Patent ID: 8836250

Claim:
A traveling wave linear accelerator for generating a plurality of dose rates and energies of electrons, the traveling wave linear accelerator comprising: an electron gun modulator configured to adjust a beam current of electrons from an electron gun; a frequency controller configured to determine a frequency of a radio frequency (RF) signal to be generated; an amplifier configured to adjust a power of the generated RF signal; an intensity controller operatively associated with the electron gun modulator, the amplifier, and the frequency controller, the intensity controller configured to receive a plurality of intensity/energy adjustment commands and to respectively determine an electron gun beam current, an RF power factor, and a frequency adjustment factor based on each intensity/energy adjustment command to provide a respective output dose rate and energy of electrons, wherein, for each intensity/energy adjustment command, the electron gun modulator receives the determined electron gun beam current and adjusts the beam current of the electrons, the frequency controller receives the frequency adjustment factor and determines the frequency of the RF signal to be generated, and the amplifier receives the determined RF power factor and adjusts the power of the generated RF signal such that the traveling wave linear accelerator generates electrons having the respective output dose rate and energy; an x-ray target configured to generate x-rays responsive to irradiation with electrons, the x-rays irradiating a cargo container; a detector configured to detect x-rays transmitted through the container; and a control unit operatively associated with the detector and with the intensity controller, the control unit being configured: to send a first intensity/energy adjustment command to cause the intensity controller to determine a first electron beam current, a first power factor, and a first frequency adjustment factor to provide a first output dose rate and first energy of a first set of electrons; to determine a percent transmission of a first set of x-rays through the container based on an output of the detector, the first set of x-rays being generated by the first set of electrons; and if the percent transmission is above a predetermined threshold, to send a second intensity/energy adjustment command to cause the intensity controller to determine a second electron beam current, a second power factor, and a second frequency adjustment factor to provide a second output dose rate and second energy of a second set of electrons, wherein the intensity controller is configured to select the second output dose rate of the second set of electrons such that a dose of the second set of x-rays generated by the second set of electrons is less than a dose of the first set of x-rays.