Here is John Sheppard's message of August 12 reformatted to allow easy reference to his enclosed files, which are: AWW

Date: Fri, 12 Aug 2005 12:39:32 -0700
From: "Sheppard, John C." 
To: Kirk T McDonald, Peter Schuler 
Cc: e166-l ,
     "Walz, Dieter R."
Subject: RE: 5 basic questions

Attached are .pdf plots of the measurements that I made in September before the
dipole gaps were increased, without the vacuum chamber but with the dipoles and 
lens mounted together. The data can be found in the matlab .m files

If Alexander has the time, the mermaid modeling should be very good for these devices. 
Someone needs tell us the as built/installed geometry (Kirk and Dieter?). 

Also, if Kirk can tell us how much the gap changed, then we can estimate the 
dipole field based on the previous measurements to a reasonable accuracy. 
The data was reproducible to a fraction of a percent (surprisingly, to me).


John C. Sheppard, 
E-166 Co-Spokesman,
SLAC International Linear Collider Design Group
(650)926-3498 office     (650)926-5124 fax

Stanford Linear Accelerator Center
P.O. Box 20450 MS 66              
Stanford, CA 94309                  
2575 Sand Hill Road
Menlo Park, CA 94025                   
-----Original Message-----
From: owner-e166-l _at_  
On Behalf Of Kirk T McDonald
Sent: Friday, August 12, 2005 12:08 PM
To: Peter Schuler
Cc: e166-l
Subject: Re: 5 basic questions

Peter, Karim, et al.

(1) Is the 4th order polynomial field description of the lens that
    originated, I believe, from Alexander some 18 months ago, still
    valid, or do we have a more recent update?

No more recent update, so a good starting point.

(2) In order to relate the field to the current setting, do we know
    e.g. the central field value for the operating point of 400 amps?


(3) What was the actual spacing btw. the lens center and the e+
    production target, and what was the actual spacing to the
    spectrometer? And to what values will these change in September?

These are not well known.

Possibly knowable is the spacing from upstream edge of the steel of the solenoid to the 
center of the vertical pipe in which the targets are mounted.

Then, it may be possible to know the locations of the 3 targets relative to the center of 
the target pipe.
My "guesses" as to these things are recorded in my AutoCAD file
dated April 7, 2005.
(4) On the dipole spectrometer, for a zeroth order homogeneous field
    approximation, do we have a field value for our standard operating
    point of 200 amps?

Not really.  Since the magnet gap was widened to accommodate the vacuum chamber, 
the field is a bit lower than originally planned.

We do know the correlation between solenoid and dipole currents for good positron 
transmission.  So, if we manage to get even one of the two fields measured, 
we could extrapolate to the other...

Remember, we were not able to power the magnet until after it was installed in the tunnel 
-- with the vacuum chamber.

There is a "spare" Conflat port on the "south" end of the vacuum chamber. 
We could remove this, power up the dipoles and insert a hall probe to measure the field.  
Probably this should be done sometime in September. 
Maybe around Sept 6......

(5) Is there any quantified information on how the actual field deviates
    from the fixed value approximation?


[It was easy to answer your questions -- since NO sufficed in most cases.]