New Microfocus Linear Accelerators Called MicroBeam Linatron (MBL) at Varex Imaging

One of the factors limiting resolution in radiography with X-rays generated using Bremsstrahlung from electron beam striking a target is defined by the focal spot (spot) size of such electron beam on the target. It is well-known that obtaining a submillimeter spot in high energy sources (HES), operating at energies of 1-10 MeV is extremely difficult and the difficulty grows with increasing energy. Some reports cited on 0.95 MeV energy linac with a submillimeter spot, but never about such at higher energy without any external focusing. The typical smallest achievable spots are around 1.5 mm without focusing system and approximately 0.8 mm with focusing solenoids, measured at full-width-half maximum (FWHM). At Varex, first we obtained a spot of 0.8 mm FWHM, without any focusing devices, which set a record for the standard commercial linacs. Further, we produced a new groundbreaking design, which required unique changes to the electron beam line and radio frequency (RF) structure permitting a spot less than 0.5 mm, patent pending. The new Varex 6 MeV linac can reliably and repeatably produce a beam with a FWHM focal spot of (350+150) μm without any external focusing devices. Currently, a maximum dose rate 700 R/min@1m is obtained with the larger spot of (350+150) μm, and 230 R/min@1m in spot size of (250+100) μm. The new design generates a focal spot profile with a perfect Gaussian distribution resulting in the best beam quality for radiography and it substantially improves resolution for HES, extending range for the existing applications and opening new imaging applications. The new product line called MicroBeam Linatrons (MBL) will include 3, 6, 9, and 15 MeV linacs.