  Four NASA Science and Technology Definition Teams have been convened in order
to develop and study four mission concepts to be evaluated by the upcoming 2020
Decadal Survey. The Lynx x-ray surveyor mission is one of these four large
missions. Lynx will couple fine angular resolution (<0.5 arcsec HPD) x-ray
optics with large effective area (~2 m^2 at 1 keV), thus enabling exploration
within a unique scientific parameter space. One of the primary soft x-ray
imaging instruments being baselined for this mission concept is the
high-definition x-ray imager, HDXI. This instrument would use a finely
pixelated silicon sensor array to achieve fine angular resolution imaging over
a wide field of view (~22 x 22 arcmin). Silicon sensors enable
large-format/small-pixel devices, radiation tolerant designs, and high quantum
efficiency across the entire soft x-ray bandpass. To fully exploit the large
collecting area of Lynx (~30x Chandra), with negligible or minimal x-ray event
pile-up, the HDXI will be capable of much faster frame rates than current x-ray
imagers. We summarize the planned requirements, capabilities, and development
status of the HDXI instrument, and associated papers in this special edition
will provide further details on some specific detector options.
