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Procedures for measuring the electrical properties of superconductors for accelerator magnets

Description: There are three important electrical properties associated with the superconductor used to fabricate accelerator magnets. The most important is the critical current since this determines the performance potential of the magnet. The normal state resistivity and the volume magnetization are the other principal electrical parameters. In this report methods for measuring these parameters are presented and procedures for including self field effect and magnetoresistance are discussed.
Date: January 1, 1986
Creator: Sampson, W.B.
Partner: UNT Libraries Government Documents Department

Critical current anistropy in NbTi cables

Description: 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 given below. 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. In this note we present results of critical current measurements which are made with the applied magnetic field oriented parallel to the plane of the cable (still perpendicular to the direction of current flow) as well as perpendicular. It is found that the parallel critical current is generally larger than the perpendicular and is usually almost equal to that of the wires prior to cabling. The degradation is small for the parallel field orientation.
Date: January 1, 1984
Creator: Garber, M. & Sampson, W.B.
Partner: UNT Libraries Government Documents Department

Quench properties of high current superconductors

Description: A technique has been developed which allows the simultaneous determination of most of the important parameters of a high current superconductor. The critical current, propagation velocity, normal state resistivity, magnetoresistance, and enthalpy are determined as a function of current and applied field. The measurements are made on non-inductive samples which simulate conditions in full scale magnets. For wide, braided conductors the propagation velocity was found to vary approximately quadratically with current in the 2 to 5 kA region. A number of conductors have been tested including some Nb/sub 3/Sn braids which have critical currents in excess of 10 kA at 5 T, 4.2 K.
Date: January 1, 1980
Creator: Garber, M & Sampson, W B
Partner: UNT Libraries Government Documents Department

Magnetization and critical currents of NbTi wires with fine filaments

Description: In high energy accelerators such as the SSC, the magnetization of the superconductor is an important component in determining the harmonic fields at injection (approx.0.3T). In an effort to reduce these residual fields, interest has focused on NbTi conductors with fine filaments which are expected to have a reduced magnetization as dictated by the critical state model. With this in view, the magnetization and critical currents were measured at 4.3K for a set of NbTi wires with filament diameters, d, ranging from 1.0 to 5.0 microns. The data show that, although the magnetization scales linearly with d, it does not do so with the product J/sub c/d for d less than 3 ..mu..m. However, at these d values, the critical transport current density, J/sub c/ of NbTi was observed to decrease rapidly as a function of d. The origin of this J/sub c/ degradation and its effect on the scaling of magnetization within the framework of the critical state model is explored. We also examine the question of the observed asymmetry of the hysteretic magnetization.
Date: January 1, 1985
Creator: Ghosh, A.K. & Sampson, W.B.
Partner: UNT Libraries Government Documents Department

Fabrication techniques and properties of multifilamentary Nb/sub 3/Sn conductors

Description: Various processing techniques for multifilamentary Nb/sub 3/Sn and V/sub 3/Ga are reviewed. The critical current of commercially produced Nb/sub 3/Sn wires manufactured by both the bronze and external diffusion techniques are compared. Critical currents for in situ and powder processed Nb/sub 3/Sn are also included. New developments which promise improvements in J/sub c/ are discussed.
Date: January 1, 1980
Creator: Suenaga, M; Sampson, W B & Luhman, T S
Partner: UNT Libraries Government Documents Department

Quench propagation and training in simulated superconducting magnet windings

Description: Training behavior similar to that which occurs in full scale superconducting accelerator magnets has been observed in small test windings. The test coils are formed from approximately 20 meters of conductor wound non-inductively, in Bifilar fashion. The resulting racetrack shaped coil is molded at elevated temperature to simulate the construction techniques used for the ISABELLE dipoles. The quench current of such windings has been measured as a function of applied field and the effect of parameters such as mechanical loading and porosity have been investigated. The velocity of propagation of the normal front has been measured both along and transverse to the direction of current flow for several test windings. The minimum energy required to produce a self propagating normal zone has also been determined in an attempt to quantify the relative stability of the coils.
Date: January 1, 1981
Creator: Sampson, W.B.; Garber, M. & Ghosh, A.
Partner: UNT Libraries Government Documents Department

