Yehia M. Eyssa

Quench simulation and thermal diffusion in epoxy-impregnated magnet system

We have developed a new computer code that addresses quench simulation and analysis of a magnetically coupled epoxy-impregnated superconducting magnet system. The new computer code contains several new provisions: (1) it includes the effect of AC loss from the field variations in the winding due to field change because of the fast current transfer between the magnetically coupled solenoids; and (2) simultaneous solution of the propagation velocities in all directions in each coil by solving the thermal diffusion equation in the three directions (tangential, radial and axial). In addition to the above new features, the code solves for the currents, voltage, temperature distribution, and resistance of each coil as function of time. Thermal simulation of the protection switch and the quenching heaters is part of the new code.<<ETX>>

Quench, thermal, and magnetic analysis computer code for superconducting solenoids

An update report on the National High Magnetic Field Laboratory (NHMFL) magnet analysis code is presented. Among the recent improvements to the code is the ability to address complex conductors, windings and reinforcements in terms of thermal and magnetic diffusion. In this article we present several examples showing the capabilities of this code. For example copper/stainless steel, Cu/SS wires that are used in pulse magnets as an alternative to other conductors such as CuAg or CuNb have shown to have excellent thermal and mechanical properties. It was found that the rule of mixtures holds in predicting their properties. As a result it is expected that wires that have 10%Cu and 90%SS will essentially keep the SS high modulus and strength. However the 10% copper will improve the conductivity of this reinforcement that it can act as quench-back circuit in case of a quench. In this study we simulated a quench of a high field (20 T) magnet system and varied the Cu/SS ratio. The modeling results show that 5%Cu is enough to make the reinforcement act as quench-back circuit.

Test results and potential for upgrade of the 45 T hybrid insert

Construction of the NHMFL hybrid magnet is complete. The resistive insert was tested to full current without the background field from the superconducting magnet on May 17, 1999. Tests of the combined system have been scheduled for October 1999. The resistive insert fits into the 616 mm bore of the 14 T outsert superconducting magnet. The insert consists of a five coil, axially cooled Florida-Bitter design. The two innermost coils are electrically in parallel and this pair is in series with the other four coils. The magnet design uses Florida-Bitter disks made of Cu-Ag, Cu-Be, Cu-Zr and Cu sheet and is heavily based upon the high field resistive magnets previously built at the NHMFL. Details of the coil design, construction and testing are presented.

Special purpose high field resistive magnets

Since 1994 the National High Magnetic Field Laboratory in Tallahassee, FL has built numerous high field DC magnets for condensed matter physics and other research. Our user community is now requesting various special purpose high field magnets that are at various stages of design and development. Concepts under consideration include the following: 1) AC modulation (0.1 T AC to 100 Hz) at 27 T DC for dc Haas van Alphen; 2) AC gradient (0.05 T/cm) at 27 T DC for force magnetometry, 3) >20 T radial access magnet for two angle rotation, 4) 18 cm bore high field*field gradient magnet for levitation of large samples and 5) 50 mm bore magnet with uniform field*field gradient for precision levitation. Design concepts. field magnitude and quality, stresses, power densities and construction status will be presented for these various systems.

Conceptual design of high transverse field magnets at the NHMFL

The National High Magnetic Field Laboratory in Tallahassee, FL, USA, is designing a high field magnet for condensed matter physics with the field perpendicular to the access tube. The traditional approach to such magnets is to build a split pair of solenoids. Various novel alternate approaches have been examined and compared with split pairs. A particularly attractive option consists of concentric nested Bitter coils tilted 45 degrees to the axis. By energizing the coils in opposition, the axial components of field from the various coils can be made to cancel resulting in a purely transverse field. Preliminary designs including field, power and stress estimates are presented.

Modeling of electromagnetic and thermal diffusion in a large pure aluminum stabilized superconductor under quench

Low temperature composite superconductors stabilized with extra large cross-section pure aluminum are currently in use for the Large Helical Device in Japan, modern big detectors such as ATLAS at CERN, and other large magnets. In these types of magnet systems, the rated average current density is not high and the peak field in a region of interest is about 2-4 T. Aluminum stabilized superconductors result in high stability margins and relatively long quench times. Appropriate quench analyses, both for longitudinal and transverse propagation, have to take into account a rather slow diffusion of current from the superconductor into the thick aluminum stabilizer. An exact approach to modeling of the current diffusion would be based on directly solving the Maxwells equations in parallel with thermal diffusion and conduction relations. However, from a practical point of view, such an approach should be extremely time consuming due to obvious restrictions of computation capacity. At the same time, there exist certain ways that simplify mathematical models for the thermal and electromagnetic diffusion processes for the purpose of rapidly calculating the propagation velocity and effective simulating of quench behavior. These models explained here were tested and applied to quench simulation in the above-mentioned magnet systems.

Development and Testing of Electrical Joints for the 36-T Series-Connected Hybrid Magnet

Here, we report the development of the CICC joint design for the 36-T Series-Connected Hybrid Magnet. A novel solder-less single-box praying-hands joint has been designed to meet the mission of the SCH. A prototype sample joint, Florida Solder-less Joint A (FSJ-A), was manufactured and tested. The low DC resistance confirmed the feasibility of the concept design. In addition, a simple model describing the current transient behavior of the pray-hand joint is presented. A comparison with the experimental data is also included.

Design a Testing of a Repetitively Pulsed Magnet for Neutron Scattering

The National High Magnetic Field Laboratory in Tallahassee, Florida, USA has designed, built and tested a high field, split pair, Repetitively Pulsed Magnet (RPM) suitable for neutron scattering experiments. RPM magnets have the advantage of lower average power and lower construction costs than DC magnets. The NHMFL RPM program intends to build magnets with higher field and larger scattering space than those available elsewhere. Details of design and testing of the first prototype are presented

Superconducting solenoids for the muon collider

The muon collider is a new idea for lepton colliders. The ultimate energy of an electron ring is limited by synchrotron radiation. Muons, which have a rest mass that is 200 times that of an electron can be stores at much higher energies before synchrotron radiation limits ring performance. The problem with muons is their short life time (2.1 /spl mu/s at rest). In order to operate a muon storage ring large numbers of muons must be collected, cooled and accelerated before they decay to an electron and two neutrinos. As we see it now, high field superconducting solenoids are an integral part of a muon collider muon production and cooling systems. This report will describe the design parameters for superconducting and hybrid solenoids that are used for pion production and collection, RF phase rotations of the pions as they decay into muons and the muon cooling (reduction of the muon emittance) before acceleration.

Magnet system design with cost optimization

The problem of optimizing the design of magnet systems to simultaneously satisfy a set of constraint equations for field, geometry, protection, and stability while minimizing the total system cost is considered. A mathematical description of the problem is given, along with details concerning possible constraint algorithms and cost functions. Rules for the optimal selection of magnet technology (potted, ventilated, and cable-in-conduit coils) are presented. The resulting sets of equations can be solved by different numerical methods; the final choice is based on considerations of functional form as well as computational speed and accuracy. Depending on the choice of constraint equations, the resulting problem may or may not be smooth, and may or may not admit multiple minima. The choice of minimization algorithm can be tailored to the situation at hand to yield optimal performance. We present results pertaining to an alternating-field solenoid system being considered by the MuCool collaboration. The system design requires consideration of field profile, magnet stability, magnet structure, and protection, as well as total cost. A key application of the optimization code is the analysis of cost trade-off with respect to the imposed constraints, and examples are given in the alternating-solenoid case.