[Halld-offline] [Revised 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. 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).


[figure:1]

This 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. The value is still a bit rough
[figure:2]


The following plot was made by calculating the time for every event in run 30785 from the 250MHz clock timestamp. The red and green markers indicated the identified trip and recovery points based on the 10nA criteria. The values plotted for the trip and recovery are shifted by 84 seconds relative to what is currently in the CCDB. The source of this shift is not not known, but it may be the difference between the clock recording "unix time" in the TS crate when writing sync events and the clock used by the EPICS IOC when recording the beam current. By comparison, the EPICS archive for the beam current during the run is shown below.
[figure:3]


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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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