Astrophys Space Sci (2014) 355: DOI 10.1007/s10509-014-2150-1 ORIGINAL ARTICLE Impact of plasma sheath on rocket-based E-region ion measurements Nadia Imtiaz · Johnathan Burchill · Richard Marchand Received: 1 July 2014 / Accepted: 8 October 2014 © Springer Science+Business Media Dordrecht 2014 Abstract We model the particle velocity distribution func- tions around the entrance window of the Suprathermal Ion Imager (SII). The SII sensor was mounted on a 1 m boom carried by the scientific payload of NASA rocket 36.234 as part of Joule II mission to investigate Joule heating in the E-region ionosphere. The rocket flew above Northern Alaska on 19 January 2007. The payload was spin-stabilized with a period of 1.6 s, giving an apparent rotation of the ion flow velocity in the frame of reference of the payload. The SII sensor is an electrostatic analyzer that measures two di- mensional slices of the distribution of the kinetic energies and arrival-angles of low energy ions. The study is con- cerned with the interpretation of data obtained from the SII sensor. For this purpose, we numerically investigate ram ve- locity effects on ions velocity distributions in the vicinity of the SII sensor aperture at an altitudes of approximately 150 km. The electrostatic sheath profiles surrounding the SII sensor, boom and payload are calculated numerically with the PIC code PTetra. It is observed that the direction of the ion flow velocity modifies the plasma sheath potential pro- file. This in turn impacts the velocity distributions of NO + and O + 2 ions at the aperture of the particle sensor. The ve- locity distribution functions at the sensor aperture are cal- N. Imtiaz (B ) Theoretical Physics Division, PINSTECH, Nilore, Pakistan e-mail: diajamil@gmail.com J. Burchill Department of Physics and Astronomy, Calgary, AB T2N 1N4, Canada e-mail: j.burchill@ucalgary.ca R. Marchand Department of Physics, University of Alberta, Edmonton, AB, Canada e-mail: Richard.Marchand@ualberta.ca culated by using test-particle modeling. These particle dis- tribution functions are then used to inject particles in the sensor, and calculate the fluxes on the sensor microchannel plate (MCP), from which comparisons with the measure- ments can be made. Keywords Suprathermal · Ion imager · PIC 1 Introduction Particle sensors have been widely used on satellites and sounding rockets to provide in situ measurements of space plasma, including particle velocity distribution functions. For example, Hundhausen et al. (1967) investigated the use of particle analyzers to measure two dimensional ion veloc- ity distributions in the solar wind plasma. Measurements of three-dimensional particle velocity distributions in the mag- netosphere are also reported by many authors Carlson et al. (2001), Ogilvie et al. (1995), Pfaff et al. (2001). Geach et al. (2005) computed the corrected moments of data obtained from Cluster’s PEACE experiment in different plasma en- vironments. The correction accounts for the effects of po- tential broadening and energy range truncation. These two effects strongly depend on the spacecraft potential which is determined by the balance between the emitted and col- lected currents. The value of the spacecraft potential de- pends on the plasma parameters and in particular on the plasma temperature and density. It causes extra-broadening of the distribution functions and therefore, overestimates the values of the moments. The energy truncation is calculated from the upper and lower energy limit of the detector minus the spacecraft potential. As a result some particles are omit- ted in the on-board data, which results in an underestimate of the values of the moments. Corrected values are obtained