[Halld-tagger] Fwd: [Revised Logentry] fast raster of GlueX photon beam is working!

[Richard Jones]

fast raster of GlueX photon beam is working!
<https://logbooks.jlab.org/entry/3570432>

Lognumber 3570432 <https://logbooks.jlab.org/entry/3570432>. Submitted by
jonesrt <https://logbooks.jlab.org/user/jonesrt> on Tue, 05/01/2018 - 17:40.


Last updated on Tue, 05/01/2018 - 17:57
Logbooks: HDLOG <https://logbooks.jlab.org/book/hdlog> ELOG
<https://logbooks.jlab.org/book/elog>
We are getting a good spread in the beam position now with the fast raster
turned on. The plots of the raw wire signals make it clear when the fast
raster is turned on. Note how the inner wedge currents go from a narrow
line to a broad band, which is a signature of the beam oscillating in
position. The second and third plots show a zoomed-in view of two of this
raw wire signals, where the clear presence of a ~25Hz oscillation is seen.
The split between the two plots in the top row comes because the active
collimator DAQ decided to switch files in the middle of the raster period.
The plots that follow below are taken from the 3-4 minute period after the
start of the new AC daq run.

The following plots show the Fourier transform of the signal during the
brief period (3-4 minutes of beam) after the start of the new run. Notice
that two distinct frequency peaks show up in the Fourier spectrum,
consistent with 23 Hz and 27 Hz as programmed by the Operator. The
frequency resolution in these plots is limited by the 0.5s width of the
active collimator readout buffer. One thing I would like to try during a
following run is to increase the sample period in the AC daq. We don't
actually need anything like the 16Hz sampling frequency we have now with
the sample-averaging factor of 32. We could change this to 512 and still
cover the full bandwidth of the AC, thereby increasing our sample period to
8s, more than enough to clearly resolve the two driving frequencies. Still,
just from these plots one can see not just the dominant two driving
frequencies at 23 and 27 Hz, but their first 5 or maybe 6 harmonics as
well. And this is just with 3-4 minutes of running.

Note the presence of both frequencies in the inner x and y raw signals.
This is not surprising, as the oscillating correctors are far upstream in
the beam line, and there is plenty of opportunity in steering elements
between them and the radiator to introduce coupling between the x and y
components of the motion.
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