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Final Report Summary - QUANTUM PLASMAS (Complex ideal and non-ideal quantum plasmas)

This is an ambitious project carried out by a network that brings together 3 European and 2 non- EU overseas nodes, namely: Queen’s University Belfast – QUB (Belfast, UK), Instituto Superior Técnico – IST (Lisbon, Portugal), Chalmers University of Technology – CHT (Gothenburg, Sweden), Universidade Federal do Rio Grande do Sul – UFRGS (Porto Alegre, Brazil) and Universidade Federal Fluminense – UFF (Rio de Janeiro, Brazil). The consortium combines expertise from established researchers in the fields of Plasma Science and Nonlinear Physics.
Our research focuses on Quantum Plasmas, an exotic state of matter, describing many-body systems of interacting charged particles (electrons, ions) occurring in ultra-high density and lowtemperature conditions. These systems are not only of wide relevance in Astrophysics, but are also realised in laboratory experiments via ultra-high intensity laser interactions with matter

Objectives. Quantum plasmas, such as electron gases, are ubiquitous: they are important components of metals and semiconductors, but also of novel materials (semimetals, graphene) associated with key technological advances expected in the coming decades. Moreover, comprehending the properties of quantum plasmas is necessary to understand the physics of the next generation intense laser-solid density plasma interaction experiments and quantum x-ray free-electron lasers, as well as properties of dense astrophysical objects such as interiors of giant planets and white dwarf stars.
The aim of our research is to establish computationally viable models for analyzing collective quantum effects in plasma systems and to use these models in order to gain deeper understanding of the dynamics and applications of such systems. A comprehensive investigation of the dynamics of linear and nonlinear excitations occurring in Quantum Plasmas has been undertaken in the framework of the project. Our aim is to elucidate the conditions for the existence of electrostatic and electromagnetic waves of various forms in quantum plasmas, and to study their propagation dynamics and stability profile.
Coherent structures are nowadays observed in laser-plasma experiments in ultra-high intensity, ultra-high density and low temperature (quantum) regimes, in the form of pulses, shocks and phase-space holes, among other structures. The interpretation of such structures in such plasmas is still at an early stage, despite the tremendous potential impact of quantum plasmas in future industrial and technological applications. Our research should foster future developments in this promising field. In particular, our results will be of relevance in up-coming laser-plasma experiments. Our models are therefore developed and the resulting physics investigated with such parameter regimes in mind.

Description of the project work:
Ideal and non-ideal ultra-dense plasmas have been investigated within dedicated work programmes, including: i) kinetic theories of quantum plasmas, wave and particle interactions, linear and nonlinear processes; ii) new trends in relativistic quantum plasmas ; iii) electrostatic quantum plasma waves; iv) electromagnetic waves in relativistic quantum plasmas; v) Ultra-cold Rydberg plasmas. A number of sophisticated analytical methods developed earlier for the investigation of nonlinear plasma processes have been used for studies of collective effects in dense quantum plasmas. These include a combination of multiple scale perturbation techniques, dynamical systems analysis, and previously unexplored areas of relativistic electrodynamics.

Main results. Highlights from the project outcomes include (but are not limited to) the following:
- Relativistic model for electrostatic solitary waves in quantum plasmas. A novel analytical framework had been developed for electrostatic localized modes in the ultrahigh density relativistic quantum plasma regime, used as a rigorous basis for the investigation of the propagation characteristics of linear (waves) and nonlinear (soliton) modes. Relying on this model, we have investigated the characteristics of localized modes (solitary waves) propagating in ultrahigh density plasmas. This is a first study of its kind, in concept, content and rigor.
- Dynamical description of Ultracold Plasma (UCP) expansion. We developed a theory for self-induced electron trapping occurring in a ultracold neutral plasma that is set to expand freely. At the early stages of the plasma, the ions are not thermalized follow a Gaussian spatial profile,
providing the trapping to the coldest electrons. We have proposed a new theoretical model describing the electrostatic potential and we have performed molecular dynamics simulations that validate our predictions. We have shown that in the strong confinement regime, the plasma potential is of a Thomas-Fermi type, similar to the case of heavy atomic species. The numerically simulated spatial profiles of the particles corroborate this claim. We have also extracted the electron temperature and coupling parameter from the simulation, so the duration of the transient Thomas-Fermi can be obtained rigorously.
- Ultracold Rydberg plasmas. A kinetic theory was developed for twisted density waves (phonons), carrying a finite amount of orbital angular momentum, in large magneto-optical traps, where the collective processes due to the exchange of scattered photons are considered. Explicit expressions for the dispersion relation and for the kinetic (Landau) damping are derived and contributions from the orbital angular momentum are discussed. We show that for rotating clouds, phonons carrying orbital angular momentum can cross the instability threshold and grow out of noise,
while the usual plane-wave solutions are kinetically damped.
Final results and impact:
High density plasmas are linked to technological applications, ranging from semiconductor technology to advanced industrial applications. We envisage that our research should bear significant impact on the theoretical background and the design of actual applications. Our theoretical analysis is of relevance in current and future applications, such as nanoscale devices, plasmonics (materials), and terrahertz beam generation.
The coordinator site (QUB, UK) hosts a world known multimillion laser facility (TARANIS), able to provide ultra-high intensity ultrashort duration laser pulses. TARANIS is currently used as a platform for world class research on laser-matter interactions. Although our project was, strictly speaking, theoretically oriented, interactions with experimental colleagues have proven to be of mutual benefit, providing inspiration and ideas for further research. Our theoretical findings will be tested in the future, and hopefully confirmed; on the other hand, experimental research outcomes should provide fertile ground expected to catalyze our theoretical investigations.
Contact details.
Scientific Coordinator: Dr Ioannis Kourakis (i.kourakis@qub.ac.uk).
Project Webpage: www.quantumplasmas.eu.

Reported by

THE QUEEN'S UNIVERSITY OF BELFAST
United Kingdom

Subjects

Life Sciences
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