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Recent developments in ultrashort and intense laser systems have enabled the generation of short and brilliant proton sources, which are valuable for studying plasmas under extreme conditions in high-energy-density physics. However, developing sensors for the energy selection, focusing, transport, and detection of these sources remains challenging. This work presents a novel and simple design for an isochronous magnetic selector capable of angular and energy selection of proton sources, significantly reducing temporal spread compared to the current state of the art. The isochronous selector separates the beam based on ion energy, making it a potential component in new energy spectrum sensors for ions. Analytical estimations and Monte Carlo simulations validate the proposed configuration. Due to its low temporal spread, this selector is also useful for studying extreme states of matter, such as proton stopping power in warm dense matter, where short plasma stagnation time (<100 ps) is a critical factor. The proposed selector can also be employed at higher proton energies, achieving final time spreads of a few picoseconds. This has important implications for sensing technologies in the study of coherent energy deposition in biology and medical physics. [ABSTRACT FROM AUTHOR]

We investigate collisionless shock acceleration of spin-polarized 3 He for laser pulses with normalized vector potentials in the range a 0 = 100 − 200 . The setup utilized in the 2D-particle-in-cell simulations consists of a solid carbon foil that is placed in front of the main Helium target. The foil is heated by the laser pulse and shields the Helium from the highly oscillating fields. In turn, a shock wave with more homogeneous fields is induced, leading to highly polarized ion beams. We observe that the inclusion of radiation reaction into our simulations leads to a higher beam charge without affecting the polarization degree to a significant extent. [ABSTRACT FROM AUTHOR]

This study delves into a Pick‐Up Ion (PUI) event captured by the Mars Ion and Neutral Particle Analyzer aboard Tianwen‐1, revealing a faster acceleration than expected within the Martian magnetosheath. This event suggests the presence of a convection electric field considerably stronger than that typically observed in the solar wind. Through Magnetohydrodynamic simulation, we identified two regions of intensified convection electric fields within the inner magnetosheath, prominently manifested at mid to high solar zenith angles (SZA = 40°–70°) in the X‐Z plane of the Mars Solar Electric field coordinates. Tianwen‐1 observed that the peak of the electric field strength, up to five times of that in the solar wind, is located at the upper edge or within the Magnetic Pileup Boundary. Further study by test particle simulations showed acceleration by the electric field effectively doubles the energy gain of PUIs, in comparison to scenarios absent of this extra acceleration. It is revealed that the presence of such electric field regions within the Martian magnetosheath is a prevailing feature, shaped by the solar wind's interaction with Mars and modulated by the planet's rotating crustal magnetic fields. Plain Language Summary: The interaction between planets and their upstream solar wind holds great significance for the long‐time climate evolution of planets. Mars lacks a global dipole magnetic field, which makes it easier for these planetary ions to escape through acceleration by the solar wind convection electric field. The observations of Tianwen‐1 and Mars Atmosphere and Volatile Evolution satellites provide a great opportunity to study the acceleration of planetary ions by this electric field. Through a case study involving observation and simulation, we confirm that there are two regions in the Martian magnetosheath, where the convection electric field is stronger than in the solar wind. This electric field may rapidly energize the ions and possibly result in intensified ion escape. Key Points: In the Martian magnetosheath, joint effects of the plasma flow around Mars and the interplanetary magnetic field pileup result in enhanced convection electric fieldThe strong E field envelops a large part of the Magnetic Pileup Boundary (MPB), with the maximum at the med‐high solar zenith angles, at the upper edge or within the MPBThe crustal magnetic fields modulate the distribution of the strong E field, leading to hemispheric asymmetry [ABSTRACT FROM AUTHOR]

