Soft X-ray Imager (SXI)

Description of the Soft X-ray Imager (SXI) on the SMILE mission

The SXI is designed to image portions of the Earth's magnetosphere, primarily the regions of the magnetospgheric cusps, magnetopause and bow-shock. The imaging mechanism is the solar wind charge exchange (SWCX) process. Heavy ions (e.g. carbon, nitrogen, oxygen etc.) within the solar wind can collide with neutral particles (primarily hydrogen) in the Earth's exosphere. The result of the collisions are the emission of soft X-rays (energy of a few hundred electron volts). The strength of the emission is proportional to the solar wind density (and temperature) in geospace. Hence, this mechanism enables imaging of the flow of solar wind around the Earth.


MHD (left panel: Source T. Sun, NSSC, China) and SXI simulations (right panel; Source: University of Leicester).

Whilst X-rays from SWCX have been detected by previous missions such as ESA's XMM-Newton or the Japanese Suzaku mission, these have been narrow field-of-view instruments which have provided no imaging information. SXI on SMILE will be the first instrument to provide true global imaging of SWCX within the magnetosphere.

The SXI will focus X-rays within a field of view of 26.5 x 15.5 degrees. This is achieved using a mirror constructed from an array of micropore optic (MPO) plates (also known as microchannel plate optics). These are thin (around 1 mm in thickness) glass plates containing millions of square pores. The plates are heat slumped to a common hemispherical radius of curvature. The incoming X-rays reflect off the interior surfaces of the pores and are focused towards the detector plane. The MPOs are supplied by PHOTONIS France S.A.S. and have been developed for X-ray optics in collaboration with the University of Leicester. The detector plane is two large format CCDs (each 8.1 x 8.1 cm in size) suppled by Te2v in the UK. The effective energy range of the instrument is from 0.15 to 5.0 keV.


CAD model of main body of SXI instrument


SXI is a collaboration between several UK, European, US and Chinese institutions. Further information on specific particpation will be provided when the consortium is formalised.

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