Hall D optics revision (fwd)

[Elton Smith <elton@jlab.org>]

---------- Forwarded message ----------
Date: Mon, 25 Jun 2001 16:41:34 -0400
From: Jay Benesch <benesch@jlab.org>
To: krafft@jlab.org, douglas@jlab.org, yunn@jlab.org, tiefen@jlab.org,
     chao@jlab.org, bogacz@jlab.org, derbenev@jlab.org, denard@jlab.org,
     lir@jlab.org, merminga@jlab.org, elton@jlab.org, jonesrt@jlab.org,
     carlini@jlab.org, wolin@jlab.org
Cc: harwood@jlab.org
Subject: Hall D optics revision

After my painful experiences the last few weeks with optics and steering
during hall B commissioning of the g8 run with coherent bremsstrahlung,
I decided to revisit the hall D line.  I shortened the ramp by 15%,
increasing dipole field to 6.4 kG. Vertical emittance increases 15% in
the line, ending at 23% of the horizontal.  I was not able to get a
simultandous waist in horizontal (OK) and vertical (diverging slowly) at
the collimator, but Richard Jones found the result acceptable Friday.

I used the space provided by shortening the ramp and the waist
compromise to place two pair of correctors separated by 13m after the
last quad.  This allows 3mm  parallel offset of the beam with BdL 15,000
G-cm.  Beam pipe is 1.5" OD, so I assume a modified MBD.

The optim file is ~mccops/optics/optim/halld/hallc_cdrrev4d121.opt  The
radiator is 121m from the point of tangency; I have another solution
with 117m.

The solitary quad in the ramp is used for dispersion suppression.  The
triplet at the vertical dispersion zero-crossing about a fourth of the
way down the line is used with the final triplet for betatron match.
Iteration will be required.

This was the best I could do given the constraint that the beam remain
"on the floor" (-50cm wrt linacs) until the north stub.

I'd appreciate any comments you may have, especially about beam
diagnostics.  The radiator is 16.23 m from the end of the last quad.
The collimator is 75m beyond that.  The beam at the radiator is 1.6mm by
0.4mm x:y (one sigma); it's 2mm sigmaX at the last quad.  Commissioning
and beam stabilization will be non-trivial.

Jay