NbTi Cables Research Articles

AC loss properties of some Bi:2212/Ag Rutherford cables and a comparison with those of cables wound with NbTi and Nb 3Sn

Calorimetric measurements of AC loss have been performed on Rutherford cables wound with NbTi, Nb 3Sn, and Bi:2212/Ag strands, respectively. For the NbTi cables, various strand coatings had been applied, while for the Nb 3Sn and Bi:2212/Ag cables the strand surfaces were just bare Cu or Ag, respectively. Most of the cables contained resistive cores: ribbons of kapton or titanium (NbTi cables), stainless steel (NbTi and Nb 3Sn cables), and nichrome-80 (Bi:2212/Ag cables). In all cases the cores were found to lead to a strong suppression of the face-on (field normal to the broad cable face) coupling current loss; to such an extent that even the Bi:2212/Ag cables, which would otherwise be severely cross-sintered, evinced acceptable coupling loss. For most of the cables side-by-side interstrand contact resistances have been calculated. An `effective interstrand contact resistance', R ⊥,eff, has been defined, and an expression devised to enable its value in different-size cables to be converted to that of a `standard reference cable', R ⊥,eff.,ref., for the purpose of intercomparison.

Coupling current control in Rutherford cables wound with NbTi, Nb 3Sn, and Bi:2212/Ag

Calorimetric measurements of AC loss have been performed on Rutherford cables wound with NbTi, Nb 3Sn, and Bi:2212/Ag strands, respectively. For the NbTi cables Ni and stabrite coatings had been applied, while for the Nb 3Sn and Bi:2212/Ag cables the strand surfaces were just bare Cu or Ag, respectively. Most of the cables contained resistive cores: ribbons of kapton, or titanium (NbTi), stainless steel (NbTi and Nb 3Sn), and nichrome-80 (Bi:2212/Ag). In all cases the cores were found to lead to a strong suppression of the face-on (field normal to the broad cable face) coupling current loss; to such an extent that even the Bi:2212/Ag cables, which would otherwise be severely cross-sintered, show the possibility of acceptable coupling loss. Effective crossover interstrand contact resistances are calculated and normalized to a standard cable specification (`LHC inner') for the purpose of intercomparison.

The relation between transverse mechanical and electrical properties of the multi-twisted stage cables of CICC

The transverse resistance among strands of multi-stage twisted cables is one of the most important parameters to decide the stability and the AC losses. This value is varied with the cable compression affected by the void fraction or the Lorentz forces under charging. Furthermore it is also influenced by cyclic number of transversal compression. This paper describes the basic mechanical property of the chrome plated NbTi cable for the transverse compression, and the relation of the transverse resistance and the internal loads of the cable by measuring the impedance and the rigidity for various internal loads. It shows that the transverse resistance, which is much influenced with the performance of conductor, is always changed corresponding to the compressive load and dose not indicate the same resistance after release from the compression because of its elastic hysteresis.

Progress in the development of the 1-m model of the 70 mm aperture quadrupole for the LHC low-β insertions

Within the LHC magnet development program Oxford Instruments has built a one metre model of the 70 mm aperture low-/spl beta/ quadrupole. The magnet features a four layer coil wound from two 8.2 mm wide graded NbTi cables, and is designed for 250 T/m at 1.9 K. The magnet has previously been tested between 4.5 K and 23 K. In this paper we review the magnet rebuild and the subsequent tests. Results on magnet training at 43 K and 1.9 K are presented along with the results related to quench protection studies. We also present the first results of magnetic field measurements done at room and liquid nitrogen temperatures.

Development of 100 kVA AC superconducting coil using NbTi cables with a CuSi alloy matrix

For implementation of AC superconducting equipment, it is imperative to develop low loss cables having highly stable characteristics. Here, newly developed NbTi superconducting cables using a CuSi alloy matrix are of low loss and are very promising as cables for practical application. However, since the CuSi alloy is a new material as a matrix for NbTi superconducting cables, many unknown factors as regards to optimum conditions for the manufacture of long cables, as well as superconducting characteristics are involved. For this new superconducting cable, a long strand (km class) was manufactured as a step for practical application, and a primary twisted cable was fabricated. Using this cable, a coil of the 100 kVA class was fabricated for trial, and its performance characteristic with transport current was evaluated. This coil had no training phenomenon and had a high stabilities. Furthermore, it permitted full AC current transmission of up to DCIc. Upon analysis of the coil loss, the hysteresis loss was smaller than coupling loss, and there was little increase of loss due to the current flow to the coil. Consequently, by using CuSi alloy matrix superconducting cables, it was possible to provide an AC coil of low loss and high stability, and the present cable was found to be promising as a new AC superconducting cable in the future.

