Abstract Since May 2010 Elettra, operates in top-up at both 2 and 2.4 GeV user energies. In this paper the experience during more than a year of operation in top-up is discussed and the machine up time statistics are presented and compared with the before top up period

A Carniel

E Karantzoulis

Italy Sincrotrone Trieste

S Krecic

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TOP-UP OPERATIONAL EXPERIENCE AT ELETTRA 
E. Karantzoulis±, A. Carniel, S. Krecic, Sincrotrone Trieste, Italy
Abstract 
Since May 2010 Elettra, operates in top-up at both 2 
and 2.4 GeV user energies. In this paper the experience 
during more than a year of operation in top-up is 
discussed and the machine up time statistics are presented 
and compared with the before top up period. 
INTRODUCTION  
Elettra, the 2/2.4 GeV third generation Italian light 
source, has successfully joined the synchrotron facilities 
that operate fully in top-up mode. Located on the outskirts 
of Trieste, Elettra has operated for users since 1994, but 
during the past few years a large upgrade programme has 
taken place. This has included the construction and start-
up operation of a full-energy injector. The new injector 
chain and the other machine and beam line upgrades, 
together with the demands for intensity and thermal 
stability, naturally led to the change to top-up mode, in 
which frequent beam injections maintain a quasi constant 
beam current in the storage ring during user operations. 
This is in contrast with the decay mode, where the stored 
beam is allowed to decay to some level before refilling 
occurs.   
Elettra was not originally designed for this type of 
operation (and indeed even operated for many years 
without a full-energy injector). However, in May 2010, 
only a year after establishing the stable operations of the 
new injector, the storage ring began to work successfully 
with top-up [1,2] at both user energies, 2 GeV and 2.4 
GeV. Elettra has thus become another example showing 
how a third-generation synchrotron that previously 
operated in decay mode can advance to full top-up 
operation, in this case at multiple energies. 
With top-up operation the photon intensity produced at 
Elettra is stable and the integrated intensity is 60% higher 
over a time period equal to the beam lifetime. Thus while 
keeping the optical components of the beam lines in 
thermal equilibrium the integrated number of photons is 
also higher, so providing an additional gain in beam time 
for the experiments. At the same time the intensity-
dependent electronics also remain stable, allowing 
submicron accuracy in the position of the electron beam 
and hence a higher stability of the photon beam. 
Elettra’s 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 timing of the kicker and septa, 
as well as a revised operation strategy. A great deal of 
effort in collaboration with the radiation-protection team 
resulted in a high-level application with a “top-up 
controller” handling and controlling all aspects of the 
procedure. Careful radiation measurements at each beam 
line under various conditions of the injected beam, 
together with the high injection efficiencies achieved at 
both energies, meant that no additional shielding was 
required for the beam lines. Radiation levels in all beam 
lines remain below 1 µSv/h for efficiencies higher than 
90%. 
The storage ring beam current at 2 GeV is set by the 
users to 310 mA (270 nC) and top-up occurs every 6 
minutes by injecting 1 mA in 4 s, thus keeping the current 
level constant to 3‰. At 2.4 GeV the stored beam current 
is set to 150 mA and top-up occurs every 20 minutes, 
injecting 1 mA in 4 s to maintain the current level 
constant to 7‰. The users have chosen fixed-current 
interval top-up (1 mA) instead of a 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 two, very sensitive, beam 
lines see some interference and therefore are gated.  
The change to top-up mode required no transition 
period and once it began all went exceptionally smoothly, 
thanks to the very good preparation and the high level of 
expertise of the personnel involved. Although at the 
beginning, the operation in top-up was programmed for 
20% of users beam time, it became immediately clear that 
the users strongly preferred this mode and so Elettra has 
operated in top-up for 100% of the beam time dedicated 
to uses right from the start. 
THE INJECTOR 
The project for the full-energy injector started in 2005 
and finished by providing beam in March 2008 on time 
and within budget [3]. The injection chain consists of a 
100 MeV linear accelerator and a 2.5 GeV 3 Hz booster. 
At the very beginning the injection system was plagued 
