Atomic structure and radiative properties of He-like Ni26+ ion in dense plasma

The influence of plasma screening on the excitation energies and transition properties of He-like Ni²⁶⁺ ion under strongly coupled plasma background has been analyzed. To perform the analysis, the multiconfiguration Dirac-Fock method has been adopted by incorporating the ion sphere model potential as a modified interaction potential between the electron and the nucleus. For comparison purposes, parallel calculations have been carried out using the modified relativistic configuration interaction method. It is found that the plasma energy shifts corresponding to principal quantum number conserving transitions (Δ n = 0) are blue shifted, whereas red shifted for the transitions where the principal quantum number is not conserved (Δn ≠ 0). The variation of transition probabilities and weighted oscillator strengths with free electron densities has also been studied. The present results should be advantageous in the modeling and diagnostics of astrophysical and laboratory plasmas.

Thermodynamic processes in dusty plasma

Here, we propose a thermodynamic model for dusty plasma, where the dust is confined in a small volume within a large plasma background by external fields. In this model, the parameters of dust, e.g. Helmholtz energy, pressure, entropy and enthalpy, etc. can be calculated for given dust density and temperature. The model is solved analytically in the mean field (gaseous) limit and various processes associated with the gaseous phase of dust, e.g. adiabatic/isothermal/constant internal energy expansion/compression, specific heat, free expansion within the plasma background, and the dispersion of novel acoustic waves are studied. Some predictions of the model, e.g. electrostatic pressure of the dust and the isothermal equation of state, have been earlier verified in experiments and numerical simulations. The model is compared with an earlier thermodynamic model of dusty plasma proposed by Hamaguchi and Farouki.

Understanding Inter-Hemispheric Traveling Ionospheric Disturbances and Their Mechanisms

Traveling ionospheric disturbances (TIDs) are wave-like disturbances in ionospheric plasma density. They are often observed during both quiet (medium-scale TID) and geomagnetically disturbed (large-scale TID) conditions. Their amplitudes can reach double-digit percentages of the background plasma density, and their existence presents a challenge for accurate ionosphere specification. In this study, we examine TID properties using observations obtained during two geomagnetically disturbed periods using multiple ground and space-borne instruments, such as magnetometers, Global Navigation Satellite System (GNSS) receivers, and the SWARM satellite. Reference quiet time observations are also provided for both storms. We use a thermosphere–ionosphere–electrodynamics general circulation model (TIEGCM) results to properly interpret TID features and their drivers. This combination of observations and modeling allows the investigation of variations of TID generation mechanisms and subsequent wave propagation, particularly as a function of different plasma background densities during various geophysical conditions. The trans-equatorial coupling of TIDs in the northern and southern hemispheres is also investigated with respect to attenuation and propagation characteristics. We show that TID properties during trans-equatorial events may be substantially affected by storm time background neutral wind perturbation.

FLASHForward: plasma wakefield accelerator science for high-average-power applications

The FLASHForward experimental facility is a high-performance test-bed for precision plasma wakefield research, aiming to accelerate high-quality electron beams to GeV-levels in a few centimetres of ionized gas. The plasma is created by ionizing gas in a gas cell either by a high-voltage discharge or a high-intensity laser pulse. The electrons to be accelerated will either be injected internally from the plasma background or externally from the FLASH superconducting RF front end. In both cases, the wakefield will be driven by electron beams provided by the FLASH gun and linac modules operating with a 10 Hz macro-pulse structure, generating 1.25 GeV, 1 nC electron bunches at up to 3 MHz micro-pulse repetition rates. At full capacity, this FLASH bunch-train structure corresponds to 30 kW of average power, orders of magnitude higher than drivers available to other state-of-the-art LWFA and PWFA experiments. This high-power functionality means FLASHForward is the only plasma wakefield facility in the world with the immediate capability to develop, explore and benchmark high-average-power plasma wakefield research essential for next-generation facilities. The operational parameters and technical highlights of the experiment are discussed, as well as the scientific goals and high-average-power outlook. This article is part of the Theo Murphy meeting issue ‘Directions in particle beam-driven plasma wakefield acceleration’.