Evaluation of a NbTi cable-in-conduit prototype superconductor for the Wendelstein 7-X magnet system

Swissmetal recently completed a contract to manufacture 200 m of NbTi cable-in-conduit prototype conductors to be used in the Wendelstein 7-X superconducting magnet system. The conductor consists of a 192 strand, four stage NbTi cable in an aluminium alloy jacket cooled by forced flow helium. It will operate at 16 kA, 3.8 K and 6.2 T. To qualify this conductor electrical tests were performed on a 3.6 m long full-size specimen in the SULTAN test facility at CRPP. In preparation for these tests two conductor terminations and one electrical joint were manufactured in a relatively simple and, therefore, time and cost saving way. This paper presents the test results of critical current measurements performed on the conductor as well as of extracted strands in background fields of up to 8 T. The joint is described and its resistance is reported. In addition the results of pressure drop measurements at room temperature are presented.

Heat treatment issues for shrinkage alleviation of NbTi cable

Shrinkage of the NbTi conductor during coil curing has been observed to have a significant manufacturing impact. While controlled heat treating of superconductor cable prior to winding can dramatically improve the coil appearance and ease subsequent manufacturing operations, excessive heating can adversely affect conductor performance, e.g. critical current, interstrand resistance, residual resistance ratio and process sensitivity. Aluminum stabilized conductor, where aluminum is applied via conform cladding or co-extrusion, is also impacted by these concerns. Models of potential degradation mechanisms and the effect of heat treatment time and temperature on the superconductor properties are presented and compared to experiments. Within fairly wide limits, the considered parameters have low sensitivity to the heat treating conditions, so that process repeatability should be quite good. These results can be also be applied to stabilization of conductor with aluminum. >

Quality analysis of superconducting wire and cable for SSC dipole magnets: a comparison of recent performance and specification requirements

A critical component of the SSC (Superconducting Super Collider) dipole magnets is superconducting cable. The uniformity and reliability requirements for the dipoles place stringent demands on the cable. These needs have been defined as various contract requirements in the material specifications for NbTi alloy, superconducting wire, and cable. A supplier qualification program is being started by the SSC Laboratory (SSCL) with industry to establish reliable sources of superconductor cable. To monitor conductor performance, a computer database is being developed. The database focuses on the understanding and control of variation in the manufacture of wire and cable. A statistical and graphical summary of current data for key performance variables is presented in light of the specification requirement for uniformity. Superconductor material characteristics addressed include wire critical current, copper-to-non-copper ratio, wire diameter, wire piece-length, and cable dimensional control.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Development of NbTi based cables for LHC dipoles

The technology developed to meet LHC (Large Hadron Collider) dipole superconductive cable requirements is discussed. The program carried out includes the development of a 5- mu m NbTi filament, high J/sub c/ and low-magnetization elementary strands for high-field applications, and the manufacture of large compacted keystone cables. Characteristics of the NbTi strands and cables manufactured are presented, as well as test results performed at 4.2 K and below for magnetic field up to 11 T.

Training in test samples of superconducting cables for accelerator magnets

In the critical current measurement of some high-current NbTi cables, the samples have to be 'trained' by repeated quenching to obtain a usable voltage-current curve for I/sub c/ determination. This training behavior is most pronounced when the applied field is perpendicular to the wide face of the conductor and is strongly dependent on the copper-to-superconductor ratio and the clamping pressure. Data are given for SSC (Superconducting Super Collider) prototype cables as well as for HERA production conductors. Although a quantitative understanding of the experimental data is still lacking, some speculations regarding stability are presented.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Construction of cold mass assembly for full-length dipoles for the SSC accelerator

Four of the initial six 17m long demonstration dipole magnets for the proposed Superconducting Super Collider have been constructed, and the first one is now being tested. This paper describes the magnet design and construction of the cold mass assembly. The magnets are cold iron (and cold bore) 1-in-1 dipoles, wound with partially keystoned current density-graded high homogeneity NbTi cable in a two-layer <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\cos \theta</tex> coil of 40 mm inner diameter. The magnetic length is 16.6 m. The coil is prestressed by 15 mm wide stainless steel collars, and mounted in a circular, split iron yoke of 267 mm outer diameter, supported by a cylindrical yoke (and helium) containment vessel of stainless steel. The magnet bore tube assembly incorporates superconducting sextupole trim coils produced by an industrial, automatic process akin to printed circuit fabrication.

