Different energy transport mechanisms come into play when intense laser pulses interact with dense plasma. Here the authors provide a limit on the plasma density reachable with an intense laser and an insight into the hole boring process.
Plasma exists in a mixed form of electrons, positive ions and neutral atoms or molecules and plays an important role in many processes; from astrophysical solar flares to nuclear fusion devices for energy applications. There is a strong research interest both in theory and experiment to understand how the plasma energy is transferred into other forms and how plasma behaves in different environments. Investigating these processes under extreme conditions in a table-top setting has become feasible due to the availability of high-power lasers.
In this collection we highlight a selection of recent experimental and theoretical research papers published on this multidisciplinary topic in Nature Communications. These articles feature research on fundamental plasma processes that are relevant to astrophysical events, energy transfer from laser to the particles during their acceleration, material development for plasma confinement and nuclear reactions in plasma fusion devices. This collection showcases the variety of research that different communities can bring together to better understand the ubiquitous processes in plasma.
Fundamental properties of plasma
High intensity light with a non-zero orbital angular momentum could aid the development of laser-wakefield particle accelerators. Here, the authors theoretically show that stimulated Raman backscattering in plasmas can generate and amplify orbital angular momentum lasers to petawatt intensities.
The electrons in a plasma can further ionize the ions when the two collide. Vinko et al. now study this ultrafast process in an unconventional plasma with a density similar to that of a solid, and show that the rate is several times higher than that predicted by standard theoretical models.
Charge screening dominates the behaviour of high-energy plasmas, which exist in stars and possibly in future fusion technology. Here, the authors describe a theoretical framework for charge screening that goes beyond the conventional model and demonstrate its importance in analysing experimental data.
Short pulses of high intensity laser light usually heat the ions in dense plasmas indirectly via collisions with the electrons. Here, the authors identify an extremely rapid alternative heating mechanism based on ion-ion collisions.
The energy loss of ions in plasma is a challenging issue in inertial confinement fusion and many theoretical models exist on ion-stopping power. Here, the authors use laser-generated plasma probed by accelerator-produced ions in experiments to discriminate various ion stopping models near the Bragg peak.
Studying the properties of dense plasmas is challenging due to strong interactions between electrons and ions, and numerical methods overcome this difficulty using a static thermostat. Here the authors predict a strong diffusive ion mode at low energy by including dissipative processes in the model.
The effect of dense plasma environment on the energy levels of an ion is usually described in terms of a lowering of its continuum level. Here the authors present an isochoric-heating experiment to measure and compare continuum lowering in single-species and mixture plasmas to provide insights for models.
Exploring the plasma processes in the pre-plasma state that lead to instabilities is challenging. Here the authors probe the evolution of the plasma phase change and the instabilities in plasma created by an exploding copper wire in Z-pinch geometry using shadowgraphy.
The electric wind mechanism remains unclear. Here, the authors report evidence that electric wind is caused by an electrohydrodynamic force generated by charged particle drag as a result of momentum transfer to neutral particles.
Laser-driven plasmas can accelerate electrons in set-ups far smaller than conventional particle accelerators, but beam divergence is a problem. Here, the authors demonstrate a laser-plasma lens that can focus the beam thanks to field gradients five order of magnitude larger than using traditional optics.
Intense laser pulses can induce the propagation of coherent waves through a plasma, which are useful for accelerating electrons. Here, the authors use a genetic algorithm and a deformable mirror to optimize the wavefront and improve electron beam intensity and divergence.
Higher beam quality and stability are desired in laser-plasma accelerators for their applications in compact light sources. Here the authors demonstrate in laser plasma wakefield electron acceleration that the beam loading effect can be employed to improve beam quality by controlling the beam charge.
Extraction of ultra-low emittance bunches is an issue to be addressed for future applications of plasma wakefield accelerators. Here, the authors show that the field structure of the plasma could be suitable for this, by measuring the field's longitudinal variation produced by a relativistic electron bunch.
Single-stage plasma-based correlated energy spread compensation for ultrahigh 6D brightness electron beams
Controlling and improving electron beam parameters are crucial for their application in free electron laser and X-ray sources. Here the authors generate quality electron beams with reduced energy spread from plasma accelerators by using a tailored escort electron bunch with the main accelerating bunch.
Electron–positron pair plasma—a state of matter with a complete symmetry between negatively and positively charged particles—are found in many astrophysical object. Here, the authors use high-power laser to create an ion-free electron–positron plasma in the laboratory.
