Prototype Magnet Research Articles

Status report on the LHC magnets

Abstract CERN is finalizing the design of a new accelerator collider, the Large Hadron Collider (LHC) to be installed in the existing 27 km long LEP tunnel. To reach the wanted collision energy, dipole magnets with field of 9 to 10 T and quadrupoles of 250 T/m gradient will be used. A twin-aperture configuration of magnets in common yokes and cryostats has been adopted. The magnet system comprises about 1300, 13.5 m long dipole units, 600, 3.2 m long quadrupole units and a large number of other superconducting magnetic elements. Several prototypes of main magnets and correctors have been built. Short dipole models reached fields of 10 T, albeit with substantial training above 9 T. The causes of this behaviour are being investigated in parallel with the construction of new models. A 10 m long prototype making use of HERA type coils reached 8.3 T, the cable short sample limit at 1.8 K, showing no adverse effect of the twin-aperture configuration as compared to single-aperture magnets. The construction of ten 10 m long dipole prototypes and of two quadrupoles is well advanced.

Status of the SSC superconducting magnets

Abstract Several 50mm aperture, 15 meter long dipole magnet prototypes and five 40 mm aperture, 5 meter quadrupole models have been built and tested for the SSC magnet development effort. Five of the dipoles and one quadrupole have been connected In a string representing a collider half cell, and tested cryogenically at the SSC site. The magnets were designed and produced by a consortium consisting of the Superconducting Super Collider Laboratory (SSCL), Fermi National Accelerator Laboratory (FNAL), Brookhaven National Laboratory (BNL), Lawrence Berkeley Laboratory (LBL), along with General Dynamics Corporation (GD), Babcock and Wilcox (B&W) and Westinghouse Electric Corporation (WEC). A description of the magnets, including properties of their superconductor, is presented. The test results from individual magnet tests and the string test are reviewed with respect to meeting collider requirements. The significant features of the baseline production magnets and the plans for prototype through production will be presented. In addition the status and test results for special magnets built at the SSC Laboratory will be discussed.

Strong magnetic field microundulator with permanent magnets inserted into a solenoid

A version of the short-period undulator scheme suggested earlier [A.A. Varfolomeev et al., Nucl. Instr. and Meth. A318 (1992) 809] was investigated experimentally and by simulations. Transverse magnetic field components are provided with this scheme by a redistribution of an external magnetic field supplied by a solenoid similar to that suggested by A.H. Ho et al. [Nucl. Instr. and Meth. A296 (1990) 631]. An enhancement is achieved with an additional set of permanent magnet blocks. 2D simulations using the PANDIRA code and experimental tests with prototype magnets have shown that field values B w > 8 kG for a period λ w = 4.5 mm with a 1.5 mm gap can be obtained with a two times lower solenoid field, B s = 4kG. The undulator scheme looks very promising for microundulators.

High efficiency magnet down-leads of weak-linked REBa 2Cu 3O 7 fibres

Optimal magnet down-leads maximize current capability and minimize heat input to the coil. Down-leads made using high T c superconductors can potentially perform much better than those made from a normal metal. We have designed a prototype magnet down-lead to go from 77 K to a superconducting magnet at 4 K using REBa 2Cu 3O 7 fibres from GA's Pacific Superconductors Division. In spite of the sensitivity of weak-linked material to magnetic fields, these down-leads can be built to carry ≈100 A at the 77 K end and tolerate ≈100 G at the low temperature end. The calculated thermal conductance of this structure is divided among the superconductor, wire core and superstructure approximately in the ratio 3:1:0.1. A simple calculation suggests that the thermal efficiency of this device would be about 100 times that of optimized Cu down-leads. The down-lead could be designed for higher currents, but would have a smaller gain in efficiency. We have built a prototype magnet lead using 165 fibres which carried 35 A at 77 K, and which had a thermal efficiency without vapour cooling more than twice as good as a vapour cooled copper down-lead.

Cryogenic and magnetic tests of the twin aperture prototype dipole in the Saclay test facility

The authors describe the test facility and the cryogenic and magnetic measurements performed on the twin aperture prototype (TAP) dipole for the CERN Large Hadron Collider (LHC). The magnet, designed by CERN and built by European industries, was tested in a facility built at CE Saclay. The focus is on the cryogenic system, which enables prototype magnets to be tested in superfluid helium; on the data acquisition systems, including a system for magnetic measurements; and on the results which were obtained during the tests. >