with problems concentrated on the booster dipole and 
quadrupole digital power supplies and the stability of the 
water and air cooling system. After about one year of 
interventions and refurbishing of the power supplies by 
the constructor, the Elettra team finally was able to render 
the injector highly reliable. The booster operates in the 
on-fly mode whereby the energy required is obtained by 
adjusting the extraction time while the booster itself is 
always performing the full cycle i.e. 100 MeV to 2.5 
GeV. The booster can provide any energy from 0.1 to 2.5 
GeV but the energies used in the storage ring are 1 and 
1.5 GeV for THz, 1.8 GeV for the SR-FEL, 2 and 2.4 
GeV for the main users. Although the maximum achieved 
accumulated current in the booster was about 6 mA/s 
(above specs) for practical reasons no more that 2 mA/s 
are needed for refilling the storage ring and during top up 
this current is reduced to 0.2 mA/s due to radioprotection. 
At the same time a big effort was made to fully 
thermally stabilize the injector as well as provide for 
___________________________________________  
±
Emanuel.Karantzoulis@elettra.trieste.it 
THPC027 Proceedings of IPAC2011, San Sebastián, Spain
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02 Synchrotron Light Sources and FELs
A05 Synchrotron Radiation Facilities
redundancy of its critical parts. Thus a second thermionic 
gun and a spare modulator have being constructed, local 
knowhow on repairing the modules of the digital power 
supplies was achieved and an effort to reduce klystron 
discharges is under way. Normally those discharges do 
not hinder the top-up mode because their recovery time is 
short compared to the interval between injections 
however it is desirable that the one discharge per day at 
present, to be reduced to one per week.  
The percentage of time in top-up compared to total 
beam time delivered for users is a measure of the 
availability of the injector which for 2011 is 98.7%. 
THE STORAGE RING 
In order to satisfy the strict safety requirements of top-
up operations the control system monitors on a shot-by-
shot basis the balance of the net charge extracted from the 
booster and the charge effectively injected in the storage 
ring, using a 24-bit resolution fast current monitor. 
To control the beam losses an intensity loss budget is 
set that should not exceed 10 mA/h at 2 GeV and 5 mA/h 
at 2.4 GeV. If the budget is exceeded the top-up process 
stops for the rest of the hour. This mechanism sets the 
lower limit of a tolerable efficiency to 60% and only very 
few times within a year the top-up process stopped due to 
this reason. At the same time a radiation budget is also set 
for each beam line of about 0.4 μSv for a four hour time 
interval, exceeding this budget the shutters of the beam 
line remain shut for the rest four hours, a situation that 
has never happed until now. From the radiation protection 
point of view the Elettra experimental hall is classified as 
“free area” (i.e. an area where radiation dose is less than 1 
mSv/year) . 
The injection, refill and top-up are completely 
automatic and the operators intervene only in case of 
faults. The automation is achieved on the higher level 
with the top-up supervisor, a software process that 
coordinates and controls all the non-safety related 
operations of the top-up and estimates some parameters 
which are very useful for the control room operators. 
Thus it constantly monitors the storage ring current and 
when the lower current threshold is reached, starts a new 
top-up cycle: the booster ramping cycle is started and 
after the time needed to settle the power supplies and 
other systems to their running values, all the necessary 
triggers are enabled and injection starts.  
During injection the booster and storage ring currents 
are continuously monitored and the booster charge is 
stabilized acting on the linac gun grid voltage with a 
feedback algorithm.  
At the same time the supervisor measures the injection 
efficiency and estimates the "risk" of exceeding a 
predetermined limit of current loss both on short term and 
long term basis. If the limit is reached, the safety PLC 
inhibits the top-up injection as described before. When 
the desired storage ring current is reached, the supervisor 
stops the injection. The application is also used to 
normally refill the storage ring and/or perform top up like 
injections in top up off mode. This operation mode is for 
testing the top-up settings and for vacuum conditioning.  
The top-up supervisor is technically implemented as a 
Tango device server. The operator graphical interface is 
developed with the QTango toolkit (Fig. 2). 
 
