Instrumentation

User Timing System (UsTiSys)

The Users at ELETTRA are scientists using Synchrotron Radiation for different kind of experiments. One possible application of Synchrotron Radiation is in microscopy and spectroscopy experiments.
Sometimes, there is also the need to synchronise the acquisitions of the experimental set-up with the Synchrotron Radiation light pulses. A low-jitter trigger signal, synchronous to the Light pulses, is then needed close to the experimental station.

To obtain it, a User Timing System is presently under installation at ELETTRA. It is constituted   of a signal distribution system and of many User Timing Units (UTU), each located close to one experimental station. The RF signal (f=500MHz) from the ELETTRA Master oscillator is distributed around the Experimental Area, by means of a good-quality low-loss coaxial cable. It is, then, locally divided (modulo 432=harmonic number of ELETTRA) to yield the Storage Ring Clock signal (fSRC=1.156MHz).Furthermore, to provide the Users with the information about the Storage Ring filling, an Analogue signal from an Electro-magnetic pick-up located on the ELETTRA Storage Ring is also distributed around the Experimental stations (beam lines).

Block diagram of the User Timing Unit (UTU), showing the digital divide and delay module and the analogue part for the amplification of the Storage Ring filling signal. The RF signal is first divided-by-432 to generate the Storage Ring Clock (SRC) signal. The SRC signal is then fed to a digitally programmable delay unit which allows to locate it in any point of the Storage Ring time frame (tREV=864ns). Integrated Circuits (ICs) form the ECLinPS (by MotorolaTM) family have been used to keep the jitter at minimum level.

The jitter (defined as time fluctuations of the trigger position with respect to a reference signal) has been measured using the block diagram  using a 50GHz sampling scope by Tektronix. The measured jitter has shown to be less then 5ps. The slope of the sinusoidal RF signal is acquired using as a trigger to the scope the SRC signal.