Test Results for a High Field (13T) Nb3Sn Dipole

LHNL-39899 SC-MAG- 572 Test Results for a High Field (13T) Nb3Sn Dipole A.D. Mcinturff, R.Benjegerdes, P. Bish, S. Caspi, K.Chow, D. Dell'Orco, D. Dietderich, R. Hann afo rd, W. Harnden H. Higley, A. Lietzke, L. Morri so n, M. Morrison, R. Scanl an, J. Smithwick, C. Tay lor, and J. va n Oort Lawrence Berkeley Nation al Laboratory, Berkeley. California 94720 Abstract- A NblSn dipole magnet (D20) has been designed, constructed, and tested at LBNL. Previously, we had reported[1] tes t results from a hybrid design dipole which contained a similar inner NblSn and outer NbTi winding. This paper prese nts the final assembly characteristics and parameters which will be compared with those of the original magnet design[2]. The actual winding size was determined and a secondary calibrat ion of the assembly pre-load was done by pressure sensitive film. The actual azimuthal and radial D20 pre-loading was accomplished by a very controllable novel stretched wire technique. D20 reached 12.8T(4.4K) and 13.5T(1.8K) the hi ghest dipole magnetic fields obtained to date in the world. I. INTRODUCTION cable (37- 0.75mm dia strands) with a 1.57mm (1.65mm- meas.) thickness and a 14.66mm (I4.66mm-meas.) width under a load of 34.5 MPa. These cable strands were made by two different ma nufacturers-Teledyne Wah Chang and Interm agnetics General. The outer two layers (3&4) use another size cable (47-0.48mm di a strands) with a 1.l2mm (1.30mm-meas.) thickness and a 11. 89mm (I1.91mm-meas.) width under a load of 34.5MPa. These cable strands were manufactured by Teledyne Wah Chang. All of the cabling was done at the LBNL cabling fac ility. The coi l design numbers as well as the maximum values attained to date are given in Table I and II. Central Fietd (T) I. Layer O. Layer (T D20 Dcsign@4.35K Fietd (T) t4.4 The LBNL Advancement of Accelerator Magnet Technology program has concentrated on development of magnet construction techniques applicable to brittle superconductors. Nb3Sn was chosen as the typical brittle superconductor due to it's more extensive data base, and F~~td because prese ntly it is the only superconductor with practical current density(Jc) in the field range of 11 T to 16T. This paper 6400 A 7000 A Short Sample (SS) 6925 A @4.5K SS -t t %( De.rad 140 MPa) = 6525A 020 @4.5 K Reached 6300 A @1.8 K Reached 6712 A t3 t4. t2.8 t3.5 will compare important design parameters previously published[2] with those achieved so far by a development Nb3Sn dipole D20 . The dipole testing has produced several surprises which summarized were a) excellent ramp rate quench performance, b)excellent thermal stability (>20 watts;12T), and c) the magnet trained up to much higher fields in contrast with earlier Nb3Sn dipole test histories[3, 4, 5]. The dipole had good high field performance 12.8T(4.4K) and 13.5T(1.8K), but at 1.8K was clearly not limited by it's critical current performance. The previous high field dipole record by Twente University group was Il.03T reached by an LHC model MSUT magnet[4] . The highly interdependent coil fabrication steps of Nb3Sn require a more integrated approach to cabling, insulating, stepped multi-phased heat treatment, Table I Magnetic Field versus Ie or Iq Table II Current Densities Cable insulation is composed of single glass sleeve 0.12mm thick in the straight sections and then wrapped with extra glass tape 0.28mm thick around the ends to prevent shorts. The original fiberglass sizing is evaporated off the fabric before being replaced with the special palmitic acid and ethanol sizing and then drawn over the unreacted cable in preparation for winding. Wedges, pole pieces and end pieces are coated with alumina (0.13mm thick) for extra insulation. The training results indicate the pole surfaces are a problem. Due to the locations and sequence of the first quench set we conclude that an excellent insulation with a weak shear strength is needed{i.e. miCa) between conductor and pole. There is a layer of fiberglass tape between the mandrel and the inner coil heater! voltage tap kapton/stainless steel(ss) composite plane. There is a second layer of glass tape between coil layers I and 2, then the coil layer 2 heater/vollage tap kapton/ss composite similar expansion and contraction materials, protection heaters, epoxy impregnation, assembly, and pre-loading due to the larger temperature range that the winding must operate compared to NbTi. There is a large body of Nb3Sn data that indicates a substanti al 1e loss with increasing perpendicular strain, which up to fields of 13.5T did not appear to be the limit in the present co nfiguration of 020. II. DESIGN 020 is a four layer graded cable cosine winding di stribution 50mm bore dipole. The inner two layers (I &2) used one size Manuscript received May 16, 1997. The work is supponed under conlract # DE-AD03·76SF0Q098 by Director, Office o r Energy Research, Ortice or High Energy Physics, US Dept. or Energy. e