RE: Workspace for tagger assembly at JLab. (fwd)

[Elton Smith <elton@jlab.org>]

---------- Forwarded message ----------
Date: Mon, 19 Apr 2004 15:06:47 +0100
From: Jim Kellie <j.kellie@physics.gla.ac.uk>
To: Paul Brindza <brindza@jlab.org>, Dan Sober <sober@cua.edu>,
     Hall Crannell <crannell@cua.edu>,
     Jim O'Brian <james.o'brian@montgomerycollege.edu>,
     Jim Kellie <j.kellie@physics.gla.ac.uk>
Cc: Richard Jones <jonesrt@uconnvm.uconn.edu>, Elton Smith <elton@jlab.org>,
     Eric Scott <ebscott@indiana.edu>, Alex Dzierba <dzierba@indiana.edu>,
     Yang Guangliang <y.guangliang@physics.gla.ac.uk>
Subject: RE: Workspace for tagger assembly at JLab.

Dear All,

Following on from my e-mail of 16th April, I attach a pdf file which
compares the 'accepted' 12 GeV single magnet tagger with a two magnet system
worked out by Yang. I should make the following comments.

1. The main motivations to go to two magnets is that individually they
should be easier to work with than a single very long narrow magnet. It
should also be easier to source high quality magnet iron in lengths shorter
than 6.5 m. (Possibly the two magnets will also be cheaper.)

2. Both magnets have slightly curved output edges. Since, by varying the
curvature of the output edge, it is possible to vary both the position and
orientation of the focal plane, we found that to obtain a seamless focal
plane and an acceptable value for beta (see 7 below) for the complete
tagger, the curved faces were necessary.

3. The energy ranges of the magnets have been chosen to be 1.0 to 5.5 Gev
and 5.5 to 9 Gev corresponding to photon energy ranges of 11.0 to 6.5 GeV
and 6.5 to 3 GeV. ie, the first magnet will be ideal for providing the
energies best suited for GluEx. Since the first magnet has to analyse a
broader range, it is correspondingly larger. The magnets could be made the
same size, but we think that would not be so good for GluEx.

4. To keep the size of the first magnet to a minimum, it operates at 1.6 T,
while the second operates at 1.5 T.

5. The 3rd figure in the file compares the geometeries of the one and two
magnet systems. There should be plenty of room between the two magnets to
accommodate the coils from each magnet. The focal planes have almost the
same overall length, but since the focal plane for the two magnet system is
further away from the magnets, this gives more room for the focal plane
assembly, and there should also be less problems from fringing fields. ( It
is also possible to move the focal plane further out for the single magnet
tagger by varying the tilt angle of the output edge.)

6. Figure 4 compares resolution and dispersion. There is a small
dicontinuity in both, but this should not matter. The dispersion is better
from the first magnet in the two magnet system than for the corresponding
energies in the single magnet tagger.

7. Figure 5 compares beta (the angle at which the electrons cross the focal
plane), and the vertical half height at the focal plane. The latter is
almost identical for the two systems, but beta is larger (and better) for
the two magnet system.

8. Before we really understand the two magnet system, we shall have to check
the field with TOSCA. This will require an exact description of the system
in TOSCA, since it is important to have the shapes and relative positions of
the two magnets accurately defined.

Please let us have any comments or suggestions.

Regards,

Jim.






-----Original Message-----
From: Jim Kellie [mailto:j.kellie@physics.gla.ac.uk]
Sent: 16 April 2004 17:01
To: Jim O'Brian; Hall Crannell; Dan Sober; Paul Brindza
Cc: Yang Guangliang; Alex Dzierba; Eric Scott; Elton Smith
Subject: Workspace for tagger assembly at JLab.


Dear All,

I am just recently back in Glasgow after having been away, and I suggest it
would be good if we could reserve some workspace for the tagger at JLab as
well as asking for space for the spectrometer. This point has already been
raised at conference calls etc, if I remember, and I feel that at some stage
the complete tagger, vacuum system and focal plane should be assembled for
systematic testing at JLab before final installation.

The area occupied by the tagger dipole magnet, the vacuum system and focal
plane will be about 4m by 12m ( 13ft by 40 ft ). I think we will require at
least twice this area ( say 30ft by 40 ft ) to have sufficient room to work
on the assembly. What is the general view that this space could be found?

While I was away, Yang has been doing a lot of design work for a two magnet
tagger for 12 GeV, and he has come up with what I think is a viable
solution. Yang is making up a file which will show the main design
parameters and compare them with those for a single magnet system. We will
send them to you next week.

I also suggest it would be good if we could report on our latest design work
at Bloomington. If Yang will have a visa by then, I suggest he gives a talk,
but if he cannot come, I can substitute for him.

Cheers,

Jim.

TWO_MAGNET_SYSTEM.pdf