Introduction & History

Elettra operation configuration since 2010
In May 2010 Elettra,successfully joined the synchrotron facilities that fully operate in top-up. Elettra operates for users since 1994 and during the past few years a massive upgrade program including the construction and set in operation of a full energy injector took place. The full energy injector and other machine and beam line upgrades as well as the demand for intensity and thermal stability naturally led to top-up operations whereby the storage ring beam current is kept constant during user operations.
 
Although Elettra was not originally designed for this type of operation (and operated for many years even without a full energy injector), almost a year after establishing reliable operations of the full energy injector , successfully operates in top-up in both 2 and 2.4 GeV user energies (since May 2010). Elettra is  thus another example of how a third-generation synchrotron, that previously operated in decay mode, can successfully advance to full top-up operation and at multiple energies too. In top-up mode, the storage ring intensity is kept constant by frequent beam injections, in contrast with the decay mode where the stored beam is allowed to decay to some level before refilling occurs.    
                             
The top-up operation renders the produced photon intensity practically stable whereas the integrated intensity is 60% higher for a time period equal to the beam lifetime. Thus while keeping the optical components of the beam lines in thermal equilibrium also the integrated number of photons is higher, an additional beam time gain for the experiments. At the same time, also the intensity dependent electronics remain stable allowing submicron accuracy in the electron beam position and hence a higher stability of the photon beam.

The upgrade to top-up started in 2009 and included the addition of various diagnostic and radiation safety instruments, modification of the control and interlock software, fine tuning of the kicker and septa timing and a revised operation strategy with the laborious collaboration of the radiation protection team resulting to a high level application a “top-up controller” controlling all aspects of the procedure. The careful radiation measurements at each beam line under various conditions of the injected beam and the high injection efficiencies achieved at both energies (radiation levels in all beam linesremain below 1 µSv/hour for efficiencies higher than 90% ) resulted in no additional shielding to the beam lines.

The storage ring beam current at 2 GeV is set by the users to 310 mA and top-up occurs every 6 min by injecting 1 mA in 4 seconds, keeping thus the current level constant to 3‰. At 2.4 GeV the stored beam current is set to 140 mA, top-up occurs every 20 minutes injecting 1 mA in 4 seconds keeping the current level constant to 7‰.

The users have chosen the fixed current top-up (1 mA) instead of the fixed time interval. The injection system is perfectly tuned and for the majority of the beam lines does not produce interference with data-acquisition processes. A gating signal is also provided but up to now only few, very sensitive, beam lines see some interference and therefore are gated.

No transition period was needed or required and once the top-up started all went exceptionally smooth due to the very good preparation and the high level of expertise of the personnel involved. It is worth mentioning that although at the beginning the operation in top-up was programmed at 20% of users beam time, already from the start it became clear that the users strongly preferred this mode and thus Elettra operated in top-up at 100% of the user dedicated beam time right from the beginning i.e. May 2010.