The SXI: CCD camera onboard the NeXT mission

Abstract

The Soft X-ray Imager (SXI) is the X-ray CCD camera on board the NeXT mission that is to be launched around 2013. We are going to employ the CCD chips developed at Hamamatsu Photonics, K.K. We have been developing two types of the CCD: an N-channel chip and a P-channel chip. The effective area of the detector system will be 5-6 cm square with a depletion layer of 100-200µm. The P-channel chip will have thicker depletion layer that makes it easy to develop it to back-illuminated type CCD. It will need a year or so for us to reach the final conclusion which type will be available. Based on the Suzaku experience, we will incorporate the charge injection gate so that we can reduce the proton damage. Furthermore, we will employ a mechanical cooler to keep the CCD working temperature down to -120°C in spite that NeXT will be in the low earth orbit. We can expect the radiation damage on our system very small. The CCD will have an Al coat on the chip to prevent optical photons from entering. This also eliminates the vacuum-tight chamber and the door-opening mechanism. We are planning to employ a custom-made analog ASIC that will reduce the power consumption and the size. The ASIC may speed up the frame-time if we can use a multi-node CCD. With using the focal length of 6m, the SXI will fully function with the optics around 20" resolution. We will report the current plan of the SXI in detail.