Kasaba et al. Earth, Planets and Space (2017) 69:174 https://doi.org/10.1186/s40623-017-0760-x FULL PAPER Open Access Wire Probe Antenna (WPT) and Electric Field Detector (EFD) of Plasma Wave Experiment (PWE) aboard the Arase satellite: specifcations and initial evaluation results Yasumasa Kasaba1* , Keigo Ishisaka2, Yoshiya Kasahara3, Tomohiko Imachi3, Satoshi Yagitani3, Hirotsugu Kojima4, Shoya Matsuda5, Masafumi Shoji5, Satoshi Kurita5, Tomoaki Hori5, Atsuki Shinbori5, Mariko Teramoto5, Yoshizumi Miyoshi5, Tomoko Nakagawa6, Naoko Takahashi7, Yukitoshi Nishimura8,9, Ayako Matsuoka10, Atsushi Kumamoto1, Fuminori Tsuchiya11 and Reiko Nomura12 Abstract This paper summarizes the specifcations and initial evaluation results of Wire Probe Antenna (WPT) and Electric Field Detector (EFD), the key components for the electric feld measurement of the Plasma Wave Experiment (PWE) aboard the Arase (ERG) satellite. WPT consists of two pairs of dipole antennas with ~ 31-m tip-to-tip length. Each antenna ele- ment has a spherical probe (60 mm diameter) at each end of the wire (15 m length). They are extended orthogonally in the spin plane of the spacecraft, which is roughly perpendicular to the Sun and enables to measure the electric feld in the frequency range of DC to 10 MHz. This system is almost identical to the WPT of Plasma Wave Investiga- tion aboard the BepiColombo Mercury Magnetospheric Orbiter, except for the material of the spherical probe (ERG: Al alloy, MMO: Ti alloy). EFD is a part of the EWO (EFD/WFC/OFA) receiver and measures the 2-ch electric feld at a sampling rate of 512 Hz (dynamic range: 200 mV/m) and the 4-ch spacecraft potential at a sampling rate of 128 Hz (dynamic range: 100 V and 3 V/m), with± the bias control capability of WPT. The electric feld waveform provides (1) fundamental information± about± the plasma dynamics and accelerations and (2) the characteristics of MHD and ion waves in various magnetospheric statuses with the magnetic feld measured by MGF and PWE–MSC. The space- craft potential provides information on thermal electron plasma variations and structure combined with the electron density obtained from the upper hybrid resonance frequency provided by PWE–HFA. EFD has two data modes. The continuous (medium-mode) data are provided as (1) 2-ch waveforms at 64 Hz (in apoapsis mode, L > 4) or 256 Hz (in periapsis mode, L < 4), (2) 1-ch spectrum within 1–232 Hz with 1-s resolution, and (3) 4-ch spacecraft potential at 8 Hz. The burst (high-mode) data are intermittently obtained as (4) 2-ch waveforms at 512 Hz and (5) 4-ch spacecraft potential at 128 Hz and downloaded with the WFC-E/B datasets after the selection. This paper also shows the initial evaluation results in the initial observation phase. Keywords: Electric feld, Plasma wave, Spacecraft potential, Electron density and temperature, Wire Probe Antenna (WPT), Electric Field Detector (EFD), Plasma Wave Experiment (PWE), Arase spacecraft *Correspondence: [email protected] 1 Department of Geophysics, Tohoku University, Aoba‑ku, Sendai, Miyagi 980‑8578, Japan Full list of author information is available at the end of the article © The Author(s) 2017. This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. Kasaba et al. Earth, Planets and Space (2017) 69:174 Page 2 of 18 Introduction shows the block diagram of WPT and EFD in the PWE Te Arase/ERG (Exploration of energization and Radia- system. WPT consists of four wire antenna booms (WPT tion in Geospace) project is a mission to study the Sensor; WPT-S) and their preamplifers (WPT Pream- acceleration and loss mechanisms of relativistic elec- plifer; WPT-Pre) and forms two orthogonal pairs of trons around the Earth (Miyoshi et al. 2012, 2017a, b). dipole antennas with ~ 31-m tip-to-tip length. Te out- Te spacecraft was successfully launched on December put signals of WPT-Pre are served to three electric feld 20, 2016, and started exploring the heart of the Earth’s receivers, EFD, WFC/OFA-E, and HFA, in the PWE main radiation belt using electromagnetic feld instruments electrical box (PWE-E). EFD forms a part of the EWO covering a wide frequency range and charged particle (EFD/WFC/OFA) receiver and measures the 2-ch difer- detectors over a wide energy range. ential electric feld at 512 Hz and 4-ch spacecraft poten- Te Plasma Wave Experiment (PWE) was developed tial at 128 Hz. It also feeds the bias current to WPT. Te as one of the key instruments for this project, in order output of EFD is processed on the PWE CPU#8 unit and to observe electric felds, plasma waves, and radio waves converted to the telemetry to the ground. PWE-E also in geospace (Kasahara et al. 2016). An electric feld pro- contains the