[Bteam] H vs C arc dipole multipoles

[roblin at jlab.org]

> I have modeled the BE magnet with and without H steel with the "same"
> mesh, turning iron to air to get the C.  I am modeling the BA the same
> way now.  For the latter I have models at J=50, 100, 150, 200 and 225
> A/cm^2; I=1.265*J.  Even at low B the H magnets have higer BdL at the
> same J.  BB next.  Actually I have models to J=450 but they're not
> relevant to the final 5.6 GeV run.
>
> For multipoles I scale the beam energy to the BdL of the model, inject
> the beam at the right angle and offset to get the proper sagitta, and
> let it propagate in 2.5mm steps.  The post-processor gives me an orbit
> and velocity file which I translate into position and Euler angles.  I
> run the post-processor again to get the field at 24 points on 1cm radius
> circles with centers and angles taken from the orbit file.   I then have
> the post-processor give me mulitpoles to n=5 (12 pole).  This gets the
> quadrupole term wrong, as Mike Teifenback taught me.
>
> I plan to run the beam through the C magnet to get an orbit and then use
> this orbit for both C and H magnets.
>
> Comments?

One problem we are going to face is the loss of symmetry between hall c
and hall a dipole strings.  the hallc dipoles are going to be H whereas
the A string is going to stay as it is for 11 GeV. I suppose that we can
empirically adjust as we do now such that when FFB is in energy mode we do
not get a jump when switching from A to C.

However, this is going to be a problem to relate the absolute energy in
hall a with that in hall c. The only absolute energy measurement is in
Hall A with the ninth dipole hooked up to the 8 others.

Until now, the hall C people had calibrated their bdl's to the point they
could just read out a reasonable approximation of the energy.

That is no longer going to be the case and I am wondering if we need to do
something regarding that.


Yves