X-ray tomography of superconducting RF cavities

Field emission loading limits the performance of a significant fraction of the cavities in existing superconducting accelerators. The field emission produces an additional load to the cryogenic system; it is a source of dark current and background radiation in the accelerator; and it can lead to RF breakdown if the cavity is pushed to its limits. The field-emitted electrons are accelerated by the RF field and strike the cavity wall, generating Bremsstrahlung X-rays. The regions of X-ray emission (intensity and energy spectrum) can be located by using a collimated NaI detector placed outside the cryostat and radiation shield. The X-ray emission sites can be reconstructed using tomographic techniques. Particle tracking simulations can be used to trace the field emission electrons back to their source in order to help identify the locations of the surface defects.