[g2p_ana] Minutes of the septum meeting

[Jixie Zhang]

Minutes:

1) Jixie showed some slices to introduce the information and status of the
septum:
A) The filed map:  Bx vs. X|Z and By vs. X|Z, which shows that the current
in the Tosca is opposite to the real
B) Currently the septum center is located at z=686.46 mm, which is proved to
be wrong.
>From Jixie's Geant4 simulation, it should be 772.40 mm, which is about 8.6
cm more downstream.
John's prediction also suggested some position down stream.
C)Confirm by Al that the septum can not be moved at all due to the fact that
there is no space down stream.
D) With current design,  target located at -876.93 mm and septum at 686.46,
the prediction bending angle by theory is 5.56 degree (some offset value of
the septum itself not taken into account).
E) Jixie's G4 simulation shows that the bending angle is 5.66 degree, using
the septum map corresponding to
3400 MeV electron.   But we knew that the septum can not reach such a high
current.
F) Based on 2 map Robin provided, one for 400 MeV another one for 3400 MeV,
Jixie scale the 400 MeV one by 8.5 then
compare it with the other. There is about 0.2 Tesla difference in the field.
which shows that in the 3400 map, the iron
of the septum is saturated.  John mentioned that the number 400 and 3400
itself could have large uncertainty due to
the fact that these numbers is from a BdL accumulated along a straight line
in the Tosca model, not the real trajectory
of an electron.  But the conclusion that in high field of 3400 MeV, the iron
is saturated holds.  Robin's "B vs I" plot also proves this.
G) Robin provides the field map with the maximum current. The vertical range
covers up to +/- 25 cm (requested by Jixie),
the real opening is a rectangle with vertical cover +/-12 cm only.

2) The septum was found by Howard and John that there is one coil wired
wrongly.  Jixie will schedule with Howard to
make a cross check for each coil to make sure all coils are wired properly.


3) Al need to redesign the beam dump opening

4) Al need to change the design of the sieve slits.

5) Robin will try more efforts to check  the maximum current of the septum
and provide a new map.

6) Once have the new map, Jixie will finalize the effect angle with Geant4
then finalize the beam dump opening,
also provide some fitting to Karl to calculate the kinematics and rates


-- 
Best Regards,
Jixie Zhang
Jefferson Lab - Hall A - A112,
757-269-5352
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