Wind-and-react Bi-2212 coil development for accelerator magnets

Abstract

Sub-scale coils are being manufactured and tested at Lawrence Berkeley National Laboratory in order to develop wind-and-react Bi2Sr2CaCu20, (Bi-2212) magnet technology for future graded accelerator magnet use. Previous Bi-2212 coils showed significant leakage of the conductors' core constituents to the environment, which can occur during the partial melt reaction around 890 °C in pure oxygen. The main origin of the observed leakage is intrinsic leakage of the wires, and the issue is therefore being addressed at the wire manufacturing level. We report on further compatibility studies, and the performance of new sub-scale coils that were manufactured using improved conductors. These coils exhibit significantly reduced leakage, and carry currents that are about 70% of the witness wire critical current (/ c ). The coils demonstrate, for the first time, the feasibility of round wire Bi-2212 conductors for accelerator magnet technology use. Successful high temperature superconductor coil technology will enable the manufacture of graded accelerator magnets that can surpass the, already closely approached, intrinsic magnetic field limitations of Nb-based superconducting magnets.

Superconducting Materials and Conductors: Fabrication and Limiting Parameters

“…The main attractiveness of Bi-2212, besides the highfield properties recalled above, is that it is available as a round wire, and can thus be formed into a Rutherford cable, as has been consistently demonstrated since the 1990s [113][114][115][116]. The record J E is around 500 A/mm 2 at 20 T, 4.2 K in a 1-m-long round wire [117] (Fig.…”

“…For now, at least in small Bi-2212 coils, voltagecurrent transitions can be readily measured [116], rendering the requirement of a high NZP for quench detection less urgent, but this might change once conductors become more homogeneous and the coils larger.…”

“…The concept of Rutherford cables can be easily applied to any material that comes in the form of round wires, and it has been extended to round Bi-2212 HTS wires [113][114][115][116]. Further cable concepts, such as the Roebel bar, or tape assemblies around a stabilizer core or tube, discussed earlier, are in an early stage of development and have not yet found an accelerator application.…”

Advances in the Development of a 10-kA Class REBCO Cable for the EuCARD2 Demonstrator Magnet

“…Apart for the case of BSCCO-2212 round wire, that can be cabled in a Rutherford configuration [34], [36], there is no consensus on which geometry is best suited to thin tapes, the form in which REBCO HTS is available at present. Among the attempts performed so far, only a few geometries appear to be suitable for the high-current density required by HEP accelerator magnets.…”

“…To attain higher field and thus extend the particle energy reach it will be necessary to resort to High Temperature Superconductors (HTS) [4], profiting from the high critical field and exceptional critical current properties at the liquid helium temperature of 4.2 K [5]. Several initiatives worldwide are addressing the technology issues associated with the use of HTS materials in high-field magnets, for accelerators [6]- [14] as well as other fields [15], [16]. In the case of our work, the objective of the EuCARD2 Work Package 10 (WP10 -Future Magnets) is to demonstrate that HTS materials can be used to generate an accelerator quality dipole field of 5 T in a 40 mm aperture as a stand-alone magnet [14].…”