A dry ³He-⁴He dilution refrigerator for a transition edge sensor microcalorimeter spectrometer system mounted on a transmission electron microscope

A dry ³He-⁴He dilution refrigerator (DR) was developed for a superconducting transition edge sensor (TES) microcalorimeter installed on a transmission electron microscope. This system could be used for energy dispersive X-ray spectroscopy (EDS) with an excellent energy resolution. A Gifford-McMahon (GM)-type mechanical cryocooler was used as a pre-cooler for the DR to ensure liquid helium was not consumed during operation. To reduce sound and vibrations generated by the GM cryocooler, the DR was separated from the GM cryocooler in a split system. The TES microcalorimeter was glued onto the top of a copper rod referred to as the snout, which was attached to the mixing chamber of the DR. The cooling power in the mixing chamber was 30 μW at 105 mK. The lowest temperature in the mixing chamber was 74 mK, and that at top of the snout was 86 mK. An energy resolution of 7.6 eV full width at half maximum for Si Kα X-rays of 1.74 keV was obtained by TES microcalorimeter EDS performed with the transmission electron microscope.