The Axial Double Probe and Fields Signal Processing for the MMS Mission

Abstract

The Axial Double Probe (ADP) instrument measures the DC to ∼ 100 kHz electric field along the spin axis of the Magnetospheric Multiscale (MMS) spacecraft (Burch et al., Space Sci. Rev., 2014, this issue), completing the vector electric field when combined with the spin plane double probes (SDP) (Torbert et al., Space Sci. Rev., 2014, this issue, Lindqvist et al., Space Sci. Rev., 2014. Two cylindrical sensors are separated by over 30 m tip-to-tip, the longest baseline on an axial DC electric field ever attempted in space. The ADP on each of the spacecraft consists of two identical, 12.67 m graphite coilable booms with second, smaller 2.25 m booms mounted on their ends. A significant effort was carried out to assure that the potential field of the MMS spacecraft acts equally on the two sensors and that photo-and secondary electron currents do not vary over the spacecraft spin. The ADP on MMS is expected to measure DC electric field with a precision of ∼ 1 mV/m, a resolution of ∼ 25 µV/m, and a range of ∼ ±1 V/m in most of the plasma environments MMS will encounter. The Digital Signal Processing (DSP) units on the MMS spacecraft are designed to perform analog conditioning, analog-to-digital (A/D) conversion, and digital processing on the ADP, SDP, and search coil magnetometer (SCM) (Le Contel et al., Space Sci. Rev., 2014, this issue) signals. The DSP units include digital filters, spectral processing, a high-speed burst memory, a solitary structure detector, and data compression. The DSP uses precision analog processing with, in most cases, > 100 dB in dynamic range, better that −80 dB common mode rejection in electric field (E) signal processing, and better that −80 dB cross talk between the E and SCM (B) signals. The A/D conversion is at 16 bits with ∼ 1/4 LSB accuracy and ∼ 1 LSB noise. The digital signal processing is powerful and highly flexible allowing for maximum scientific return under a limited telemetry volume. The ADP and DSP are described in this article.

Magnetic depression and electron transport in an ion-scale flux rope associated with Kelvin–Helmholtz waves

“…At this scale, data from individual satellites appear almost identical, and we primarily present the data from MMS1. We use plasma data from the fast plasma investigation (FPI) , magnetic field data from the fluxgate magnetometer (FGM) and the search coil magnetometer (SCM) (Russell et al, 2014;Le Contel et al, 2014), and electric field data from the electric field double probes (EDP) Ergun et al, 2014). Figure 1 shows an overview of the fast survey between 19:50 and 20:09 UT, when the solar wind is relatively steady and presents an extended northward interplanetary magnetic field (IMF) from OMNI data: n sw = 8.5 ± 0.5 cm −3 , V sw = [−600.0 ± 5.8, −5.2 ± 11.6, −42.5 ± 9.3] km s −1 , P dyn = 6.2 ± 0.4 nPa and B IMF = [−4.6 ± 1.4, 2.6 ± 3.7, 7.9 ± 1.6] nT in GSM.…”

Magnetospheric Multiscale Satellites Observations of Parallel Electric Fields Associated with Magnetic Reconnection

“…This event, in particular, an encounter with the electron diffusion region by MMS2 has been discussed in detail [27]. The mission and its instruments are described in several articles [1,2,[28][29][30][31][32]. [28,31] at 128 samples/s in Geocentric Solar Ecliptic (GSE) coordinates.…”

“…The black lines are from the double probe electric field instrument [28][29][30] at 32 samples/s. During this period, the uncertainty in the E x and E y is ~1 mV/m.…”

“…During this period, the uncertainty in the E x and E y is ~1 mV/m. The alternating (positive/negative) orange trace in panel (g) represents the uncertainty in E z [29], which at the time is ~3 mV/m. The blue lines (− !…”

Optimized merging of search coil and fluxgate data for MMS

“…This required common clocks and synchronization, as instruments are sampled by different means. AFG and DFG are sampled by their own electronics, whereas the SCM is sampled by the digital signal processing unit (DSP; Ergun et al, 2016). In both cases, depending on downlink data rate, digital filters for sample rate conversion are also applied, which also needs to be taken into account for time tagging.…”