Carl and all-
	We're going to try to drive the field lower, starting this morning. 
I'm not sure either how low we can go, but we'll know more about that
subject tomorrow.
	I think that the limit is likely somewhere between 2G and 10G.  I
intended my 2G not as a real estimate of the limiting field, but rather
as a ballpark estimate.  I think that if we were using Michel positrons,
we'd want the field to be less than ~5G, based on the 2G senstivity. 
120MeV/c pions at a few degrees may be a slightly  different matter, but
on the same order.
	Certainly 300G is far too high.

			nate
	

Carl Gagliardi wrote:
> 
> Nate and Don:
> 
> I don't think we need a lot of fancy Monte Carlo to estimate the residual
> field we can tolerate.  In fact, I think a calculator and some common sense
> will suffice (at least up to a factor of 2 or so).  Here is my attempt:
> 
> To estimate what we can tolerate, remember that, in addition to
> straight-through beam particles at momenta up to ~120 MeV/c, the alignment
> studies will include "straight" positron tracks from Michel decays.  The
> latter will be a far more stringent constraint, especially since we want
> them to be "straight" even at relatively low energy.  So, for a figure of
> merit, consider a positron with a pT of 10 MeV/c.  At 100 G, this will have
> a radius of curvature of 334 cm.  If I did my arithmetic correctly, such a
> positron, if it has a total energy of 50 MeV, will deflect 1.6 mm over a
> longitudinal distance of 50 cm.  A 14 MeV positron with the same pT would
> deflect 5 times this much.
> 
> Clearly this is too much to tolerate.  In fact, these calculations indicate
> that even 10 G is probably too much to treat as precisely straight, given
> the chamber resolution, but at least it's in the ballpark.
> 
> My conclusion:  Nate's 2 G "reach and grab" number isn't crazy. (!?!)  We
> might be able to tolerate twice that, but not five times.  Thus, my own
> original reach and grab guess -- 10 G -- was too high.
> 
> Carl
> 
> +-----------------------------------------------------------------+
> | Carl A. Gagliardi                                               |
> | Cyclotron Institute              Phone:   (979)  845-1411       |
> | Texas A&M University             FAX:     (979)  845-1899       |
> | College Station, Texas  77843    E-mail:  cggroup@comp.tamu.edu |
> +-----------------------------------------------------------------+

-- 

--------------------------------------------------
Nathan Rodning
Professor of Physics, University of Alberta
**** 2001/02 at TRIUMF:  (604) 222-7549
**** TRIUMF Fax:  (604) 222-1074
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