Influence of Proton Irradiation on Angular Dependence of Second Generation (2G)HTS

Description: In the Facility for Rare Isotope Beams (FRIB) the quadrupoles in the fragment separator are exposed to very high radiation and heat loads. High Temperature Superconductors (HTS) are a good candidate for these magnets because they can be used at {approx}30-50 K and tolerate higher heat generation than Nb-Ti magnets. Radiation damage studies of HTS wires are crucial to ensure that they will survive in a high radiation environment. HTS wires from two vendors were studied. Samples of 2G HTS wires from SuperPower and American Superconductor (ASC) were irradiated with a 42 {mu}A, 142 MeV proton beam from the Brookhaven Linac Isotope Producer (BLIP). The angular dependence of the critical current was measured in magnetic fields at 77K.
Date: May 1, 2011
Creator: Shiroyanagi, Y.; Greene, G.; Gupta, R. & Sampson, W.
Partner: UNT Libraries Government Documents Department

Critical current studies on fine filamentary NbTi accelerator wires

Description: The magnets for the Superconductig Super Collider, a high energy proton colliding beam accelerator, require a superconductor with very high current density (>2400 A/mm/sup 2/ at 5 T) and very small filaments (approx. 2..mu..m in diameter). Previous work has shown that by controlling the formation of Cu/sub 4/Ti compound particles on the filament surfaces it is possible to make fine filamentary NbTi wire with high critical current density. The performance of multi-filamentary wire is characterized by the current density and the quantity ''n'' which describes the superconducting-normal transition. Micrographs of wires having high J/sub c/ and high n show smooth, uniform filaments. Recently wires of very high critical current and high n have been produced in experimental quantities by commercial manufactures.
Date: January 1, 1985
Creator: Garber, M.; Suenaga, M.; Sampson, W.B. & Sabatini, R.L.
Partner: UNT Libraries Government Documents Department

Magnetization, critical current, and injection field harmonics in superconducting accelerator magnets

Description: The very large energy ratio of machines such as the SSC dictates rather low injection field (for 6T, 20 TeV it is approximately 0.3T). Since the harmonic content at such low fields is largely determined by magnetization currents in the superconductor, the random errors depend on the uniformity of the superconducting wire. In principle the magnitude of the residual fields can be reduced indefinitely by using finer filaments, but in practice there is a lower limit of a few microns. We have compared the injection field harmonics for a number of accelerator dipoles with magnetization measurements made on samples of the conductor used to wind the coils. In addition both the magnetization and harmonics have been compared with short sample critical current measurements made at 5T. The results indicated that an accurate estimate of the variation in injection field harmonics can only be obtained from direct measurements of the magnetization of the cable. It appears feasible to use such measurements to ''shuffle'' magnets for a large accelerator by predicting the low field properties of a magnet before actually winding the coils. 10 refs., 4 figs., 2 tabs.
Date: January 1, 1985
Creator: Ghosh, A.K.; Sampson, W.B. & Wanderer, P.
Partner: UNT Libraries Government Documents Department

Effect of Cu/sub 4/Ti compound formation on the characteristics of NbTi accelerator magnet wire

Description: High critical current density, J/sub c/ > 2500 A/mm/sup 2/, and small filament diameter, d approx. 3 ..mu..m, are required in multifilamentary NbTi wire used for superconducting accelerator magnets. Wires obtained from various commercial sources had J/sub c/'s in the range 1000 to 2800 A/mm/sup 2/ amd d's in the range 1 to 23 ..mu..m. The filaments were examined by means of scanning electron microscopy in order to determine the reason for the variation in J/sub c/. It was found that the filaments in high J/sub c/ wires had clean smooth surfaces and uniform cross section along their lengths. Filaments in low J/sub c/ wires show formation of Cu/sub 4/Ti compound particles on their surfaces and large variations in cross section. The lower critical current measured in these wires is believed to be largely due to this effect. The superconducting-normal state transition is relatively wide in these wires.
Date: January 1, 1985
Creator: Garber, M.; Suenaga, M.; Sampson, W.B. & Sabatini, R.L.
Partner: UNT Libraries Government Documents Department

