Аннотация:A novel high speed Adaptive Railroad Cargo Inspection System (ARCIS) is being developed at RadiaBeam Technologies. The ARCIS concept relies on linac-based, adaptive, ramped energy source of short X-ray packets of pulses, a new type of fast X-ray detectors, rapid processing of detector signals for intelligent control of the linac, and advanced radiography image processing. The requirements for this system include better than 5 mm line pair resolution, penetration greater than 400 mm of steel equivalent, scan speeds up to 60 km/h, material discrimination within 100% of image and minimal average dose. To meet these requirements a new S-band travelling wave linac with deep energy control has been designed. This paper discusses the linac design approach and its principal components, as well as engineering and manufacturing aspects.