High power lasers can produce electron-positron pairs at GeV energies, but doing so through laser–laser collisions would require exceedingly high intensities. Here the authors present an all-optical scheme for pair production by irradiating near-critical-density plasmas with two counter-propagating lasers.
Efficient energy transport by laser-driven relativistic electron beams is crucial in many applications including inertial confinement fusion, and particle acceleration. Here the authors demonstrate relativistic electron beam guiding in dense plasma with an externally imposed high magnetic field.
With excellent resolving power and tissue contrast, X-ray phase-contrast imaging holds great promise but the source requirements have limited its use. Here, Wenz et al. show a phase-contrast microtomogram of a biological sample using X-ray radiation driven by a high-power laser.
It is a challenge to scale up laser-ion acceleration to higher ion energies. Here the authors demonstrate a hybrid acceleration scheme based on the relativistic induced transparency mechanism using linearly polarised laser interaction with foil targets and its future implication in using high power lasers.
Towards optical polarization control of laser-driven proton acceleration in foils undergoing relativistic transparency
Intense laser pulse interaction with ultra-thin foils constitutes a promising approach for proton acceleration. Here the authors show that the degree of ellipticity in the laser beam polarization can be used to control the proton beam profile.
Experimental investigations of the response of matter to ionization would require extremely fast ion pump pulses. Here, the authors explore a different approach observing ionisation dynamics in SiO2glass by generating synchronized proton pulses from the interaction of high-power lasers on a solid target.
Neutron beams are useful studying fundamental physics problems, fusion process and material properties. Here the authors use intense laser irradiation of deuterated nanowire array targets to create high energy density plasmas capable of efficient generation of ultrafast neutron pulses.
Table-top laser-plasma ion accelerators have many potential applications, but achieving simultaneous narrow energy spread and high efficiency remains a challenge. Here, the authors produce ion beams with up to 18 MeV per nucleon whilst keeping the energy spread reduced through a self-organized process.
Plasma wakefield accelerators produce gradients that are orders of magnitude larger than in conventional particle accelerator, but beams tend to be disrupted by transverse forces. Here the authors create an extended hollow plasma channel, which accelerates positrons without generating transverse forces.
Recently, there has been significant progress on the application of laser-generated proton beams in material science. Here the authors demonstrate the benefit of employing such beams in stress testing different materials by examining their mechanical, optical, electrical, and morphological properties.
Self-generated surface magnetic fields inhibit laser-driven sheath acceleration of high-energy protons
Laser-generated ion acceleration has received increasing attention due to recent progress in super-intense lasers. Here the authors demonstrate the role of the self-generated magnetic field on the ion acceleration and limitations on the energy scaling with laser intensity.
Electron beam quality in accelerators is crucial for light source application. Here the authors demonstrate beam conditioning of laser plasma electrons thanks to a specific transport line enabling the control of divergence, energy, steering and dispersion and the application to observe undulator radiation.
Magnetic fusion reactors with higher ratio of plasma kinetic pressure to magnetic pressure are economically desirable. The authors demonstrate a path to such a reactor in a field reversed configuration that can attain microstability and reduced particle and thermal fluxes by manipulating the shear flow.
Vapour shielding is one of the interesting mechanisms for reducing the heat load to plasma facing components in fusion reactors. Here the authors report on the observation of a dynamic equilibrium between the plasma and the divertor liquid Sn surface leading to an overall stable surface temperature.
A stable plasma state with a high ratio of plasma to magnetic pressures is likely to be a key requirement for any future magnetic fusion reactor. Here, the authors create such a plasma using a field reversed configuration and active plasma boundary control and demonstrate its stability.
Early stellarator designs suffered from high particle losses, an issue that can be addressed by optimization of the coils. Here the authors measure the magnetic field lines in the Wendelstein 7-X stellarator, confirming that the complicated design of the superconducting coils has been realized successfully.
It is important to understand the fast plasma dynamics in the operation of fusion plasma devices. Here the authors demonstrate the inference on the internal field reversed configuration magnetic topology and their occurrence during fast Alfvenic transient phenomena in C-2U device.
Understanding the transport of ions, electrons and heat in magnetized plasmas is important to the development of fusion power as well as our understanding of the behaviour of astrophysical objects. Ida et al.find that stochastization of magnetic field lines in a plasma damps plasma flow more strongly than expected.
Laboratory & astrophysical plasma
Laboratory measurements of resistivity in warm dense plasmas relevant to the microphysics of brown dwarfs
Brown dwarfs are small stars that are believed to be made of a warm dense plasma that cannot support hydrogen fusion as larger stars do. Here, the authors present a method for studying the properties, such as resistivity, of warm dense plasmas in the laboratory.