Mechanical performance of 5-cm-aperture, 15-m-long SSC dipole magnet prototypes

The authors summarize the mechanical performance of the most recent 5-cm-aperture, 15-m-long SSC dipole magnet prototypes. The magnets were produced at Brookhaven National Laboratory (BNL) and Fermi National Accelerator Laboratory (FNAL) under contract with the Superconducting Super Collider Laboratory (SSCL). The BNL magnets rely on a horizontally split yoke with collared ends, while the FNAL magnets rely on a vertically split yoke with collet-style end clamps. Magnets of both designs are equipped with strain gauges enabling measurement of the azimuthal pressures exerted by the coils against the collar poles as well as the axial forces transmitted from the coil ends to the end plates. A comparison of the mechanical behaviors measured by the strain gauges is presented. How the behavior of the 5-cm-aperture magnets compares to that of the 4-cm-aperture prototypes is also discussed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Current dependence of harmonic field coefficients of 5-cm-aperture, 15-m-long SSC dipole magnet prototypes

Eighteen 5-cm-aperture, 15-m-long Superconducting Super Collider (SSC) dipole magnet prototypes have been produced and cold tested. On each prototype, the dependence of harmonic field coefficients on magnetic current was measured as part of a study of the magnetic field quality. For most of the magnets, the observed behavior conforms to what can be expected from the effects of persistent magnetization currents and iron yoke saturation. A few prototypes, however, exhibited anomalies during current ramp at 4 A/s which can be attributed to large cable eddy currents.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Quench characteristics of 5-cm-aperture, 15-m-long SSC dipole magnet prototypes

The quench performance and ramp rate sensitivity of 18 5-cm-aperture, 15-m-long Superconducting Super Collider (SSC) dipole magnet prototypes are discussed. All the magnets appear to reach a quench plateau near their extrapolated short sample current limit and well in excess of the operating current with very little training. Most of the magnets, however, exhibit a dramatic degradation of their quench current as a function of ramp rate, which, for the most part, can be attributed to large cable eddy currents.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Calculation of magnetic field and electromagnetic forces in MHD superconducting magnets

A superconducting prototype magnet for MHD (magnetohydrodynamic) energy conversion is under development in Italy. The authors discuss analytical methods developed at the Department of Electrical Engineering of Padova University for calculating magnetic field and electromagnetic forces in MHD superconducting magnets and utilized in the preliminary design of the prototype. Due to the flexibility, speed, and ease of use of the corresponding computer programs, the described analytical methods for field computation proved to be useful in rapid parametric studies in the preliminary design of superconducting magnets with cylindrical or rectangular saddle coils. Some examples of application are presented concerning the choice of the number and shape of coils and the evaluation of the far field of the prototype magnet.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The Italian National Program on superconducting MHD magnets technology

In late 1989, a five-year national program on superconducting magnets technology was started in Italy. The main objectives of the research activities are: the design and the construction of a superconducting prototype magnet (2-m active length) with a stored energy of 62 MJ, and the reference design of a superconducting demonstration magnet (8-m active length), both for MHD (magnetohydrodynamic) applications. The magnets are designed to produce 5 T on axis field with 5% and 10% field uniformity in the cross section, respectively, and a field taper less than 0.15 T/m. The design and construction of high-field superconducting magnets are also included in the frame of the project, with particular attention given to the insulation technology and stress calculation.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A 50 Hz dipole magnet for the TRIUMF KAON factory booster ring

The 3-GeV booster synchrotron for TRIUMF's KAON Factory will need 24 dipole magnets each 3.0-m long operating with a resonant power system designed to give a 50-Hz AC field superimposed onto a DC field. The maximum and minimum field levels are 1.118 and 0.295 T, respectively. The magnet design is presented and compared with measured results from a prototype which was constructed to evaluate fabrication procedures and to verify the AC loss calculations. The experiences gained from this fabrication are described. The prototype magnet measured parameters were very close to the design values, giving confidence in the methods of calculation and fabrication techniques. The prototype also served as a test of the power supply and its components and highlighted some of the control aspects that must be incorporated for a working synchrotron ring. >

The Fermilab Main Injector dipole construction techniques and prototype magnet measurements

The Fermilab Main Injector Project will provide 120-150-GeV proton and antiproton beams for Fermilab Fixed Target Physics and Colliding Beams Physics use. A dipole magnet has been designed and prototypes constructed for the principal bending magnets of this new accelerator. The design considerations and fabrication techniques are described. Measurement results on prototypes are reported, emphasizing the field uniformity achieved in both body field and end field at excitation levels from injection at 0.1 T to full field of 1.7 T.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Design of superconducting MHD saddle magnets

As part of the Italian National project on superconductive and cryogenic technologies, the design of superconductive magnets for MHD (magnetohydrodynamic) applications has been carried out. The design of a prototype magnet (active length 2 m) and the conceptual magnetic design of a demonstration magnet (active length 8 m) are reported. The computation techniques used and the optimization procedure developed are described for the set of saddle magnets investigated. The study performed for the prototype has been scaled up to define the basic parameters of the demonstration magnet, and optimization studies have also been performed for this magnet size. Comparisons of results obtained for cylindrical and rectangular saddle magnets, in both sizes, show the possibility of designing magnets meeting design specifications and lead to the choice of the rectangular saddle magnet as the one offering the best performance. >

