The X-ray microcalorimeter spectrometer (XMS): a reference cryogenic instrument for Constellation-X

Abstract

The first two of four observatories in the constellation will be launched together in 2013 and followed a year later by the launch of the remaining pair. The four will independently orbit the Sun–Earth Lagrange point L2. An instrument compliment resides in the focal plane module (FPM) of each observatory 10 m from the optics module and consists of three hard X-ray telescope (HXT) detectors, a reflection grating spectrometer (RGS) focal plane CCD camera (RFC) and an X-ray microcalorimeter spectrometer (XMS). Instrument awards are scheduled for early 2006. The reference detector system for XMS is a 32 × 32 array of microcalorimetric superconducting transition edge sensors (TES) with SQUID based multiplexed readout and amplification. A multi-stage continuous ADR will provide the stable 50 mK desired for the TES array and a stable 1 K for the SQUID amplifiers while also lifting thermal parasitic and inefficiency loads to a 6 K cryocooler interface. The 6 K cryocooler is expected to emerge from the joint-project advanced cryocooler technology development program (ACTDP) in which Constellation-X is an active partner. Project pre-formulation activities are marked by extensive technology development necessitating early, but realistic, thermal and cooling load requirements for ADR and ACTDP-cryocooler design points. Such requirements are driven by the encompassing XMS cryostat and ultimately by the thermal environment imposed by the FPM. It is further desired that the XMS instrument be able to operate horizontally in the laboratory, with a warm vacuum shell, during an extensive calibration regime. It is that highly integrated reference instrument (microcalorimeter, ADR, cryocooler and cryostat) that will be examined here.