BLTWG Meeting 1/18/2008

• Time: 9:00 EST
• Place: EVO and ESNET
• Present:

Agenda

1. Review Tim's interface drawings
2. Review answers to vendors' questions
3. Interface with accelerator

Tagger Interface Specification

1. Qradrupole inner clearance: The tagger specification states that the clearance hole through the field region of the tagger quadrupole is of diameter 30 ± 2 mm. This leaves unspecified the inner diameter of the beam pipe. Jay Benesch wrote that:

   The quads in the hall D line will have 1.375" OD, 1.25" ID beam pipes. The tagger quad beam pipe should be as close to this as possible.

   This is useful guidance. Yang confirms that the field strength of these beamline quads would be sufficient for the tagger quad as well. Adopting that design would make spec'ing the tagger quadrupole very easy. An ID of 1.25" is 31.25 mm, within the specified tolerances. In the tagger simulation, Richard used 30mm for the inner diameter of the vacuum pipe between the radiator and the tagger vacuum box. Tim will communicate with Mark Wiseman and see if there are any drawbacks to our adopting the design of the beamline quadrupoles for the tagger quadrupole.
2. Thin vacuum box exit window: The tagger specification does simply states that the exit window should be composed of aluminum and be "thin". It was suggested at the meeting that other materials, eg. kapton, aluminized mylar, or carbon fiber sheet might be alternatives to aluminum with greater strength per gram. Richard used a window thickness of 1mm of aluminum in the simulation, without any apparent degradation in the performance of the hodoscopes coming from radiation in the window. The consensus of those present was that 1mm is thicker than we need, even if aluminum is chosen. Richard will contact Dan Sober and Franz Klein to ask what considerations should drive this choice.
3. Tagger vacuum box downstream exit region: There is currently a thick flange with a lot of material producing interactions close to the tagging hodoscopes in the interface design. It has been suggested to replace this flange with a rectangular window with a large horizontal extent. Richard looked up what was used in that region in the simulation:

   The tagger simulation included a rectangular extension to the downstream end of the tagger vacuum box. It had inner dimensions of 8cm x 4cm and extended 280cm from the downstream end of the vacuum box proper. The rectangular pipe was not constructed symmetrically about the nominal electron beam path. Instead, the full-energy electron beam component is aligned 2cm from 3 of the 4 walls of the rectangular pipe, while the fourth wall (low-energy side of the electron beam) is 6cm from the beam and only 1mm (stainless steel) thick.