The present invention is directed to a particle beam processing apparatus that is smaller in size and operates at a higher efficiency, and also directed to an application of such apparatus to treat a coating on a substrate of a treatable material, such as for flexible packaging. The processing apparatus includes a particle beam generating assembly, a foil support assembly, and a processing assembly. In the particle beam generating assembly, electrons are generated and accelerated to pass through the foil support assembly. In the flexible packaging application, the substrate is fed to the processing apparatus operating at a low voltage, such as 110 kVolts or below, and is exposed to the accelerated electrons to treat the coating on the substrate.