MASS SPECTROMETER CALIBRATION OF COSMIC DUST ANALYZER

Abstract. The time of flight mass spectrometer of the Cosmic Dust Analyzer (CDA) instrument aboard the Cassini spacecraft, is expected to be placed in orbit about Saturn to sample the ring material and satellite impact ejecta. Upon impact of an incident dust particle against the target plate at velocities of 5-100 km/s, some 10q8 to low5 times the particle mass of positive valence, single-charged ions is induced. These are analyzed via a time-of-flight mass spectrometer. Initial experiments employing a pulsed Nz laser (>300 &l/pulse, 4ns, 337nm) acting on a suite of samples are described. The laser beam is focussed to deliver the light pulses onto a laser power density ( 101 ’ W/cm2) to simulate the impact of particles. Laser ionization produced a charge of 4.6 pC per pulse for aluminum alloy. Estimating that each Al+iion require energy of 5.98 eV ionization energy/ion implies that 10m5 % of the laser energy produced ions and the present system has a 5 % efficiency of collecting the laser-irradiation induced ions. Employing a multi-channel plate detector in this mass spectrometer yields for Al-Mg-Cu alloy and kamacite (Fe-Ni mineral) targets well defined peaks at 24 (Mg”), 27(Al+‘) and 64 (CL?), and 56 (Fe+‘), 58 (Ni+‘) and 60 (Ni+‘) dalton, respectively