In recent years, CTD has pioneered the development of radiation-resistant, cyanate ester-based resins suitable for insulating superconducting and normal magnets for fusion energy applications. These materials have been shown to exhibit very good radiation resistance, excellent mechanical properties, and good processing characteristics. More recently, a cyanate ester/epoxy formulation was qualified for use in constructing the ITER Toroidal Field coils. This product, designated CTD-425, has also been selected for use in upgrading the center stack for the National Spherical Torus Experiment (NSTX), in building the correction magnets for the Wendelstein 7-X stellarator in Germany, and is under consideration for use in the upgrade to MAST being constructed in the UK. CTD has worked closely with the Princeton Plasma Physics Laboratory and others to qualify the CTD-425 for these new applications. This paper will discuss the test methods and test philosophy used to qualify CTD-425 for use in NSTX and how this qualification procedure can be useful for future fusion and other magnet systems.

The U.S. Department of Energy is leading the development of alternative energy sources that will ensure the long-term energy independence of our nation. One of the key renewable resources currently being advanced is geothermal energy. To tap into the large potential offered by generating power from the heat of the earth, and for geothermal energy to be more widely used, it will be necessary to drill deeper wells to reach the hot, dry rock located up to 10 km beneath the earth’s surface. In this instance, water will be introduced into the well to create a geothermal reservoir. A geothermal well produced in this manner is referred to as an enhanced geothermal system (EGS). EGS reservoirs are typically at depths of 3 to 10 km, and the temperatures at these depths have become a limiting factor in the application of existing downhole technologies. These high temperatures are especially problematic for electronic systems such as downhole data-logging tools, which are used to map and characterize the fractures and high-permeability regions in underground formations. Information provided by these tools is assessed so that underground formations capable of providing geothermal energy can be identified, and the subsequent drilling operations can be accurately directed to those locations. The mapping of geothermal resources involves the design and fabrication of sensor packages, including the electronic control modules, to quantify downhole conditions (300°C temperature, high pressure, seismic activity, etc.). Because of the extreme depths at which these measurements are performed, it is most desirable to perform the sensor signal processing downhole and then transmit the information to the surface. This approach necessitates the use of high-temperature electronics that can operate in the downhole environment. Downhole signal processing in EGS wells will require the development and demonstration of circuit boards that can withstand the elevated temperatures found at these depths. At present, the highest-temperature commercially available circuit boards are based on polyimide materials, and those have maximum use temperatures of 200 to 250°C. In addition to thermal stability, downhole electronics must also be fabricated into high-aspect-ratio packages. For example, the multilayer assemblies produced at SNL were approximately 2.5 cm wide and 50 cm long. Because of this very high form factor, glass-fiber-reinforced polymers are much more desirable than multilayer ceramic modules (MCM). MCMs have many advantages for some applications, but are susceptible to damage induced by the mechanical and vibrational loads commonly experienced by data-logging tools. Thus, as EGS technology continues to advance, there is a strong need for multilayer electronics that can provide the necessary thermal performance while also being compatible with high-form-factor circuit designs. This project involved the design and development of high-temperature circuit materials, as well as the fabrication and testing of circuit components. The material development included the evaluation of various polymer/fiberglass composites, whereas the circuit components were tested using conventional microelectronic evaluation techniques. This effort targeted development of a new class of high-temperature multilayer circuit boards for use in downhole data-logging applications where temperatures are on the order of 300°C. This is consistent with DOE’s multiyear plan for advancing technologies for use in enhanced geothermal systems. Organic and inorganic polymer systems, both with glass reinforcements, were considered to provide the following performance at elevated temperatures: • Mechanical strength and durability • High dielectric strength and electrical resistivity • Thermal stability • Strong adhesion to copper to ensure the reliability of the multilayer assemblies • Processing characteristics that are consistent with state-of-the-art multilayer circuit board manufacturing practices

The Toroidal Field (TF) coils for the ITER device will represent the largest superconducting magnet system assembled to date, and thus creates several challenges related to the manufacture of these magnets. Most notably, the electrical insulation for the TF coils must address four simultaneous constraints: high radiation, large mechanical stresses, high voltage operation, and operation in a vacuum. In addition, these materials must meet all shipping and local environmental regulations for use in large quantities in both Europe and Japan. The TF coil insulation will undergo fast neutron fluences up to 3.2 × 1021 n/m2, which is equivalent to 10 MGy, and still be able to withstand the estimated operation in-plane shear stress in the range of 45 MPa. To address this need, CTD has developed and qualified two epoxy/cyanate ester resin systems, CTD-425 and CTD-435. These materials meet the processing requirements, mechanical strength after 30 000 load cycles, and radiation exposure specifications established by ITER IO. Both materials are qualified for use in constructing the ITER TF coils, and are supplied to European and Japanese customers by Lord Corporation. This paper summarizes the performance characterization, qualification tests, and supply chain for these materials.

