[Halld-cal] [Revised Logentry] FCAL HV scan

[gasparan at jlab.org]

  Thanks Colin for information and suggested solution. I think we go on
 that way and see how to get maximum from the current FCAL for the
 possible Compton cross section measurement.

 Ashot


> Hi Ashot,
>
> I do not think you will need to run at 1800V. Most of the FCAL is
> calibrated properly (we know the inner and outer layers need to be
> calibrated) and when new HV set points are determined it's unlikely that a
> lot of new channels will need to be set to 1800V. The bases that are
> exhibiting this behavior all have high currents being drawn from them. The
> max value we can see on EPICS is 15mA, but it's likely the current being
> drawn is higher than this. We have been aware of this for some time now
> and
> are taking steps to address it. If for some reason a base can not hold the
> HV at which you want, it can be replaced with a spare. Since we've seen
> the
> failure rate of bases dying decrease this run period, we plan on removing
> more bases with large current draw in the future.
>
> -Colin
>
> On Mon, Nov 19, 2018 at 12:23 PM <gasparan at jlab.org> wrote:
>
>>
>>   Hi Sasha,
>>
>>  a very good test. It looks like we may have serious problems if we need
>>  to set 1800 V range.
>>  We will need to have more information (gains, electronic noise, ...)
>>  before making some decision.
>>
>>  Thanks,
>>  Ashot
>>
>>
>> >
>> > Logentry Text:
>> > --
>> > FCAL readout: RAW mode (mode 10)
>> >
>> > Use violet LED, 500 Hz
>> >
>> > 1500 V
>> > ----------
>> >
>> > Run  51604,  130 K events,  17 V
>> > Run  51605,  122 K events,  22 V
>> >
>> > 1550 V
>> > ---------
>> >
>> > Run 51606,  120 K events, 17 V
>> > Run 51607,  120 K events,  22 V
>> >
>> > 1600 V
>> > ----------
>> >
>> > Run 51608, 17 V
>> > Run 51609,  22 V
>> >
>> > 1650 V
>> > ----------
>> >
>> > Run 51610, 17 V
>> > Run 51611, 22 V
>> >
>> > 1700 V
>> > ----------
>> >
>> > Problems with setting HV on channel (22,22 ;  -8,-8)
>> >
>> > Run 51612,  17 V
>> > Run 51613,  22 V
>> >
>> >
>> > 1750 V
>> > ----------
>> >
>> > Not able to set this voltage on the following channels:
>> > Channel, Read back voltage
>> >
>> > (1, 31) 1610 V
>> > (7, 46) 1601
>> > (13, 23) 1618
>> > (13, 47) 1651
>> > (20, 26) 1600
>> > (22, 22) 1607
>> > (25, 26) 1620
>> > (29,7) 1640
>> > (33,47) 1609
>> > (35, 37) 1630
>> > (44, 30) 1590
>> > (41, 39) 1660
>> > (44, 30) 1590
>> > (47, 38) 1625
>> > (49, 31) 1612
>> >
>> > Run 51614,  17 V
>> > Run 51615,  22 V
>> >
>> > 1800 V
>> > ---------
>> >
>> > Cannot set HVs on 41 channels
>> >
>> > Run 51616,  17 V
>> > Run 51617,  22 V
>> >
>> >
>> >
>> >
>> >
>> >
>> > ---
>> >
>> > 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/3628470_______________________________________________
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>>
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>
>
> --
> Colin Gleason
> Postdoctoral Fellow
> Indiana University
> Department of Physics
>