A novel scheme for electron optics of a high-power microfocus X-ray source for phase contrast imaging

Abstract

Phase contrast X-ray imaging has huge potential for applications in medical radiography, imaging of biological samples, discrimination within soft tissues, non-destructive testing, environmental science and material science. An important requirement in X-ray phase contrast imaging is the spatial coherence of the source, which can be provided by electron-beam microfocus X-ray sources. To obtain better resolution and to minimize exposure times, the source power needs to be enhanced by increasing the electron-beam power. To circumvent the problem of melting of solid anode at high electron beam power, recently liquid metal jet anodes have been used. But if the power is increased using a straight electron beam, the liquid metal at the e-beam impact point may be evaporated or ionised and may flow towards the electron gun region causing repeated high voltage discharges, erosion of cathode material and metallic coatings on insulation. By bending the electron beam through ~180° or more before impact on the liquid metal jet, the vapor and ions can be prevented from entering the high voltage cathode region. A crucial requirement is that this bending does not affect the size and circular symmetry of the electron beam spot on the target so as not to affect the spatial coherence of the source. To achieve this objective, based on the principle of distortion-less bending of a converging electron beam (B Dikshit et al, Nucl. Instr. Methods Phys. Res. A, 596, 300 (2008)), schematic design of a high power 180° bent electron-beam microfocus X-ray source is described in this paper.