High critical current joint of MgB₂tapes using Mg and B powder mixture as flux

Abstract

Persistent current (PC) operation is important for superconductive magnets used in magnetic resonance imaging (MRI) systems, which demands at least two high critical current joints to form a superconductive circuit. Moreover, the joint resistance and the critical current of the joints always play significant roles in the design and development of large scale applications because the working current and the heat load of the system depend greatly on them. In this work, a joining method using a Mg and B powder mixture as flux is proposed. The voltage-current (V -I ) curves of the sample joints made by such a method were measured using the four-probe method. At 1 T, 4.2 K, the critical current density J c of the best sample was ∼7.19 × 10 4 A cm −2 , and its estimated joint resistance dV /dI was ∼7.44 × 10 −12 . These results demonstrated a promising future for the use of composite MgB 2 tapes in MRI magnets and other large scale superconductive devices.

MgB2superconducting joints for persistent current operation

“…Several superconducting joint techniques for both in-situ and ex-situ MgB 2 conductors have been reported [13,[16][17][18][19][20][21][22][23] comparison of the critical current (I c ) of the joint with the wire, the closed-loop coil, and the microstructural analysis of the joints are presented in detail.…”

Close circuit test of MgB2coil with superconducting joints and a persistent current switch

“…it was firstly winded and joint using the "raw" wires as reported in the previous work [19], then put into the furnace and heat treated. To qualify the winding and processing conditions, an open circuit, i.e.…”

“…The joint area was compressed at room temperature in air, and then sintered in a furnace, as shown in figure 1d). For tapes with rectangular cross sections, the jointing method was the same as reported in the previous work [19]. The sheath material, cross section, superconductor core size and number of filaments of the four types of samples used in this work, named A to D, were listed in table 1.…”

Joints in ${\rm MgB}_{2}$ Tapes and Wires for Persistent Current Operating Magnet

“…It is difficult to use soldering and other common connection methods to fulfill this requirement, and the current carrying ability of the commonly prepared joint, judged by the 1 criteria, is also strictly limited by the cross section of the joint area and thus often not satisfying. Hence, encouraged by the successful early attempts of the superconducting jointing in wires [7], [8], a jointing method in analogy to the powder in the tube (PIT) approach of the tape fabricating processes is put forth based on the chemical and physical properties of Mg, B and compounds at the designed pressure, temperature and ambient atmosphere in the jointing area [9]. Utilizing the method, joints Manuscript in tapes and wires are made and tested at variable fields and temperatures.…”