Signal Collection / Timing
As shown in the following figure, mainly two inputs are necessary for the collection of signals: The signal from
- the detector (APD) in the experiment and
- the bunch-clock, which is a trigger signal delivered by the radio frequency signal (352.2 MHz) from the storage ring (timing modes).
Setup of the fast timing electronics for the experiments.
The amplified detector signal is fed into
two constant fraction discriminator (CFD)
- to select a timing point on each input pulse
that is independent of the pulse amplitude.
In reality at high prompt count rates the timing point is unfortunately not independent of the pulse amplitude, which can introduce an uncertainty of maximal 0.1ns in the determination of time zero.
The outgoing signal can serve as monitor for the incident radiation (prompt signal) as long as the detector is not saturated.
- another CFD which is gated.
The gate pulse is generated from the bunch clock signal.
This means, that only pulses are transferred to the time to amplitude converter (TAC), which occur during this gate pulse in order to separate prompt and delayed counts.
This gating procedure is necessary because the TAC can not handle the high count rates of the prompt pulse.
The TAC is started by the delayed pulses and stopped by the bunch clock. The output is converted with an analog-digital-converter (ADC) and fed into a multi channel analyser (MCA), which records the time dependence of the NRS. The delayed signal from the CFD is also used to record the energy dependence (time integrated) of the NRS (delayed signal).