operating conditions. A loading fixture capable of applying loads of up to 700kN has been developed by NHMFL for LBNL. This fixture permits uniform loading of straight cables over a 122 nun length in a split-pair solenoid in field s up to 12 T at 4.2 K. The first results from this system for Rutherford cables of internal-tin and modified jelly roll strand of Nb,Sn produced by IGC and TWC showed that lillie permanent degradation occurs up to 210 MPa. However, the cable made from internal· tin s't rand showed a 40 % reduction in at lIT and 210 MPa while a cable made from modified jelly roll material showed onJy a 15 % reduction in Ie at liT and 185 MP•. I. INTRODUCTION Large forces are produced when superconducting magnets are ene rgized . Therefore, it is necessary to support the conductor to prevent large displacements that can strain the conductor beyond its elastic limit. These same forces also reduce the critical current of the conductor before the elastic limit is reached. To produce an optimum magnet design which best utilizes the superconductor material and maximizes the field the critical current variation with pressure is required. For a cosine 0 magnet design large pressures are produced at the mid-plane of the magnet on the large face of the Rutherford cable. The magnets (i.e. common coil) presently being designed and built in the Superconducting Magnet Group (SMG) of Lawrence Berkeley National Laboratory such that the cable will be bi-axially loaded on both the face and the edge with the edge loading being about twice that applied to the face. Therefore information for loading in both orientations is required. The results presented here are the first measurements performed at the National High Magnetic Field Laboratory (NHMFL) in a system designed for the SMG. These tests were performed on cable designed for and used in the inner coi ls ofthc world record dipole magnet D20 [I]. Manu sc ript received September 14, 1998. Thi s work was supported by the Director, Office of Energy Research, Office of High Energy and Nuclear Physics, High Energy Physics Division, U. S. Department of Energy, under Contrac t No. DE-AC03-6SFOOO98 . These cables were fabricated in our Group from modified jelly roll wire produced by Teledyne Wah Chang (TWC) and from internal tin wire manufactured by Intermagnetics General Corporation (IGC). The results for both cables showed that very little if any permanent degradation occurred for transverse loads up to 185 to 210 MPa. However, the critical current of the cable with IGC strand was reduced by 40 % with a transverse pressure of 210 MPa at II T. ·The I, of the cable with TWC strand was only reduced by 15 % at II T and 185 MPa. The behavior of both cables with loading was also different. The TWC strand showed a quadratic behavior with increasing press ure while the IGC strand showed a linear behavior. These results have important ramifications for high field magnet designs beyond the 13.5 T of D20. Not only must the strain level be controlled to prevent irreversible damage at these hi gher field s but the reduction in critical current due to the lower T, and B with high pressure must be controlled. II. MATERIALS AN D TEST SYSTEM A. Strand and Cable Characteristics Two strands made by two manufacturers were used jn the Rutherford cables of this study. Cable 523 was made from IGC strand while cable 522 was made from TWC strand. Each cable was rectangular and contained 37 strands. The cabling parameters are listed in Table I. Strand specifications are given in Table II. The two strands had very different internal geometries. The TWC strand had more Cu stabili zer and each of its 120 sub·e1ements had its own diffusion barrier. (Fig. I (a» The IGC strand had less Cu stabilizer and a diffusion barrier around all of its 19 sub· elements (Fig. I (b». Both cables were hea t treated at the same time and received the following schedule: 210 °C for 121 h, 340 °C for 60 h, and 660 °C for 259 h. For heat treatment the samples were sealed in a stainless steel retort that was continuously purged with fl owing argon. The data has not been corrected for self· field but due to the bifilar nature of the test arrangement the correction s h o ~ld be small.