As part of a brief review, a classification is made and information is provided about four experimentally discovered plasma effects, where unexpected behavior of the ionic component appeared and for which there is no unambiguous interpretation. 1. Ions with the highest energies for a quasi-neutral current sheet were recorded at the O-point (island) with the direction of their movement opposite to the electric field at the X-point. 2. In a self-sustaining discharge in crossed electric and magnetic fields (E×B discharge), a large number of ions (not the tails of the distribution function) with energies significantly exceeding the energies equivalent to the discharge voltage are generated. This occurs in a certain range of pressures of the plasma-forming gas and magnetic fields. 3. The discovered region of effective ionization — the “anode layer”, with increasing pressure, moves abruptly from one plasma region to another, which is accompanied by a jump in the ion density up to 16 times. An increase in the magnetic field induction causes, on the contrary, the “anode layer” to jump in the opposite direction with the ion density decreasing 3–4 times. 4. Ion distribution functions in the E×B discharge contain isomagnetic density jumps with a relative amplitude from ~30 to 80 % of the total current at the released energy. Taking into account the “anomalous” behavior of ions in the plasma of quasi-neutral current sheets and discharges in crossed electric and magnetic fields will provide further insight into the processes in space plasma, the physics of coronal heating, and the formation of the solar wind.

Recent developments in ultrashort and intense laser systems have enabled the generation of short and brilliant proton sources, which are valuable for studying plasmas under extreme conditions in high-energy-density physics. However, developing sensors for the energy selection, focusing, transport, and detection of these sources remains challenging. This work presents a novel and simple design for an isochronous magnetic selector capable of angular and energy selection of proton sources, significantly reducing temporal spread compared to the current state of the art. The isochronous selector separates the beam based on ion energy, making it a potential component in new energy spectrum sensors for ions. Analytical estimations and Monte Carlo simulations validate the proposed configuration. Due to its low temporal spread, this selector is also useful for studying extreme states of matter, such as proton stopping power in warm dense matter, where short plasma stagnation time (

Next generation high-power laser facilities are expected to generate hundreds-of-MeV proton beams and operate at multi-Hz repetition rates, presenting opportunities for medical, industrial and scientific applications requiring bright pulses of energetic ions. Characterizing the spectro-spatial profile of these ions at high repetition rates in the harsh radiation environments created by laser–plasma interactions remains challenging but is paramount for further source development. To address this, we present a compact scintillating fiber imaging spectrometer based on the tomographic reconstruction of proton energy deposition in a layered fiber array. Modeling indicates that spatial resolution of approximately 1 mm and energy resolution of less than 10% at proton energies of more than 20 MeV are readily achievable with existing 100 μm diameter fibers. Measurements with a prototype beam-profile monitor using 500 μm fibers demonstrate active readouts with invulnerability to electromagnetic pulses, and less than 100 Gy sensitivity. The performance of the full instrument concept is explored with Monte Carlo simulations, accurately reconstructing a proton beam with a multiple-component spectro-spatial profile.

The impact of radiation reaction and Breit–Wheeler pair production on the acceleration of fully ionized carbon ions driven by an intense linearly polarized laser pulse has been investigated in the ultra-relativistic transparency regime. Against initial expectations, the radiation reaction and pair production at ultra-high laser intensities are found to enhance the energy gained by the ions. The electrons lose most of their transverse momentum, and the additionally produced pair plasma of Breit–Wheeler electrons and positrons co-streams in the forward direction as opposed to the existing electrons streaming at an angle above zero degree. We discuss how these observations could be explained by the changes in the phase velocity of the Buneman instability, which is known to aid ion acceleration in the breakout afterburner regime, by tapping the free energy in the relative electron and ion streams. We present evidence that these non-classical effects can further improve the highest carbon ion energies in this transparency regime.

A possibility of obtaining particles with an energy of as high as a few GeV using Coulomb explosion of laser-irradiated spherical microtargets is discussed for the Exawatt Center for Extreme Light Studies (XCELS) facility, characterized by the record-high power and ultrashort duration of generated laser pulses. Theoretical justification is given for the possibility of experimental implementation of the relativistic Coulomb explosion of large (micron and submicron) spherical targets using multi-side irradiation with several high-intensity laser beams, which is currently unattainable for the existing high-power laser systems. The proposed experiment is substantiated by the results of theoretical and analytical studies of ion acceleration at relativistic Coulomb explosion of microtargets composed of either one-type ions or a combination of impurity light ions and majority heavy ions. Spatial–temporal and spectral characteristics of accelerated ions having a relativistic energy and quasi-monochromatic spectrum are found. This study makes it possible to predetermine the characteristics of ions with record-high energies from Coulomb-exploded spherical microtargets and introduce theoretical justification of the experiment on the XCELS facility in the single-beam and multibeam modes. [ABSTRACT FROM AUTHOR]

