[Halld-tagger] Quadrupole magnet question

[Richard Jones]

Alex,

You wrote:

    It was asked at the run meeting for a method to check the polarity
    of the quadrupole. Do you have a process? I remember taking data
    with both positive and negative currents and sending you the data.

My response:
Ok, but in that case you are not really checking the polarity of the
quadrupole as much as you are checking the spot size and divergence of the
beam at the radiator. What one measures is the height of the
post-bremsstrahlung electron swathe at the microscope, counting only the
portion of those electrons that tag photons that get through the
collimator. Is that what you want to measure?

The first time we did this we were checking the sign of the quadrupole
gradient, but that was well into the spring 2016 run, after we had
established that the beam optics were good, and we knew we had stable
conditions after running for several weeks.

At the start of a new run with a fresh tune of the beam, if you see a
difference in this distribution from the last run, a reversal of the sign
of the current in the quadrupole would be WAY DOWN the list of possible
explanations. We can include such a measurement in the start-of-run
procedures, but just keep in mind that this is a check of the general
emittance properties of the electron beam at the radiator, and NOT SIMPLY a
check of the quadrupole current direction, and it should not be labeled as
such in the run plan.

-Richard Jones

On Thu, Nov 17, 2016 at 10:03 AM, Alex Barnes <barnes at phys.uconn.edu> wrote:

> Hi Richard,
>
> I think the idea was that it should be checked as part of the "beginning
> of run" checklist.
>
> Richard Jones wrote:
>
>
> Alex,
>
> Yes, that is correct. I can make a logbook entry showing what the
> optimal settings are. I think it is difficult to get that reversed
> from one run to the next, isn't it?
>
> -Richard Jones
>
> On Thu, Nov 17, 2016 at 9:10 AM, Alex Barnes <barnes at phys.uconn.edu
> <mailto:barnes at phys.uconn.edu>> wrote:
>
>     Hi Richard,
>
>     It was asked at the run meeting for a method to check the polarity
>     of the quadrupole. Do you have a process? I remember taking data
>     with both positive and negative currents and sending you the data.
>
>     Thanks,
>
>   & nbsp; --
>     Alex Barnes
>     PhD Student
>     Experimental Nuclear Physics
>     University of Connecticut
>
>
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