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Magnetization measurements have been made on several high J/sub c/ Nb/sub 3/Sn strands fabricated by different internal-Sn designs. In general these conductors have high magnetization at low fields, often exhibiting flux-jumps that are characteristic of large superconductor diameter. The effective filament size d/sub eff/ is approximately the size of the sub-element because the filament pack within each sub-element is fully coupled. Dividing the filament pack of the sub-element by adding Ta is effective for reducing d/sub eff/ and magnetization instability. But, some residual coupling across the dividers seems to remain below 6 K, perhaps due to Ta/sub 3/Sn. Implications for accelerator magnets are discussed.

Rutherford-type cables made of high critical current Nb/sub 3/Sn strands are being used in several laboratories for developing new generation superconducting magnets for present and future accelerators and upgrades. Testing of cable short samples is an important part of these R&D programs and the instability problem found in some short model magnets at Fermilab made these tests even more significant. Fermilab in collaboration with BNL, CERN and LBNL has developed sample holders and sample preparation infrastructure and procedures for testing Nb/sub 3/Sn cable short samples at BNL and CERN test facilities. This paper describes the sample holders, sample preparation and instrumentation, and test results. Several samples made of MJR or PIT strands 1 mm in diameter have been tested. Some samples were unstable (i.e. quenched at low transport currents) at low fields and reached the critical surface at higher fields.

Magnetization measurements show that modern high current-density Nb/sub 3/Sn strands made for HEP programs exhibit flux-jump instabilities at low fields, due to their having large effective filament diameters. Such instabilities might be problematic because they can initiate a quench in low-field regions of magnets. We explored magnetization and transport measurements of the most recent high J/sub c/ Nb/sub 3/Sn strands and cables to probe the instability behavior. In the regime where flux jumps are seen by magnetization measurements, transport current measurements show a threshold for stability. This threshold is significantly lower than the critical current at higher fields, and above this threshold, quenching in the strand could be initiated by ramping the magnetic field. The threshold current depends on the wire size and internal filament design, and is consistent with stability criteria. In cables, quench currents were nearly independent of field after training, and were far below the expected critical currents. Details of these measurements and their implications for testing and use in magnets are discussed.

The new heavy ion synchrotron facility proposed by GSI will have two superconducting magnet rings in the same tunnel, with rigidities of 300 T /spl middot/ m and 100 T /spl middot/ m. Fast ramp times are needed. These can cause problems of ac loss and field distortion in the magnets. For the high-energy ring, a 1-m model dipole magnet has been built, based on the RHIC dipole design. This magnet was tested under boiling liquid helium in a vertical dewar. The quench current showed very little dependence on ramp rate. The ac losses, measured by an electrical method, were fitted to straight-line plots of loss/cycle versus ramp rate, thereby separating the eddy current and hysteresis components. These results were compared with calculated values, using parameters which had previously been measured on short samples of cable. Reasonably good agreement between theory and experiment was found, although the measured hysteresis loss is higher than expected in ramps to the highest field levels.

Cored Nb-Ti Rutherford cables with high crossover resistance R/sub c/ are being investigated to minimize ac losses in a set of superconducting dipole magnets for the proposed rapid cycling heavy ion synchrotron facility at the Gesellschaft fur Schwerionenforschung (GSI) in Darmstadt, Germany. This ring of magnets is based on the Relativistic Heavy Ion Collider (RHIC) design. R/sub c/ in cored cables is significantly larger than the contact resistance between adjacent strands R/sub a/. The latter, however, dominates the voltage profile when the interstrand contact resistance is measured via the usual VI technique. This makes the extraction of the magnitude of R/sub c/ out of the voltage profile very difficult. Knowledge of R/sub c/ is important to predict ac losses, because if R/sub c/ and R/sub a/ were equal, perpendicular field induced losses due to R/sub c/ would be around 50 times greater than those induced by R/sub a/. Because of the importance of the crossover resistance, we have developed a novel measurement technique for R/sub c/ in cored Nb-Ti Rutherford cables. The procedure involves removing the edges of the conductors along the region to be measured. We have measured the cables using the new technique and the usual VI technique. We describe the novel measurement technique and present results for cables made with different core materials. While measuring R/sub c/, we found evidence that R/sub a/ is nonuniform over the length of a twist pitch and is in fact significantly lower at the cable edge. We report on this as well.

