The Plasma X-ray Source (PXS) is a vacuum chamber system that facilitates the generation of X-ray in the LUXD system. It consists of two storage sections positioned above and below a narrow interaction chamber. The interaction chamber
The laser is focused tightly down onto a thin (~20 μm) moving copper tape. Electrons are ripped out of the copper tape every half cycle of the intense electric field of the laser, these electrons are then accelerated away from the tape into the surrounding vacuum. Once time passes and direction of the oscillating electric field reverses the electrons are slowed, stopped and then re-accelerated back towards the copper tape and ultimately slam into the surface. The copper tape is supported at an angle of ~60° to the horizontal in order to maximise this process. During this process the kinetic energy that the electron received from the field is deposited into the copper resulting the formation of a plasma. This copper plasma will primarily radiate at its characteristic X-ray transition of Kα (8.04 keV) but a smaller portion at Kβ (8.9 keV) as well as a small portion of Bremsstrahlung radiation. Due the laser driven nature of the plasma generation mean that the plasma, and therefore the X-ray emission for the approximate duration of the laser pulse as such by using an ultrashort laser pulse will results in a similarly short X-ray pulse emission.
This process is repeated at the 1 kHz repetition rate of the laser and each pulse causes the destruction of the copper tape within the laser focal spot which is why the tap must be continuously moving to replace the target. It is also result in the creations of a significant amount of ablated copper which could potentially coat the internal windows of both the laser input and X-ray output windows. Therefore moving Mylar tapes also run down each side of the generation chamber to protect these windows. To allow long term operation between tape loading, when the tape reaches the end of its reel the entire chamber is horizontally translated and the movement of the tape reversed to allow generation of multiple tracks across the tape.
The generated X-rays are incoherent and are emitted in all directions, a proportion of the X-ray (~1°) are collected by an diffracting X-ray optic to both monochromate the refocus the X-rays onto the target. Significant effort is being put into the design of the optic to both maximise the collected flux, minimise focal spot size, not temporally stretch the ultrashort X-ray pulse while maintaining a suitable convergent angle for diffraction studies.
A Diagram of the PXS is shown below
