Intra pulse multi-energy method and apparatus based on RF linac and X-ray source

#This invention relates to X-ray sources.

#A radiographic method with an X-ray source is usually the most cost effective method for container inspection. Traditional methods include generation of an electron beam, accelerating the beam energy, decelerating the electrons in a target thereby producing an X-ray beam, forming a spatial X-ray field that illuminates a container, and analyzing the X-ray photons with a detector array.

#Recently, detection systems for X-ray cargo systems that can make use of multi-energy X-ray pulses have been considered, e.g., in U.S. Pat. No. 8,457,274 and in WO 2012/054381. Although the X-ray sources considered in this work provide multi-energy X-ray pulses, these multi-energy X-ray pulses do not have fully controllable intra-pulse energies.

#FIGS. 1A-C show examples of controlling the energy delivered to electron bunches by controlling the relative position of the electron bunches and an RF waveform.

#FIG. 2A shows an example of controlling the energy delivered to electron bunches by controlling the relative position of the electron bunches and an amplitude modulated RF waveform.

#FIG. 2B shows an example of controlling the energy delivered to electron bunches by controlling the relative position of the electron bunches and a phase modulated RF waveform.

#FIGS. 1A-C show examples of controlling the energy delivered to electron bunches by controlling the relative position of the electron bunches and an RF waveform. In the example of FIG. 1A, electron bunches 104 are at peaks of RF waveform 102, leading to maximum energy transfer from RF waveform 102 to electron bunches 104. In the example of FIG. 1B, electron bunches 104 are away from peaks of RF waveform 102, leading to reduced energy transfer from RF waveform 102 to electron bunches 104. In these examples, the RF waveform is not modulated, and has a period equal to the electron bunch spacing. Thus all bunches in a bunch train have substantially the same position relative to features of the RF waveform (e.g., peaks). The following examples show how more specific control of electron bunch energy can be provided by amplitude and/or phase modulation of the RF waveform.

#FIG. 1C shows the basic idea. Here curve 110 is an electromagnetic wave that is propagated in the accelerating structure and curves 112 and 114 illustrate two different electron bunch phase positions versus the wave phase. Bunch position 112 has a bunch phase that leads to less energy than the bunch phase of bunch position 114. During a long RF pulse, bunches of different time intervals will be accelerated at the different energies. The phase sweep during the pulse is slow compared to RF cycle.

#FIG. 2A shows an example of controlling the energy delivered to electron bunches by controlling the relative position of the electron bunches and an amplitude modulated RF waveform. In the example of FIG. 2A, electron bunches 204 get larger amounts of energy from left to right on the figure because of amplitude modulation of RF waveform 202.