The Line Emission Mapper (LEM) Microcalorimeter Spectrometer

The Line Emission Mapper (LEM) Probe is a powerful, general-purpose soft X-ray observatory that is optimized to reveal how hot gas assembles and transforms cosmic ecosystems on scales from 1 to 10 million parsecs. LEM combines a high angular resolution (10”) telescope with the LEM Microcalorimeter Spectrometer (LMS), which provides 1-2 eV spectral resolution over a 0.1-2 keV bandpass in each 15” pixel across a 29’ FOV. The LMS detector comprises 4,248 transition-edge sensors (TES), which are optimized to achieve an energy resolution of 1 eV (at 1 keV) in the central 9’ and 2 eV outside. The 4,248 TESs are read out with 72 channels of time-division multiplexing (TDM). The microcalorimeter is cooled to a temperature of less than 50 mK using a continuous adiabatic demagnetization refrigerator (CADR). The CADR cools from a temperature less than 4.5 K, with cooling down to 4.5 K provided by a single 4-stage pulse tube cryocooler. The cryogenic components are housed inside a Dewar, and an aperture assembly with a gate valve allows X-rays to reach the microcalorimeter array with high throughput, while also mitigating against long-wavelength radiation and contamination. We will describe the design and development status of each major component of the LMS and will present estimates for the mass, power, and size of the instrument.