Bremsstrahlung emission from high power laser interactions with constrained targets for industrial radiography

Abstract

Laser–solid interactions are highly suited as a potential source of high energy X-rays for nondestructive imaging. A bright, energetic X-ray pulse can be driven from a small source, making it ideal for high resolution X-ray radiography. By limiting the lateral dimensions of the target we are able to confine the region over which X-rays are produced, enabling imaging with enhanced resolution and contrast. Using constrained targets we demonstrate experimentally a $(20\pm 3)~\unicode[STIX]{x03BC}\text{m}$ X-ray source, improving the image quality compared to unconstrained foil targets. Modelling demonstrates that a larger sheath field envelope around the perimeter of the constrained targets increases the proportion of electron current that recirculates through the target, driving a brighter source of X-rays.

Application programmes at the Scottish Centre for the Application of Plasma-based Accelerators (SCAPA)

“…A wide part of the electromagnetic spectrum is covered in SCAPA by available photon sources, either direct from the plasma or as a secondary source, from high energy gamma rays generated via bremsstrahlung radiation 56,57 to THz radiation, 58,59 the latter being produced with energies as high as tens of millijoules via irradiation of metal foils. 60 For imaging purposes, the small plasma source size leads to excellent image resolution that may be further enhanced by coherent effects, such as in betatron radiation phase-contrast imaging.…”

“…60 For imaging purposes, the small plasma source size leads to excellent image resolution that may be further enhanced by coherent effects, such as in betatron radiation phase-contrast imaging. 7,61 Gamma rays can also be produced direct from the plasma as in the case of LWFA resonant betatron radiation 7 or, in dense targets, via the generation of multi-mega-Ampere currents of relativistic electrons, 57 the latter process also driving the generation of mega-Gauss magnetic fields. The acceleration of light ions enables beamed neutron emission via fusion and transmutation reactions in a secondary target position downstream 62 , which enable a great variety of potential imaging applications.…”

“…Imaging of dense material, for example, for security application, radiometric assaying or industrial radiography can be achieved with gamma rays or neutrons. 28,57 The ultrashort pulse nature of the radiation will look to be exploited in remote sensing applications.…”

Development of control mechanisms for a laser wakefield accelerator-driven bremsstrahlung x-ray source for advanced radiographic imaging

“…Direct laser-solid interaction bremsstrahlung sources can readily achieve multi-MeV energies with high flux and sub-millimetre source size, capable of penetrating even the densest materials [23]. The refluxing fields generated in the solid target work to increase the X-ray source size, although this may be overcome using a target with reduced lateral dimensions [24]. Small source sizes (∼ 20 µm) [24] may be achieved using such targets, although the target must be replaced on each shot.…”

“…The refluxing fields generated in the solid target work to increase the X-ray source size, although this may be overcome using a target with reduced lateral dimensions [24]. Small source sizes (∼ 20 µm) [24] may be achieved using such targets, although the target must be replaced on each shot. The replacement and alignment of targets complicate the implementation of such systems at high repetition rate.…”