Correlation of superconductor strand, cable, and dipole critical currents in CBA magnets

Description: A calibration between vendor critical current data for 0.0268'' diameter superconductor strand supplied to Fermilab, and the BNL 10/sup -12/..cap omega..cm critical current specification is presented. Vendor critical current data for over 400 Fermilab type billets are shown, both as supplied by the vendor and converted to BNL units. Predictions of cable critical current are made using the sum of the critical currents of the 23 strands, where all strands from the same half billet are assigned the same critical current. The measured critical current shows excellent correlation to the predicted value and is approximately 14 +- 2 percent below it. Colliding Beam Accelerator (CBA) full length dipoles reach the conductor critical current limit, essentially without training. Magnet performance is predictable from the measured critical current of a short sample of cable to within 2%.
Date: January 1, 1982
Creator: Tannenbaum, M.J.; Garber, M. & Sampson, W.B.
Partner: UNT Libraries Government Documents Department

ISABELLE insertion quadrupoles

Description: Beam focussing and control at the beam intersection regions of ISABELLE is accomplished by a number of superconducting insertion quadrupoles. These magnets differ from the standard ISABELLE quadrupoles in various ways. In particular, the requirements of limited space near the intersections and aperture for beam extraction impose constraints on their configuration. To achieve optimum beam focussing and provide tuning flexibility calls for stronger quadrupole trim windings than those in the standard quadrupoles. The magnetic and mechanical design of the insertion quadrupoles and their associated correction and steering windings to accomplish the above tasks is presented.
Date: January 1, 1979
Creator: Kaugerts, J.; Polk, I.; Sampson, W. & Dahl, P.F.
Partner: UNT Libraries Government Documents Department

Correlation of superconductor strand, cable and dipole critical currents in ISABELLE magnets

Description: A calibration between vendor critical current data for 0.0268'' diameter superconductor strand supplied to Fermilab, and the BNL 10/sup -12/ OMEGA cm critical current specification is presented. Vendor critical current data for over 400 Fermilab type billets are shown, both as supplied by the vendor and converted to BNL units. Predictions of cable critical current are made using the sum of the critical currents of the 23 strands, where all strands from the same half billet are assigned the same critical current. The measured cable critical current shows excellent correlation to the predicted value and is approximately 14 +- 2% below it. ISABELLE full length dipoles reach the conductor critical current limit, essentially without training. Magnet performance is predictable from the measured critical current of a short sample of cable to within 2%.
Date: January 1, 1982
Creator: Tannenbaum, M.J.; Garber, M. & Sampson, W.B.
Partner: UNT Libraries Government Documents Department

Critical current measurements of ISABELLE superconducting cables

Description: Short sample critical measurements on ISABELLE superconducting cables are described. The purpose is to provide a basis for assessing magnet performance and to provide Quality Assurance data on materials purchases. The measurements are made on 1 m samples in a dipole magnet. Voltages on the V-I curve are determined to a precision of several tenths of a microvolt. The critical current is defined as that at which rho = 1 x 10/sup -12/..cap omega..cm/sup 1/ and is determined to a precision of 1 to 2%. Similar techniques are employed in determining the critical currents of the wires of which the cables are made. The relation between cable and wire critical currents will be discussed. It is found that well insulated, slowly ramped cables of the ISABELLE design are stable for currents up to approximately rho = 2 x 10/sup -12/..cap omega..cm. The value of current corresponding to the resistivity determines the limit of magnet performance. Additional properties of the cabled conductors such as the normal state resistance and the longitudinal quench propagation velocity are also measured.
Date: November 30, 1982
Creator: Garber, M.; Sampson, W.B. & Tannenbaum, M.J.
Partner: UNT Libraries Government Documents Department

Normal state resistance and low temperature magnetoresistance of superconducting cables for accelerator magnets

