• Accelerators
• beam diagnostic

Synchrotron Light sources are accelerator facilities producing synchrotron radiation to perform
several kinds of experiments in many fields of science.
ALBA is a third generation Synchrotron Light source, located close to Barcelona (Cerdanyola del
Vall ́s), with a 3 GeV electron beam available for users since May 2012.
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The facility currently operates in multi-bunch mode. The quality of the radiation strongly de-
pends on the electron distribution in the different bunches. To have high quality photon beams for
experiments, the bunch filling pattern has to be flat and the current has to remain constant in order
to guarantee a uniform flux of radiation. This can be achieved with the machine operating in the
so-called top-up mode.
During top-up operation the current of each bunch is refilled. To calculate the quantity of current
to be re-injected in the different buckets, it is necessary to have a full real-time characterization of the
Filling Pattern distribution.
The present thesis describes the work I personally did to obtain this real-time characterization of
the Filling Pattern.
ALBA beam structure is composed on 448 buckets that can be filled with different configurations.
The only measurement of the Filling Pattern was previously provided by a Fast Current Transformer
(FCT) connected to an oscilloscope. This device is affected by large noise, produced by electronics
and cable connections: as a consequence filled buckets could not be resolved clearly and no direct
relation between the FCT signal and the bunch current can be defined.
During my job, I tested different experimental techniques and I provided a real-time data analysis
to estimate the filling status of each bucket.
First a real-time data treatment was created to analyze data from the FCT and from a button of a
Beam Position Monitor (BPM): the output of the analysis consists of a Filling Pattern array with 448
elements, corresponding to the 448 ALBA buckets and containing the respective quantity of current
calculated with an estimated precision of the order of 1%. This on-line program is now running in the
ALBA device server and the output is stored in a general archive every minute. A Graphical Users
Interface (GUI) has been developed to allow users to have the desired information about the Filling
Pattern.
To improve the precision of the measurement another technique was tested: a photomultiplier
(PMT) was used to detect the synchrotron light reaching the ALBA diagnostic beamline (named
Xanadu). The temporal distribution of the radiation directly depends on the electron distribution
in the beam: connecting the PMT to an oscilloscope the filling pattern can be observed. Data were
collected and analyzed with a program similar to the one used for FCT and BPM, in order to provide
as output the same 448 elements Filling Pattern array. In this case the precision of the measurement was estimated to be 0.4%, consistent with the resolution of the 8 bits scope. However the PMT is not
sufficiently fast and the consequent systematic error does not to allow an improvement of the results
obtained for FCT and BPM.
At the end of each of the three procedures described in the thesis, a 448 array long, containing the
charge to be re-injected into each bucket, was calculated.
In 2014, when top-up operation will start, these procedures will be used to provide all the necessary
information for the bunch refilling.