Minutes, February 16, 2012
Participants: G. Bonvicini (WSU), R. Gillard (WSU), G. Mazzitelli (LNF),
S. Tomassini (LNF), M. Zobov (LNF)
The proposed LABM consists of a Beam Pipe insert located in the outgoing
pipes of each beam (downstream of the IP). The location is to be
determined, and two were proposed by S. Tomassini at 3.5 meters from the
IP and 4.5 meters from the IP. The former is considered acceptable and the
latter is considered ideal. The proposed locations can be seen at
https://motor1.physics.wayne.edu/~giovanni/LABM@DAFNE.pdf
The exact length of the proposed insert can not be determined at this
point, due to uncertainties in the length of the spoilers located in the
back of the mirrors, and also how thick the flanges will be. However, a
reasonable estimate would be 4 millimeters for the mirrors, 20 millimeters
for the spoilers, and 1 cm for the flange. Since we have two of each, and
with 5 mm clearance between each element, the total length of the insert
would be 83 millimeters. However, under no circumstances an insert longer
than 15 cm is foreseen.
There are no further demands on real estate along the Beam Line, because
the Optical Channels are reflected at 90 degrees horizontally (along the
x-axis), about 30 cm below and above the Beam Pipe, and the light is taken
to an Optics Box located meters away where the light is analyzed.
The mirror should be diamond-polished copper, 3 or 4 millimeters in width,
and because it is at 45 degrees the length would be 4.24 or 5.66
millimeters in length. The SuperKEKB mirrors, which are being built now,
are 2 millimeters. The mirrors would be located at x=0, directly above and
below the Beam Pipe Axis. Mirro technical designs from Cornell are
available but they need to be scaled for the different Beam Pipe and
mirror sizes.
It was established during the discussion that the beams are on the Beam
Pipe axis at the IP, and that therefore the mirrors are viewing the beams
at an angle that is equal to the distance of the mirror from the axis,
divided by the distance from the IP. For the 4.5 meters location, and 4 mm
mirror, this would be 8.9 mrad to 9.8 mrad.
The mirrors are also the main collimator along the optical lines, and the
suggested primary windows are 1 mm wider than the mirrors, or 4-5 mm.
The next steps to decide on the feasibility of this project include:
1) Calculation of the impedance of the mirrors and primary windows. This
can be done by a combination of Frascati and WSU.
2) Calculation of stay-clear envelope to insure the mirrors do not
infringe on it.
3) We must insure that there is a direct line of sight between the chosen
location and the IP. At SuperKEKB, for example, there is no direct line of
sight on the LER side, and the mirrors must be built so as to protrude
further into the Beam Pipe.
4) A presentation will be given during SuperB week, March 19-23.
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