The supersonic ion jet generated in vacuum arc plasma has numerous applications, but the ion acceleration mechanism is incompletely understood. In this paper, a one-dimensional spherical vacuum arc discharge model is established, and the ion acceleration from vacuum breakdown to steady arc stage is investigated using particle-in-cell direct simulation Monte Carlo method. The results show that a potential hump exists and locates about 1 μ m far away from the cathode, but the potential drop provides a small contribution to the ion acceleration. A potential valley forms near the plasma–vacuum boundary and propagates towards the anode as the plasma expands during the vacuum breakdown stage. The ion mounting this valley experiences continuous acceleration by the dynamic electric field of the potential valley. As the plasma reaches the anode, a steady arc stage is gradually build-up, and the potential valley disappears. Consequently, the maximum mean ion velocity decreases. The source dominating the ion acceleration in this stage is turned into the electron–ion Coulomb collision. [ABSTRACT FROM AUTHOR]

In this paper we report the measurement of laser-driven proton acceleration obtained by irradiating nanotube array targets with ultrashort laser pulses at an intensity in excess of 1020 W cm-2. The energetic spectra of forward accelerated protons show a larger flux and a higher proton cutoff energy if compared to flat foils of comparable thickness. Particle-In-Cell 2D simulations reveal that packed nanotube targets favour a better laser-plasma coupling and produce an efficient generation of fast electrons moving through the target. Due to their sub-wavelength size, the propagation of e.m. field into the tubes is made possible by the excitation of Surface Plasmon Polaritons, travelling down to the end of the target and assuring a continuous electron acceleration. The higher amount and energy of these electrons result in turn in a stronger electric sheath field on the rear surface of the target and in a more efficient acceleration of the protons via the target normal sheath acceleration mechanism.

The potential for protons and ions accelerated by ultra-intense high power laser systems was investigated to perform space radiation tests for electronic components and materials which will be used in space. Currently, conventional accelerator systems, which produce monoenergetic particle beams, are employed for space radiation testing. All components must be tested with several different monoenergetic proton and ion beams selected from their continuous energy spectra in space because their broad energy range is a difficult to mimic with discrete energy beams coming from conventional accelerators. Therefore, each component is subjected to at least five different energy proton tests as well as a selection of beams of different ions, which increases the cost of determining the radiation hardness of these components and makes it unpractical. However, laser driven accelerators (LDAs) are capable of producing a mixed environment of particles such as electrons, protons, neutrons, and ions, as well as photons in a wide energy range. The parameters of the laser-plasma interaction can be selected so that the energy spectra and particle fluences of the space radiation environment can be recreated in the laboratory. By using LDA systems, the impact of space radiation on space electronics can be tested using table-top lasers. We performed particle-in-cell (PIC) codes to calculate the energy spectra of accelerated particles via laser plasma interactions. In our simulations, H+ and C+6 energy spectra produced from high power laser and plasma interactions were obtained using EPOCH 2D PIC code. These spectra were compared with proton and C+6 energy spectra and fluences in four different Earth orbits at different altitudes in space, obtained using the NASA AP-8MIN, the CREME-96 and the ESP-PSYCHIC models from the SPENVIS program. The comparisons between the results of EPOCH simulations and SPENVIS look promising in terms of the similarities of these spectra up to 190 MeV for protons and up to 1150 MeV for carbon ions. The idea of using accelerated particles from ultra-intense lasers rather than the conventional accelerator systems is promising for space radiation tests due to their wide energy range. [ABSTRACT FROM AUTHOR]