The U. S. Department of Energy (DOE) is participating in a series of high-energy physics projects that require the use of high-field superconducting magnets that operate in high radiation environments. For high-energy physics accelerators, the superconducting magnets represent the largest (in size, volume, mass, and cost) subsystem of the machine. Technologies that can advance the performance of these machines, reduce the size, improve the reliability, reduce the manufacturing risk, and reduce the cost of these devices are of critical need. Electrical insulation is one of the smaller subsystems in a magnet, yet is critical to the successful operation, reliability, and longevity of magnets. Electrical insulation with improved radiation performance, mechanical strength, thermal properties (including thermal conductivity), and high dielectric strength will allow a minimal thickness of insulation to be applied and thus increase the effective current density within the coil. Insulation performance goals for future accelerator magnets include radiation resistance at doses up to 200 MGy, compressive strengths up to 200 MPa, and improved heat transfer from the conductor and through the insulation. This paper will discuss approaches proposed by Composite Technology Development, Inc. to achieve these insulation goals.

This chapter contains sections titled: Introduction Experimental Approach Theoretical Approach Results and Discussion Future Work Conclusions Acknowledgements

Geothermal energy is a key renewable source of energy, which unlike wind and solar power, is not affected by changing weather and is always available to meet power demands. For geothermal energy to be widely utilized, deeper wells to reach hot, dry rock, located beneath the Earth's surface are required. Water will be introduced to create a geothermal reservoir, or an Enhanced Geothermal System (EGS). EGS reservoirs are at depths of up to 10 km, and the temperatures at these depths are limiting the use of available downhole equipment. Downhole submersible pumps are a key component for large-scale power generation from geothermal resources. Both Hydrothermal and Enhanced Geothermal Systems require a robust serviceable pump capable of bringing heat to the surface. The critical attributes of such a pump are temperature tolerance and low service needs. Development of geothermal will depend on the flow of high temperature resources. At that point, reliability and robustness will be key operating features. Existing pumps are limited to 190 degrees C, preventing high value hydrothermal resources in the 190 to 220 degrees C range from being developed. Novel high-temperature composite materials are being developed and demonstrated for use in new ESPs that can meet the challenging demands of EGS wells and can accelerate the exploitation of this large renewable source of energy.

The design of the ITER Toroidal Field (TF) coils requires an insulation system that is amenable to the very large scale vacuum impregnation processes planned for the construction of these devices, and that will provide reliable electro-mechanical performance after radiation exposure. To address this need, CTD has developed an epoxy/cyanate ester resin system designated CTD-425. This material meets the processing requirements for use in the TF coils, and cyclic mechanical testing of conductor assemblies has demonstrated its electro-mechanical strength after 60,000 mechanical cycles. In addition, this product recently passed radiation exposure tests coordinated by the ITER International Organization and is now qualified for use in constructing the TF coils. This paper summarizes the performance characterization and qualification test results for this insulation.

As HTS wire technology continues to advance, a critical need has emerged for dielectric materials that can be used in superconducting components such as terminations, fault current limiters, transformers, and motors. To address this need, CTD is developing nanocomposite insulations based on epoxy and benzoxazine chemistries. Depending on part geometry, some processing methods are more efficient than others. For this reason, CTD is investigating both fiber-reinforced and filled resin systems for use in these applications. A thorough set of electrical testing including AC breakdown, breakdown as a function of thickness, and flashover shows promising performance characteristics. In addition, mechanical testing (short beam shear and compression) indicate that these new materials to have as good or better performance than G10.

