Operation of a TES microcalorimeter cooled by a compact liquid-helium-free He-He dilution refrigerator directly coupled to a Gifford-McMahon cooler

A superconducting transition edge thermosensor (TES) microcalorimeter was irradiated with LX-ray photons emitted by an ²⁴¹Am source maintained at an operating temperature of 120 mK using a compact liquid-helium-free ³He-⁴He dilution refrigerator directly coupled to a Gifford-McMahon (GM) cooler. The first and second stages of the GM cooler were directly coupled to the first and second pre-cool heat exchangers of a stick shaped dilution unit through copper plates in a vacuum chamber. The helium-free dilution refrigerator provided a cooling power of 20 μW at 100 mK. Detection signals of LX-ray photons emitted by the ²⁴¹Am source were observed by operating the TES microcalorimeter in a severe noise environment induced by the mechanical vibrations of the GM cooler.