Minutes of the IR Engineering and Physics Meeting of 16 Feb 96		20 Feb 96


Q1 Radial Fields

Stan Ecklund investigated the total field in the dipole blocks of Q1.  This had 
been done for the quad blocks, to look at the combined fields from self-, dipole, 
and radial solenoid fields.  However, it was never checked for the dipole blocks.  
The outside radius of the dipole blocks is 177 mm;  at 200 mm, the radial 
solenoid field is 2.3 kG (backward end), according to Orrin Fackler's model.  
Stan assumed that the radial field decreased linearly with radius (a fairly good 
assumption), then modelled the dipole blocks in MATLAB, using 40 sub-blocks 
per block.  The results show that the highest de-magnetizing field a dipole block 
is subjected to is 12 kG at the outside radius of the block at top dead center.  
This is only marginally less than the expected peak bucking field in the quad 
blocks, so the specification for the blocks should be the same.

Two issues arose regarding the fields in the Q1 P.M. blocks.  First, based on 
David Humphries' work on Q2, we should expect to see external fields 
generated by the quad blocks in the dipole blocks.  These external fields could 
add apppreciably to the fields in the dipole blocks.  Stan will looked at this.

Second, the analyses on both sets of blocks have used radial solenoid fields 
which are generated from a 15 kG solenoid.  Since we are pushing the limit on 
the SmCo material, small increases (2-3 kG) in the solenoid field during 
operation could cause large, and possibly damaging, changes to Q1.  Harvey 
Lynch said that the 15 kG would be the maximum field for the solenoid, but the 
power supply for the solenoid may need to be included in the MPS system.

Another question arose regarding the peak fields during a solenoid quench.  
Lew Keller has looked at the structural and thermal loads and expected 
temperature rises in various components due to a quench, but not necessarily 
at the induced fields in Q1.

Martin Nordby will follow up on this.



Q2 Shielding

David Humphries reported on progress in the Q2 HEB shield development.  He 
found that 2-D Halbach quad external fields can be satisfactorily reduced in the 
HEB passage by adding a 1 mm shield around the HEB beampipe.

By adding a disk at the end, as well as a 1 mm thick cylinder around the quad 
blocks, the end external fields can also be shielded.  Previously, David showed 
that a 1 mm thick end disk reduces the normalized field at the HEB centerline 
from -50 G to -35 G.  By increasing the end disk thickness to 1 cm, David 
brought the normalized stray field down to +5 G.  Furthermore, the shield is not 
saturated, as for the 1 mm thick model.  The change in sign suggests that there 
is an optimal thickness betwenn 1 mm and 1 cm.

However, the end disk reduces stray fields by effectively short-circuiting the 
nominally 2-D magnet circuit by adding a very-low-reluctance plate at the end.  
This also reduces the main quad field.  For the 1 cm thick disk, the main field 
decreases by 10%.  With the current design, there is no room to increase the 
quad by 10%.  David will look for the compromise solution which should 
minimize this loss of main field without increasing the stray fields appreciably.



Radiation Monitors

Hobey DeStaebler reported on discussions he has had regarding the radiation 
monitors surrounding the ends of the Be Vertex Vacuum Chamber, at the ends 
of the SVT support cone.  The SVT group needs to nail down cable runs and 
final volume envelopes for this by mid-April, so some issues need to be 
addressed.  Specifically, Roy Kerth felt that they now have room for cables with 
a 100 micro-second response time.  If faster read-out were needed, the cables 
would probably have to be bigger.  This raises bigger questions regarding the 
function of the monitors.  They could be used for:

	1.	Detector protection
	2.	Machine tuning using background information
	3.	Machine physics studies
	4.	Bunch-to-bunch readback on backgrounds

We will discuss this more at the 1 March IR Meeting, and bring in a larger group 
to get more feedback from both machine and detector people.



These minutes, and agenda for future meetings, are available on the Web at:
	http://www.slac.stanford.edu/accel/pepii/near-ir/home.html