To:		Distribution				11 Dec 95
	From:		Martin Nordby
	Subject:	Minutes of Near IR Engineering Meeting of 8 Dec 95



Announcements

The 15 Dec 95 Near IR Engineering and Physics Meeting will be devoted to a 
Mini-Review of the Q2 Magnet design options.  This will focus on the feasibility 
of the permanent and electro-magnet designs.



Motion of an Isolated Detector

Martin Nordby presented results of ongoing work investigating the impact of a 
base-isolated detector on the machine-detector interface.
One design for the Q2/4/5 Raft with an isolated detector is a Raft which is 
mounted to the ground for operation, but is "grabbed" by the detector during an 
earthquake.  Break-away in-board supports allow the Raft's in-board end to 
move with the detector, pivoting around its out-board support point.  However, 
the location of the in-board pivot point can affect relative motions inside the 
detector.
With the in-board pivot point at the out-board end of the Q2 shielding plug, the 
Q2 septum chamber can swing inside the tight inner diameter of the shielding 
plug.  At the Q1/Q2 Bellows at 2200 mm, the relative motion between the Raft-
mounted Q2 chamber, and the detector-mounted Q1 chamber, can be 1.6 
inches (for an 8 inch detector motion).  Furthermore, the Q2 chamber also 
moves with respect to the Q2 shielding plug.  This requires that the inner 
diameter of the plug be increased by 2 inches, to leave enough clearance so 
the one-of-a-kind Q2 chamber is not damaged by being pinched in the Q2 plug.
An alternative pivot point is in-board of the Q2 plug, in-line with the Q1/Q2 
Bellows.  This essentially eliminates the offset at the bellows.  However, the 
inner diameter of the Q2 plug would still need to be increased by 2.25 inches, 
as would the slots in the shielding plug for the structural members of the Raft 
which would reach in through the plug.
The bottom line is that, with either design, the inner diameter of the Q2 shielding 
plug must be increased by around 2 inches to prevent damage to the Q2 
Chamber.  Furthermore, the 3-D magnetic analysis becomes that much more 
important, as more material may neeed to be removed from the plug.
Also, if the detector is sensitive to yawing on its isolators, the angle of yaw will 
add to the required clearances.  This potential yawing is being investigated by 
Jim Krebs and Les Dittert.



Q2 P.M. Correction Using a Harmonic Correction Ring

Ross Schleuter presented a correction method for tuning out the harmonics in a 
permanent magnet Q2.  The method uses a technique of rotating pairs of 
magnetic dowels.   A "Harmonic Correction Ring" contains a ring of 32 such 
pairs.  By rotating the pair to adjust the field orientation, and counter-rotating 
dowels within a pair to adjust field strength, the 16 pairs can be used to correct 
for errors in the main Q2 quad.
These pairs of dowel shims can be placed at an arbitrary radius, and have any 
size.  As the radius of the shim location increases, they become more sensitive 
in eliminating harmonics, but the size of the shim must get bigger.  Thus, radius 
and size must balance so that the dowels are sensitive enough to tune down to 
the desired field quality, yet strong enough to tune out the largest expected 
errors (without requiring overly-large shims).
Once the geometry of the corrector ring is established, the corrector program 
produces a list of rotation angles for the various shim elements, given a set of 
harmonics which need correction.  Theoretically, this is a one-step correction 
process, but the corrector elements themselves will contain errors of field 
strength, orientation, and dowel size.  These errors can also be corrected-for 
using a secod iteration of the correction method.  However, Ross estimated that 
these errors are sufficiently small that they could be ignored.
With the program up and working, Dave Humphries and Ross will look at how to 
correct for expected harmonics from "real" tolerances for both Q2 and Q1 
magnets.



Correction of Q1 Harmonics

Stan Ecklund presented an estimate of how the Q2 correction method could be 
used for the Q1 permanent magnet.  Because space is at a premium, the 
magnetic dowel shims were placed radially outside the dipole blocks at 180 mm 
radius.  However, at this radius, only the dipole and quad errors could be 
corrected.  This is because the 5/16 inch dowels are not big enough to affect the 
higher-order field harmonics at the beam stay-clear.
Stan estimated that if the dowels could be moved inward between the quad and 
dipole blocks, they would be strong enough to correct for the expected 
magnitude harmonics up to n=7.
This clearly impacts the design of the Q1 magnet, and warrants investigation 
before the Q1 prototype is ordered.  Andy Ringwall and Mike Sullivan will follow 
up on this, and Dave Humphries will confirm Stan's work using Ross' correction 
program.



These minutes, and agenda for future meetings, are available on the Web at:

	http://www.slac.stanford.edu/accel/pepii/near-ir/home.html