A study of the minimum wall thickness for an extruded aluminum vacuum chamber

Decreasing an ID vacuum chamber wall thickness is a way to achieve a smaller ID gap and a higher magnetic field without decreasing the clear beam aperture of the chamber. Multiple extruded aluminum ID vacuum chambers with 1-mm wall thickness were developed and fabricated at Argonne for the APS and several other synchrotron radiation facilities [1]. Thinner walls have been avoided due to fear that porosity and defects from the extrusion process would result in vacuum leaks. There were also concerns that thinner walls may have excessive deformation or may not withstand the stresses. Recently, several extrusions have been machined to a wall thickness of less than 1 mm to determine the practical limits. Using the extrusion for the insertion device vacuum chamber (ID VC) for the DESY FEL project with a 9.5-mm inner diameter and the LCLS test vacuum chamber extrusion, we decreased the wall thickness to 0.6, 0.5, and 0.4 mm to test the vacuum integrity for a thin wall in these extrusions. Structural analysis and test results are presented.