Gia Ky Hoang

Investigation of ITER Use Internal-Sn

By means of a SQUID magnetometer, the irreversibility temperatures and magnetization transitions of an ITER-type internal-Sn Nb3Sn superconducting wire were measured during warming and cooling cycles at a fixed magnetic field. The results obtained show that the irreversibility temperature T*(H) is strongly dependent on A15 phase composition and can be used to optimize the heat treatment process for the internal-Sn Nb3Sn wire. The A15 phase composition in internal-Sn Nb3Sn wire is temperature independent for full-time reaction. From T*(H) and magnetization transition analysis, the heat treatment condition of our ITER use wire is optimized as 675 degC/128 h, which results in the best A15 phase composition suitable for high-field application

{\rm Nb}_{3}{\rm Sn}

Through magnetization measurement with a SQUID magnetometer the heat treatment optimization of an international thermonuclear experimental reactor (ITER)-type internal-Sn Nb3Sn superconducting wire has been investigated. The irreversibility temperature T*(H), which is mainly dependent on A15 phase composition, was obtained by a warming and cooling cycle at a fixed field. The hysteresis width ΔM(H) which reflects the flux pinning situation of the A15 phase is determined by the sweeping of magnetic field at a constant temperature. The results obtained from differently heat-treated samples show that the combination of T*(H) with ΔM(H) measurement is very effective for optimizing the heat reaction process. The heat treatment condition of the ITER-type wire is optimized at 675°C/128 h, which results in a composition closer to stoichiometric Nb3Sn and a state with best flux pinning.

Superconducting Wire Through Irreversibility Temperature Measurement

A trial cable for LHC dipole inner layers made up of the Nb ternary alloy Nb44wt%Ti 25wt%Ta has been manufactured by GEC Alstrom Intermagnetics within the framework of a CERN development program. This cable is composed of 28 strands of 1.065 mm in diameter. The purpose of the study is: (i) to improve the superconducting behaviour of LHC cables at 1.9 K, the operating temperature of the Large Hadron Collider (LHC), and (ii) to evaluate the cabling feasibility of wires made with this alloy. Ic tests performed on wire samples before and after cabling at 4.2 K and 1.8 K show that at 4.2 K NbTi25wt%Ta wires exhibit lower Jc than those of the conventional binary alloy Nb47wt%Ti or those of a ternary alloy with only 15wt%Ta. But they have a larger magnetic field shift when cooled down from 4.2 to 1.8 K (about 1 T). The cabling of NbTi25wt%Ta wires presented no particular problem. Jc degradations due to cabling and evaluated on extracted strands are comparable to those observed on NbTi material. The performances achieved are reported and discussed in this paper.<<ETX>>

Magnetization study of ITER-type internal-Sn Nb3Sn superconducting wire

Four sets of monoelementary (ME) and two kinds of multifilamentary (MF) internal-Sn Nb3Sn superconducting strands were designed and fabricated, in which various component ratios, different composite configurations, and some third-element additions were arranged. All strands were submitted to a first heat treatment (HT) of 210 °C/50 h + 340 °C/25 h for Cu-Sn mixing, followed by the A15 phase formation HT. The four ME strands were reacted at 675 °C, 700 °C, and 725 °C for 100 and 200 h, respectively, and the two MF strands at 650 °C, 675 °C, 700 °C, and 725 °C for 128 and 200 h, respectively. The analysis of the reacted strands comprised the A15 phase composition distribution by means of X-ray energy-dispersive spectroscopy and the critical temperature Tc by means of superconducting quantum interference device magnetization measurements. The obtained results indicate that, for sufficiently reacted internal-Sn Nb3Sn strands, the final A15 phase composition and Tc are determined by the diffusion and solid reaction mechanism of the A15 phase formation. In particular, the onset Tc values and the average Sn content in a grain do not depend on the reaction temperature, the local compositions in the strand, the composite configuration arrangement, and the third-element addition.

Development of Nb44wt%Ti 25wt%Ta based superconducting conductors for LHC magnets

Four sets of mono-element internal-Sn (MEIT) wires which have different Sn-Cu ratio and 1 at% Zr addition in one wire were designed and fabricated for investigating A15 phase formation kinetics of ND3 Sn superconductors. All samples underwent a 210degC/50 h + 340degC/25 h thermal duration for Cu-Sn alloying prior to the A15 phase formation heat treatment (HT). Four reaction temperatures of 650degC, 675degC, 700degC, and 725degC were chosen to study the temperature and time influence. All the heat- treated samples were examined by scanning electronic microscope for A15 layer thicknesses that were then plotted versus HT time at different temperatures and were nonlinearly fitted. Superconducting quantum interference device magnetization measurements were used to determine the inductive JC variations for the heat- treated wires. The obtained results demonstrate that the A15 phase growth is promoted by four factors: reaction temperature elevation, reaction time extension, Sn-Cu ratio enlargement, and the alloyed Zr addition. The phase formation kinetics of MEIT Nb3Sn superconducting wires is in agreement with Yn = K(T)t relation and the A15 growth exponent n is affected by HT temperature and Zr alloying.