Injection Related Background due to the Transverse Feedback Page: 2 of 3
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(-20, 100) VAL-10.7664
(-200, 100011) VAL-092.73
_ _ _ _ _ _arts
(-400. 2000) VAL-1563.04
4- 4 144 + 4 14 FTS # O
Feb 05, 03
Figure 4: Three minutes top off injection. The top two lines show the HER and LER currents, then background
signals SIGIO for HER and SIG11 for LER.
3.2 Electromagnetic Calorimeter
The BaBar electromagnetic calorimeter provides
detailed information on backgrounds during injection.
This detector consists of 6580 Th-doped CsI crystals,
each readout by a pair of photodiodes. The photodiode
response is amplified, shaped, and digitized at 3.72 MHz.
The resulting readout stream is split onto two paths, one
path to the BaBar trigger electronics and another to an
intermediate buffer in the calorimeter readout boards
where up to 256 samples (68.8 s) can be processed after
a trigger decision. The BaBar trigger system generates
trigger decisions from input on the first path, and a
timestamp is recorded from a counter based on the PEP-II
476 MHz clock divided by 8.
The single-cluster trigger times (E > 100 MeV) are
compared with the times of individual injection shots.
This data source has small deadtime (2.7 s per trigger)
and runs in parallel to the normal BaBar data acquisition.
On the other hand, during periods of abnormally high
backgrounds in HER injection the trigger system can
suffer inefficiency from detector saturation effects.
An example of background trigger timing with respect
to HER injection is shown in Fig. 5. Background trigger
rates are typically heightened for the first 30 s after
injection and then rise again over the next 3 - 5 ms. The
trigger rates fall over a time scale of roughly 5 ms. Finer
analysis of the timing confirms that the additional triggers
occur at intervals of 7.34 s, the revolution period of the
injected bunch. The injection backgrounds also depend
upon the progress into a fill. Figure 6 displays the
injection backgrounds for both the LER and HER when
filling from 0 to maximum current. A Fourier transform
of the background trigger timing, also in Fig. 6, shows a
distinct contribution from synchrotron oscillations. The
observed HER synchrotron oscillation frequency drift
could be from time-lacking of the HER RF cavity tuners.
- 30 .... ...
0o 0005 0.01 0.015
Time After Iniection (sec)
Figure 5: Calorimeter triggers show a large background
increase several ms after an injection.
The second calorimeter readout path can be used to
obtain unbiased sampling at well-defined times using the
PEP injection timing signal and a programmable delay
generator. This data includes the detector response
magnitude and its sampling is immune to detector effects
associated with high backgrounds. Figure 7 shows an
example of the calorimeter energy measurements
accumulated over several scans of the 7 ms period
following an injection. The LER synchrotron oscillation
component is observed to be a greater exposure
contribution than indicated by the trigger analysis.
StripT-1 Graph Wirdow mmm n
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Decker, F.J.; Akre, R.; Fisher, A.; Iverson, R.; Weaver, M. & /SLAC. Injection Related Background due to the Transverse Feedback, article, March 18, 2008; [Menlo Park, California]. (digital.library.unt.edu/ark:/67531/metadc902756/m1/2/: accessed December 14, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.