When in the solar wind, the Moon is exposed to its embedded discontinuities such as interplanetary (IP) shocks. In this study we utilize 3‐D electromagnetic hybrid (kinetic ions, fluid electrons) simulations and observations of two events, by THEMIS/ARTEMIS spacecraft to understand the interaction of IP shocks with the Moon. Simulation parameters are based on one of the ARTEMIS events and include the presence of supra‐thermal ions in the solar wind. The results show that the absorption of the cold solar wind protons on the Moon's dayside leads to a density hole in the shock front behind the Moon. This density hole refills and recovers as the IP shock moves down the lunar tail. Penetration of the interplanetary magnetic field through Moon's body leads to the survival of a steepened magnetic structure associated with the shock surface. However, due to the lower pressures in the lunar tail the structure broadens in space and is expected to steepen when the IP shock is beyond the tail. The IP shock is also found to interact with the energetic ions in the lunar tail resulting in their acceleration to higher energies. Comparing the densities measured by ARTEMIS in the solar wind and lunar tail shows the absence of a shock front in density in the tail consistent with the formation of a density hole at the shock front. Similarly, comparing the magnetic field profiles in the solar wind and lunar tail shows the expected broadening of the magnetic field shock front. Key Points: Interaction of interplanetary (IP) shock with the Moon forms a density hole which refills down the tailThe magnetic structure associated with the shock broadens in the lunar tailEnergetic ions in the tail are further accelerated by the IP shock [ABSTRACT FROM AUTHOR]

We employ two-dimensional particle-in-cell simulations to examine, in detail, the effect of a kilo-Tesla magnetic field applied along the normal of a flat TNSA target on the cutoff energy of protons/ions. The two cases of (i) normally incident single laser pulse, and (ii) two obliquely incident laser pulses are thoroughly examined. It is shown that the two-oblique-pulse configuration combined with an external magnetic field results in a stronger enhancement (56 MeV–75 MeV) in the protons’ cutoff energies than the normally incident single laser pulse with an external magnetic field (19 MeV–24 MeV). This combination of two-oblique laser pulses along with a kilo-Tesla level external magnetic field is therefore found to be highly effective in accelerating protons/ions in the TNSA regime.

The improvement of laser-driven proton energy with the use of nano-structured hemispherical targets of 100 nm thickness over conventional flat foil has been reported in this work. The curvature of the target is found to result in focussed particle density at the center of the hemispherical target followed by emergence of energetic ions due to combined action of sheath electric field and ambipolar expansion. The presence of nano-rods on the curved hemispherical target further increases the laser energy absorption by the electrons, thus resulting in increase in the maximum proton energy. Use of hemispherical target embedded with nanorods is possibly reported here for the first time that may generate protons with energy 92 MeV by using linearly polarised laser of intensity 10 ^21 W cm ^−2 and pulse duration of 30 fs. At this laser intensity, the energy gain by the protons is much higher compared to the conventional flat foil targets. The maximum proton energy can be increased further to 103 MeV by using truncated hemispherical target of similar parameter.

The ionosphere is the ionized part of the upper atmosphere that is caused mainly by photoionization by solar extreme ultraviolet (EUV) emission and the atmospheric photochemistry process. The ionospheric ions escape from the ionosphere and populate the Earth's magnetosphere. In this case study, ion outflows from two different origins were obtained by spacecraft Cluster C1 in the magnetospheric cusp region. One of the outflows was from the reflection of the dispersed solar wind particles. The other was the ionospheric outflow passing through the low latitude boundary layer of the cusp (LLBL/cusp), which was energized by downward Poynting flux. Similar to the reflected solar wind particles, outflowing ionospheric cold ions could also extend to the high-latitude region with magnetic field line convection, which mixed it up with solar wind particles. Based on the Cluster observation in the cusp region, two different origins of the outflowing particles were determined, and their unique mechanisms of formation were discussed. Results suggest that the strong electric field associated with solar wind particle precipitation may additionally accelerate the cold ionospheric ion flow in the LLBL/cusp. [ABSTRACT FROM AUTHOR]

