Advanced X-ray spectroscopic methods provide unique and critical data to study matter under extreme environmental conditions induced by high-intensity and high-energy lasers. The aim of this paper is to contribute to a contemporary discussion of the role of X-ray spectroscopy in the investigation of radiative properties of strongly coupled, highly correlated, and frequently weakly emissive plasma systems formed in matter irradiated by sub-petawatt and petawatt class lasers. After reviewing the properties of different X-ray crystal spectrometers, high-resolution X-ray diagnostic methods are surveyed with respect to their potential to study plasma-induced and externally induced radiation fields, suprathermal electrons, and strong electromagnetic field effects. Atomic physics in dense plasmas is reviewed with emphasis on non-Maxwellian non-LTE atomic kinetics, quasi-stationary and highly-transient conditions, hollow ion X-ray emission, and field-perturbed atoms and ions. Finally, we discuss the role of X-ray free electron lasers with respect to supplementary investigations of matter under extreme conditions via the use of controlled high-intensity radiation fields.

Interaction of twisted strong laser radiation with electrons in the classical regime is considered. We investigate transfer of the angular momentum of absorbed laser photons to the emitted radiation. An interaction regime is considered where radiation reaction is negligible and the formation length of radiation is comparable to or larger than the laser wavelength. The latter condition ensures that the structure of the laser field plays a role in the electron dynamics during the formation of radiation. We distinguish the case of a single electron from that of an electron beam. For a single electron, the spin angular momentum of the driving laser photons is transferred to the radiation field, while the orbital angular momentum of the laser field is not. We conclude that in the classical regime, to imprint the angular momentum of twisted light on radiation, an electron beam is a prerequisite. In the latter case, nonlinear Thomson scattering of twisted light off an ultrarelativistic electron beam produces high-frequency radiation that is twisted, with a topological charge proportional to the harmonic order.

The design of ellipsoidal plasma mirrors (EPMs) for the PEARL laser facility is presented. The EPMs achieve a magnification of 0.32 in focal spot size, and the corresponding increase in focused intensity is expected to be about 8. Designing and implementing such focusing optics for short-pulse (<100 fs) systems paves the way for their use in future high-power facilities, where they can be used to achieve intensities beyond 10²³ W/cm². A retro-imaging-based target alignment system is also described, which is used to align solid targets at the output of the ellispoidal mirrors (with a numerical aperture of 0.75 in this case).

A method based on the laser differential confocal principle is proposed for measurement of the uniformity of the inner and outer radius and shell thickness for an inertial confinement fusion (ICF) capsule. Firstly, this method uses the laser differential confocal measurement system (LDCS) driven by a precision air-bearing slide to scan and measure radially the outer radius, R, inner radius, r, and shell thickness, T, accurately. Secondly, a precision air-bearing rotation system is used to drive the capsule to rotate an angle, θ, in sequence, and the LDCS is used to measure R, r and T at the corresponding angle. Finally, the uniformity of the ICF capsule’s R, r and T can be calculated by the values of R, r and T measured at the position of each rotation angle. This method provides an approach for achieving high-precision, non-destructive, comprehensive, and rapid measurement of the uniformity of the inner and outer radius and shell thickness of an ICF capsule. Preliminary experiments indicate that measurement precision, using the proposed method for the uniformity of the outer radius, shell thickness and inner radius of the capsule, can reach 7.02 × 10^?5, 5.87 × 10^?4 and 6.52 × 10^?5, respectively.

The results of experiments with rapidly exploding thin conductors in the current-pause regime are presented. Copper wires 25 μm in diameter and 12 mm in length serve as loads for a GVP pulsed generator based on a low-inductance capacitor. The generator produces current pulses of up to 10 kA with dI/dt up to 50 A/ns. A 100–800-ns current-pause regime is obtained for charging voltages of 10–15 kV. The discharge channel structure is studied by shadow photography using 0.53-μm, 10-ns second-harmonic pulses from a Nd³⁺:YAG laser. In the experiments, three types of secondary breakdown are observed, with different symmetry types, different current-pause durations, and different dependences on the energy deposited into the wire during its resistive heating. All of these breakdown types develop inside a tubular core that is produced in the current-pause stage and that remains almost undamaged by the breakdown.

In this paper, the effects of an electron beam on X-pinch-produced spectra of L-shell Mo plasma are investigated for the first time by principal component analysis (PCA); this analysis is compared with that of line ratio diagnostics. A spectral database for PCA extraction is arranged using a non-Local Thermodynamic Equilibrium (non-LTE) collisional radiative L-shell Mo model. PC vector spectra of L-shell Mo, including F, Ne, Na and Mg-like transitions are studied to investigate the polarization types of these transitions. PC1 vector spectra of F, Ne, Na and Mg-like transitions result in linear polarization of Stokes Q profiles. Besides, PC2 vector spectra show linear polarization of Stokes U profiles of 2p⁵3s of Ne-like transitions which are known as responsive to a magnetic field [Tr?bert, Beiersdorfer, and Crespo López-Urrutia, Nucl. Instrum Methods Phys. Res., Sect. B 408, 107–109 (2017)]. A 3D representation of PCA coefficients demonstrates that addition of an electron beam to the non-LTE model generates quantized, collective clusters which are translations of each other that follow V-shaped cascade trajectories, except for the case f = 0.0. The extracted principal coefficients are used as a database for an Artificial Neural Network (ANN) to estimate the plasma electron temperature, density and beam fractions of the time-integrated, spatially resolved L-shell Mo X-pinch plasma spectrum. PCA-based ANNs provide an advantage in reducing the network topology, with a more efficient backpropagation supervised learning algorithm. The modeled plasma electron temperature is about T_e ～ 660 eV and density n_e = 1 × 10²⁰ cm^?3, in the presence of the fraction of the beams with f ～ 0.1 and centered energy of 5 keV.

Many papers have been published on the theory of magnetic insulation and the use of Z_flow analysis of magnetically insulated transmission lines (MITLs). We describe herein a novel design process using the circuit code SCREAMER for a real-world MITL for z-pinch loads based on the Z_flow model of magnetic insulation. In particular, we design a 15-TW, 10-MA, 100-ns double-disk transmission line using only circuit modeling tools and Z_flow analysis of the MITL. Critical issues such as current loss to the anode during the setup of magnetic insulation and the transition from a non-emitting vacuum power feed to an MITL play a large role in the MITL design. This very rapid design process allows us for the first time to explore innovative MITL designs such as variable-impedance MITLs that provide a significantly lower total inductance and improved energy delivery to the load. The tedious process of modeling the final MITL design with highly resolved 2D and 3D electromagnetic particle-in-cell codes occurs as a validation step, not as part of the design process.

Polymerization of fullerenes is an interesting topic that has been studied for almost three decades. A rich polymeric phase diagram of C₆₀ has been drawn under a variety of pressure P and temperature T conditions. Knowledge of the targeted preparation and structural control of fullerene polymers has become increasingly important because of their utility in producing novel fullerene-based architectures with unusual properties and potential applications. This paper focuses on the polymeric phases of fullerenes and their derivatives under high P and/or high T. First, the polymerization behavior and the various polymeric phases of C₆₀ and C₇₀ under such conditions are briefly reviewed. A summary of the polymerization process of intercalated fullerenes is then presented, and a synthetic strategy for novel structural and functional fullerene polymers is proposed. Finally, on the basis of the results of recent research, a proposal is made for further studies of endohedral fullerenes at high P.