A new measurement system for wall thickness uniformity of a thin wall small aperture vacuum chamber

Abstract The vacuum external undulator is a critical component in synchrotron radiation light sources and free-electron lasers, featuring a small-aperture vacuum chamber that precisely guides the electron beam through the undulator. The uniformity of the wall thickness of the vacuum chamber significantly influences its beam quality. However, accurately measuring the thickness uniformity of long and narrow vacuum chambers poses significant challenges. A testing system utilizing a specific magnetic field has been developed to measure the wall thickness uniformity of vacuum chambers. The system synchronously measures the voltage between the permanent magnet and the iron ball, as well as the distance between the vacuum chamber’s outer surface and the permanent magnet. By calibrating the relationship between voltage and the iron ball’s height variation, the system enables rapid and accurate evaluation of wall thickness uniformity along the beam direction. Successful tests are conducted on an aluminum alloy vacuum chamber with a length of 4 meters and an inner diameter of 8 mm.