Superconducting Super Collider Dipole Magnets Research Articles

Influence of azimuthal coil size variations on magnetic field harmonics of superconducting particle accelerator magnets

The superconducting super collider (SSC) would have required dipole and quadrupole magnets with a very high field quality. The field quality is determined mainly by the dimensions of the magnet coils and their positions with respect to the iron yoke. It is thus very sensitive to manufacturing errors. A model is here developed to estimate the field distortions in a dipole magnet due to azimuthal coil size variations. This model is applied to the data collected during the fabrication and testing of a series of 5 cm aperture, 15 m long SSC dipole magnet prototypes. A clear correlation is observed between the predicted field distortions from the azimuthal coil sizes and the measured skew quadrupole and skew sextupole coefficients.

Locating the magnetic center of the SSC CDM using a temporary quadrupole field

For the Superconducting Super Collider (SSC) to meet its physics requirements, the magnetic center of each collider dipole magnet (CDM) must be accurately aligned. A technique has been developed to determine the magnetic center of the SSC dipole magnet under ambient test conditions. This technique involves flowing current in the upper half of the coils in the direction opposite to the current in the lower half. This is done using a temporary lead connected to the splice joining the two coil halves and two matched power supplies. The resulting field is primarily skew quadrupole and has high field gradients which allow the center to be accurately located. The viability of this method has been verified by analysis using a Taylor series expansion of the resulting magnetic field. The analysis has also verified that off-the-shelf power supplies have low enough mismatch to be used in this technique. The analytical results have been verified through the test of a short dipole magnet at the Brookhaven National Laboratory.< <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>

Magnetic performance of the SSC dipole magnets

The authors report on the status of the magnetic design of the Superconducting Super Collider (SSC) dipole magnets. A two- and three-dimensional design optimization was performed that included the effects of permeable collar, yoke, cryostat, beam tube, crescent yoke end pieces, cool-down, and Lorentz loads. A field quality plan was developed that represents the approach to tuning the design for satisfying the systematic and RMS multipole specifications. The VSA tool is being used to simulate the effects of random parts, tool and process variations on the expected multipole distributions, both between many magnets, and within a single magnet. >

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>

Mechanical behavior of Fermilab-built 1.5 m model SSC collider dipoles

Several model SSC (Superconducting Super Collider) dipole magnets (50-mm aperture, 1.5-m magnetic length) have been built and tested at Fermilab. These magnets are instrumented with strain gauges to measure stresses in the coil, the cold mass shell, and the coil end clamp assembly. Measurements are made of these quantities during assembly, cooldown, excitation, and warmup. The collar vertical deflection with prestress and the shell azimuthal tension agree quantitatively with design expectations. Coil prestresses within the desired range have been achieved without pole shims. Prestress loss with cooldown compares favorably with 40-mm models. Most of the axial I*B force is transmitted to the shell via collar-yoke-shell friction, and not by compressive loading of the coil end. The yoke parting plane gap remains closed to well above the operating point, and end clamp deflections are >

Tests of Fermilab built 40 mm aperture full length SSC dipole magnets

Several 40-mm-aperture, 17-m-long dipoles have been built by Fermilab as developmental prototypes for the Superconducting Super Collider (SSC). These magnets have an external inner-outer coil splice design, a collet style end clamp assembly, a new, analytically designed minimum stress coil end design, and a new insulation system which does not employ shims or 'shoes'. In addition, the magnets were built using production-style tooling. The magnets were tested at the Fermilab Magnet Testing Facility. Quench testing and mechanical measurement results are presented and analyzed with emphasis on the new design and fabrication features of these magnets. The performance of these magnets was very good from a quench and mechanical behavior standpoint. The magnets did not exhibit excessive training behavior and only one training quench was below the nominal operating current. The coil prestress remained positive to >7 T in both magnets and most of the quenches originated in the high field region of the pole turn.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Cryostat design for the Superconducting Super Collider 50 mm aperture dipole magnet

The design of the SSC (Superconducting Super Collider) dipole magnet cryostat is described, and discussions of the thermal, structural, and dynamic considerations involved in the development of each of the major systems are included. The SSC development program has afforded the opportunity to extend the design of cryostats for superconducting magnets far beyond the state of the art achieved at the end of the Fermilab Tevatron program. Advances in new materials technology have opened up options for cryostat designers in both thermal and structural materials. Strict limits on allowable heat load have made it necessary to develop new mechanisms for structural support and thermal shielding. The end result is a cryostat design which meets the demands of the SSC and which will serve as the starting point for the development of other magnet systems.

