A checklist for designers of cryogen-free MgB₂coils

Abstract

Intensive research has been directed at MgB2 since its discovery in 2001, focusing first on the material properties and conductor development and recently also on coil demonstrations. The relatively cheap and easy fabrication makes MgB2 a tempting material for superconducting applications. It can also be operated in the vicinity of 20 K, at which the commercial LTS materials are still in the normal state. However, commercial breakthrough requires practical applications and demonstrations. Therefore, we built a solenoidal react-and-wind MgB2 coil consisting of 46 m of commercially available MgB2 /Ni/Fe/Cu tape manufactured by Columbus Superconductors. We tested the coil in a cryogen-free environment and measured the effect of repeated cooldowns and current ramp rate on the coil critical current. Also, temperature homogeneity in the winding was studied. Based on the test results we point out features which should be checked when cryogen-free magnet systems are designed or their performance is discussed. For example, the coil critical current and n value can depend notably on the current ramp rate.

Transverse Thermal Conductivity in an Epoxy Impregnated ${\rm MgB}_{2}$ Coil

“…Measurements were made for a small section of the react-and-wind coil originally manufactured for demonstration purposes in order to test the suitability of for magnets [8].…”

“…Before measurements, excess epoxy was removed from the sides of the coil. More detailed manufacturing procedure and voltage-current performance for this coil can be found from [8].…”

Test Coil for the Development of a Compact 3 T ${\rm MgB}_{2}$ Magnet

“…The conceptual design of a compact 3 T magnet with a 30 cm bore was implemented using a React & Wind process, which is a more practical way to manufacture the coils for industrial use [2], [3] than a Wind & React procedure [4], [5]. To verify wire handling, coil manufacturing, and wire performance, the smallest coil of the designed magnet was chosen and adjusted slightly so that stresses and pressures could be compared to those of the designed magnet.…”

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

“…As long MgB 2 wires and tapes became commercially available [1][2][3][4][5][6][7], the large scale applications of MgB 2 , such as the magnetic resonance imaging (MRI) magnets were taking more and more interests of the world wide researchers [8][9][10][11][12][13][14][15][16]. Manufactured via powder in the tube (PIT) method, the piece length of the commercialized MgB 2 wires were commonly from 100 m to several kilometers with the critical current density of better higher than 10 5 A/cm 2 , at 4.2 K, self field, and better higher than 10 4 A/cm 2 at 20 K, self field [3,4,10].…”