[Halld-tagger] Tungsten tube in primary collimator

[Richard Jones]

Mark,

The reason we are doing this is so that the accelerator can "see" the beam
(at 10 nA this is easy, at 1 nA it is impossible, in between it is ??) to
hold it steady and at the same time have low enough photon flux to run the
TAC in the direct beam without pile-up issues. This collimator insert is
probably the best way. The goal there is not to measure the tagging ratio
(that will change as soon as the collimator insert is removed) but to
normalize the PS rate to the absolute beam flux for a given converter.

-Richard Jones

On Thu, Jan 21, 2016 at 7:54 PM, Mark Ito <marki at jlab.org> wrote:

> Impressive study.
>
> My question is whether we can have the accelerator turn down the wick
> enough so that the TAC rate is acceptable. Note that to do what we want to
> do, namely measure the "tagging ratio", knowledge of the absolute flux is
> not required from any source other than the TAC itself. The electron
> current needs to be stable, but it does not need to be well known. If low
> current can be delivered, then clearly the time and effort toward
> non-standard collimation could be saved.
>
>
> On 01/21/2016 09:19 AM, Richard Jones wrote:
>
> Dear colleagues,
>
> Yesterday I promised to do a quick MC study to determine what a steel
> collimator insert with an aperture adjusted to allow the TAC to run safely
> with a 10 nA electron beam and a 2e-5 radlen radiator. The answers are
> given in a quick tech note that I link below. I am not done writing it yet,
> so if there are plots or results that you would like to see added please
> let me know. The bottom line is that steel will work just fine, and it only
> needs to be 15 cm long. The inner aperture diameter should be 1.1 mm. In
> response to Tim's question, tungsten would be better of course, but steel
> seems to work just fine and might be easier to work with.
>
> http://zeus.phys.uconn.edu/halld/collim-1-2016/collim-1-2016.pdf
>
> -Richard Jones
>
> On Thu, Jan 21, 2016 at 7:55 AM, Timothy Whitlatch < <whitey at jlab.org>
> whitey at jlab.org> wrote:
>
>> Hi All,
>>
>> In speaking with the machine shop, we can take a precision ground
>> tungsten rod and cut it in half long wise with wire EDM.
>> We can then cut a 1.5mm diameter half hole in each half.
>>
>> Both halves would then be put in the 5mm primary collimator hole together
>> giving us a 1.5mm hole (or what diameter is needed).
>>
>> Tim Whitlatch
>> Hall D Engineer
>> Jefferson Lab
>> 600 KELVIN DR STE 5
>> Newport News, VA 23606-4468
>> 757-269-5087
>>
>
>
>
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