The unbiased Langmuir probe (LP) method was used to perform measurements on HfO2 and ZrO2 samples around the laser ablation threshold on a wide range of irradiation conditions. Important changes in the lifetime (from ms to μs) and the shape of the charge particle current were seen with the increase of the laser fluence. The ablation threshold was estimated by evaluating the overall average ablated charge as a function of the laser fluence. Above the ablation threshold, the generation of high kinetic species is seen, which can reach several keV. An important jump in ion acceleration potential is observed for values above 1 J/cm2, which coincides with the dominant presence of negative ions in the plasma. The evolution of several plasma parameters (ion density, expansion velocity, electron temperature, Debye length) was investigated and correlated with the fundamental ablation mechanism involved in various irradiation regimes. The LP data were correlated with COMSOL simulations on the maximum surface temperature reached during irradiation. Important correlations between the evaporation and melting processes and ablation threshold fluence and ion acceleration phenomena are also reported. [ABSTRACT FROM AUTHOR]

In this work, we reviewed our results on the prospect of increasing the quality of ion acceleration driven by high-intensity laser pulses using low-Z structured targets. It is shown that the radiation pressure acceleration mechanism dominates over target normal sheath acceleration for assumed laser target parameters when the laser intensity is high enough. The target thickness is optimized for this regime and double-layer structure is investigated. When a corrugation is fabricated on the interface of such a target, a relativistic instability with Rayleigh–Taylor and Richtmyer–Meshkov like features can be driven by the target interaction with a high intensity laser pulse. The proper development of this instability leads to the generation of a collimated quasi-monoenergetic ion beam with lower emittance, divergence, and energy spread compared to a single and double-layer target with planar interface. A steep-front laser pulse is used in our simulations to mitigate other type of instabilities arising at the target surface from the laser–target interaction. We discuss the use of a plasma shutter to generate the required pulse profile, which also locally increases intensity. The obtained shape improves the ion acceleration, including higher maximal energy and lower beam divergence, in our simulation of a high-Z target. [ABSTRACT FROM AUTHOR]

We experimentally investigated the accelerated proton beam characteristics such as maximum energy and number by varying the incident laser parameters. For this purpose, we varied the laser energy, focal spot size, polarization, and pulse duration. The proton spectra were recorded using a single-shot Thomson parabola spectrometer equipped with a microchannel plate and a high-resolution charge-coupled device with a wide detection range from a few tens of keV to several MeV. The outcome of the experimental findings is discussed in detail and compared to other theoretical works.

The development of small satellites weighing as little as 1 kg has accelerated along with the miniaturization of technology. However, there is still a lack of efficient micropropulsion systems at these scales. A possible solution is the pulsed plasma thruster, which has an inherently simple structure that is conducive towards miniaturization. As these thrusters were primarily developed in an era of larger satellites, there are systematic considerations that need to be taken into account. One of these is the propellant, where the conventional solid polytetrafluoroethylene (PTFE) propellant can be replaced with a non-volatile liquid perfluoropolyether (PFPE), enabling liquid-feeding approaches for propellant feeding. The physics behind the operation of a non-volatile liquid-fed pulsed plasma thruster still remains relatively unknown compared with the well-studied solid-fed archetype. We focus here on the use of emission spectroscopy to better understand the spatial distribution and temporal behavior of plasma components within a pulsed plasma thruster using non-volatile liquid PFPE. This is directly compared with solid PTFE to give us an understanding of the similarities and differences between the two propellant types. The overall results suggest that liquid PFPE may be a useful propellant in scenarios with a high thrust-to-power requirement and lower emphasis on electromagnetic acceleration. One such use-case is in coaxial or capillary discharge miniaturized pulsed plasma thrusters, where a significant portion of thrust is obtained from thermodynamic gas expansion rather than electromagnetic acceleration. • Perfluoropolyether (PFPE) produces highly-charged ions between inside thruster. • PFPE appears to exhibit sustained plasma production. • The degree of ionization of PFPE may be lower than conventional propellant. • PFPE may be useful as a propellant for future high thrust-to-power microthrusters. [ABSTRACT FROM AUTHOR]