Description: The normal state resistivity of the superconducting NbTi cable used in accelerator magnets is usually specified by the resistance per unit length at room temperature (295 K) and the residual resistance ratio (RRR). Using these resistance parameters, the amount of copper in the multifilamentary wire can be calculated. This method is consistent with the traditional etch and weigh technique, and as such is a alternative and convenient way of specifying the copper to superconductor ratio. In principle the magnetoresistance can be calculated from the RRR and the ''Kohler Plot'', for copper. In practice however, measurements of magnetoresistance for a wide variety of SSC inner cables show considerable disagreement with calculation. In this paper the magnetoresistance data on cables with RRR ranging from 50 to 175 are analyzed taking into account the conductor geometry and the effect of the small interfilamentary spacing on the resistivity of copper. 8 refs., 5 figs., 1 tab.
Date: January 1, 1988
Creator: Sampson, W.B.; Garber, M. & Ghosh, A.K.
Partner: UNT Libraries Government Documents Department

The effect of self field on the critical current determination of multifilamentary superconductors

Description: In determining the short sample critical current of conductors of large cross section or high current density the self field produced by the transport current must be taken account in order to obtain a ''true value'' for the critical current. A simple model calculation for determining this effect is described. Measurements on wires, cables, and monoliths show the validity and self consistency of the procedures. 9 refs., 13 figs., 1 tab.
Date: January 1, 1988
Creator: Garber, M.; Ghosh, A.K. & Sampson, W.B.
Partner: UNT Libraries Government Documents Department

Magnetization measurements on multifilamentary Nb/sub 3/Sn and NbTi conductors

Description: The effective filament size has been determined for a number of high current Nb/sub 3/Sn multifilamentary composites. In most cases it is much larger than the nominal filament size. For the smallest filaments (approx. 1 micron) the effective size can be as much as a factor of forty times the nominal size. Samples made by the internal tin, bronze route, and jelly roll methods have been examined with filaments in the range one to ten microns. Rate dependent magnetization and flux jumping have been observed in some cases. NbTi composites ranging in filament size from nine to two hundred microns and with copper to super-conductor ratios between 1.6:1 and 7:1 have been examined in the same apparatus. Low field flux jumping was only observed in conductors with very large filaments and relatively little stabilizing copper. 9 references, 6 figures, 3 tables.
Date: January 1, 1984
Creator: Ghosh, A.K.; Robins, K.E. & Sampson, W.B.
Partner: UNT Libraries Government Documents Department

The location of the quench origin in a superconducting accelerator magnet

Description: A method of calculating the initial rate of rise of the resistive voltage in a quenching superconducting magnet is described. Comparison of such calculations with data from spontaneously occurring quenches gives the location of the quench origin since the normal state resistance of the conductor is determined by its position in the windings due to the magnetoresistance of the copper matrix. The characteristics of the voltage buildup is used to separate quenches occurring in low field regions, such as the magnet ends, from those starting in the two-dimensional straight section of the coil. The magnitude of V dot is a measure of performance and can be used to determine if the magnet is reaching the maximum current permitted by the conductor parameters.
Date: January 1, 1987
Creator: Ghosh, A.K.; Robins, K.E. & Sampson, W.B.
Partner: UNT Libraries Government Documents Department

Quench propagation across the copper wedges in SSC dipoles

Description: The effect of copper wedges on quench propagation in SSC windings has been studied. The results indicate that the turn-to-turn quench transit time for conductors separated by an insulated copper wedge can be predicted with reasonable accuracy from the bulk quench properties and the mean wedge thickness.
Date: January 1, 1986
Creator: Ghosh, A.K.; Robins, K.E. & Sampson, W.B.
Partner: UNT Libraries Government Documents Department

Induced axial oscillations in superconducting dipole windings

Description: When superconducting accelerator magnets wound from multi-stranded conductor are energized a periodic variation appears in the magnetic field along the axis. This oscillation is present in al 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 t;he angle of the applied field. These field variations could be completely 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.
Date: December 31, 1994
Creator: Sampson, W. B. & Ghosh, A. K.
Partner: UNT Libraries Government Documents Department