Figure 1: Top-up supervisor panel. The graph in the panel 
shows the injection events and the % of efficiency. 
It was highly expected that top-up would improve the 
availability of the storage ring. In fact in the next Figure 2 
one can see the net availability (blue) during the 3 phases 
of operations of Elettra while with red is shown the 
downtime, with yellow the time lost for refilling and with 
light turquoise the time lost due to electricity surges. 
 
Figure 2:  Availability of Elettra since 2004.  
In fact before 2008 the storage ring ramped in energy, 
whereas since 2008 operated with a full energy injector 
and since 2010 functioned in top-up. It is clear from 
Another important number for the reliability of a light 
source is the mean time between failures. Also in this case 
(see Figure 3) a clear improvement can be observed after 
2008. The tendency for 2011 is for higher mean time 
between failures (MTBF) and in fact for the two first runs 
of 2011 the machine had 130 hours of MTBF. At the 
same time the longest top up duration between failures 
Figure 2 that a net improvement occurred after 2008. 
Proceedings of IPAC2011, San Sebastián, Spain THPC027
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has been 200 hours, a very remarkable result indeed. 
 
Figure 3: Mean time between beam losses since 2004. 
Top-up mainly has been invented for keeping source 
and experiments thermally stable and the electronics 
stable. The orbit was monitored over a long period of time 
i.e. 100 hours with the machine in top up and both the 
horizontal and vertical position of the bpms were 
registered.  
 
Figure 4: Horizontal orbit stability (y axis in mm) during 
top up for a period of 100 hours.  
Figure 4 shows the horizontal beam position in one bpm 
and the peak to peak value is 4 um while the 
corresponding vertical measures 1.5 um. 
Since air conditioning is old and under refurbishing 
occasionally when a big temp gradient between day and 
night exists the e-orbit follows a day night thermal 
pattern. The mean orbit feedback changes the radio 
frequency by about 50Hz that corresponds to 26 um in 
circumference to keep the mean horizontal orbit at zero. 
The orbit reproducibility depends mainly on the 
thermal equilibrium. The orbit needs some time after refill 
following a beam dump to arrive to the previous position 
settings due to the vacuum chamber heating. It was found 
that 20 C difference (about 10 minutes after the beam 
dump) affects by 90 um rms the horizontal orbit and only 
4 um rms the vertical. When re-injecting from zero to full 
intensity after a typical mean failure duration (which at 
present is about 0.8 h) almost 1.5 hours are needed for 
having the orbit back to its previous “golden orbit” values 
as seen in the next Figure 5. 
 
Figure 5: Bpm offset value drift towards “golden orbit” 
setting versus time after refill. 
CONCLUSIONS 
The top-up operations mode is the only operational 
mode for users since May 2010. The top up percentage to 
the given user beam time is 98.7% a number that reflects 
also the high availability of the injector. The storage ring 
availability and the mtbf are very high showing clearly 
the beneficial effect of the full energy injection and the 
top up. The injection efficiencies are normally high i.e. 
more than 90% although the system tolerates also lower 
efficiencies up to ~60%, it is important however to note 
that the efficiency is calculated by comparing the booster 
and storage ring current therefore if the booster does not 
accumulate well the efficiency appears low even if all 
available current is injected from the transfer line into the 
storage ring. The stability and the reproducibility have 
been also greatly improved. It is important to note that 10 
degrees Celsius difference in the temperature of the 
vacuum chamber translates to about 20-30 μm shift in the 
reading of a single bpm while the shift due to electronics 
is about 1μm/10mA.  
To keep the synchrotron light source points as stable 
and reproducible as possible, (after performing a total 
realignment of the storage ring at the end of 2010 and 
afterwards a  beam based alignment) the orbit is set to 
zero position and angle at the source points without 
permitting the users to change them.  
REFERENCES 
[1] E. Karantzoulis, A. Carniel, K. Casarin, S. Ferry, G. 
Gaio, F. Giacuzzo, S. Krecic,   E. Quai, C. Scafuri, G. 
Tromba, A. Vascotto, L. Zambon, “Top up 
implementation and operation at Elettra”, 
Proceedings of  IPAC10 (2010), Kyoto, Japan 
[2] E. Karantzoulis, A. Carniel, S. Ferry, S. Krecic, 
“Operational Advances at Elettra and its New Full 
Energy Injector”, Proceedings of PAC09 (2009), 
Vancouver, Canada 
[3] M. Svandrlik on behalf of the booster project team, 
“Overview of the status of Elettra booster project”, 
Proceedings of  EPAC08 (2008), Genoa, Italy 
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TOP-UP OPERATIONAL EXPERIENCE AT ELETTRA

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TOP-UP OPERATIONAL EXPERIENCE AT ELETTRA

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