A statistical evaluation of recent SSC conductors produced at IGC/ASI

One of the requirements for uniform field quality in the SSC (Superconducting Super Collider) dipole magnets is the consistency in the superconducting strand characteristics from start to finish to the production phase. As full-scale production of strand and cable approaches, the consistency in performance of the early batches of conductor needs to be examined. A number of 300-mm billets have been manufactured with tight process controls. The performance of the final conductor in terms of piece lengths, current density, Cu/Sc ratio, and wire diameter has been evaluated. The data are analyzed in order to understand the variations that are related to the conductor design and processing. The current density of the strand is examined over the length of the billet to determine inherent variability in the NbTi alloy itself.

A conductor, with uncoupled 2.5 mu m diameter filaments, designed for the outer cable of SSC dipole magnets

A conductor with a stabilizer-to-superconductor ratio of 1.8/1 and containing 22900 2.5- mu m diameter filaments at a wire diameter of 0.65 mm has been produced for the outer cable of the Superconducting Super Collider (SSC). The fabrication procedures used to make this material from a full production-size billet 305 mm in diameter are described. Metallographic, electrical, and magnetization data are presented, and these illustrate the filaments are completely uncoupled at the size used in the outer SSC cable. This work indicates the feasibility of the commercial manufacture of such a 2.5- mu m-diameter filamentary material. Preliminary tests show relatively low J/sub c/ and n values. It is likely that materials with smaller spacings than those used here will be required before the J/sub c/ values specified for the SSC can be obtained reproducibly. >

Source location of quenches in SSC dipole magnets

Superconducting-to-normal transitions in two 16.6-m-long superconducting dipole magnets for the Superconducting Supercollider (SSC) were monitored with six axially-distributed acoustic emission (AE) sensors. The origin of each quench was determined by examination of AE data captured at quench. In one magnet, these data showed that the first few quenches started from various locations along the magnet while most later quenches started from the feed end. In the second magnet, most of the spontaneous quenches started near the feed end of the magnet. By supplementing AE data captured at quench with AE attenuation data taken at room temperature, it was determined that, of these, more than half started in the region within 25 cm of the feed end. The results are in general agreement with temperature and pressure post-quench histories. >

Control of the fields due to superconductor magnetization in the SSC magnets

Field uniformity of better than one part in 10,000 is required for the dipole magnets for the Superconducting Super Collider (SSC). The high field dipole and quadrupole magnets proposed for the SSC generate higher multipole components of field due to magnetization (persistent currents) in the superconductor. When the superconductor filament diameter is of the order of 20μm, the sextupole term alone is about 17 parts in 10,000 at an injection induction of 0.3 tesla in the SSC dipole magnets at a radius of 1 cm. This paper shows calculations of the magnetization phenomena which agree very well with magnetic measurement. Several passive methods for removing the sextupole component and higher components of the field generated by magnetization of the superconductor in the SSC dipole magnets are presented in the paper.

Quench pressure analysis of adiabatically stable magnets

Adiabatically stable magnets are used in applications such as magnetic resonance imaging and high energy physics. The maximum pressure induced during a quench is more severe for long magnets such as dipole magnets required in constructing the Superconducting Supercollider (SSC). Following an adiabatically stable magnet quench, joule heating is generated through the magnet windings causing helium heating and inducing flow both within the windings and along the magnet cooling channel. The helium trapped in the windings is expelled as it is heated, transferring energy to the helium coolant in the channel. The maximum pressure during a quench strongly depends on the magnet length and is higher for longer magnets. To determine the maximum pressure induced in the cooling channel, it is necessary to simultaneously solve the time-dependent continuity, momentum, and energy equations for the helium flow in the channel, the heat conduction equation in the windings, and the current decay equations. A quasi-steady state solution of the fluid flow equations is valid as long as the magnet length divided by the speed of sound ratio is much less than the quench time. This particular case can be analyzed using General Dynamics code MAGPRES (1) and will not be discussed in this paper. The analytical approach, including the model developed to determine the mass and energy transfer associated with the helium flow from the windings, is presented in this paper. Quench pressure results employing a simplified model of an adiabatically stable magnet are also presented for some special cases to test the newly developed General Dynamics computer code QMAG. Also included are results of one computer run for SSC dipole magnets for the case of uniform quenching. The computer code will be used for more detailed analysis of SSC magnets; the results will be published as they become available.