High-Time Resolution Measurements of Heavy Ions with SOHO/CELIAS/CTOF

Abstract:

The Charge Time-Of-Flight (CTOF) mass spectrometer as part of the Charge, ELement and Isotope Analysis System (CELIAS) onboard the SOlar and Heliospheric Observatory (SOHO) is designed to measure the kinetic properties and elemental/ionic composition of solar wind ions heavier than H+, which we refer to as heavy ions. This is achieved by the combined measurement of the energy-per-charge, the time-of-flight and the energy of the incident ions. The CTOF instrument combines a remarkable time-of-flight resolution with a large effective area which allows to determine the velocity distributions of a wide range of heavy ions with 5 minute cadence. Based on a sophisticated in-flight calibration and count rate analysis we derived 5-minute velocity distributions for typical charge states of solar wind carbon, oxygen, silicon and iron for the CTOF measurement period between day of year 150 and 220 in 1996. In contrast to previous studies we used pure Pulse Height Analysis (PHA) data, which yields the full mass and mass-per-charge and velocity information. We analyzed the velocity spectra for differential streaming relative to the solar wind bulk proton speed, measured simultaneously with the CELIAS Proton Monitor (PM). Here we present our results which should provide experimental constraints for theories of resonant wave-particle interaction and preferential acceleration of heavy ions in the solar wind.