MAST (extendable mast) and WPT deploy- vides information about plasma transports and accelera- ment control Electronics (MWE). tions and plays an important role in controlling the global Trough the combination of WPT and EFD, PWE can dynamics of the inner magnetosphere. Plasma waves pro- investigate an electric feld waveform as (1) the funda- vide the characteristics and strength of nonlinear energy mental information of the plasma dynamics and accelera- and momentum exchanges and enable us to study the pro- tions and (2) the characteristics of MHD and ion waves, cesses of high-energy particle accelerations. Plasma waves including their Poynting vectors in the inner magneto- such as whistler mode chorus, electromagnetic ion cyclo- sphere, in combination with the magnetic feld measure- tron wave, and magnetosonic wave interact with plasma ment by MGF and PWE–MSC. PWE can also provide over a wide energy range and consequently contribute to spacecraft potential as the diagnostics for thermal elec- loss and acceleration processes of high-energy particles tron plasma variations and structure, supported by the in geospace. Radio waves can be used as remote-sensing electron density from the UHR frequency provided by tools of auroral and magnetospheric activities such as PWE–HFA and low-energy particle measurements. auroral kilometric and continuum radiations. PWE pro- Te specifcation and the development team of these vides electron density information from the upper hybrid units are summarized in Table 1. On the Van Allen resonance (UHR) frequency. Spacecraft potential from Probes which have fown in the Geospace before Arase’s PWE also includes information about both electron tem- launch, the EFW instrument (Wygant et al. 2013) inten- perature and density. By those data, PWE is expected to sively observed the electric feld. EFW can measure provide key information about the structure, dynamics, three-dimensional electric felds using two pairs of spher- and physical processes governing the geospace, through ical dipole probes in the spin plane with 100-m tip-to- collaborations with other instruments aboard Arase and tip length and one pair of spin-axis dipole antenna with multiple spacecraft fying in the inner magnetosphere. 15-m tip-to-tip length. Although Arase PWE has only To meet the above-mentioned scientifc objectives, two-dimensional electric felds using the pair of shorter PWE uses two sets of orthogonal electric feld sensors dipole antenna, we will establish the good collaborative (WPT; Wire Probe Antennas) and three-axis magnetic sciences together, not only with them but also with EFI sensors (MSC; Magnetic Search Coil). Teir signals are aboard the THEMIS probes (Bonnell et al. 2008) and served to three receivers, named EFD (Electric Field FIELD aboard the MMS probes (Torbert et al. 2016). Detector) covering less than ~ 100 Hz in electric feld; Tis paper shows the specifcations of WPT ["Wire WFC/OFA (WaveForm Capture and Onboard Frequency Probe Antenna (WPT)" section] and EFD ["Electric Field Analyzer) covering from 10 Hz to 20 kHz in both elec- Detector (EFD) in EWO (EFD-WFC-OFA)" section], tric and magnetic felds; and HFA (High-Frequency Ana- onboard data scheme (Onboard data processing and data lyzer) covering from 10 to 10 MHz in electric feld and pipeline on the ground" section), and the initial operation from 10 to 100 kHz in magnetic feld. Descriptions of and evaluation results ("Initial evaluation status" section). PWE, including its design and specifcations, are detailed in Kasahara et al. (2017) for overall PWE and EWO (and Wire Probe Antenna (WPT) WFC/OFA), Kumamoto et al. (2017) for HFA, Ozaki et al. Wpt‑s (2017) for MSC, and Matsuda et al. (2017) for onboard Te WPT system comprises two pairs of spherical dou- data processing. ble-probe sensors at the ends of booms orthogonally Tis paper summarizes the specifcations and initial deployed in the spin plane, designed on the heritage of evaluation results of the WPT and EFD systems. Figure 1 the Geotail PANT system, which is connected to two Kasaba et al. Earth, Planets and Space (2017) 69:174 Page 3 of 18 WPT Electric field Analogue I/F DC-10MHz PWE Inner Digital I/F Power I/F WPT-Pre-U1 EWO-99MV Exclusive link WPT-S-U1 EWO-EFD PWE-E (for Bias control) Mission network ±99V ADC MGF WPT-Pre-U2 WPT-S-U2 HFA Other instruments WPT-Pre-V1 ADC PWE-CPU#8 WPT-S-V1 Mission WPT-Pre-V2 ADC Network MDP/ WPT-S-V2 MDR EWO- WFC/OFA(E) MSC-PA MSC-S PWE-CPU#9 EWO- B WFC/OFA(B) LEP B ADC FPGA Bγ Other instruments S-WPIA clock MSC LVDS XEP S-WPIA clock magnetic field HEP 0.1 Hz – 100kHz S-WPIA clock ±12V MEP +5V PWE-PSU +3.3V PDU MAST & WPT +28V Motor- deployment MWE1 MWE2 +15V PSU Fig.