Research On Vacuum Multilayer Insulation Of LHe Transfer Pipe For NBI System

The Neutral Beam Injection (NBI) system requires a clean high vacuum environment. The liquid helium cryocondensation pump with high pumping speed is an ideal vacuum obtain device. Transferring large quantity of liquid helium to the cryocondensation pump timely is essential. Liquid helium with small latent heat is expensive and leans to evaporate. Therefore the high efficiency liquid helium transfer pipe is of important meaning in reducing operating cost. Meanwhile, the good heat insulation performance is an important factor that guarantees the good operating performance of the cryocondensation pump.In this thesis, the heat insulation type was selected and the heat transfer mechanisms of vacuum multilayer insulation (VMLI) were discussed in detail. A mathematic model of cool loss in vacuum multilayer insulation was developed. The nonlinear equations of the mathematic model were solved. The parameter of the VMLI was determined and a VMLI liquid helium transfer pipe was designed by using the mathematic model. The cool loss performance test showed that the heat transfer rate of per meter pipe is 0.188 W/m. The pipe met the requirements of the NBI system in a practical experiment.It is proved that the mathematic model of cool loss in vacuum multilayer insulation can be used in VMLI design. This research provides theoretic basics and engineering practice data for heat insulation design in a higher pumping speed cryopumps and other areas where VMLI design is needed for cryogenic liquid.