Advanced targets based on thin foils of graphene oxide (GO) covered by metallic layers show many advantages with respect to others because permit high proton and light ion acceleration using high intensity pulsed lasers in Target‐Normal Sheath‐Acceleration (TNSA) regime. GO foils contain parallel micrometric graphene sheets, have low density, show high penetration, and low scattering by energetic electrons accelerated by laser, inducing electron channelling effects. They contain high concentrations of hydrogen, water, and functional oxygen groups, can be realized as thin films with high mechanical resistance, and show high photon absorbance for laser beams. In this work, we present experimental results obtained by our research group using thin GO targets covered by thin gold films, prepared in our laboratories. Advanced targets have been irradiated in TNSA regime with 40 fs laser pulses at the intensity of the order of 1019 W/cm2, using a laser spot of about 10 microns diameter, permitting to accelerate ions at energies of the order of 6 MeV per charge state. The electric field of ion acceleration can be increased by optimizing the irradiation conditions and the GO and Au film thicknesses. The novel findings of this work concern the high forward ion acceleration obtained using thin targets containing GO which induces the effect of electron channelling and production of high‐density forward plasma. The plasma diagnostics are developed with fast SiC semiconductor detectors connected in time‐of‐flight (TOF) configuration. The fast semiconductor detector response permits to optimize the ion acceleration conditions by changing the distance of the laser focus with respect to the target surface, the incidence angle and the laser parameters. [ABSTRACT FROM AUTHOR]

Transient magnetic reconnection plays an important role in energetic particle acceleration in planetary magnetospheres. Jupiter's magnetosphere provides a unique natural laboratory to study processes of energy transport and transformation. Strong electric fields in spatially confined structures such as plasmoids can be responsible for ion acceleration to high energies. In this study we focus on the effectiveness of ion energization and acceleration in plasmoids. Therefore, we present a statistical study of plasmoid structures in the predawn magnetotail, which were identified in the magnetometer data of the Juno spacecraft from 2016 to 2018. We additionally use the energetic particle observations from the Jupiter Energetic Particle Detector Instrument which discriminates between different ion species. We are particularly interested in the analysis of the acceleration and energization of oxygen, sulfur, helium, and hydrogen ions. We investigate how the event properties, such as the radial distance and the local time of the observed plasmoids in the magnetotail, affect the ion intensities close to the current sheet center. Furthermore, we analyze if ion acceleration is influenced by magnetic field turbulence inside the plasmoids. We find significant heavy ion acceleration in plasmoids close to the current sheet center which is in line with the previous statistical results based on Galileo observations conducted by Kronberg et al. (2019, https://doi.org/10.1029/2019JA026553). The observed effectiveness of the acceleration is dependent on the position of Juno in the magnetotail during the plasmoid event observation. Our results show no correlation between magnetic field turbulence and nonadiabatic acceleration for heavy ions during plasmoids. Key Points: Intensity of heavy ions is strongly increased during plasmoids close to the current sheet centerSignificant increase of heavy ion intensities is observed in plasmoids with larger wave powerAcceleration of heavy and light ions in plasmoids due to resonant interaction with the magnetic field fluctuations could not be observed [ABSTRACT FROM AUTHOR]

In order to accelerate ions by a laser, we go back to the original and the fundamental idea of how longitudinal field structure generation can be carried out in an ionized media and how particles may be trapped by the created wakefield. The latter condition is characterized by the phase velocity of the longitudinal structure vph be equal to the particle trapping width vtr. Since the trapping width is inversely proportional to the square-root of the mass of the accelerated particles, this width is much shorter for ions than for electrons. Thus, our dictum for laser ion acceleration is to impose a near critical density trap to decelerate laser group velocity, vg and subsequently to generate longitudinal wakefield to be able to trap ions under the condition of vtr = vph. We demonstrate this concept by PIC simulation and find that this method is effective, and the efficiency of laser ion acceleration is enhanced by a couple of orders of magnitude toward unity. [ABSTRACT FROM AUTHOR]

