Abstract
We numerically investigate the impact of Coulomb collisions on the ion dynamics in high-Z, solid density caesium hydride and copper targets, irradiated by high-intensity (), ultrashort (∼10 fs), circularly polarized laser pulses, using particle-in-cell simulations. Collisions significantly enhance electron heating, thereby strongly increasing the speed of a shock wave launched in the laser-plasma interaction. In the caesium hydride target, collisions between the two ion species heat the protons to ∼100−1000 eV temperatures. However, in contrast to previous work (A E Turrell et al 2015 Nat. Commun. 6 8905), this process happens in the upstream only, due to nearly total proton reflection. This difference is ascribed to distinct models used to treat collisions in dense/cold plasmas. In the case of a copper target, ion reflection can start as a self-amplifying process, bootstrapping itself. Afterwards, collisions between the reflected and upstream ions heat these two populations significantly. When increasing the pulse duration to 60 fs, the shock front more clearly decouples from the laser piston, and so can be studied without direct interference from the laser. The shock wave formed at early times exhibits properties typical of both hydrodynamic and electrostatic shocks, including ion reflection. At late times, the shock is seen to evolve into a hydrodynamic blast wave.
Highlights
The use of lasers to accelerate ions is a field of intense research [1], with many demonstrated or envisioned applications, such as imaging of electromagnetic fields in plasmas [2, 3], creation of warm dense matter [4,5,6], production of intense neutron sources [7], material testing [8, 9], laboratory astrophysics [10], and ion-beam therapy [11, 12]
The first case we consider is motivated by the work by Turrell, Sherlock & Rose [28], where it was reported that inter-species collisions in a caesium hydride (CsH) target induce ultrafast collisional ion heating, and essentially affect the shock dynamics
Using particle-in-cell simulations, we have numerically investigated the impact of Coulomb collisions on the ion dynamics in high-Z∗, solid density caesium hydride and copper targets, irradiated by high-intensity (I ≈ 2−5 × 1020 Wcm−2), ultrashort (10−60 fs), circularly polarized laser pulses
Summary
The use of lasers to accelerate ions is a field of intense research [1], with many demonstrated or envisioned applications, such as imaging of electromagnetic fields in plasmas [2, 3], creation of warm dense matter [4,5,6], production of intense neutron sources [7], material testing [8, 9], laboratory astrophysics [10], and ion-beam therapy [11, 12]. As the shock front passes by, the plasma is rapidly compressed and directional kinetic energy is converted into thermal energy This can take place either through collisional processes, such as in hydrodynamic shocks – relevant in, e.g., inertial fusion plasmas [21, 22] and relativistic laser-plasma experiments [23] – or collisionless mechanisms, involving longitudinal electrostatic fields generated by space charge effects from shock compression [14]. The first case we consider is motivated by the work by Turrell, Sherlock & Rose [28] (hereafter referred to as TSR), where it was reported that inter-species collisions in a caesium hydride (CsH) target induce ultrafast collisional ion heating, and essentially affect the shock dynamics. The other case we address was first considered in a recent study of ours [29] investigating ionization and collisional electron heating effects in solid copper targets, relevant for warm-dense-matter generation. Collisional friction between the upstream and reflected ions heats the upstream ion population, which enhances the fraction of reflected ions
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
