No-insulation (NI) high temperature superconducting (HTS) coils possess much higher thermal stability than similar traditionally insulated HTS coils. Some NI coils are self-protecting in the sense that they fully recover after a quench without any external protection mechanism to dissipate the stored energy. The underlying mechanisms that make NI coils highly stable or even self-protecting, however, remain unclear. To answer this question, a numerical multiphysics quench model for NI pancake coils is built to study the electrical, thermal and magnetic behavior of NI coils subjected to local heat disturbances. The multiphysics model is built from an electric network model, tightly coupled to a two-dimensional thermal coil model and a three-dimensional magnetic field coil model. The results show that when heat disturbance initiates a local normal region on a turn, the transport current is redistributed not only from the local normal region, but also along the entire turn. The redistributed current flows in the form of radial current across the turn-to-turn contact resistance along the entire turn to the neighboring turns which are still in the superconducting state, driving these turns to an overcurrent state. This full-turn current sharing and overcurrent operation accelerate the redistribution of current away from the hot-spot, reducing localized Joule heating that would otherwise cause a sustainable quench. The results also show that the magnetic field generated at the coil center drops rapidly and the coil voltage changes dynamically during the early stage of normal zone formation. These phenomena can be utilized as effective methods for quench detection in NI coils by monitoring the magnetic field and coil voltage.

The objectives of this research were to evaluate the anaerobic biodegradability of benzene, toluene, ethylbenzene, xylenes, phenol and p-cresol by microorganisms present in decomposing refuse and to study the effects of environmental conditions, pertinent to landfills, on the anaerobic degradation of phenol and p-cresol by refuse derived microbial consortia. Microbial inocula were derived from refuse from both landfills and laboratory reactors. While toluene biodegradation was only measured with one inoculum, broad degradation for phenol and p-cresol was measured. Cultures enriched on refuse were then derived from two samples to evaluate conservation of degradative activity against phenol. In one enrichment, phenol degrading activity was maintained after 6 months, while this activity decreased in a second culture. Phenol and p-cresol enrichment cultures also exhibited activity against other hydroxyl-substituted aromatics but not mono-chlorinated phenols. Cellulosic carbon and soluble trace constituents extracted from fresh refuse stimulated phenol degradation with one enrichment. However, the cellulosic carbon was inhibitory to the other phenol and p-cresol enrichment cultures. The pH optima for all cultures were between 6.5 and 7.0. Finally, a high concentration of acetate prevented the efficient removal of benzoate and consequently inhibited phenol degradation. Landfills were shown to be a habitat harboring anaerobic microbial populations capable of degrading toluene and hydroxyl-substituted aromatics, suggesting that contaminant degradation may be maximized with proper landfill management. z 1998 Federation of European Microbiological Societies. Published by Elsevier Science B.V.