This paper is a sequel to the 1998 review paper “Scientific status of the Dense Plasma Focus” with 16 authors belonging to 16 nations, whose initiative led to the establishment of the International Center for Dense Magnetized Plasmas (ICDMP) in the year 2000. Its focus is on understanding the principal defining characteristic features of the plasma focus in the light of the developments that have taken place in the last 20 years, in terms of new facilities, diagnostics, models, and insights. Although it is too soon to proclaim with certainty what the plasma focus phenomenon is, the results available to date conclusively indicate what it is demonstrably not. The review looks at the experimental data, cross-correlated across multiple diagnostics and multiple devices, to delineate the contours of an emerging narrative that is fascinatingly different from the standard narrative, which has guided the consensus in the plasma focus community for several decades, without invalidating it. It raises a question mark over the Fundamental Premise of Controlled Fusion Research, namely, that any fusion reaction having the character of a beam-target process must necessarily be more inefficient than a thermonuclear process with a confined thermal plasma at a suitably high temperature. Open questions that need attention of researchers are highlighted. A future course of action is suggested that individual plasma focus laboratories could adopt in order to positively influence the future growth of research in this field, to the general benefit of not only the controlled fusion research community but also the world at large.

Three-dimensional numerical simulations were used to study the dependence of maximum energy of ions (protons) accelerated from low-density targets on the duration of the accelerating femtosecond laser pulse at its given total energy which, in particular, is important due to the latest achievements in the so-called postcompression of laser pulses to very short durations. It was shown that an optimum pulse length exists, which leads to maximum proton energy acquired in the regime of their maximum efficient synchronized acceleration by the "slow light" (A. V. Brantov et al., Phys. Rev. Lett. 116, 085004 (2016) [1]) and that the ultra shortening of the laser pulse does not lead to the increase in the maximum ion energy despite the increased intensity of laser light. [ABSTRACT FROM AUTHOR]

High-energy proton beams with low energy spread and angular divergence are highly valuable in various applications, such as proton therapy, ultrafast science, and nuclear physics. Laser-driven ion sources are being explored as a more compact and cost-effective alternative to conventional accelerators. However, producing high-quality proton beams using lasers has been a significant challenge. In this study, we propose a novel approach to achieve high-energy quasi-monoenergetic proton beams by utilizing a Laguerre–Gaussian (LG) laser to irradiate a solid hollow tube target. Our three-dimensional particle-in-cell simulations demonstrate that the LG laser efficiently pulls out and accelerates electrons. As these electrons exit the rear side of the tube, a charge-separation electric field for proton acceleration is self-established. Meanwhile, a considerable part of the electrons are confined to the laser axis by the ponderomotive force of the LG laser, generating a longitudinal bunching field and transverse focusing field. As a result, protons are accelerated and focused in these fields, producing a high- quality proton beam with high energy (247 MeV) and low energy spread (∼2%) using an LG laser with an intensity of $1.9 \times 10^{21}$ W cm ^−2 and a tube target with an electron density of 40 n _c . In comparison to a standard Gaussian laser, the LG laser exhibits superior performance in terms of proton cut-off energy, energy spread, and angular divergence.

High quality energetic carbon ions produced via laser-plasma have many applications in tumor therapy, fast ignition and warm dense matter generation. However, the beam achieved in current experiments is still limited by either a large energy spread or a low peak energy. In this paper, a hybrid scheme for the generation of quasi-monoenergetic carbon ions is proposed by an ultra-intense laser pulse irradiating a double-layer target. Multi-dimensional particle-in-cell (PIC) simulations show that the carbon ions are first accelerated via laser piston mechanism in the former carbon layer and then further accelerated by Coulomb repulsion force in the attached neon target. Since electrons are bunched synchronously in longitudinal and transverse direction by radiation reaction during the whole acceleration process, a quasi-monoenergetic carbon ion beam is eventually produced. In the following stage, the neon target provides the Coulomb field required for the continuous acceleration of the carbon ions which helps to prevent the carbon ion layer from diffusion. It is demonstrated that quasi-monoenergetic carbon ions with peak energy of 465 MeV u ^−1 , energy spread of ∼13%, a divergence of ∼15 ^∘ , and laser-to-ion energy conversion of 20% can be achieved by using a laser pulse with intensity of 1.23 × 10 ^23 W cm ^−2 . An analytical model is also proposed to interpret the carbon ion acceleration, which is fairly consistent with the PIC simulations.