Magnetic reconnection occurs close to the surface of the sun, in the Earth’s magnetosphere and in astronomical plasmas. Here, the authors investigate magnetic reconnection in a laboratory-based experiments with an asymmetric configuration similar to those found in real astrophysical situations.
Understanding the role of magnetic turbulence in the atmosphere is difficult as direct access is limited, but latest laser technology can enable such studies in the lab. Here the authors probe the evolution of such turbulence in laser-generated plasma with its implications to astrophysical environments.
Exploring astrophysical turbulent effects in laboratory plasma is challenging due to high threshold values of relevant parameters, such as the magnetic Reynolds number. Here the authors demonstrate the turbulent dynamo effect at large magnetic Reynolds numbers in laser-generated magnetized plasma.
Stationary radiative shocks are expected to form above the surface of highly-magnetized white dwarves in binary systems, but this cannot be resolved by telescopes. Here, the authors report a laboratory experiment showing the evolution of a reverse shock when both ionization and radiative losses are important.
The Van Allen radiation belts are two zones of energetic particles encircling the Earth, but how electrons are accelerated to relativistic energies remains unclear. Here, the authors analyse a radiation belt event and provide evidence in favour of the ULF wave-driven radial diffusion mechanism.
Since the 1970s space missions have observed `equatorial noise' — noise-like plasma waves closely confined to the magnetic equatorial region of Earth s magnetosphere. Here, the authors uncover their structured and periodic frequency pattern, revealing that they are generated by proton distributions.
Relativistic electrons trapped in the Van Allen radiation belts sometimes exhibit a minimum of their pitch angle distribution at 90°. Here, the authors explain the origin of this phenomenon in terms of chorus and magnetosonic waves through simulations and observations of a geomagnetic storm data.
Alfvén waves are fundamental plasma modes that provide a mechanism for the transfer of energy between particles and fields. Here the authors confirm experimentally the conservative energy exchange between Alfvén wave fields and plasma particles via high-resolution MMS observations of Earth’s magnetosphere.
Turbulent mass transfer caused by vortex induced reconnection in collisionless magnetospheric plasmas
Vortex-induced reconnection originates from non-linear vortex flows due to Kelvin-Helmholtz instability in the Earth’s magnetosphere. Here, the authors perform a large-scale kinetic simulation to unveil dynamics of the vortex-induced reconnection and resulting turbulent mixing process.
Magnetic reconnection is a fundamental process giving rise to topology change and energy release in plasmas, of particular relevance for the Sun. Here the authors report the observation of fast reconnection in a solar filament eruption, which occurs between a set of ambient fibrils and the filament itself.
Magnetic reconnection is a fundamental energy release process taking place in various astrophysical environments, but it is difficult to observe it directly. Here, the authors provide evidence of three-dimensional magnetic reconnection in a solar eruption using combined perspectives of two spacecraft.
Alfvénic waves are oscillations that occur in a plasma threaded by a magnetic field and their propagation, reflection and dissipation is believed to be partly responsible for the solar wind. Here, the authors observe the counter-propagating Alfvénic waves that most models require for solar-wind acceleration.
Although magnetic reconnection is recognized as the dominant mode for solar wind plasma to enter the magnetosphere, Kelvin–Helmholtz waves (KHW) have been suggested to also be involved. Here, the authors use 7 years of THEMIS data to show that KHW occur 19% of the time, and may be important for plasma transport.
Observationally quantified reconnection providing a viable mechanism for active region coronal heating
The solar corona heating mechanism is still subject to debate. Here, the authors report that impulsive reconnection can give rise to an active region corona that is compatible with extreme-ultraviolet observations.
Both fast and slow solar winds emanate from our Sun, although the source of the slow component remains elusive. Towards identifying this, Brooks et al. present full-Sun spectral images from Hinode, combined with magnetic modelling, to produce a solar wind source map.
Plasma releases magnetic energy by magnetic reconnection but the clear evidence of this phenomenon in relativistic regime is still lacking. Here the authors present a scheme for laboratory observation of the relativistic magnetic reconnection driven by laser-produced energetic electrons in the plasma.
Radiation and conduction are generally considered as the main energy transport mechanisms for the evolution of early supernova remnants. Here the authors experimentally show the role of electron heat transfer on the growth of Rayleigh–Taylor instability in young supernova remnants.
The periodical change of the Crab nebula’s jet direction challenges our understanding of astrophysical jet dynamics. Here the authors use high-power lasers to create a jet that can be directly compared to the Crab nebula’s, and report the detection of plasma instabilities that mimic kink behaviour.