From carlini@jlab.org Thu Sep  9 07:38:40 2004
Date: Wed, 08 Sep 2004 21:46:23 -0400
From: Roger Carlini 
To: finn@physics.wm.edu
Cc: 'Neven Simicevic' ,
     'Jim Birchall' ,
     'Dave Mack' , 'Juliette Mammei' ,
     'Klaus Grimm' , armd@jlab.org, 'Mark Pitt' ,
     'Allena Opper' , 'Greg Smith' ,
     'Norman Morgan' , 'Mike Finn' ,
     'Yongguang Liang' ,
     'Shelley Page' ,
     'Tony Forest' 
Subject: Re: Qweak working group - next meeting

Hi Mike:

With regards to your second point. Jim did those cases last year when he was at JLab and I don't believe there was a 
significant inprovement in focusing by rotating the coils outward. Jim could you please cross check my memory if you 
have your log books handy.

Also, Jim ran your case of moving the target upstream, indeed the average Q**2 drops, but the FOM decreases: Jim's 
recent email to me:

"A quick result using the 10-8-22 collimator and moving the target 50 cm upstream (and widening the front of the 
collimator so it's out of the way). The rate above 1000 MeV is 1465 MHz, Q2 = 0.01662, figure of merit = 0.405. The 
original 10-8-22 collimator had 782 MHz, Q2 = 0.0317, FOM = 0.784."

This option might still prove attractive if acceptance could be increased by going to an aggressive 10-8-28 phi 
acceptance (overlapping images maybe) if we have to live with a large "B" term. Our beam related systematics will be 
larger as the average asymmetry will decrease and our sensitivities to angle/position motion will also increase somewhat.

Best Regards

Roger



John M. Finn wrote:
> Dear Roger,
> 
> I guess we will have to agree to disagree, pending 3-d views of the
> acceptance.
> 
> If you want to increase the phi acceptance, then you should consider
> attacking the problem at its roots. The problem with defocusing occurs due
> to edge focusing at large theta angles, which now exit from the top of the
> magnet, instead of the exit face. No edge defocusing = large phi angles.
> This edge focusing can have been reduced or eliminated by 1) reducing the
> angle of incidence (increasing the focal length and softening the focus) or
> 2) by rotating the back of the coils outwards, to a more favorable grazing
> angle, which will make better use of the magnetic volume. The first requires
> a detailed optics optimization, and a willingness to reconsider the
> positions of all elements along the beam line. The second requires a change
> request in the support structure, which depends on how close they are to
> finalizing he bid package.
> 
> 
> Regards,
> Mike
>