Compact LWFA-Based Extreme Ultraviolet Free Electron Laser: Design Constraints

The combination of advanced high-power laser technology, new acceleration methods and achievements in undulator development offers the opportunity to build compact, high-brilliance free electron lasers driven by a laser wakefield accelerator. Here, we present a simulation study outlining the main requirements for the laser–plasma-based extreme ultraviolet free electron laser setup with the aim to reach saturation of the photon pulse energy in a single unit of a commercially available undulator with the deflection parameter K0 in the range of 1–1.5. A dedicated electron beam transport strategy that allows control of the electron beam slice parameters, including collective effects, required by the self-amplified spontaneous emission regime is proposed. Finally, a set of coherent photon radiation parameters achievable in the undulator section utilizing the best experimentally demonstrated electron beam parameters are analyzed. As a result, we demonstrate that the ultra-short, few-fs-level pulse of the photon radiation with the wavelength in the extreme ultraviolet range can be obtained with the peak brilliance of ∼7×1028 photons/pulse/mm2/mrad2/0.1%bw.

Two-stage PVD method for protective coating formation

The CVD methods are typically used for the formation of aluminum oxide coatings since aluminum oxide is a dielectric. The adhesion between the protective coating and the substrate material is normally improved by growing thin intermediate layers based on titanium oxides and nitrides. These intermediate layers are mainly formed using the PVD methods. In this paper, we propose a two-stage PVD method for forming a layered structure on the titanium substrate. The formation of intermediate layers was carried out by the magnetron method (first stage), and the main protective layer was deposited at the second stage using a fore-vacuum electron source. The dense beam plasma generated during the electron beam transport in a fore-vacuum gas medium compensates for the negative electrical charge accumulating on the surface of the aluminum oxide target and facilitates its effective evaporation. The electrical properties of the intermediate layers and the resulting layered coatings have been investigated, including the tangent of dielectric loss angle, the real and imaginary parts of the conductivity and the dielectric constant dependencies on frequency.

Features of the electron avalanche formation process in a strongly inhomogeneous electric field under high overvoltages

The simulation of the electron avalanche formation process in subnanosecond discharges of high pressure was carried out by means of the Monte-Carlo approach. The discharge gap under consideration was of the configuration “the finger-shaped cathode – the hemispherical anode”. The presence of a conic-shaped microprotrusion on a cathode surface was assumed. Such the electrode configuration provided the strongly inhomogeneous distribution of an electric field. A gas simulated was nitrogen at a pressure of 6 atm. An average electric field strength across the discharge gap was varied from 200 kV/cm up to 400 kV/cm. Microprotrusion height was varied from 0 um up to 30 um. The critical size and formation time of an electron avalanche were determined under various conditions simulated. The threshold electric field strength for electrons to transit into the continuous accelerating regime was calculated for various heights of the microprotrusion. The applicability of the non-self-consistent Monte-Carlo technique for the investigation of the runaway electron kinetics and the correct simulation of the runaway electron beam transport across the discharge gap was shown.