An improved ACE/SWICS efficiency model including uncertainty estimates

SWICS (Solar Wind Ion Composition Spectrometer) is a linear time-of-flight mass spectrometer on ACE (Advanced Composition Explorer), launched 1997, and now at L1. SWICS determines the ion composition of the solar wind and of suprathermal particles in interplanetary space. For the purpose of an improved data analysis technique we have developed an advanced mathematical model of SWICS that calculates the detection probabilities as a function of ion species, energy, and flight trajectory. Based on careful analysis of calibration data and detailed comparison with flight data, we have included several effects in the model: Energy loss in the carbon foil was simulated with SRIM and adapted to flight and calibration results. Pulse height defects were derived from calibration data. Scattering in the foil has been improved by using results from dedicated scattering experiments performed at the University of Bern, Switzerland. Finally, we use the full 3-d information of the instrument to obtain accurate active areas. We present the operational breakdown of the efficiency model and the data products the program provides, and present uncertainty estimates for them.