Re: PS target issues

[Richard Jones <richard.t.jones@uconn.edu>]

Hrachya,

Yes, the intensity profile of the collimated beam also has some 
azimuthal structure, although the azimuthal dependence is much weaker in 
the intensity profile than it is in the polarization profile.  See the 
plots below.

http://zeus.phys.uconn.edu/halld/glueXmeetings/mtg-9-2008/phi_intens.gif
http://zeus.phys.uconn.edu/halld/glueXmeetings/mtg-9-2008/phi_polar.gif

I am not clear on what you mean by "beam nuclei instability inside of 
photon collimation".  Could you explain?  I agree that we definitely 
need a direct polarimetry measurement, but because of cost it is 
currently outside the budget envelope for the Hall D beam line.  Let's 
talk some time about ideas for this.  I am not convinced that we can do 
a good job using silicon microstrips in the flight distance of 1-2m that 
we have available to us right now.  We need to go back to the drawing 
board and consider all of the options, and argue for the best one.  As 
you point out, the device in Hall B was never shown to work 
convincingly, certainly not at the few-percent level that we need for 
GlueX.  That is a topic for discussion as soon as we have a finished 
design for the pair spectrometer.

Richard Jones

Hrachya.Hakobyan wrote:
> Richard,
>
> The plot is impressve  in the sense of the quantitatively atrong 
> variations . Qualitatively it was clear, having expressions for CB 
> intensity and polarization, there is expected a noticeable azimutal 
> asymmetry both in CB intensity and polarization spectra.If you 
> remember we discussed in 2003 the  problem of beam nuclei instability 
> inside of photon collimation and it was one of the arguments of the 
> need in CB polarisation calculation methods , because Monte-Carlo 
> simulation can not reproduce unexpected beam flowing.
>  In 2006 I told you that is possible to use an azimutal variation of 
> CB intensity for photon polarimetry using strip like PS converter and 
> alternation of CB polarization setting,oriented vertically(phi=90deg) 
> or horisontally(phi=0deg) to pair production plane.
>
> Hrachya
>
>