EFW electric field double probe instrument

The EFW (Electric Field and Wave) instrument consists of four spherical probes deployed orthogonally on wire booms in the spin plane of each spacecraft. The potential differences between opposing probes, separated by 88 m tip-to-tip, are measured to provide electric field measurements in two directions, thus providing the full electric field vector in the spin plane of the spacecraft. Additionally, the potential differences between each of the probes and the spacecraft are measured, providing an estimate of the spacecraft potential relative to the plasma, which can be used as a proxy for the ambient electron density. In normal mode telemetry the electric field is sampled at 25 samples/s and low-passed filtered at 10 Hz, and in burst mode the electric field is sampled at 450 samples/s and low-pass filtered at 180 Hz. For both modes, the spacecraft potential is sampled at 5 samples/s. For short time intervals, the potential difference between the individual probes and the spacecraft can be sampled at rates up to 9000 samples/s and stored in an internal memory, which can be used to perform inter-probe interferometry to determine phase speeds. Potential differences for the two probe pairs can be sampled at rates up to 18000 samples/s. The output analogue signals from the preamplifiers connected to the spherical probes are also provided to the wave instruments (STAFF, WHISPER and WBD) for analysis of high frequency wave phenomena. All EFW datasets are available on the ESA Cluster Science Archive at https://csa.esac.esa.int/

EFW（电场与波）仪器由四个球状探头组成，这些探头以正交方式安装在每艘航天器旋转平面的线杆上。通过测量相对探针之间的电位差，这些探针尖端之间的距离为88米，从而在两个方向上提供电场测量，确保在航天器旋转平面内完整地获得电场矢量。此外，测量每个探头与航天器之间的电位差，以估算航天器相对于等离子体的电位，该电位可用作环境电子密度的代理。在正常模式遥测中，电场以每秒25个样本的速率进行采样，并以10赫兹的低通滤波进行处理；在突发模式中，电场以每秒450个样本的速率进行采样，并以180赫兹的低通滤波进行处理。在这两种模式中，航天器的电位以每秒5个样本的速率进行采样。对于短时间间隔，个体探头与航天器之间的电位差可以以高达每秒9000个样本的速率进行采样并存储在内置内存中，用于执行探头间干涉测量以确定相位速度。对于两个探头对，电位差的采样速率可高达每秒18000个样本。连接到球状探头的放大器输出的模拟信号也提供给了波仪器（STAFF、WHISPER和WBD），以分析高频波现象。所有EFW数据集均可在欧洲空间局Cluster科学存档中找到，存档地址为https://csa.esac.esa.int/。