Ultra thin beam pipes for internal target experiments

Experiments looking for particles from B-decays at colliders, especially at large eta, find that the material presented by typical beam pipe walls (0.5 mm Be) present a significant mass causing multiple scattering. Under external pressure conditions, wall thickness is needed to resist deformation of the pipe. The pipe is unstable if the energy released by the reduction of internal volume exceeds the energy stored in the deformed pipe wall material. Both energies are proportional to the cube of the deformation. The deformation mode depends on pipe length between stabilizers, and can range from oval (basic mode) to high order open-quotes ripple typeclose quotes modes. Very low mass pipes can be designed by combining a thin wall pipe with periodic ring type stiffeners. This design can be made compatible with the very low outgassing requirements by using a two step process. The thin pipe open-quotes sleeveclose quotes is made by brazing a thin Be sheet into a cylinder, and by brazing on appropriate ends. This sleeve can be vacuum baked and tested at reduced differential pressure, but not be fully evacuated. After the sleeve has been leak checked and vacuum baked, the external stiffening rings are attached using adhesives. Such structures are currently in development at the Fermilab Physics Department