From: "Stephen Brooks" <sbrooks@bnl.gov>
To: "Jain, Animesh" <jain@bnl.gov>; "Tsoupas, Nicholaos" <tsoupas@bnl.gov>; "George Mahler" <mahler@bnl.gov>; "George Mahler" <mahler@bnl.gov>; "Holger Witte" <hwitte@bnl.gov>; "Dejan Trbojevic" <trbojevic@bnl.gov>; "Vadim Ptitsyn" <vadimp@bnl.gov>; "John Cintorino" <cintorino@bnl.gov>; "Scott Berg" <jsberg@bnl.gov>
Cc: "Stephen Brooks" <sbrooks@bnl.gov>
Subject: Re: Field harmonics in PMQ_005A with new set of iron shims
Date: 2015 October 15; Thursday 11:49

I've loaded the values Animesh provided into a couple of spreadsheets. 
Perhaps the most interesting graph is Magnet5,5Afields.xls chart "Relative 
Error on X-axis", which divides the nonlinear poles by the quad magnitude to 
give relative error across the X axis.

The one iteration of shimming went from Run 1/red to Run 3/purple (Run 
2/green was a test of sextupole correction only).  Relative errors are 
1.9e-3 at X=+15mm and 5e-4 at X=-15mm.

Comparison of parameters with eRHIC:

This magnet (PMQ_005A) is 27.562 T/m (I was trying to get 27.500) and the 
aperture with <1e-3 field error runs from below -15mm to +12mm.

The BD2 magnet in the latest eRHIC design requires 28.87 T/m and beams are 
from -5.37mm to +16.73mm.  If you invert this range, it fits within the 
<1e-3 quality range of the magnet we constructed.  I'm also going to try a 
2nd iteration of shimming to see if I can fix the remaining errors.

There are spaces between the chunks (see photo) and it's actually made of 
SmCo, so getting the extra 5% gradient strength should be easy with a proper 
NdFeB redesign.

    -Stephen


-----Original Message-----
From: Stephen Brooks [mailto:sbrooks@bnl.gov]
Sent: Thursday, October 15, 2015 11:05 AM
To: Jain, Animesh; Tsoupas, Nicholaos
Cc: Mahler, George J
Subject: Re: Field harmonics in PMQ_005A with new set of iron shims

Great!  Thanks Animesh for measuring and George for putting the wires in 
this time.

I'll be doing a 2nd iteration of this shimming, starting from where it is, 
to find out if I can get rid of the last 3 units of normal octupole, or 
whether we've hit the precision limit for this particular method.

Animesh - any preference for when you'd want to measure this again (soon, 
later)?

    -Stephen


-----Original Message-----
From: Jain, Animesh
Sent: 2015 October 14; Wednesday 17:37
To: Brooks, Stephen ; Tsoupas, Nicholaos
Cc: Mahler, George J
Subject: Field harmonics in PMQ_005A with new set of iron shims

Hi Stephen,

  We finally got around to measure the permanent magnet quadrupole #5A with 
the new set of iron shims (we are still struggling to get the solenoid 
measurements started!).  The latest measurement results are attached.

  I believe the new field quality is very good.  In particular, the most 
prominent skew octupole term has been tamed very well without harming other 
harmonics much.  Impressive job!

  Thanks,
  Animesh

****************************************
Animesh K. Jain
Superconducting Magnet Division
Brookhaven National Laboratory
Upton, NY 11973-5000
Phone: 1-631-344-7329
Fax:   1-631-344-2190
jain@bnl.gov
****************************************