Simulated Characteristics of an Advanced Dust Telescope

A dust telescope is a combination of a dust trajectory sensor together with an analyzer for the chemical composition of dust particles in space. Dust particles' trajectories are determined by the measurement of the electric signals that are induced when a charged grain flies through a position sensitive electrode system. The objective of the trajectory sensor is to measure dust charges in the range 10^-16 to 10^-13C and dust speeds in the range 6 to 100 km/s. The trajectory sensor has four sensor planes consisting of about 20 wire electrodes each. Two adjacent planes have orthogonal wire direction. Computer simulations of such an instrument show that induced dust charge signals can be identified at a SNR = 3. At a noise level corresponding to 200 electrons or less the goal of measuring dust charges of 10^-16C is feasible. Two different designs of the charge-sensitive amplifiers are studied: one made from discrete electronic components and a highly integrated ASIC design.

The dust chemical analyzers will have a sufficient mass resolution in order to resolve ions with atomic mass number up to 100. The annular impact area of the mass analyzer will be 0.1 m². We have constructed a numerical (SIMION) model of the mass spectrometer consisting of the target area with acceleration grid and the single-stage reflectron consisting of two grids, and the central ion detector. Ions of varying starting positions at the target, emission angles 0 to 90 degrees and energies 0 to 50 eV are flown through the spectrometer. A first result is that ions with different perpendicular (to the target normal) energies will arrive at the ion detector at different radial positions, with zero perpendicular energy in the center. A mass resolution of M/Δ M 150 is obtained for impacts onto the annular target between 10 and 24 cm from the center.

Acknowledgements: This research is supported by NASA grant NAG5-11782 and by DLR grant 50OO0201.