[Halld-offline] [New Logentry] Follow-up Re: Beam trip map for reconstruction

[davidl at jlab.org]

Logentry Text:
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I have made an initial population of the CCDB tables that contain beam current information for runs 30343 to 30815 (runs 30745 to 30815 are ongoing but should complete within a couple of hours). The tables are:

/ELECTRON_BEAM/current_map_epics
/ELECTRON_BEAM/timestamp_to_unix

The first gives the current map as obtained from the EPICS archive using times relative to the start time of the run as recorded in the RCDB. 
The second gives the parameters needed to convert from tics of the 250MHz clock (read out every event) to seconds since the start time of the run as recorded in the RCDB. It also has a copy of the RCDB recorded start time for convenience though it is not used in DBeamCurrent at the moment.

A pull request has been submitted that updates DBeamCurrent factory to use this format. For the conversion from tics to seconds of the 250MHz clock, the value stored in CCDB is actually ignored for the moment and a fixed value of 250.011MHz is used based on the plot below. This is because the values for the slope and offset of the 250MHZ clock tics recorded in CCDB are obtained from just the first 3 files of the run. This is sufficient to accurately determine the offset to within 1 second. However, to calculate the time in seconds from the 250MHz clock to within 1 sec over a 5000-6000 sec run, the slope needs to be known at the 10^-4 level. Thus, the first and next-to-last file from a long production run (30804) was used to fit the slope. The quoted error was the result of the ROOT fit using error bars of 1sec/sqrt(12).

The bottom figure shows the report from the hdbeam_current utility (also updated in the recent pull request). This should be more immediately useful if one wants the total "beam ON" time for a given run for normalization.

[figure:1]

[figure:2]

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This is a plain text email for clients that cannot display HTML.  The full logentry can be found online at https://logbooks.jlab.org/entry/3462743
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