The new heavy ion synchrotron proposed by GSI will comprise two superconducting magnet rings in the same tunnel, having rigidities of 200 T.m and 100 T.m. Fast ramp times are needed, which can cause significant problems for the magnets, particularly in the areas of ac loss and field distortion. This paper discusses the 200 T.m ring, which will use Cos /spl theta/ magnets based on the RHIC dipole design. We describe options for the low loss Rutherford cable that will be used, together with a novel insulation scheme designed to promote efficient cooling. Measurements of contact resistance in the cable are presented and the results of these measurements are used to predict the ac losses, temperature rise and field distortion in the magnets during fast ramp operation.

The Superconducting Magnet Division at Brookhaven National Laboratory (BNL) is building 20 insertion region dipoles of various types for the Large Hadron Collider (LHC) at CERN. These 9.45 m-long, 8 cm aperture magnets use the same coil design as the arc dipoles for the Relativistic Heavy Ion Collider (RHIC) at BNL. The most challenging of these dipoles are the twin aperture magnets. The two apertures are separated by 188 to 234 mm, and the dipole fields in both the apertures point in the same direction. In order to test the design and determine various operating parameters of these magnets, two three m-long prototypes were built and tested at BNL. Tests were done to measure spontaneous quench performance, conductor temperature at quench, coil stress behavior during cool-downs, warm-ups and excitation ramps, and quench protection heater performance. Extensive magnetic field measurements were done with a 3.58-meter long integral coil, as well as a one-meter long coil at the axial center of the magnet. Dynamic effects, such as time decay and snapback at injection, and harmonics due to cable magnetization and eddy currents were studied with a time resolution of 2 s.

Brookhaven National Laboratory (BNL) has completed production of the superconducting multi-function magnets that are now installed as part of the HERA luminosity upgrade at DESY. The magnets, cryostats, and lead assemblies were designed and built at BNL. To fit inside the existing detectors, the coils plus cryostat structure had to meet a challenging radial budget (e.g., 39 mm horizontally). Two types of magnets were needed and three of each type were built. Each magnet contained normal and skew quadrupole, normal and skew dipole, and sextupole coils. The magnets operate in the /spl sim/1.5 T solenoid field of a detector. The quadrupole coils produce gradients up to 13 T/m. The dipole coils generate fields up to 0.3 T. Coils were wound under computer control using either seven-strand round cable or a single strand. To simultaneously avoid excessive synchrotron radiation background scattered from the beam pipe and yet have a small cryostat, one type of magnet used a tapered coil structure. The cryogenic system incorporates cooling with both 40 K helium and supercritical helium. All of the coils were tested in liquid helium in a vertical dewar. Quench test results have been excellent. The field quality of the magnets has met the stringent requirements imposed on interaction region magnets. One magnet of each type was tested at BNL as a completed assembly to verify the performance of the leads and cryostats. Two of each type were tested at DESY and then installed in the Zeus and H1 experiments. The remaining magnets are spares. Final results of quench testing, field quality measurements and cryogenic performance are reported.

