First demonstration of high current canted-cosine-theta coils with Bi-2212 Rutherford cables

Abstract

Future high energy physics colliders could benefit from accelerator magnets based on high-temperature superconductors, which may reach magnetic fields of up to 45 T at 4.2 K, twice the field limit of the two Nb-based superconductors. Bi2Sr2CaCu2O8-x (Bi-2212) is the only high-T c cuprate material available as a twisted, multifilamentary and isotropic round wire. However, it has been hitherto unclear how an accelerator magnet can be fabricated from Bi-2212 round wires and whether high field quality can be achieved. This paper reports on the first demonstration of high current Bi-2212 coils using Rutherford cable based on a canted-cosine-theta (CCT) design and an overpressure processing heat treatment. Two Bi-2212 CCT coils, BIN5a and BIN5b, were made from a nine-strand Rutherford cable. Their electromagnetic design is identical, but they were fabricated differently: both coils underwent heat treatment in their aluminum–bronze mandrels, but unlike BIN5a that was impregnated with epoxy in its reaction mandrel, the conductor of BIN5b was transferred to a 3D printed Accura Bluestone mandrel after the heat treatment, a process attempted here for the first time, and was not impregnated. BIN5a reached a peak current of 4.1 kA with a self-field of 1.34 T in the bore. This corresponds to a wire engineering current density (J e) of 912 A mm−2, which is two times that of BIN2-IL, a previous Bi-2212 CCT coil fabricated at LBNL, which used a six-around-one cable processed with the conventional 1 bar pressure melt processing. On the other hand, BIN5b reached 3.1 kA. The coils exhibited no quench training. All the quenches were thermal runaways that occurred at the same location. In addition, we report on the field quality and ramp-dependent hysteresis measurements taken during the test of BIN5a at 4.2 K. Overall, our results demonstrate that the CCT technology is a route that should be further investigated for making high field, potentially quench training free dipole magnets with Bi-2212 cables.

An initial magnet experiment using high-temperature superconducting STAR® wires

“…Since then, various authors have further developed and demonstrated the concept [27][28][29][30][31][32][33][34][35][36][37][38][39][40]. The MDP is developing high-field CCT dipole magnet technology for Nb 3 Sn [41][42][43] and two high-temperature superconductors: Bi 2 Sr 2 CaCu 2 O 8+x [44][45][46][47] and rebco [19,48,49].…”

A 6-around-1 cable using high-temperature superconducting STAR ® wires for magnet applications

“…In collaboration with industry partners, the U.S. Magnet Development Program (MDP) is developing magnet technology for both conductors [3][4][5][6][7][8][9][10][11]. * Authors to whom any correspondence should be addressed.…”

Investigation of transport mechanisms induced by filament-coupling bridges-network in Bi-2212 wires

“…The last tenyears have seen a renewed interest in the Bi-2212 wire that has pushed several research groups towards performance optimization [1][2][3][4][5][6][7]. Today, we can say that the Bi 2 Sr 2 Ca 2 Cu 2 O x (Bi-2212) has become a true prospect for high magnetic field magnets above 18-20 T, going beyond the practical limit of state-of-the-art Nb 3 Sn conductors [8][9][10]. * Author to whom any correspondence should be addressed.…”