Today we had a small, focussed (?) meeting on the design of the beam line for the polarized target. Dave Kashy, Mike Seely, Derek Branford, Volker Burkert and myself were present. We decided to design the beam pipe around a "reference position" for the target center at -55 cm (upstream) relative to the nominal target position (0,0,0). We also decided to try and keep the forward direction unobstructed for angles down to 7 degrees (for all possible raster positions). This means that the downstream beam pipe with all shielding should fit inside a cone of +/- 7 degree opening angle, with a vertex 6.5 cm DOWNstream from the actual target center (this takes different starting positions over a 1.5 cm rastering diameter into account). The downstream beam pipe will have to begin about 315mm downstream from the target center. The actual vacuum pipe should start out with an inner diameter of 30 mm and will increase to match "smoothly" to the existing beam pipe inside the Torus bore. The shielding around this (most likely lead) will start out at an outer envelope of 6 cm diameter, increasing to a maximum of 3 cm thickness of lead all around. It would be very helpful if somebody could run GSIM studies to see what this would do to the Moellers.

On the upstream end, we already have some design drawings. What needs to be done still is a design for the window and the beam pipe from the target port to the outside of the insertion cart.

Dave Kashy will work on these plans, and hopefully present us with a first set of drawings 2 weeks from now (we will have our last regular meeting this year on December 15, at the usual time - 3:00 p.m. - and place - A110).

We also briefly discussed additional optical elements that we might need, in particular a small steering magnet (about 100 Gauss-meter) to offset missteering by the target field, and possibly even a quadrupole pair to counteract the rather serious multiple scattering spread. I came up with a spatial 1/e angle due to multiple scattering of 1.6 mrad for 1.6 GeV beam, which translates into a radius of about 5 cm at the Faraday cup. As far as I understand, the entrance opening of the cup is only 15 cm diameter (7.5 cm radius); that means only about 90% of the beam is contained in that area. We will have to work on that!

- Sebastian