A technique has been developed for testing long lengths of superconducting cable made from BSCCO 2212 wires in liquid nitrogen. The cable is tested as a large diameter spiral with removable voltage taps so that the conductor can be recovered for use in fabricating developmental magnets. Since the transition temperature of BSCCO 2212 conductors is often lower than 77 K the nitrogen bath must be pumped to reduce its temperature. As the pressure is slowly reduced the transition temperature can be determined and the current carrying capabilities measured as a function of temperature. 55 K can be easily achieved with the same equipment used for superfluid testing in liquid helium. Four cables have been tested ranging in length from 30 in to 0.6 m. A steady improvement in the superconducting properties of these cables was observed, reflecting the experience gained in strand fabrication and heat treatment by the manufacturer. For some of these cables, measurements were also made at 4.2 K to establish a correlation between the transition temperature and the expected current carrying capabilities in liquid helium.

The Levitated Dipole Experiment (LDX) is a novel approach for studying magnetic confinement of a fusion plasma. In this approach, a superconducting ring coil is magnetically levitated for up to 8 hours a day in the center of a 5 meter diameter vacuum vessel. The levitated coil, with on-board helium supply, is called the floating coil (F-Coil). Although the maximum field at the coil is only 5.3 tesla, a react-and-wind Nb/sub 3/Sn conductor was selected because the relatively high critical temperature will enable the coil to remain levitated while it warms from 5 K to 10 K. Since prereacted Nb/sub 3/Sn tape is no longer commercially available, a composite conductor was designed that contains an 18 strand Nb/sub 3/Sn Rutherford cable. The cable was reacted and then soldered into a structural copper channel that completes the conductor and also provides quench protection. The strain fabrication steps such as: soldering into the copper channel, spooling, and coil winding, to prevent degradation of the critical current. Measurements of strand and cable critical during state of the cable was continuously controlled currents are reported, as well as estimates fabrication, winding and operating strains on critical current.

As part of the US LHC program to develop high gradient superconducting quadrupoles for the LHC interaction regions, a series of 2 meter long model magnets has been built and tested at Fermilab. This R&D program was used to refine the mechanical and magnetic design, optimize fabrication and assembly tooling and ensure adequate quench performance. The final design, fabrication, and assembly procedures developed in this program have produced magnets which meet the LHC requirements of operating at 215 T/m with excellent magnetic field harmonics. This paper summarizes the test results of the last five model magnets, including quench tests over several thermal cycles, and excitation current ramp rate and temperature dependence studies.

The production of two types of superconducting multi-function magnets, needed for the HERA Luminosity Upgrade is underway at BNL. Coil winding is now completed and cryostat assembly is in progress. Magnet type GO and type GG cold masses have been satisfactorily cold tested in vertical dewars and the first fully assembled GO magnet system has been horizontally cold tested and shipped to DESY. Warm measurements confirm that the coils meet challenging harmonic content targets. In this paper, the authors discuss GO and GG magnet design and construction solutions, field harmonic measurements and quench test results.

A series of one-meter long racetrack-shaped windings has been fabricated from BSCCO tape conductors obtained from four manufacturers. Two coils were built from each conductor type and tested in the "common coil" dipole configuration in liquid helium. The effect of the remnant magnetization currents determined by measuring the residual dipole sextupole fields after cycling the magnets to progressively higher currents. Two coil sets have been measured and the results are compared to those obtained from a Nb/sub 3/Sn ribbon magnet of the same geometry.

A common coil design for a high-field accelerator dipole magnet using a Nb/sub 3/Sn cable with the React-and-Wind approach is pursued by a collaboration between Fermilab and LBNL. The design requirements for the cable include a high operating current so that a field of 10-11 T can be produced, together with a low critical current degradation due to bending around a 90 mm radius. A program, using ITER strands of the internal tin type, was launched to develop the optimal cable design for react-and-wind common coil magnets. Three prototype cable designs, all 15 mm wide, were fabricated: a 41-strand cable with 0.7 mm diameter strands; a 57-strand cable with 0.5 mm diameter strands; and a 259-strand multi-level cable with a 6-around-1 sub-element using 0.3 mm diameter wire. Two versions of these cables were fabricated: one with no core and one with a stainless steel core. Additionally, the possibility of a wide (22 mm) cable made from 0.7 mm strand was explored. This paper describes the first results of the cable program including reports on cable fabrication and reaction, first winding tests and first results of the measurement of the critical current degradation due to cabling and bending.

