[b1_ana] Fwd: TAC Report for PR12-13-011

[O. A. Rondon]

Typo alert: I'm sure everyone has noticed the error on the estimate of
the pf change per period: it should be .5E-4, not 5E-4.

So, the extremely unlikely issue of 2-3 fragments falling out of the
raster region every cycle would only cause a ~ 1E-4 effect.

Cheers,

Oscar

Oscar Rondon-Aramayo wrote:
> Hi,
> 
> Basically, on the dilution item, they are saying that the target length
> could change from the pol. half-period to the unpol. half-period, so they 
> wouldn't cancel in our  eq. (26).
> 
> Of course, if we use targets of known geometry, that change would be totally
> negligible. But for fragments we can estimate the change due to one fragment
> that *might* fall out of the slow raster area during one period.
> 
> Since the average fragment is about 0.008 cm^3 (2 mm on the side) and the
> raster volume, for p.f. = 0.6, is pi*1.1^2 cm^2*3 cm*0.6 = 6.8 cm^3 the 
> change would be 1 part in ~ 850.
> 
> During SANE, there was one instance in about 500 h of beam time, of sudden 
> polarization increase (about 8% absolute in under 1-2 min), which could be 
> attributed to fragment loss/rearrangement about the NMR coil. Nothing was 
> seen during RSS (about 250 beam hours). The jumps seen at SLAC happened with 
> the SLAC beam of 20 muA per 4 mu s pulses at 120 Hz, not CW beam.
> 
> So I would estimate a less than 20h/500h*1/850 ~ 5E-4 change per period.
> 
> The data taking sequence:
> - unpol. top target
> - pol. top target
> - unpol. bottom target
> - pol. bottom target
> - anneal
> 
> for the first cycle would optimize the low temperature irradiation to build 
> up the ND3 polarization. The unpol. data could be taken at 150 nA to speed 
> up the dose build up.
> 
> For the later cycles, it would be best to take pol. data first, so the 
> initial dose is lowest. Dumping the LHe in the nose does not change the 
> dilution factor (all data are taken with LHe), and it's extremely unlikely 
> it would cause any material loss. But this could be studied during the run, 
> by comparing yields for the same cup from one period to the next.
> 
> Research on making known geometry material would be most valuable.
> 
> Third arm luminosity monitors would need to do a better job than watching
> the yields, with acceptance and raster cuts, of the data itself.
> 
> The other change, due to the acceptance dependence of beam position could be
> tricky, although at forward angles and with longitudinal target field, it
> should be easier to control. The problem is that the beam offsets affect the
> reconstruction of kinematic quantities with software spectrometers such as 
> the
> HMS.
> 
> Cheers,
> 
> Oscar
> 
> 
> On Tue, 28 May 2013 23:10:24 -0400
>   Karl Slifer <karl.slifer at unh.edu> wrote:
>> ---------- Forwarded message ----------
>> From: Stephen Wood <saw at jlab.org>
>> Date: Tue, May 28, 2013 at 11:06 PM
>> Subject: TAC Report for PR12-13-011
>> To: Karl Slifer <slifer at jlab.org>
>>
>>
>> Karl:
>>
>> Attached please find the TAC report for PR12-13-011.
>>
>> This proposal was also reviewed by the the independent Technical review
>> committee.  This report should come to you through official channels, but I
>> will send you a copy if I can get it.
>>
>> Steve
> 
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