Improving MRI magnet thermal performance using variable density multilayer insulation

Careful techniques for multilayer insulation (MLI) wrapping of MRI magnet cryostats have been shown to be critical in establishing a net Zero Helium Boil Off. Traditional MLI together with a cryocooler have been used in such 'Zero Boil Off' cryostats for many years. This paper discusses how the evolution in design of MRI magnet cryostats is challenging traditional MLI. By looking at the fundamental design equations for MLI, new insight can be gained into improving the design using variable density insulation. A new, proprietary method for creating variable density in MLI was devised and the resulting blankets were applied to MRI magnets. Results show a 10% improvement in insulation performance and a 42% improvement in material cost of the MLI. This new Variable Density MLI also holds promise for application to other liquid helium cryostats.