Note: The analysis tools described in this page has been updated in the new project FFG 873685. Please go to the page here
The Active Spacecraft Potential Control (ASPOC) aboard Magnetospheric Multiscale (MMS) generates beams of indium ions at energies of order 4-12 keV and variable currents of up to 70 μA in order to limit positive spacecraft potentials within several volts and, e.g., thereby improve the measurements obtained by the instruments FPI, HPCA, ADP, and SDP (Torkar et al., 2014). There are two ASPOC per MMS spacecraft, each unit contains four ion emitters and one emitter per instrument is operated at a time.
Plasma density derivation
By determining statistically the photoelectron curve for different science phases, Phase 1 and 2, using, plasma current, spacecraft potential, and ASPOC current, plasma density estimation is performed assuming ASPOC current to be a bias current of the spacecraft potential using the method by Andriopoulou et al. (2015).
The usage is given in (ASPOC Iphoto). The users can run the code to derive the photo electron curve themselves or simply use the input parameters (ASPOC Iphoto curves) to calculate the photo electron curve to calculate the density. Or, retrieve directly the estimated density data product (density proxi), open the zip-file with "aspoc#2017".