Abstract
This paper describes the science motivation, measurement objectives, performance requirements, detailed design, approach and implementation, and calibration of the four Hot Plasma Composition Analyzers (HPCA) for the Magnetospheric Multiscale mission. The HPCA is based entirely on electrostatic optics combining an electrostatic energy analyzer with a carbon-foil based time-of-flight analyzer. In order to fulfill mission requirements, the HPCA incorporates three unique technologies that give it very wide dynamic range capabilities essential to measuring minor ion species in the presence of extremely high proton fluxes found in the region of magnetopause reconnection. Dynamic range is controlled primarily by a novel radio frequency system analogous to an RF mass spectrometer. The RF, in combination with capabilities for high TOF event processing rates and high current micro-channel plates, ensures the dynamic range and sensitivity needed for accurate measurements of ion fluxes between ∼1 eV and 40 keV that are expected in the region of reconnection events. A third technology enhances mass resolution in the presence of high proton flux. In order to calibrate the four HPCA instruments we have developed a unique ion calibration system. The system delivers a multi-species beam resolved to M/ΔM∼100 and current densities between 0.05 and 200 pA/cm2 with a stability of ±5 %. The entire system is controlled by a dedicated computer synchronized with the HPCA ground support equipment. This approach results not only in accurate calibration but also in a comprehensive set of coordinated instrument and auxiliary data that makes analysis straightforward and ensures archival of all relevant data.
Highlights
Magnetic reconnection is a fundamental universal plasma process that converts energy stored in magnetic fields into particle acceleration and heating
The cable carrying −15 kV from the high voltage (HV) supply to the TOF analyzer (TOFA) is routed via a 30 kV-rated HV capacitor and HV distribution network located in a small volume inside the TOFA housing (Fig. 14)
The second is the potential inability of the TOF processing electronics to keep up with high rates corresponding to coincident rate dead times ∼100 ns
Summary
Because of its complexity the HPCA is a very demanding instrument to calibrate (see Wuest et al 2007 for an excellent discussion of particle instrument calibration) For this reason, and because four separate units had to be calibrated over a long period of time including EQM calibration post-launch, we built a dedicated calibration system incorporating several novel elements including a compact ion source and ion beam generating optics, and a highly accurate system used to calibrate the beam itself. An important component of the calibration system is the HPCA’s Electrical Ground Support Equipment (EGSE), which acts as a power source, control system, and data collection and processing system. It supports ordinary engineering tests, once the EGSE is synchronized with the EPIC facility electronics the two coordinate facility functions with HPCA operations.
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