Field measurements of prototype magnets for the SPring-8 storage ring

Prototypes of a dipole, a quadrupole, and a sextupole magnet for the SPring-8 storage ring have been built. Their fields were measured with four types of field measurement equipment. Their excitation curves, effective lengths, and strengths of higher multipole fields were determined. On the basis of the measurement results, design was modified with the aim of reducing production and operation costs.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Precision heat inleak measurements on cryogenic components at 80 K, 4.2 K and 1.8 K

We have built and are operating a test bench for precision heat inleak measurements and thermal qualification of components for the superfluid helium cryostats of the CERN Large Hadron Collider (LHC) project. The bench features the three temperature levels used for heat interception in the LHC cryostats. The heat loads are measured using both calibrated thermal conductances (“heatmeters”) and standard boil-off methods. After validation of the measurement methods, we compare experimental results with thermal design calculations on a prototype magnet support post.

Finite-element structural analysis of the 10 m long dipole prototype magnet for the LHC

In the framework of the R&D program for the LHC (Large Hadron Collider) superconducting magnets, a series of dipole prototypes, manufactured by European firms, will be placed in a test cell of the LHC machine to be tested in the second part of 1992. The design of the cross-section of the full length dipole prototype is a natural evolution from the solutions adopted in the CERN models and prototypes developed and built so far. A detailed finite-element stress and strain analysis was carried out and the results were used to complete the design of the prototype. The optimization of the design was done by studying the magnet behavior at room temperature, and at 1.8 K in both energized and nonenergized conditions. The Lorentz body forces distribution, corresponding to a 10-tesla central field, was computed from a magnetic field analysis by means of the same finite-element package used in the stress-strain analysis. The authors report on the main results obtained, and illustrate the guidelines which were followed in optimizing the design of the cross section.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The Pohang light source project: Status report

Design of a 2-GeV synchrotron radiation facility is well in progress in Pohang, Korea. The first portion of the injector linac has been delivered and installation will be from July 1991. Prototype storage ring magnets are to be delivered soon. Prototype magnet power supplies have been fabricated and tested. Detailed design studies are being carried out at present.

A flexural in-line actuator for magnetic recording disk drives

An actuator for magnetic recording disk drives based on flexures and coupled to a voice coil motor (VCM) was developed for a 3.5-in disk drive. The design and performance of this system is described. This high-performance flexural actuator has been shown to have unique advantages over conventional designs, demonstrated in a magnetic recording disk file prototype. >

Measurement of time dependent fields in high gradient superconducting quadrupoles for the Tevatron

Magnetic field measurements have been performed on prototype and production magnets from two high-gradient superconducting quadrupole designs. One design is a double-shell quadrupole with 36-strand Rutherford cable. The other design is a single-shell quadrupole with five individually insulated monolithic strands connected in series. These magnets have similar bore diameters and cable dimensions. However, there are significant differences between the two designs, as well as differences between prototype and production magnets within each design, with regard to Cu-to-superconductor ratio, filament diameters, and filament-spacing-to-strand-diameter ratio. The time dependence at fixed currents of the measured magnetic field is discussed.

Human adults and human infants show a “perceptual magnet effect” for the prototypes of speech categories, monkeys do not

Many perceptual categories exhibit internal structure in which category prototypes play an important role. In the four experiments reported here, the internal structure of phonetic categories was explored in studies involving adults, infants, and monkeys. In Experiment 1, adults rated the category goodness of 64 variants of the vowel i parallel on a scale from 1 to 7. The results showed that there was a certain location in vowel space where listeners rated the i parallel vowels as best instances, or prototypes. The perceived goodness of i parallel vowels declined systematically as stimuli were further removed from the prototypic i parallel vowel. Experiment 2 went beyond this initial demonstration and examined the effect of speech prototypes on perception. Either the prototypic or a nonprototypic i parallel vowels was used as the referent stimulus and adults' generalization to other members of the category was examined. Results showed that the typicality of the speech stimulus strongly affected perception. When the prototype of the category served as the referent vowel, there was significantly greater generalization to other i parallel vowels, relative to the situation in which the nonprototype served as the referent. The notion of a perceptual magnet was introduced. The prototype of the category functioned like a perceptual magnet for other category members; it assimilated neighboring stimuli, effectively pulling them toward the prototype. In Experiment 3, the ontogenetic origins of the perceptual magnet effect were explored by testing 6-month-old infants. The results showed that infants' perception of vowels was also strongly affected by speech prototypes. Infants showed significantly greater generalization when the prototype of the vowel category served as the referent; moreover, their responses were highly correlated with those of adults. In Experiment 4, Rhesus monkeys were tested to examine whether or not the prototype's magnet effect was unique to humans. The animals did not provide any evidence of speech prototypes; they did not exhibit the magnet effect. It is suggested that the internal organization of phonetic categories around prototypic members is an ontogenetically early, species-specific, aspect of the speech code.