Previous work, reported at last year's meeting, has been continued. One model section of an SSC outer coil has had it's stress relaxation measured for nearly two years. In addition, the stress relaxation of SSC cable without insulation has been measured. Kapton insulation alone has been studied both in creep and stress relaxation. Creep has been measured parallel to the plane of the film. These measurements are dependent on internal stresses that may be present in the film and on the moisture content of the film. They indicate that any measurements of coil relaxation are not likely to be repeatable if these factors are not controlled. The measurements on Kapton film alone are being done at different temperatures to obtain a time-temperature shift factor so that measurements at one temperature may be used to predict relaxation at any other temperature.

We aremeasuringthestress relaxation ofSSC 50mm outercoils withthe goalof predicting how much ofthe coil prestress willbe lostwhilethe coils are warehoused between manufactureand cooldown. We manufacture3 inch(76.2mm)longsegmentsofcoil with the same materials and techniques thathave been used forprototype coils. We are running foursimultaneous testsin an attempt to separatethe contributions of the different coil materials. Test one is a completelyinsulatedcoilsectionwhere the insulation istheallpolyimide systembeingtested at Brookhaven; test two isa wirestackinsulated onlywith thenormal Kapton overwrap;testthreeisa stackof bare cable;and testfouris a completelyinsulatednormal coil section. All,exceptforthe bare cable, includethe ground insulation. The insulated coil sections are carefully driedbeforeloadingand testing in order to eliminate stress changes due to varying moisture content. The temperaturedependenceofthe stress relaxation isbeingstudiedseparately. Three companion papers presented at this conference will be: 1)"Temperature dependence of the viscoelastic propertiesof SSC coil insulation" 2)"Measurement oftheelastic modulus ofKapton perpendicular tothe planeofthe filmat room and cryogenic temperatures" 3) "Theoretical methods forcreepand stress relaxation studies ofSSC coil."

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In order to simulate the effect of accidentally introduced debris on SSC coil insulation integrity, models consisting of two pieces of insulated SSC cable have been loaded in an hydraulic press after introducing foreign particles between the layers. The tests were originally suggested by R. Palmer of the SSC Laboratory. A high voltage (2 Kv) was continually applied between the two cables and the load gradually increased until an electrical short occurred. The high voltage was used as an easy method of detecting insulation punctures and to continue the general type of testing begun at Brookhaven by J. Skaritka, now at the SSC Laboratory, and continued at Fermilab by F. Markley and presented at last year's session of the Conference. A range of particles of different size, shape, and hardness were used, and both conducting and insulating particles were included. Fine wires were also used.When the data are normalized using the control (no particles added), data for each cable batch used, there is a slight correlation between pressure at breakdown and particle size for cables insulated with Kapton only. Adjustment must be made for soft particles that tend to deform and for particles with aspect ratios greater than one. Additional measurements have also been made where the epoxy-fiberglass layer was added to the Kapton insulation overwrap. These show a correlation between conductivity and breakdown pressure.

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