Conception and Development of a Small-Focal-Spot Compact Linear Accelerator at Varex Imaging Corporation

The commercially available compact electron linear accelerator (LINAC) products used for high-energy imaging of dense and/or thick objects offer accelerated electron beams in an energy range from 1 MeV to 10 MeV with focal spot sizes generally from 1.0 mm to 2.0 mm on a stopping target measured at Full Width at Half Maximum (FWHM) of usually close to a Gaussian distribution profile. Reducing the focal spot used to generate Bremsstrahlung for imaging is very important, as smaller focal spots permit less penumbra for much better resolution in the produced images. Meeting such demand presents several serious challenges. Common methods for such focal spot reduction add extra elements, complexity, deliver insufficient beam power, etc., making them unsuitable for compact commercial machines. An alternative method to obtain a submillimeter electron beam focal spot FWHM of less than 0.5 mm with a “clean” Gaussian distribution using a novel RF structure design and tuning method (patent pending) is presented, used in the first 3, 6, and 9 MeV Accelerator Beam Centerlines (ABC). This invention started a New MicroBeam LINATRON™ (MBL) product line with the first MBL6 prototype LINAC, built and tested by the High Energy Systems (HES) group at Varex Imaging Corporation.