[Halld] Proposed intensity scan for Fall 2018

[Richard Jones]

Hello Justin,

If we want to understand rate-related systematics, wouldn't it be better to
push the upper limit of the scan higher? This way we learn something about
what starts to go wrong at lower intensities, where we might want to run
during the high-intensity period.

If it doesn't break anything, we should take some data at higher
intensities, even if we have to prescale the trigger. I propose running two
or three more points up to 700 nA on this diamond. This 700uA comes from
the original design intensity for GlueX which was 1e8 photons per second on
the target in the range 8.4 - 9.0 GeV (or 8.2 - 8.8 GeV with the present
endpoint).

I realize that this 5e-4 radlen in the spreadsheet for this diamond is just
a placeholder, but that value should be closer to 3e-4. Radiation length is
not really a valid metric for a coherent bremsstrahlung spectrum, but in
the low-energy tail it is valid, where the radiation length of diamond is
close to 15um as long as you stay away from the channeling condition. To
get this, you cannot just take amorphous carbon and rescale it by the
density, of course, as the crystal structure modifies the radiation length
at all orientations.

-Richard

On Mon, Nov 19, 2018 at 10:11 AM Justin Stevens <jrsteven at jlab.org> wrote:

> Dear Collaborators,
>
> Following the discussion at this morning’s RC meeting for an intensity
> scan this Fall, here is what I would propose:
> https://urldefense.proofpoint.com/v2/url?u=https-3A__docs.google.com_spreadsheets_d_1UT3o4yJ-2DavlIQzmZKJo2nRrgVPzYKJvGPJ0oqAn81Oo_edit-3Fusp-3Dsharing&d=DwIFaQ&c=lz9TcOasaINaaC3U7FbMev2lsutwpI4--09aP8Lu18s&r=Mwj7jqW_Gg8VvugDHdwA5w&m=OgxGKSIJROSN2rUZ0VJwy7aDxd5O7BGRcWyUi5XP5rU&s=ZJyuRUa6ERnTXK5jDRChrMO8IMLFlbiXHRAubNIgp1M&e= 
> <https://urldefense.proofpoint.com/v2/url?u=https-3A__na01.safelinks.protection.outlook.com_-3Furl-3Dhttps-253A-252F-252Fdocs.google.com-252Fspreadsheets-252Fd-252F1UT3o4yJ-2DavlIQzmZKJo2nRrgVPzYKJvGPJ0oqAn81Oo-252Fedit-253Fusp-253Dsharing-26data-3D02-257C01-257Crichard.t.jones-2540uconn.edu-257C2a054bc8dc824538f06908d64e314804-257C17f1a87e2a254eaab9df9d439034b080-257C0-257C0-257C636782370905211494-26sdata-3D9Sov7Fn68-252F0EsSrmdAiZ-252BHwwCC8KslfwMZPmqOufmqM-253D-26reserved-3D0&d=DwIFaQ&c=lz9TcOasaINaaC3U7FbMev2lsutwpI4--09aP8Lu18s&r=Mwj7jqW_Gg8VvugDHdwA5w&m=OgxGKSIJROSN2rUZ0VJwy7aDxd5O7BGRcWyUi5XP5rU&s=wvTwzIxUvHOhTYjExQRIS2tQ5VHhgBjX6JckyH3jzzY&e= >.
> There are two sheets at this link: RunPeriod-2018-08 (the proposal for this
> week) and RunPeriod-2018-01 (the data we've collected previously).  As a
> reminder, in Spring 2018 we did not have any high-statistics intensity scan
> with the final Tungsten foil installed in the beamline.
>
> The proposal covers the same range of intensity (Beam current x RL) as we
> had in Spring 2018, with 100M events at each setting (aside from the very
> low intensity, where the rate is too low).  As Sergey requested, this also
> includes a raw mode run at each setting of 1M events, assumed to run at ~3
> kHz.  The goal is to have a complete set of intensity scan data for
> efficiency studies with this Fall 2018 data.
>
> The estimated beam time required for this proposal is ~28 hours at 100%
> efficiency, so it would likely take at least 2 days of calendar time to
> complete.
>
> Comments/suggestions welcome,
> Justin
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>
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