Compact cryogenic hydrogen test environment for small devices and material characterization

Abstract

Currently, there is a great need for testing capabilities for material samples and components in LH2. This includes low temperature compatibility at 20 K, H2 compatibility and potential degradation or permeation effects. The test environment required for this is challenging and quite costly due to LH2 supply. Therefore, an alternative test concept was developed whereby the required amount of LH2 (typically 2–3 L) is generated directly on-site by simple condensation. This is achieved with a power-controlled cryocooler (115 W @ 80 K, 18 W @ 20 K). A cylindrical pressure vessel with an inner diameter of d = 109 mm and a length of approx. 500 mm designed for 2.1 MPa is used to hold the LH2 bath and the samples. The cryocooler and the sample chamber are installed in a common vacuum cryostat and are thermally coupled at the lower end. At the 20 K level, thermal coupling is achieved by a sophisticated thermosiphon arrangement. Hydrogen is taken from a pressure reservoir, pre-cooled at the cryocooler 80 K level, and then injected and liquefied within a couple of hours.