[BTeam] [New Logentry] arc dipoles calibrations

[benesch at jlab.org]

Logentry Text:
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Joe Grames reminded me yesterday that Yves Roblin and Doug Higinbotham had determined that the energy gain per linac on first pass was 1092.5 MeV/c from energy measurement and spin precession.     The injector momentum is low by 2.5 MeV/c per BEM, 2%.  It should be checked in the 0L06 spectrometer at some point.  

If the injector momentum reads 123 MeV/c at 0L06, either the spectrometer dipole or MBL calibration is wrong. 

In either event, since the energy in hall A was ~5 MeV high, arcs 1 and/or 2 are in error since they appear to be on design.  

Assume the energy exiting the injector is 123 MeV/c and that the two linacs are at 1092.5 MeV/c as spin precession to arcs 4 and 5 suggest per Joe. 

Energies for  arcs 1-6, where synchrotron radiation is not a big  loss, would be 
arc 1	1215.5	(1213)
arc 2	2308	(2303)     
arc 3	3400.5	(3399)
arc 4	4493	(4499)
arc 5	5585.5	(5591)
arc 6	6678	(6664)

Compare these values to the BEM momentum numbers in figure 1, in parentheses above.   There are five discrepancies at the 0.001 - 0.002 level.    Polarimetry measurements in hall A in all five passes would provide information for correction of the arc dipole field maps so Ops can more accurately establish the beam energy in the future.  

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Figures 2 and 3: I wondered why the hall A BEM indicator was red, so I opened the BPM screen.  Most of the BPMs were red.  Most of the BPMs should not be in the calculation at all: I'd include at most 1C07 to 1C17, two BPMs each at entry and exit and those in the arc proper.   In figure 3 I show BEM with only the five green BPMs included.    Figure 4 is the Hall A spike screen.   1C20 and the Compton BPMs show no wire sums, but all the BPMs before 1C20 and after Compton do.   No beam in Compton.    Figure 5 shows that 1C20 does respond.  


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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/3399533
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