Routine Electron Drift Instrument Measurements
Fig.1 shows four seconds of counts per ms received by the two detectors (first and third panel from the top) and the correlator channels that recorded these counts (second and fourth panel from the top). When the beams are not directed at the target, only background counts from natural plasma electrons are recorded (at about 50 cts/ms). As their arrival times are random, they appear in any of the 15 correlators. When the beams are on target, the counts rise to several hundred counts/ms. As the beams are modulated and coded with a PN-code, the beam counts appear in the correlator whose time-delay matches the time-of-flight of the electrons. A time-track feature shifts the delay until the signal appears in channel 7 and then tries to keep it there. This way the time-of-flight is measured.
Fig. 2: Beam firing directions for the same four seconds as Figure 1. The beams are continuously re-aimed to follow the motion of the target on the sky. Yellow, green and red symbols means angle track, time-track, and time-track with high signal-to-noise ratio, respectively. As already apparent from Figure 1, the target is periodically lost and must be acquired again by searching in the plane perpendicular to the magnetic field. This is visible in Figure 2 by the tracks of open black symbols that indicate firing directions that do not return a signal.
© Max-Planck-Institut für extraterrestrische Physik