When quench occurs, the temperature of liquid helium will rise rapidly. It is easy to understand that liquid helium changes from liquid to gas at this time, and its volume will expand rapidly. If it cannot be discharged from the scanning room normally, it will do great harm to the patient. The so-called quench pipe is a pipe that can transport helium to a reasonable position quickly, timely and properly when quench occurs.
Extended data:
Half an hour after demagnetization is very important, which is related to the time and workload of restoring magnets. When the magnet is out of time, the hospital engineer needs to replace the explosion-proof membrane at the outlet of the quench pipe at the first time to isolate the magnet from the air, so as to achieve the purpose of protecting the magnet, and immediately contact the Philips engineer to go to the scene for further treatment.
There are many factors that cause quench: the structure and coil of the magnet, the unstable performance of superconducting materials, the destruction of the ultra-low temperature environment of the magnet and human factors. Usually, there are five situations:
First, when the magnetizing current exceeds the rated value during excitation, or the magnetizing current increases too fast, the whole superconducting coil will be subjected to radial and axial electromagnetic extrusion force, which will cause local cracking of epoxy resin impregnated between coil windings, and the release of this deformation energy will be converted into heat energy, thus causing quench;
The second type: when the liquid helium is injected too fast and the injection tube is not completely cooled to 4.2K, inserting it into the magnet injection hole will make the liquid helium in the Dewar container boil, vaporize and erupt quickly, destroying the superconducting environment and leading to quench;
Category III: When the liquid helium level in the magnet Dewar container drops to a certain limit (the lower limit capacity of liquid helium specified by various manufacturers is different, and the general empirical limit value is 30% of the full capacity), if it is still not replenished in time according to the regulations, it will lead to quench;
The fourth category: after the vacuum environment of the magnet vacuum insulation layer is destroyed, quench will definitely occur;
Category 5: Misoperation of emergency quench switch leads to "accidental" quench.