Date: Tue, 07 Sep 2004 10:35:58 -0400 (EDT)
From: Dave Mack 
To: Allena Opper 
Cc: neven@phys.latech.edu, pitt@vt.edu, tony@phys.latech.edu, grimm@jlab.org,
     finn@jlab.org, jmammei@vt.edu, nmorgan@vt.edu, carlini@jlab.org,
     smithg@jlab.org, birchall@physics.umanitoba.ca, armd@jlab.org,
     yl0094a@jlab.org
Subject: Re: Qweak working group - next meeting


        Allena et al,

        The mini-torus is a perturbation on the trajectory. I do not think
it is true to say that the acceptance-defining collimator MUST go before
the mini-torus. When Greg and I briefly looked at this long ago, one only
needed a crude field map (say 5%? help, Mark) for the resulting error on
absolute Q^2 to be negligible. Admittedly, it is more difficult to measure
a weak field to 5% accuracy than a strong field (due to zero errors in the
Hall probes), and presumably the error derivative for misaligments of the
1/r mini-torus field are pathologically large. But I do not think there is
a hard constraint here, only a trade-off.

        regards,

        Dave