Ion Velocity Spectrometer (IVS) for Solar Wind Monitor

Abstract:

We are developing an Ion Velocity Spectrometer (IVS) which could be used as a solar wind monitor that will cover the velocity range from 200 km/s to 2500 km/s with no gaps in velocity with resolution Δv/v ≤ 5% and typical time resolution ~ 20s for protons, but burst modes for single species can also be done. The figure shows ion beam measurements of H₂⁺ ions from 100 V to 5 kV showing the IVS high velocity resolution capability Δv/v ~ 5%. Additional species ⁴He⁺⁺ and minor ions can be provided with dynamic range in particle intensities ~ 9-10 decades, should be achievable. It does not require the high voltages typical for time-of-flight mass spectrometers. Due to its wide dynamic range in particle intensities can be used over a wide range of radial distances within the heliosphere. The key feature of this design is a Circular Wien Filter (CWF) which uses spoke pattern for its permanent magnets and electric field plates (i.e., electric field orthogonal to the magnetic field) to adjust the ion velocity being selected. The energy analyzer (toroidal electrostatic tophat analyzer (ESA) with 90° deflection) is used to select the ion mass. The mass resolution M/ΔM ~ 10. In combination with the CWF the ESA can de-tune the solar wind proton beam with variable geometric factor (GF) 3x10^-7 ≤ GF ≤ 10^-4 cm²-ster-eV/eV. This variable GF allows for the instruments wide dynamic range in ion intensities. Simulations show angular resolution better than 5° x 5° and energy resolution ~ 7.5% can be achieved. For non-spinners, steering lens can be added with N-S coverage ±22.5°. The IVS has the capability for 360° field-of-view coverage with angular sectors ~ 20° when not looking at the solar wind. It can also be used for planetary magnetospheres and ionospheres due to its wide dynamic range in ion intensities.