The fusion devices currently being developed present several challenges for magnet designers. One challenge lies within the electrical insulation, which must be able to withstand extreme temperatures, large shear and compressive stresses, high operating voltages, and high levels of incident radiation. To address the need for better performing insulation systems, Composite Technology Development (CTD), Inc. has developed CTD-403, a cyanate ester resin with increased radiation resistance, ease of processing and fabrication, low moisture absorption characteristics, and high mechanical and electrical strength at cryogenic and elevated temperatures. The moisture absorption trends of CTD-403/S2 glass composite insulation were studied. The effects of humidity exposure on interlaminar shear strength (ILSS), compressive strength, dielectric strength, and glass transition temperature were also studied. The saturation level of the insulation was seen to increase with the relative humidity of the aging environment. Fickian behavior was seen at room temperatures below 97% relative humidity exposure. Non-Fickian behavior was seen at elevated temperatures. Saturation levels after 6 months exposure were seen to be below typical epoxy-based insulation systems, averaging 0.5% weight gain. Degradation of mechanical and electrical properties was seen with increased humidity exposure and moisture absorption. ILSS showed an average retention rate of 75% after 6 months exposure. The compressive strength showed no decrease after 6 months exposure at room temperature, and show retention rates greater than 90% at 75°C/79% RH. An average dielectric strength of 98.6 kV/mm was seen for all specimens at room temperature (above 90% retention) after 6 months exposure.

The cyanate ester polymer, CTD 403, is being considered for use as an insulation material in future fusion devices. In this study, the moisture resistance of neat polymer, glass fiber/CTD 403 and copper foil/CTD 403 was studied. The results show that while prolonged exposure to moisture cause property degradation, however, most of the property loss is recovered after drying the specimens.

Future magnet systems require electrical insulation that can withstand high levels of incident radiation, while also providing the necessary mechanical robustness and dielectric strength to operate these devices. Moreover, the insulation must also be compatible with industrial fabrication processes to enable their efficient, large-scale manufacture. Cyanate ester-based insulations provide the necessary electro-mechanical performance and radiation resistance for these applications, but more information is needed to demonstrate application-specific issues related to magnet production. To accomplish this, a series of tests were performed to validate the long-term processing behavior of cyanate ester resins, their adhesion to Kapton, and the fabrication of small-scale coils. The results of this work demonstrated a working time of greater than 85 hours, good adhesion to Kapton, and the successful fabrication of test coils. Larger-scale industrial trials are ongoing at various sites to further demonstrate the use of cyanate ester insulation for the ITER TF coils, as well as commercial applications.

Wind‐and‐react processes offer a cost‐effective means of fabricating large‐scale Nb3Sn magnets, while also eliminating the need to manipulate the brittle superconductor after the high‐temperature reaction process. Composite Technology Development, Inc. (CTD) has developed a hybrid inorganic/organic insulation system that can be co‐processed with the Nb3Sn magnet at elevated temperatures. In this work, a new process was demonstrated for applying a thin, ceramic‐based insulation that is compatible with wind‐and‐react processing. The insulation was applied to Rutherford cables using a continuous manufacturing process, and cable assemblies (i.e., 10‐stacks) were fabricated and tested. The results of this work show that the insulation possesses a high strain tolerance, as well as the dielectric strength and fatigue resistance needed for high‐field magnet applications.

The adhesive shear strengths of copper/insulation interfaces were evaluated using a novel specimen design in which thin copper foils were embedded in laminate structures. In each instance, the copper surface was either chemically or physically treated prior to laminate fabrication. Once produced, the specimens were subjected to in-core reactor irradiations providing total radiation doses of 10, 22, and 100 MGy with a gamma/neutron ratio representative of conditions in fusion systems. Post-irradiation short-beam-shear tests indicate that the best-performing copper treatments retain 65-70% of their original interfacial shear strength at 76 K after receiving a total dose of 100 MGy. Previous findings showed that the initial adhesive strength could be improved through the use of copper surface treatments, and these results confirm that the copper/insulation interface remains strong after exposure to high-radiation environments.

The wind-and-react production of complex Nb3Sn magnets requires that the coils be wound using un-reacted conductor materials, which are then reacted at 600 to 700degC to produce the superconducting phase. Application of the electrical insulation prior to the heat treatment enables more efficient construction of these magnets and minimizes handling of the strain-sensitive superconductor. Ceramic-based composite insulation materials have been successfully used to produce Nb3Sn magnets via a wind-and-react process. In this work, the mechanical and thermal properties of lower-cost ceramic insulation materials are reported. This insulation provides the compression and shear strengths needed for magnet applications, and offers increased stiffness and thermal conductivity as compared to S2-glass-reinforced polymers.

