Focusing Optics X-ray Solar Imager (FOXSI)

The Sun is a unique and ideal target in the sense that it can be investigated in great detail with good spatial, temporal and energy resolutions.

The Focusing Optics X-ray Solar Imager (FOXSI) is a NASA sounding rocket project which studies particle acceleration and coronal heating on the Sun through unprecedented high-resolution imaging in the hard X-ray energy band (5-20 keV). With a combination of high-resolution focusing X-ray optics and fine-pitch imaging sensors, FOXSI is the first solar mission to use direct focusing optics in such a high energy range and achieves superior sensitivity; two orders of magnitude better than the indirect imaging methods of the past.

To achieve such a sensitivity, we have provided fine-pitch Double-sided Si Strip Detectors (Si DSSD) as the focal plane detector, since the first FOXSI-1 experiment. These detectors fulfill the scientific requirements for the spatial resolution, energy resolution, lower threshold energy and time resolution. Si DSSD has a thickness of 500 μm and a dimension of 9.6 mm×9.6 mm, containing 128 strips separated by a pitch of 75 μm, which corresponds to 8 arcsec at the focal length of 2 m. In proper to improve the performance, the CdTe (Cadmium Telluride) Double Sided Detectors (CdTe DSD) were developed and used from FOXSI-2, CdTe has much higher efficiency for detection of hard X-ray photons than Si. Through the project, we have succeeded to implement a fine strip pitch of 60 μm. With the strip pitch,CdTe DSD can make full use of the high angular resolution of the FOXSI optic (5 arcsec in FWHM, corresponding to 50 μm with the focal length of 2 m).

For the FOXSI-3 experiment, CdTe DSDs are replaced by the ones with higher performance.
A new Si-CMOS sensor for covering soft X-rays as low as 0.5 keV is adopted for one of seven X-ray telescope onboard FOXSI-3.
(Last update: 2019/01/15)