The ACIS Model

Modeling the ACIS device consists of estimating the spatially-dependent spectral transmission function of the ACIS UV/optical blocking filters (OBFs) and simulating the output of the CCD detectors. The OBFs are described above (Sec. 5.1). The CCDs are simulated using a Monte Carlo technique and assuming a slab model of the devices. Details of the basic model used at PSU are described in Section 7.1.

Recently, Dr. George Pavlov at PSU has reconsidered the physics assumed in this simulator. He has completed a solution of the diffusion equation for electrons in silicon including recombination; these conditions are present in the field-free parts of CCDs and these new solutions are necessary for correct modeling. We have just completed new code implementing Pavlov's solutions. This new code also allows the user to supply the device operating temperature and employs the appropriate temperature dependence for all quantities necessary to describe the ACIS CCDs, a feature that the old code did not have. Testing of these new algorithms is underway; enhancements employing new physics will be implemented as time allows, guided by comparison with the calibration data.