Future magnet designs for fusion devices and particle accelerators will require cost-effective, radiation-resistant materials. The use of hybrid inorganic/organic composite insulation systems will improve the lifetime, reliability, and performance of these systems. Previously, Composite Technology Development, Inc. (CTD) developed a highly-radiation-resistant, hybrid inorganic/organic insulation system, CTD-1012PX, which can be co-processed with the magnet's Nb3Sn superconductor. This process allows the coil to be wound and insulated prior to heat treatment. However, the cost of the CTD-1012PX insulation system is generally higher than organic insulations due to the higher prices of the ceramic fibers and ceramic-matrix precursor materials. Recently, CTD demonstrated the potential for significantly reducing the cost of hybrid ceramic/organic insulation through the development of a lower-cost inorganic-matrix system and the use of lower-cost reinforcement fibers. Without accounting for the cost of a yet-to-be-developed fiber/matrix interface material, the new insulation system costs approximately 16 percent of the currently used CTD-1012PX system. This paper summarizes an on-going effort to develop this new low-cost, hybrid inorganic/organic insulation system. The options evaluated for cost reduction, as well as mechanical test results showing the effects of these changes on the properties of the insulation system, are presented..

Magnet insulation materials in many Next-Step Option fusion research devices will be subjected to high shear stresses at both cryogenic and elevated temperatures. The low shear strength and poor adhesion of the insulation to copper conductors can be limiting design factors in these systems. While cyanate ester resins have been shown to provide the necessary electrical and mechanical properties for fusion magnet insulation applications, the adhesion of the resin to copper at temperatures ranging from 77 to 373 K is a critical aspect of long-term operational performance. This work compares the shear strengths of copper/cyanate-ester-insulation interfaces prepared using various copper surface treatments, including grit blasting, alkaline cleaners, oxidizers, and primers. The shear strengths of the copper/cyanate-ester-insulation interface were measured using a novel specimen design in which thin copper foils were treated and embedded in laminate structures. Short-beam-shear tests were conducted at 76, 293, and 373 K to assess the performance of the various surface treatments. The results of this investigation indicate that the adhesive shear strengths of copper/cyanate-ester-insulation interfaces can be improved by as much as 50% by treating the copper surfaces prior to impregnation with the cyanate ester resin.

Inorganic (ceramic) insulation materials are known to have good radiation resistance and desirable electrical and mechanical properties at cryogenic and elevated temperatures. In addition, ceramic materials can withstand the high-temperature reaction cycle used with Nb3Sn superconductor materials, allowing the insulation to be co-processed with the superconductor in a wind-and-react fabrication process. A critical aspect in the manufacture of ceramic-based insulation systems is the deposition of suitable fiber-coating materials that prevent chemical reaction of the fiber and matrix materials, and thus provide a compliant interface between the fiber and matrix, which minimizes the impact of brittle failure of the ceramic matrix. Ceramic insulation produced with CTD-FI-202 fiber interfaces have been found to exhibit very high shear and compressive strengths. However, this material is costly to produce. Thus, the goal of the present work is to evaluate alternative, lower-cost materials and processes. A variety of oxide and polyimide coatings were evaluated, and one commercially available polyimide coating has been shown to provide some improvement as compared to uncoated and de-sized S2 glass.

An aging study was performed to determine the stability of YBa sub 2 Cu sub 3 O sub 7 - x ceramics in humid environments at 20 degrees C. In this study, fired ceramic specimens were exposed to humidity levels ranging from 30.5 to 100 percent for 2-, 4-, and 6-week time intervals. After storage under these conditions, the specimens were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and electrical resistance measurements. At every storage condition evaluated, the fired ceramics were found to interact with H sub 2 O present in the surrounding environment, resulting in the decomposition of the YBa sub 2 Cu sub 3 O sub 7 - x phase. XRD data showed that BaCO sub 3, CuO, and Y sub 2 BaCuO sub 5 were present after aging and that the peak intensities of these impurity phases increased both with increasing humidity level and with increasing time of exposure. Additionally, SEM analyses of the ceramic microstructures after aging revealed the development of needle-like crystallites along the surface of the test specimens after aging. Furthermore, the superconducting transition temperature T sub c was found to decrease both with increasing humidity level and with increasing time of exposure. All the specimens aged at 30.5, 66, and 81 percent relative humidity exhibited superconducting transitions above 80 K, although these values were reduced by the exposure to the test conditions. Conversely, the specimens stored in direct contact with water (100 percent relative humidity) exhibited no superconducting transitions.