  Swept Charge Devices (SCD) are novel X-ray detectors optimized for improved
spectral performance without any demand for active cooling. The Chandrayaan-1
X-ray Spectrometer (C1XS) experiment onboard the Chandrayaan-1 spacecraft used
an array of SCDs to map the global surface elemental abundances on the Moon
using the X-ray fluorescence (XRF) technique. The successful demonstration of
SCDs in C1XS spurred an enhanced version of the spectrometer on Chandrayaan-2
using the next-generation SCD sensors.
  The objective of this paper is to demonstrate validation of a physical model
developed to simulate X-ray photon interaction and charge transportation in a
SCD. The model helps to understand and identify the origin of individual
components that collectively contribute to the energy-dependent spectral
response of the SCD. Furthermore, the model provides completeness to various
calibration tasks, such as generating spectral response matrices (RMFs -
redistribution matrix files), estimating efficiency, optimizing event selection
logic, and maximizing event recovery to improve photon-collection efficiency in
SCDs.
  We compare simulation results of the SCD CCD54 with measurements obtained
during the ground calibration of C1XS and clearly demonstrate that our model
reproduces all the major spectral features seen in calibration data. We also
describe our understanding of interactions at different layers of SCD that
contribute to the observed spectrum. Using simulation results, we identify the
origin of different spectral features and quantify their contributions.
