B. Lesch’s research while affiliated with Florida State University and other places

The construction techniques for High Performance Pulse Magnets produced at the NHMFL pulse coil winding facility in Tallahassee are described. The mechanical design, parts fabrication and manufacturing of these magnets are discussed. In conclusion, proposed changes made in the construction of the coils after analyzing failure tests carried out at the NHMFL pulsed field facility in Los Alamos are noted.

High performance pulse magnets using the combination of CuNb conductor and Zylon fiber composite reinforcement with bore sizes of 24, 15 and 10 mm have been designed, manufactured and tested to destruction. The magnets successfully reached the peak fields of 64, 70 and 77.8 T respectively with no destruction. Failures occurred near the end flanges at the layer. The magnet design, manufacturing and testing, and the mode of the failure are described and analyzed.

Sandia National Laboratories is investigating and developing high-dose, high-brightness flash radiographic sources. We are in the process of designing; fabricating and conducting engineering tests on the next-generation magnetically immersed electron diodes. These diodes employ unique, large-bore (80-110 mm), high-field (28-45 T), cryogenically-cooled solenoid magnets to help produce an intense electron beam from a needle-like cathode ``immersed'' in the strong Bz field of the magnet. The diode designs and status of the engineering development are described. Later this year we plan to conduct experiments with these sources on the new Radiographic Integrated Test Stand (RITS) [1], now in operation at Sandia. In its present three-stage configuration, RITS provides a 4-MV, 150-kA, 70-ns pulse to the diode. Fully three-dimensional particle in cell LSP code [2] simulations are used to investigate relevant physics issues and the expected radiographic performance (spot size and dose) of this system. Preliminary results from these simulations are described.

A cobalt multiphase alloy, MP35N, is studied as one of the reinforcement materials for pulsed magnets. The mechanical properties of this alloy at room temperature and 77 K are examined. The cold-rolled and aged MP35N produces a hardness of 5650 MPa and yield strength of 2125 MPa at room temperature. At 77 K, the yield strength reached 2500 MPa and the work hardening rate was higher than that at room temperature. The Young's modulus increases about 6% upon cooling from 300 to 5 K. Therefore, the increase of the strength at low temperatures is attributed mainly to the increase of the work hardening rate rather than modulus. The potential for further increasing the strength of this alloy is discussed.

Various tests have been undertaken to study the effects of annealing, testing temperatures and volume fraction of the Cu cladding on the properties of Cu-Nb conductors being developed for pulsed magnet applications. The results demonstrate that short time annealing used for insulation had no significant effect on the tensile property of Cu-Nb conductors. The cryogenic temperatures are beneficial to both the conductivity and mechanical properties of the conductors, especially the tensile strength of the Cu cladding. The wire-drawing fabrications showed that wires of 4 mm×6 mm cross-section-area with a significant volume fraction of Cu cladding could be obtained, leading to final tensile strengths of up to 1100 MPa at room temperature. The strength is increased by about 20% at 77 K. The 77 K-conductivity is about 4.5 times of the room temperature one. The strengthening mechanisms and resistivity variation of the Cu-Nb composite are discussed and it is argued that the distance between the Nb ribbons plays an important role in the variation of these properties.

The design of a new pulsed magnet system for the generation of intense electron beams is presented. Determined by the required magnetic field profile along the axis, the magnet system consists of two coils (Coil 1 and 2) separated by a 32-mm axial gap. Each coil is energized independently. Both coils are internally reinforced with HM Zylon fiber/epoxy composite. Coil 1 made with Al-15 Glidcop wire has a bore of 110-mm diameter and is 200-mm long; it is energized by a 1.3-MJ, 13-kV capacitor bank. The magnetic field at the center of this coil is 30 T. Coil 2 made with CuNb wire has a bore diameter of 45 mm, generates 60 T with a pulse duration of 60 ms, and is powered by a 4.0-MJ, 17.7-kV capacitor bank. We present design criteria, coupling of the magnets, and normal and fault conditions during operation

The effort in materials program related to the first 100 T non destructive (100 T ND) magnet has been concentrated on four areas: (a) development of the fabrication routes for various conductive wires in collaboration with other institutes and industrial partners, (b) investigation of the properties of a variety of candidate high strength high conductivity materials, (c) selection of the reinforcement materials for the coils and development of fabrication routes for these materials, (d) characterization of the commercially available insulation materials. This paper deals with the conductor issues. The properties and the microstructure of Cu-Ag, UNS-C157XX (Cu-Al₂O₃), Cu+Stainless Steels (SS) and Cu-Nb composites have been investigated for their potential use as conductors in pulsed high field magnets. These conductors demonstrate a combination of good conductivity, high strength, adequate workability, and the availability of final section sizes needed for the magnet design. Examination of the initial portion of the stress strain curve of cold worked conductors reveals that the internal stresses developed during the fabrication influence the mechanical response of the materials. Thus, the properties of the drawn materials have been measured as a function of cyclic loading and thermal annealing cycles, and the cyclic properties are related to the internal stresses

The first 100 T non-destructive (100 T ND) magnet and power supplies as currently designed are described. This magnet will be installed as part of the user facility research equipment at the National High Magnetic Field Laboratory (NHMFL) Pulsed Field Facility at Los Alamos National Laboratory. The 100 T ND magnet will provide a 100 T pulsed field of 5 ms duration (above 90% of full field) in a 15 mm diameter bore once per hour. Magnet operation will be nondestructive. The magnet will consist of a controlled power outer coil set which produces a 47 T platform field in a 225 mm diameter bore. Located within the outer coil set will be a 220 mm outer diameter capacitor powered insert coil. Using inertial energy storage a synchronous motor/generator will provide AC power to a set of seven AC-DC converters rated at 64 MW/80 MVA each. These converters will energize three independent coil circuits to create 170 MJ of field energy in the outer coil set at the platform field of 47 T. The insert will then be energized to produce the balance of the 100 T peak field using a 2.3 MJ, 18 kV (charged to 15 kV), 14.4 mF capacitor bank controlled with solid-state switches. The magnet will be the first of its kind and the first non-destructive, reusable 100 T pulsed magnet. The operation of the magnet will be described along with special features of its design and construction

The use of internal reinforcement in pulse magnets has been proven to be an efficient way to obtain reliably very high magnetic fields. An optimum design should be such that both the reinforcement and the conductor reach their failure criteria simultaneously. This requires the mechanical properties of the reinforcement to match those of the conductor under all operating conditions. The decision criterions for the selection of the internal reinforcement materials for different conductors are presented and discussed. Several pulsed magnets with high strength conductors and internal reinforcement with high modulus materials have been designed, fabricated and tested. The performance of these magnets is presented and discussed

The design of the capacitor bank driven insert of the first 100 T non-destructive magnet is described. The coil is wound with 8 conductor layers, and is internally reinforced with the multiphase alloy MP35N^TM in combination with a Zylon^TM fiber/epoxy composite. The deformation of the conductor is limited by the high modulus reinforcements, therefore, the coil will operate in the elastic state after conditioning. This ensures long magnet life. The insert coil will be energized by a 2.3 MJ, 18 kV capacitor bank operating at 15 kV. The mechanical deformation, heating and the magnetic field reduction due to the eddy currents in the MP35N^TM reinforcement are analyzed