epics variable in baryon

Epics variables during Baryon experiment

General Info
                       Epics information from various equipment is stored with the data. What data is stored is determined by the file epics.dictionary during data taking. In the beginning of the file are comments explaining the format. Most epics variables have comments explaining what they are. Some variables are saved every 2 seconds and some every 30 seconds.

                     When replaying the epics info can be written out to a file, epics####.txt. For most runs this was done during the online replay and the epics files are in /work/hallc/e01002/charge_scalers. For subsequent replay the epics files are in /work/hallc/e01002/pass#/scalers .

            A tcl script , extract_epics.tcl ,which goes through the   epics files and extracts the epics info that one wants is available. The script extracts the data for each "epics read" and then get the mean and standard deviation for the epics variable for the run. The info is stored in the file epics.out .

SOS magnets
         Plots of the SOS Q1, D1 and D2 magnet currents versus run number in sos_magnets_p=1.0.ps and sos_magnets_p=1.74.ps . For the 1.74 setting, the currents are unstable for Q1 and D1 at the beginning of the experiment but after that they are stable.   For pass1 and pass2 replay, all runs which had SOS nominally set to 1.74 used spcentral = 1.74 in the standard.kinematics file. For pass 3 replay, the spcentral was modified for each run by spcentral = 1.74*(D1 current)/985.5 . A plot of the ratio (D1 current)/985.5 versus run number. The values of spcentral used are given in this file ( listing: run number, spcentral, standard deviation of spcentral).

Beam Energy
            The beam energy was not measured during the BARYON experiment. A table of the beam energies during the Spring03 running is here. The beam energy should have been 5.5015 GeV as it was during the measurement on April 24th, 2003. There was a brief change in the linac energy between this measurement and the start of the BARYON experiment, but then the linac energy was suppose to be set to the previous value. One can see in the table of beam energies that there is a epics variable HALLC:p which is a measurement of the beam energy determined by accelerator ( using ARC dipole setting and beam positions) . The HALLC:p value is usually very close to the measured value using the ARC beam energy technique. A plot of the value HALLC:p versus run number shows that at the start the beam energy is dropping. After around run 46260 the beam energy is fairly stable at around 5499 GeV. The "error" in the plot is the standard deviation of all the measurements of HALLC:p during the run. For some run periods the standard deviation is almost zero which probably indicates that the epics values of HALLC:p wasn't being updated. There is a file of the beam energy values ( run number, HALLA:p, std dev. , HALLC:p, std dev. ) .
           During pass 3 replay a value of 5496 GeV was used for the beam energy for all runs.

Beam position.
         Plots of the beam positions at BPMA (z = 327.15cm) , BPMB (z =231.46 cm) and BPMC (z = 135.35cm) . During the experiment, we tried to keep position at BPMC constant. It was fairly stable except for a couple of regions. Y is the vertical beam position with +Y up. X is the horizontal beam position with +X towards beam right.
           Projecting to the target ( z= 0 ) to get the target positions one can use different combinations of the BPMs. A plots of the target position using BPM AC   , AB , and BC   combinations have been made. A plot comparing are three combinations shows that different combinations are not consistent with each other and that offsets in the relative positions of the BPMs are needed to get them to give the same target positions. But the different combinations show the same relative behavior. The X ( horizontal position) is fairly constant ( except for a dip at runs 46260-46290), but the Y (vertical position) has a couple of periods of different positions.

Run periods	Vertical position
46068-46259	0.15mm
46260-46293	0.40mm
46294-46319	0.10mm
46320-46804	0.45mm

The vertical position effects delta reconstruction. It is 0.077 % delta per mm offset in vertical position. So if we don't put in the vertical beam position then if the beam is off by 1mm then delta would shift by .077% ( or almost 10-3) [ for SOS this is .039%/mm ]. We corrected for the raster but we didn't include movements in the centroid of the beam during replay ( up through pass 3) .
Plots of the beam angle using BPM AC , AB , and BC combinations have been made. A plot comparing are three combinations shows similar discrepancies between the different combinations as seen for the positions.