Extracted Strand Magnetizations of an HQ Type Nb3Sn Rutherford Cable and Estimation of Transport Corrections at Operating and Injection Fields
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Citation:Published version: IEEE Transactions on Applied Superconductivity (Volume: 24, Issue: 3, June 2014) Article Sequence Number: 4802605. https://doi.org/10.1109/TASC.2013.2286860
One of the goals of the Large Hadron Collider Accelerator Research Program (LARP) is to demonstrate the feasibility of Nb3Sn technology for a proposed luminosity upgrade based on large aperture high gradient quadrupole (HQ) magnets. For such magnets field quality at the bore is a critical requirement for which reason the parasitic magnetization of the windings must be reduced to manageable limits. In other words it is necessary to minimize (i) the static intrastrand persistent current magnetization of the cable and (ii) the cable’s coupling magnetization caused by coupling currents passing through interstrand contact resistance during field ramping. This report focuses on persistent-current magnetization as measured by vibrating-sample magnetometry on pieces of strand removed from a section of heat treated HQ cable.
The bench-mark data for the NbTi-wound LHC are Msh,inj,LHC = 10.3 kA/m and Mcoup,LHC = 2.64 kA/m. The present cable, HQ1021ZB, with an 8 mm stainless steel core wound at LBNL, is similar to a previously measured LBNLwound HQ-KC3 cable. As such we would expect to find the same 8-mm-core-moderated ICR and coupling magnetization, 1.02 μ and 70.3 kA/m, respectively. Clearly such a narrow core width is inadequate to properly suppress Mcoup. With regard to persistent-current magnetization at injection, Nb3Sn’s large Jcdeff product guarantees a large value, estimated here to be Msh,cable,inj,1T = 171 kA/m. On the other hand as the magnet is ramped up to operating field Msh,cable steadily decreases such that at 15 T in the windings it hasdropped to 5.8 kA/m, clearly an acceptable value. The Mcoup results of  indicated that a full width corewould be needed to adequately suppress coupling magnetization and the Msh,cable data of Table II indicates that although Msh,cable is not a problem close to operating field, strong compensation will be required near injection .
Funding was provided by the U.S. Dept. of Energy, Office of High Energy Physics, under Grants No. DE-FG02- 95ER40900 (OSU) and DE-AC02-05CH11231 (LBNL).