User name paschke/secrest
Log entry time 02:41:39 on October16,2002
Entry number 88342
keyword=Study of injector charge asymmetry
Measured charge asymmetry at injector to compare G0 and HAPPEx parity DAQ
results. Recent measurements with the HAPPEx parity DAQ in Hall A have shown
a charge asymmetry (Aq) distribution that was widely double peaked, with the peaks
corresponding to different orderings of helicity in the pair. No independent
measurement has confirmed these results.
Two measurements were taken by both the G0 and HAPPEx DAQs, one with the
G0 beam (currently running to the BSY) on and one with the G0 beam off.
Electronics problems kept us from measuring the same monitors. Both DAQs
recorded monitors downstream of the chopper, so the effects from the Hall B beam
The analysis discussed here is preliminary only. In particular, pedestals are a major question. Without an opportunity to take pedestal data, the correct pedestals for the new hardware configurations could not be found.
The summary of results from the PRELIMINARY analysis:
1) The double peaking is not observed in the 5MeV region by the G0 DAQ, while
the expected double-peak is seen by the HAPPEx injector DAQ (consistent with
the HAPPEx Hall A DAQ). The G0 DAQ does observe a double-peak in the
100 keV region, but these peaks do not appear to correspond to the ordering
of helicity states in the pair. This inconsistency is not easily explained, for example,
by the possiblity of mis-set pedestals, because there is excellent agreement for
the mean and RMS of Aq (in the 0L region) when the G0 beam is off.
2) There appears to be a non-negligible effect on Aq due to the G0 beam.
Measurements in the 5MeV region show changes of several hundred ppm when
the G0 beam is turned off. However, these changes are not consistent between
the HAPPEx and the G0 DAQs.
3) There were two distinct states of the beam observed while the G0 beam was off.
During the run, the Aq distribution suddenly "cleaned up", in the each observed peak
(one in the G0 DAQ, two in the HAPPEX DAQ) narrowed. MCC reported that beam was stable to both Halls A and B during this time, with no RF trips or other obvious changes to running configuration.
Several subsequent log entries will contain figures demonstrating these results.
Figures from the G0 DAQ show bpms 0I02A and 0I04 (pre-chopper) and 0L01 and
0L02 (labeled 0L0X and 0L0Y in the figure, downstream of the chopper).
The HAPPEx DAQ read out 0I05 and 0L03, both downstream of the chopper.