PSI System Controls and Diagnostics
F3200E User Manual
F3200E_UM_180726 Page 74 of 107
16.4 Sweep mode
16.4.1 Repetitive signals
Sweep mode provides the highest available effective sampling rate, but requires a repetitive
signal. A typical application is particle accelerators where the beam is scanned across an array of
detectors. This schematic illustration shows a linear particle sweep backwards and forwards
across a beam dump which includes multiple equispaced beam collector slots, each connected to
an F3200E channel. The objective is to create a uniform beam fan from a narrow pencil beam.
The signal from the beam collectors is nominally completely repetitive, and synchronized by the
scan generator clock. High performance magnet systems are capable of doing such beam scans at
rates up to 1 kHz.
Figure 60. Illustrative scanned beam example.
Assume that the sweep frequency in this example is 500 Hz, so that a single pass of the beam
takes 1 msec. Setting up the F3200E in sweep mode with 1 MHz ADC rate and 1000 points per
sweep will generate 1000 readings for each pass of the beam and take 1 msec. In practice there
needs to be some extra time, about 5-10 µsec, before the next synchronization trigger arrives so
that data can be transferred inside the F3200E and a new trigger edge can be detected. So a more
sensible setup would be 980 points to provide a 20 µsec period for data transfer.
The number of sweep averages to use will depend upon the signal to noise ratio and the temporal
frequency components you need to see in the beam. When it has overlaid and averaged the
requested number of sweep averages, the F3200E will return the result and repeat the process.
The “comb” of peaks is a mapping into the time domain of the spatial behavior of the beam
across the scan. The F3200E is also providing spatial information if the spacing of the slots is
well-known, so a measurement of the local beam spot velocity is possible. The data can also be
analyzed to check parameters such as constancy of the beam profile and intensity across the
sweep. Combining all the data allows the uniformity of the fan beam line to be assessed.
