Performance of compact liquid helium free ³He-⁴He dilution refrigerator directly coupled with GM cooler in TES microcalorimeter operation

A superconducting transition edge thermosensor (TES) microcalorimeter was cooled by a compact liquid-helium-free ³He-⁴He dilution refrigerator with loading a Gifford-McMahon (GM) cooler for detection of LX-ray photons emitted from an ²⁴¹Am source. The first and second stages of the GM cooler are directly coupled with the first and the second precool heat exchangers of a stick shaped dilution unit through copper plates in the vacuum chamber, respectively. The circulating ³He-⁴He gas through the precooled heat exchangers is condensed into a liquid of condense mixture by the isoenthalpic expansion through the Joule-Thomson impedance. A cascade of two mixing chambers are employed for achieving sufficient cooling power. The helium-free dilution refrigerator performs the cooling power of 20 μW at 100 mK. The TES and SQUID chips suffered from mechanical vibrations induced by a reciprocating motion of the displacer of the GM cooler. Detection signals of LX-ray photons emitted from ²⁴¹Am source were observed by operating the TES microcalorimeter in severe noise environment induced by mechanical vibrations.