Soft X-ray Imager (SXI) is a CCD camera onboard the ASTRO-H satellite which is scheduled to be launched in 2015. The SXI camera contains four CCD chips, each with an imaging area of 31mm x 31 mm, arrayed in mosaic, covering the whole FOV area of 38′ x 38′. The CCDs are a P-channel back-illuminated (BI) type with a depletion layer thickness of 200 _m. High QE of 77% at 10 keV expected for this device is an advantage to cover an overlapping energy band with the Hard X-ray Imager (HXI) onboard ASTRO-H. Most of the flight components of the SXI system are completed until the end of 2013 and assembled, and an end-to-end test is performed. Basic performance is verified to meet the requirements. Similar performance is confirmed in the first integration test of the satellite performed in March to June 2014, in which the energy resolution at 5.9 keV of 160 eV is obtained. In parallel to these activities, calibrations using engineering model CCDs are performed, including QE, transmission of a filter, linearity, and response profiles.
X-ray CCDs are widely used as the focal plane detectors of the X-ray telescopes. Among them, backside illuminated CCDs with a deep depletion layer are preferred because of their high quantum efficiency in both soft and hard X-ray bands. However, they tend to have poorer energy resolution and higher background due to the relatively large charge diffusion. We carried out simple experiments to apply a magnetic field of 0.25 T or 0.4 T to the CCD, which is expected to suppress the charge diffusion very slightly and to bring subtle improvement in the performance of the CCD. We found unexpectedly that grade branching ratios of Grade 3 and Grade 4, both are horizontal split events, symmetrically changed depending on the direction of the applied magnetic field. Although the cause of the change is not understand yet, it clearly demonstrate that the charge cloud in the CCD is affected by the externally applied magnetic field. We also found a decrease of Grade 7 only in the experiment 2. We consider this may be caused by the supress of the charge diffusion by the magnetic field, although other possibilities can not be excluded. No significant improvement was detected in the energy resolution. We could show with these experiments that the charge cloud in the CCD may be controlled by the externally applied magnetic field. Magnetic field may become useful tool in future to improve the performance of CCDs.