In the superconducting magnetic *** vibration excitation or work process, the superconductor for some reason suddenly lose superconducting properties and enter the normal state of the process. Because the superconductor is working under extremely high current density, need to be in a low temperature environment, this time the temperature rises sharply, the liquid helium volatilization, the magnetic field strength drops rapidly, that is, the loss of super.
The temperature of liquid helium rises rapidly when a loss of super occurs. It is easy to understand that the liquid helium changes from a liquid to a gas and expands rapidly, which can cause great harm to the patient if it is not properly discharged from the scanning room. The so-called loss-of-ultrasound tube is the tube that delivers the helium quickly and appropriately to the proper location in the event of a loss-of-ultrasound.
Extended information:
The half hour after the loss of an ultrasound is the time it takes for the tube to deliver helium quickly and properly. p>The half hour after the loss of super is very critical and is related to the time and workload to recover the magnet. In case of magnet loss of super, need the hospital's engineers the first time to replace the loss of super tube outlet bursting film, so that the magnet isolation of air, to achieve the purpose of protecting the magnet, and immediately contact Philips engineers rushed to the scene to do further processing.
There are many factors that can cause a loss of super: magnet structure and coil, superconducting material performance is not stable, the magnet ultra-low temperature environment is damaged, and human factors, etc. There are usually the following five categories:
The first category: excitation magnetization current exceeds the rated value, or the magnetization current increases too fast, will lead to the superconducting coils as a whole is subjected to the radial and axial electromagnetic extrusion pressure, so that the epoxy resin impregnated in the The epoxy resin impregnated between the coil windings will crack locally, and the release of this deformation energy will be converted into heat, which will lead to the loss of superconductivity;
The second category is: filling liquid helium too fast and inserting the infusion tube into the magnet's infusion hole when it is not yet cooled down to a temperature of 4.2K, which will lead to the liquid helium inside the Dewar container boiling, vaporizing and erupting out quickly, resulting in the superconducting environment being destroyed, and thus leading to the loss of superconductivity;
The third category: the liquid helium level in the magnet's Dewar container drops to a certain limit (the low limit of liquid helium capacity varies from manufacturer to manufacturer, but the general limit is 30% of full capacity), if it is not replenished in time according to the regulations, it will lead to failure of superconductivity;
The fourth category: the vacuum environment of the magnet's vacuum isolation layer will be destroyed, and then the failure of superconductivity will be certain;
The fifth category: the emergency failure switch is misused, which will lead to the destruction of superconductivity environment. : Misoperation of the emergency loss of ultra-switch caused by "accidental" loss of ultra-switch.