[A1n_d2n] To do items from today's meeting

[Xiaochao Zheng]

Hi Jianping:

The space between the top of the central foil and the bottom of the 3He cell is only 0.24", so there is no way to increase the central foil size by 0.25". Perhaps a combination of:

- increase the central foil size by 0.1", and move the single foil position to 0.1" or 0.15" above the current single-hole position (will be 0.25" or 0.2" below the top edge of the long foil).
- move the hole to 0.1" below the current single foil position (will be 0.15" above the top of the short foils)
- The new medium length foil can be 1.05" (hole will be 0.15" below the top of this foil)

will do the trick. Otherwise the solid target holder has to be moved vertically and I don't think that's possible at this stage.

For whether to make the 2nd foil at + or -13.67cm, I have a slight preference for z=+13.67cm (downstream) because the collimators are all upstream, although I understand the cross section will be smaller (larger scattering angle).

I updated the plot to reflect the changes. Let me know if you need a better sketch to facilitate the discussion with Bert.  I can join by phone as well if the timing works for me.
https://hallcweb.jlab.org/experiments/A1n/meetings/20180515/target_beamview_edit_alternate.png

Thanks,

Xiaochao

----- Original Message -----
> From: "J. P. Chen" <jpchen at jlab.org>
> To: "Xiaochao Zheng" <xiaochao at jlab.org>, "Jay Benesch" <benesch at jlab.org>
> Cc: "A1n d2n" <a1n_d2n at jlab.org>
> Sent: Thursday, 17 May, 2018 17:37:51
> Subject: Re: [A1n_d2n] To do items from today's meeting

> Hi, Xiaochao and All,
> 
> Put a metal tube in the middle inside RF coils (and near pickup coils)
> will affect RF field and will have an impact on AFP NMR and pulsed NMR.
> If possible, we should avoid it.
> 
> I had a discussion with Brad, seems the idea of two hole carbon foils
> as Xiaochao suggested coupled with a collimator at the harp girder as
> Jay suggested might be a viable solution. We will need to either
> increase 0.25" of the central foil size (or reduce size for each
> target), then increase the size of another carbon foil
> down (or up) stream to have an hole. The distance between the two
> hole-foils should be large enough to allow easy z-targ cut to separate
> the two foils and also provide level arm for the angle determination,
> but not on the edge to fall out of acceptance at large angle. Probably 2
> foil distance (~ 13 cm) would be reasonable.
> 
> I will talk with Bert next week (after he comes back from vacation)
> to work out the detail.
> 
> Let me know if you have any further input on this.
> 
> Best regards.
> 
> Jian-ping
> 
> 
> On 5/17/18 12:22 PM, Xiaochao Zheng wrote:
>> Sorry, the alternate picture had a few typos. Here is a better version:
>> 
>> https://hallcweb.jlab.org/experiments/A1n/meetings/20180515/target_beamview_edit_alternate.png
>> 
>> vs. current version:
>> 
>> https://hallcweb.jlab.org/experiments/A1n/meetings/20180515/target_beamview_edit.png
>> 
>> Xiaochao
>> 
>> 
>> ----- Original Message -----
>>> From: "Xiaochao Zheng" <xiaochao at jlab.org>
>>> To: "Jay Benesch" <benesch at jlab.org>
>>> Cc: "A1n d2n" <a1n_d2n at jlab.org>
>>> Sent: Thursday, 17 May, 2018 12:14:39
>>> Subject: Re: [A1n_d2n] To do items from today's meeting
>> 
>>> I have made a sideview of the target to show the current design vs. the two
>>> options proposed ("alternate"). The red is the long central foil and the blue
>>> is the short multi foil (the other six).  I used two other colors for the
>>> proposed options:
>>>
>>> JP, what is the typical clearance we need for each beam position?
>>>
>>> 1) Option 1 (magenta): make the foil at z=13.67cm (or -) longer, from 0.75" to
>>> 1.05" to make a double hole. The hole position of the central foil needs to be
>>> switched with the single foil position.  There is a problem with beam
>>> clearance, because with the new option the beam hitting the new single foil
>>> position is too close to the hole position (not a problem for the central foil
>>> but will be a problem with the new longer foil).  The new foil can be made not
>>> at the full length of 1.25" (0.25" longer than the short foils), hence 1.05"
>>> (Leaving only 0.1" for the raster).  can the beam position be moved by 0.1"
>>> too, to accommodate?
>>>
>>> 2) option 2 (green): add an aluminum tube at the empty position as Brad proposed
>>> (and Jay liked).
>>>
>>> Xiaochao
>>>
>>>
>>>
>>> ----- Original Message -----
>>>> From: "Jay Benesch" <benesch at jlab.org>
>>>> To: "A1n d2n" <a1n_d2n at jlab.org>
>>>> Sent: Thursday, 17 May, 2018 11:39:15
>>>> Subject: Re: [A1n_d2n] To do items from today's meeting
>>>
>>>> Ryerson stock list has 6061-T6 tubes with 7/8" OD (2.223 cm) and wall
>>>> thicknesses 0.035, 0.049, 0.058, 0.065, 0.083 and 0.125".   Ops can
>>>> thread the beam through any one of these, or a 3/4" OD tube for that
>>>> matter.  Same wall thicknesses available for latter.  I like Brad's idea.
>>>>
>>>> Jay
>>>>
>>>> https://www.ryerson.com/stocklist
>>>>
>>>>>
>>>>> the empty target position now has +/-0.522" or +/-1.325cm of space both above
>>>>> and below. This is the full distance to the solid target holder and to the
>>>>> reference cell wall.  Sounds like a 2.5cm OD Al tube is too big to fit in.
>>>>> Jianping probably can comment on this.
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