Performance of Four 4.5 M Two-in-One Superconducting R &amp; D Dipoles for the SSC

Four 4.5 m long superconducting dipoles built to specifications similar to those for SSC Reference Design A have been successfully tested. They were wound with NbTi cable in two-layer cos? coils of 3.2 cm inner diameter. The coil ends were flared to increase thie minimum bending radius, anticipating coils wound from prereacted Nb3Sn. The coils were mounted in a reusable two-in-one iron yoke prestressed by means of a bolted stainless steel shell. The first two magnets as well as the fourth one, a special magnet designed to study cross-talk between the bores, used CBA/Tevatron cable. The third utilized cable with improved (high homogeneity) NbTi conductor. All four reached central fields corresponding to their short sample limits at 4.5K without training, nearly 6. OT for the first two magnets, 6.5T for the third, and 5.4T for the fourth. At 2.5K modest training was required to reach short sample limits of 7.2T, 7.1T, 7.8T, and 6.6T respectively. The measured values of the allowed harmonics were within several × 10-4 of the calculated ones.

Critical current anisotropy in NbTi cables

The short sample critical current of multifilamentary NbTi cables is usually measured in a magnetic field which is oriented perpendicular to the broad face of the cable. This is the same orientation that occurs at the equatorial turns of a cos theta type dipole magnet and is, therefore, usually specified in quality control short sample tests. It is generally found that the current density in cables is less than in wires. This degradation, as it is commonly called, may be as large as 15%. The effect is illustrated in a statistical way, which shows the distribution of wire and cable results for the Colliding Beam Accelerator Project at BNL. The current densities were calculated using geometrical data. Some 200 cable and 750 wire tests are included in the normal curve distributions shown. The mean cable Jc is 14% lower than that of the wire. Similar results were obtained in previous work.

A 40 mm bore Nb-Ti model dipole magnet

Preliminary R and O has been started on magnets for a next-generation high-energy-physics accelerator, the 20 TeV Superconducting Supercollider (SSC). One design now being developed at LBL is described in this paper. The design is based on two layers of flattened Nb-Ti cable, a 40 mm I.D. winding with flared ends, and an operating field of 6.5 T. Experimental results are presented on several one-meter-long models tested at both He I and He II temperature. Measurement of field, residual magnetization, quench propagation velocity, and winding prestress are presented. (A 2-in-1 magnet based on this coil design is being Jointly developed by LBL and Brookhaven National Laboratory, and 15 ft. long models are being constructed at BNL).

Effect of Intermediate Heat Treatments on Superconducting Properties of Nb-Ti Cables

Effect of Intermediate Heat Treatments on Superconducting Properties of Nb-Ti Cables

Multifilamant Nb&amp;lt;inf&amp;gt;3&amp;lt;/inf&amp;gt;Sn multistrand cable performance using supercritical helium

We have measured the effect of change of supercritical helium flow on stability of a cabled multifilamentary (MF) Nb <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> Sn conductor. We varied the flow of supercritical He through the cable and measured the ability of the cable to absorb single pulses of magnetic energy while the cable was carrying about 73% of its measured critical current in an applied 9.0T magnetic field. We have quantified the pulse energies in terms of the thermodynamic behavior of the helium fluid within the cable. Varying fluid mass flow rate <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">G</tex> in the range <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0 \leq G \leq 36</tex> g/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> s, we have observed stability of the MF Nb <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> Sn cable which is apparently as independent of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">G</tex> as were previously investigated MF NbTi cables. Thus our present and previous findings in 3m length MF superconductor cables suggest the dominance by flow independent heat transfer mechanisms, rather than the flow generated turbulence previously considered dominant.

Quench development in magnets made with multifilamentary NbTi cable

An experimental study of the normal zone propagation and total resistance as a function of time is described. The normal zone propagation velocity in a single strand was measured as a function of both current and magnetic field with particular interest in the neighborhood of the short sample limit. The study proceeded from measurements in single multifilamentary strands to measurements in 23 strand cables under different cooling environments to finally measurements in actual ramping dipole magnets made with this cable. Interpretation of the results led to the determination of safety limits for the Energy Doubler/Saver magnets and to safeguards implemented by an energy dumping circuit which effectively protects these magnets from self-destruction.

AC losses of transposed superconductors

Eastham and Rhodes published results of loss measurements on transposed superconducting NbTi cables and concluded basing on an extrapolation to very large numbers of wires that transposed superconductors could be used favourably in cables for power transmission. There are some reasons to question the correctness of their extrapolation. We calculated losses for transposed superconductors in self field and got results different from those of Eastham and Rhodes. Loss measurements were performed the results of which give evidence for the correctness of our calculations. Our results lead to the conclusion that the use of transposed cables of irreversible type 2 superconductors for power transmission is not advantageous.