sPHENIX discussion of the superconducting solenoid

["Yip, Kin" <kinyip AT bnl.gov>]

Dear Pasquale,

This is Kin Yip, a physicist from Collider-Accelerator Dept. of BNL.  I look 
forward to talking with you tomorrow.

As promised, here the questions before the meeting (I put the simpler ones at 
the top and longer one at the bottom):

1) Do you have the Ansaldo CAD drawing 771620BA.DWG (and others) ?

2) Do you have the electronic versions of the Lake Shore temperature sensors 
calibration from Tallerico ?

3) Wiring diagrams showing connector/instrument assignments to the "C" 
labeled connectors etc. ?

4) Do we know what readings should we get from the strain gauges (if we make 
them work) ?

5) Why is hypot voltage limited to 520V ?  And what is the suggested voltage 
for impulse testing ?

6) During BaBar operation, did they monitor the field and how ?

7) In the paper by Bell, et al., The BaBAR Superconducting Coil: Design, 
Construction, Test (Nuclear Physics B, 78, 1999, 559-564), it was stated that 
the coil inside of the non-symmetric flux return yoke was offset by 
approximately 30 mm axially, in the forward direction.  At 3800 amps this 
created an axial force of 8 tons, which in turn stressed the Inconel tie rods 
(in effect the tie-rods provided the axial restraint to keep the coil from 
moving).  It appears that this was intentionally done in order to generate an 
offset axial force that always acted in the same direction which in turn 
always loaded in tension the tie rods placed at the backside of the 
coil/cryostat.  It also provided the benefit of preventing any force 
inversion during coil ramp-up.  Is my interpretation of this correct?  If 
these forces created by offsetting the coil were done intentionally, do you 
recommend that sPHENIX create the same condition in our magnet design (in 
effect offsetting the coil with respect to the nominal center of the yoke 
geometry)?  

7) If this offset axial force exists, the load path (offset force) is 
directed from the coil/mandrel to the downstream tie-rods and through the 
tie-rods to the downstream cryostat end flange that the tie-rods are 
connected to.  And from the end flange back up through the cryostat barrel 
(inner and outer) to the upstream end flange which in turn connects the 
cryostat (at the forward end) to the external cryostat axial supports (which 
now act in compression)?  Is this the correct interpretation of the 
anticipated load path of this offset force?

8) Even though there is this net effective offset axial force as described 
above that is restrained by the tie-rods, the paper states that there is a 
pair of corresponding internal magnetic axial forces of approximately 380 MT 
each acting on the forward and backward ends of the coil.  These forces act 
in opposite directions with their resultant force vectors pointing axially 
towards the center of the coil.  Does this then create a net effective 380 MT 
compressive force internal to the coil, which in theory would be restrained 
by the stiffness/strength of the mandrel from crushing the conductor?  It is 
presumed that the mandrel has been designed to withstand these large 
compressive forces.  However, what happens during a quench?  Does this 
compressive force as well as the nominal 8 ton offset force simply collapse 
to zero, or are there transient forces that may in fact reverse direction or 
possibly increase before decreasing to zero? 

9) BNL will be required to perform a high-field test of the coil prior to 
installation into sPHENIX.  The temporary flux return that will be used 
incorporates a rectangular geometry that is not symmetrically placed 
circumferentially with respect to the coil.  Also the pole tips (end caps) 
placement will be 14" off the face of the cryostat.  In the detector design 
for the experiment (final design) the pole tip locations will be 
approximately 45" off the face of the cryostat end flanges.  Will the 
rectangular flux return geometry or pole tip locations create internal forces 
on the coil that cannot be supported or restrained by the mandrel without 
overstressing the mandrel or cause the mandrel/coil composite to buckle?  

10) There has also been a request by BNL management to consider running the 
sPHENIX detector without pole tips in order to reduce the overall cost of the 
detector.  Can the coil run in a configuration without a pair of pole tips?

See you tomorrow !

Kin