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Thermal Event Monitoring from Electromagnetic Field Systems
Superconducting magnets and inductors are capable of generating high magnetic fields and thereby storing large amounts of energy. Every superconducting material has a critical temperature Tc for a given ambient magnetic field above which the material is no longer superconducting. If a region of a superconducting conductor loses its superconducting property (i.e., becomes normal or quenches) while current is flowing in the conductor, joule heating occurs in the normal or nonsuperconducting region. If the region is small enough, the small amount of heat will be dissipated and the region will return to its superconducting state. If not, large amount of joule heating could overcome the system's ability to dissipate the heat, the normal zone will propagate and grow larger, causing a catastrophic condition which can result in severe damage to the inductor or magnet, as even more energy is dissipated in portions of the inductor or magnet. Quenching effect of the superconducting phase to normal phase transition can be detected by thermal detection. The great challenge lies in using a conventional thermocouple for measuring hot spots from magnetic coils. In fact, for such applications any electronic sensing device would suffer from interference noise so that any detection device must be completely nonmagnetic. Fiber sensor is entirely nonmetallic dielectric material (silicon dioxide), which could be used for quenching effect and hotspot detection with axial thermal profile sensor for dynamic thermal event monitoring and detection. The fiber sensing cable could use Teflon and PTFE nonmetallic material as sheath for protection. The dynamic thermal signal will include “dynamic temperature”, “averaged coil temperature: “localized coil temperature”, and whole “magnet coil thermal trend” analyses etc.
Similar to MRI high-magnetic coil situation, there are many other applications from CT, x-ray and high-energy detector development, radioactive therapy dosage control, and microwave-assisted coal gasificaiton. Dynamic thermal profile detection will provide real-time transient event monitoring. In addition, utilizing a probe package of the fiber bundle based displacement sensor can be used for high magnetic field of >10T displacement detection from a superconducting magnets. In general, fiber optical based temperature, strain, vibration, and displacement sensors have demonstrated to be a desirable measurement technique to avoid electromagnetic interference issue. AtGrating could provide very dynamic thermal event monitoring with 250Hz to 5kHz thermal response rate under high-magnetic field condition.
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