A total of 72 corrector magnets of 13 cm aperture and 0.5 m length are required in RHIC to correct for field errors in the interaction region quadrupoles and for other global corrections. The coils for these magnets were wound on a flat substrate using a computer controlled machine. Each corrector has four such coils of multipolar orders ranging from the dipole through the dodecapole, wrapped onto support tubes and concentrically assembled inside an iron yoke. There are five different model types depending on the combination of coils used. A critical issue was the alignment of the magnetic centers and the field angles of various coils. Adjustable shims were incorporated in the design to deal with unacceptable misalignments that could result from construction tolerances. Each magnet was partially assembled with nominal shims and was warm-measured with a rotating coil system. The shims were then adjusted as necessary to keep the field angles within /spl plusmn/1 mrad, and the relative alignment of the magnetic centers within /spl plusmn/0.2 mm. The field error harmonics are typically below 1% of the dominant multipole term at a reference radius of 40 mm, with some exceptions. All the magnets were tested for reliable operation at 4.35 K by performing bipolar power cycles to the maximum test current of 70 A for the dipole and 100 A for all the other coils, well above the maximum operating current of 50 A.

The magnet program at Brookhaven National Laboratory (BNL) is focussed on superconducting magnets for particle accelerators. The effort includes magnet production at the laboratory and in industry, magnet R&D, and test facilities for magnets and superconductors. Nearly 2000 magnets-dipoles, quadrupoles, sextupoles and correctors for the arc and insertion regions-were produced for the Relativistic Heavy Ion Collider (RHIC), which is being commissioned. Currently, production of helical dipoles for the polarized proton program at RHIC, insertion region dipoles for the Large Hadron Collider (LHC) at CERN, and an insertion magnet system for the Hadron-Elektron-Ring-Analage (HERA) collider at Deutsches Elektronen-Synchrotron (DESY) is underway. The R&D effort is exploring dipoles with fields above 10 T for use in post-LHC colliders. Brittle superconductors-Nb/sub 3/Sn or HTS-are being used for these magnets. The superconductor test facility measures short-sample currents and other characteristics of samples up to 1 m in length, in liquid and superfluid helium, in dipole fields above 7.5 T at 4.2 K (8.7 T at 1.9 K), and up to 25 kA. This facility performed the short-sample testing of the productions runs of NbTi wires and cables for the HERA-p and RHIC magnets, and is preparing for similar work for the LHC project. The staff also tests samples of superconductors from government laboratories and industry around the world.

The US-LHC Accelerator Project is responsible for the design and production of inner triplet high gradient quadrupoles for installation in the LHC Interaction Region. The quadrupoles are required to deliver a nominal field gradient of 215 T/m in a 70 mm bore, and operate in superfluid helium. As part of the magnet development program, a series of 2 m model magnets have been built and tested at Fermilab, with each magnet being tested over several thermal cycles. This paper summarizes the quench performance and analysis of the model magnets tested, including quench training, and the ramp rate and temperature of the magnet quench current.

For the HERA luminosity upgrade two types of compact multifunction superconducting magnets, denoted GO and GG, are needed for installation inside the existing ZEUS and H1 experimental detectors in the year 2000. These magnets contain multiple concentric coil layers organized into independently powered quadrupole, dipole, skew quadrupole and skew dipole coil windings. Production of the first of three GO magnets using a newly constructed coil winding machine is currently in progress at BNL. The GG design is being completed and parallel production at BNL of three GG units will start soon. In this paper we highlight HERA upgrade magnet design challenges, present our production solutions and relate experience and results gained from warm and cold testing of short model magnets.

