[Tpe] Tagger calibration

[Will Brooks]

Dear all,

  I think this might be even better than simply repeating the previous 
calibration. There could be changes since the previous calibration was 
performed, and the results of this procedure could be cross-compared 
with what was obtained before.

  I believe the measurement will take longer than an hour or two to 
perform. The magnet setting procedure, I think, includes a hysteresis 
compensation that requires some time. If the plan is to hit the beam 
onto 300+ detectors, and you take a minute per detector, that gives 300+ 
minutes. Also, has anyone thought about the optics? If the beam is 
converging or diverging, it will have a different spot size at one end 
of the array than the other.

It also might be good to think about what peak rate the detectors can 
handle, and whether that's compatible with what the accelerator can 
deliver and monitor. In some sense, all you need to know is which 
detector was hit, and if the response is not linear, it is still ok. On 
the other hand, you probably don't want the signal size to be orders of 
magntitude beyond the normal. And yet if the beam current is too small, 
it will be hard for the accelerator to monitor its position; if its 
position drifts around, it can spoil the measurement.

In any case, if there are no show-stoppers, it has the very attractive 
feature that it is an independent procedure from the previous one, so it 
can help to understand the tagger calibration even better.

Thanks,

  - Will



On 7/2/10 12:54 PM, Larry Weinstein wrote:
> Dear Folks,
>
> One possibility suggested by Dave Kashy (with modifications from 
> Stepan and Eugene) is to use the primary electron beam to calibrate 
> the tagger.
>
>    1. Put a 300 MeV pulsed low-current electron through the tagger magnet
>    2. Sweep the magnet field slowly.
>    3. Read out the tagger detector scalers and the tagger magnet
>       current in epics.
>    4. Correlate the magnet current with the location of each of the
>       tagger detectors.
>
> After the TPE run, when we have replaced the detectors, repeat the 
> procedure to determine the precise locations of the detectors.
>
> According to Arne, it would take about 12 hours to configure the 
> machine in this way.  It would take an hour or two to do the 
> measurement, so the total time required would be less than one day of 
> exclusive beam (ie: no other expt can run during this time).
>
> If Qweak is willing to let us do this, we can do this before the 
> summer shutdown.  Alternatively, if Primex runs before TPE, we could 
> do this at the end of the Primex run.  It would be better do this 
> before the summer shutdown to allow us the flexibility of removing low 
> energy tagger counters during the summer shutdown (assuming that 
> Primex won't use them).
>
> Note that this assumes that TPE will run this fall.
> -- 
> 				Sincerely,
> 				Larry
>
> -----------------------------------------------------------
> Lawrence Weinstein
> University Professor
> Physics Department
> Old Dominion University
> Norfolk, VA 23529
> 757 683 5803
> 757 683 3038 (fax)
> weinstein at odu.edu  <mailto:weinstein at odu.edu>
> http://www.lions.odu.edu/~lweinste/  <http://www.lions.odu.edu/%7Elweinste/>
>
>
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