Cryogenic properties of inorganic insulation materials for ITER magnets:

Abstract

Results of a literature search on the cryogenic properties of candidate inorganic insulators for the ITER'*' TF* magnets are reported. The materials investigated include: AI 2 O 3 , AlN, MgO, porcelain, Si 02 , MgAl 20^, Zr 02 , and mica. A graphical presentation is given of mechanical, elastic, electrical, and thermal properties between 4 and 300 K. A companion report* reviews the low temperature irradiation resistance of these materials.Key words: cryogenic properties, electrical properties, inorganic insulation, ITER magnets, mechanical properties, thermal properties FOREWORD For insulator downselection and design, data are required on the 4-K compressive and shear strengths and the electrical breakdown strength. However, for most of these inorganic insulators, very few measurements of these and other 4-K properties were retrieved in the literature search, with the notable exception of thermal properties, which have been adequately measured for most of the candidate insulators. Using existing bibliographic data bases to locate cryogenic data is difficult, owing to the inadequate indexing of the data bases and the circumstance that much basic cryogenic information predates 'Materials Reliability Division, Materials Science and Engineering Laboratory. Technology, Boulder, CO. 430 pp iii the effective date of the databases. Therefore, additional "manual" searching was done, often with excellent yields, to supplement the on-line retrieval systems.However, these procedures are extremely time-consuming. Concept sketch of the TF magnet shear plates and conductor-incable configuration:"solid" rib option.From Reed [1993] 3 Figure 1.0.2. Concept sketch of the TF magnet shear plates and conductor-incable configuration:"bonded" rib option.From Reed [1993] 4Figure 1.1.1. Dependence of the compressive strength upon grain size for AI2O3. Data from Rice [1971] Dependence of the compressive strength upon the percent porosity for quartz ceramic. Data from Borodai and Suzdal 'tsev [1975] Dependence of the compressive strength upon the percent porosity.The curves depict two theoretical predictions. Data from Nielsen Effective fracture energy is proportional to the square of the fracture stress at constant initial crack length.Data from Fetch [1971] 12Figure 1.1.6. Effect of hydrostatic pressure on the compressive strength of AI2O3 , AIN, and MgO.Data from Heard and Cline [1980] 16 Chamber for dielectric breakdown measurements in an electron beam.From Goland [1978] 28 Figure 1.3.3. Dependence of electrical breakdown strength upon specimen thickness for several forms of AI2O3. Data from Morse and Hill [1970] 29 Comparison of thermal expansion coefficients of several alumina ceramics.Data from Burk [1962] ..,.51 Compressive strength of quartz at 77 and 513 K. Data from Charles [1959] ....90 Breaking strength of unabraded glass specimens at 76 and 296 K at 5.5 MPa/s stress increase. Data from Kropschot and Mikesell [1960] 92Figure 6.1.5.Breaking strength of abraded glass specimens at 296 K at 5.5MPa/s str...