Fermilab, in collaboration With LBNL and BNL, is in the process of developing a focusing quadrupole for installation in the interaction region inner triplets of the LHC. This magnet is required to have an operating gradient of 215 T/m across a 70 mm coil bore, and operates in superfluid helium at 1.9 K. The design is based on a two layer cos (20) coil, mechanically supported by standalone steel collars. The collared coil assembly is surrounded by a iron yoke for flux return, and the assembly enclosed by a stainless steel shell. The development program has addressed mechanical, magnetic, quench protection, and thermal issues, through a series of model magnets constructed at Fermilab. This paper summarizes results from the recent model tests, and the status of the program.

The stability of magnet conductors can be characterized by their minimum quench energies (MQE), i.e. the minimum energy pulse of small extent and short duration needed to initiate a quench. The MQE of a considerable number of prototype strands for the superconducting LHC magnets have been measured at BNL within the framework of the US-CERN accelerator collaboration. The main interest of this work was to study the effect of different strand designs, copper to superconductor ratios (Cu/Se) and the source of the niobium-titanium alloy on MQE. Although MQE varied significantly between the strands, the measurements revealed that except for Cu/Se ratio, these above stated parameters do not affect MQE in a consistent way. Numerical simulations indicate that these tests made with a restricted helium volume and heat exchange surface were quasi-adiabatic in nature, and hence the influence of the cooling even in superfluid helium was minimal.

A small saddle coil for quadrupole magnets was made in industry from BSCCO-2223 high temperature superconducting tape. The coil was made to help develop methods for winding the ends of small-aperture magnets. This coil has a radius of 35 mm. It was tested in liquid helium, and liquid nitrogen. Voltage taps have been installed so that V-I characteristics of both straight and curved elements can be examined. The performance of the coil is compared to short sample measurements of pieces of conductor taken from the start and finish of the windings.

The minimum energy of short duration (MQE) required to quench superconducting cables at fixed field for currents close to the critical current has been measured for several prototype LHC inner type cables. Measurements done both in normal helium at 4.4 K and also in superfluid helium at 1.9 K show that the level of cable compaction has a substantial effect on the conductor stability. It also appears that another parameter that significantly influences the ability of the conductor to absorb transient energy pulses is the inter-strand resistance, which can vary greatly depending on the cable design and the nature of the strand surface. This parameter seems to make a bigger difference to MQE at 1.9 K than at 4.4 K. Details of these measurements are presented.

The critical currents of several NbTi wires have been measured in boiling helium in the temperature range 4.2-1.8 K and at magnetic fields up to 10T. In some instances, I/sub c/ (defined at a resistivity of 10/sup -14/ ohm) can be measured over the entire temperature range while for other conductors the quench drops below I/sub c/ as the temperature is reduced and the critical current cannot be determined. For most of these strands I/sub c/ can again be measured once the helium bath is in the superfluid state but for some wires it is not possible to measure the effective resistivity even in superfluid. Conductors fabricated by the same manufacturer can exhibit completely different behavior. In general there is a tendency for wires with high intrinsic current density and relatively low copper content to perform erratically at the lower temperature.

When superconducting accelerator magnets wound from a multi-stranded conductor are energized, a periodic variation appears in the magnetic field along the axis. This oscillation is present in all components of the field and has a period that is equal to the transposition pitch of the superconducting cable. Such axial variations have been observed even in windings which are not carrying any transport current. A magnetic field was applied to a portion of a dipole winding using a second magnet. Axial oscillations were induced along the total length of the windings including the portion not in the applied field. The amplitude of these oscillations varied with the amount of inert winding inside the energizing magnet and with the angle of the applied field. These field variations could be completely eliminated in the external portion of the coil by heating a small section of the winding above the transition temperature. >

The first of a series of 90 cm long racetrack shaped coils has been tested at 77 K and 4.2 K in a common coil configuration. The conductor used was selected from a number of available lengths by testing in liquid nitrogen in pancake form. The performance of this coil is compared with shorter versions fabricated from similar conductor.