Heat shields: Materials and cost considerations

Heat shields reduce the operating cost of a system by intercepting radiated heat that would otherwise add to the load on the low-temperature stage of the system. While always a consideration, recent fluctuations in the cost of helium have made the use of effective heat shields all the more critical to the cost effective operation of liquid helium systems. Heat shields come in many forms; they may be completely passive; relying on a low emissivity for effective operation, or they may be actively cooled by helium vapor, an intermediate stage of a refrigerator or by liquid nitrogen. For actively cooled heat shields a high thermal conductivity as well as a low emissivity is desirable. Structural considerations, such as the need to support the cold stage of the system, as well as space limitations may also factor in to heat shield design. Heat shields have traditionally been fabricated from copper and aluminum, when the highest possible thermal conductivity is required, and to a lesser extent from stainless steel. These materials have very different mechanical properties, are assembled with different fabrication techniques and have very different installed costs. In this paper we examine heat shield design options over a range of conditions and compare the costs of different materials and design options