Hideshige Moriyama

Effect of epoxy cracking resistance on the stability of impregnated superconducting solenoids

The stability and quench positions of superconducting test solenoids impregnated with three types of epoxy resin, with different crack resistances, have been studied. Voltage signals and acoustic emission (AE) were monitored during training tests. Premature quenches in the solenoids almost occurred at the innermost layer of windings; voltage spikes and AE appeared just prior to the premature quench initiation. This suggested that premature quenches were due to friction or debonding between ground insulation and winding. The solenoid with a release film between ground insulation and winding showed high stability and reached critical current at the second charging. From the results, the effects of epoxy cracking resistance on the stability of impregnated superconducting test solenoids are discussed.

Several Properties of Impregnating Epoxy Resins Used for Superconducting Coils

In order to find the most appropriate vacuum-pressure impregnating epoxy resin for superconducting coils, three types of epoxy resin were experimentally investigated from various points of view. Those epoxy resins were amine curing type A, anhydride curing type B with tertiary amine accelerator, and anhydride curing type C without accelerator.

Effect of ground insulation contact on stability of epoxy-impregnated superconducting solenoids

To clarify the effect of ground insulation contact on the stability of epoxy-impregnated superconducting solenoids, test coils with ground insulation between a winding and a metal former were fabricated. Aluminium and stainless steel were used as the former materials. The training effects of coils and the circumferential strains of former inner surfaces were measured. The training effects of aluminium former coils were larger than those of the stainless steel former coils. The strains of stainless steel formers became greater as the exciting current increased, but the strains of the aluminium formers did not change. These results show that the insulation of aluminium former coils became a floating state, the insulation of stainless steel former coils maintained a pressed state, and the floating state caused the large training effects.

Design and fabrication of highly stabilized close-packed superconducting solenoid

The highly stabilized superconducting solenoid has been fabricated successfully by the dry winding method with the appropriate design of former and ground insulators. In this work the unexpected decrease of quench current was remarked as the index of the instability in the superconducting solenoids because it becomes a serious problem in practical application. The change of the contact condition between the former and the winding was thought to induce the instability therefore the optimization of the contact condition was tried. The former with high thermal contraction and high rigidity and the ground insulator coated with the release film were selected for the solenoid design. It was found that the highly stable superconducting solenoids could be designed and fabricated by this selection.

Rearrangement of Superconducting Wires in Solenoidal Magnets

The strain behavior of the superconducting solenoidal coil form has a close relationship with the training behavior of the quench current. This relationship can not be explained by means of models of wire motion, friction and resin cracking, which are known as mechanical disturbances, as the cause of quench. Therefore, a wire rearrangement model was proposed, where the accumulation of the microscopic displacements of the multiple turns of superconducting wire manifests itself in the strain behavior of the form. Based on this model, the strain energy of superconducting wire released by rearranging the turns was investigated theoretically and experimentally. As a result it was confirmed that the released energy exceeds the minimum quench energy, MQE, resulting in the instability of a sample coil. From this result, it is expected that the wire rearrangement model is useful for estimating the stability.

Mechanical and thermal properties of self-bonded superconducting winding

The stability of self-bonded superconducting solenoids has been studied by investigating the mechanical and thermal properties of self-bonded superconducting windings. An adhesive-bonded superconducting solenoid can be fabricated by winding superconducting wire coated with self-bonding resin and by heating the winding. Although the interlaminar shear strength of the self-bonded winding was lower than that of the impregnated one, the self-bonded winding also exhibited high compressive modulus and slightly lower thermal contraction. It could be, therefore, assumed that the instability caused by friction between the winding and the former could be repressed. This was confirmed experimentally, that is, the high stability self-bonded test coils which did not show training were successfully constructed.