The fast plasma analyzer EU-1 of the SCA-1 complex plasma spectrometer provides fast three-dimensional measurements of the ion distribution function. The EU-1 ion spectrometer with virtual aperture consists of two detectors with 16 E/Q narrow-angle analyzers and electrostatic scanners. This configuration allows the measurement of the ion distribution function in three dimensions (over 15 logarithmically-spaced energy steps in the range 50 eV/Q - 5.0 keV/Q) in 64 directions in 7.5 seconds, which makes it independent of the slow rotation speed (period about 2 minutes) of the satellite. The FWHM of the energy passband is about 10 %. Both 15-step and 30-step energy scans are used in different modes of the instrument. One analyzer, EU-1/1, has its field of view pointed along the spin axis toward the Sun, while the other, EU-1/2, is oriented in the opposite, antisolar direction.
Due to memory and telemetry limits, the full information capacity of SCA-1 can be used only along a limited part of the satellite trajectory, and the rest of the orbit is covered by slow modes. The typical data rate from EU-1 in fast mode is 256 bytes/second.
Modes are selected by telecommand, as a result of internal data processing, or by alert signals from other instruments (IMAP, ELECTRON, PRAM, OPERA, DOK, VDP). Turning on the accelerated mode from a slow mode occurs if one of the instruments gives an unconditional alert signal or if three or more instruments give conditional alert signals.
The instrument is described in detail in the paper by Vaisberg et al. in Ann. Geophysicae 15, 570-586 (1997), which is available online at the following URL:<br> http://www.copernicus.org/EGU/annales/15/ag15/570.pdf [EOB]