The ionosphere is the ionized part of the upper atmosphere that is caused mainly by photoionization by solar extreme ultraviolet (EUV) emission and the atmospheric photochemistry process. The ionospheric ions escape from the ionosphere and populate the Earth’s magnetosphere. In this case study, ion outflows from two different origins were obtained by spacecraft Cluster C1 in the magnetospheric cusp region. One of the outflows was from the reflection of the dispersed solar wind particles. The other was the ionospheric outflow passing through the low latitude boundary layer of the cusp (LLBL/cusp), which was energized by downward Poynting flux. Similar to the reflected solar wind particles, outflowing ionospheric cold ions could also extend to the high-latitude region with magnetic field line convection, which mixed it up with solar wind particles. Based on the Cluster observation in the cusp region, two different origins of the outflowing particles were determined, and their unique mechanisms of formation were discussed. Results suggest that the strong electric field associated with solar wind particle precipitation may additionally accelerate the cold ionospheric ion flow in the LLBL/cusp.

In this work, we reviewed our results on the prospect of increasing the quality of ion acceleration driven by high-intensity laser pulses using low-Z structured targets. It is shown that the radiation pressure acceleration mechanism dominates over target normal sheath acceleration for assumed laser target parameters when the laser intensity is high enough. The target thickness is optimized for this regime and double-layer structure is investigated. When a corrugation is fabricated on the interface of such a target, a relativistic instability with Rayleigh–Taylor and Richtmyer–Meshkov like features can be driven by the target interaction with a high intensity laser pulse. The proper development of this instability leads to the generation of a collimated quasi-monoenergetic ion beam with lower emittance, divergence, and energy spread compared to a single and double-layer target with planar interface. A steep-front laser pulse is used in our simulations to mitigate other type of instabilities arising at the target surface from the laser–target interaction. We discuss the use of a plasma shutter to generate the required pulse profile, which also locally increases intensity. The obtained shape improves the ion acceleration, including higher maximal energy and lower beam divergence, in our simulation of a high-Z target.

Over three decades of in-situ observations illustrate that the Kelvin–Helmholtz (KH) instability driven by the sheared flow between the magnetosheath and magnetospheric plasma often occurs on the magnetopause of Earth and other planets under various interplanetary magnetic field (IMF) conditions. It has been well demonstrated that the KH instability plays an important role for energy, momentum, and mass transport during the solar-wind-magnetosphere coupling process. Particularly, the KH instability is an important mechanism to trigger secondary small scale (i.e., often kinetic-scale) physical processes, such as magnetic reconnection, kinetic Alfvén waves, ion-acoustic waves, and turbulence, providing the bridge for the coupling of cross scale physical processes. From the simulation perspective, to fully investigate the role of the KH instability on the cross-scale process requires a numerical modeling that can describe the physical scales from a few Earth radii to a few ion (even electron) inertial lengths in three dimensions, which is often computationally expensive. Thus, different simulation methods are required to explore physical processes on different length scales, and cross validate the physical processes which occur on the overlapping length scales. Test particle simulation provides such a bridge to connect the MHD scale to the kinetic scale. This study applies different test particle approaches and cross validates the different results against one another to investigate the behavior of different ion species (i.e., H+ and O+), which include particle distributions, mixing and heating. It shows that the ion transport rate is about 1025 particles/s, and mixing diffusion coefficient is about 1010 m2 s−1 regardless of the ion species. Magnetic field lines change their topology via the magnetic reconnection process driven by the three-dimensional KH instability, connecting two flux tubes with different temperature, which eventually causes anisotropic temperature in the newly reconnected flux.

The geospace plume couples the ionosphere, plasmasphere, and magnetosphere from sub-auroral regions to the magnetopause, on polar field lines, and into the magnetotail. We describe Van Allen Probes observations of ionospheric O+ ions at altitudes of 3–6 RE in the near vicinity of the geospace plume in the noon and post-noon sector. The temporal variation of warm ion fluxes observed as a function of time on a moving spacecraft is complicated by changing spacecraft position and complex ion drift paths and velocities that are highly sensitive to ion energy, pitch angle and L value. In the “notch” region of lower density plasma outside the morning-side plasmapause, bi-directionally field aligned fluxes of lower energy (20 keV in the dusk sector outer plasmasphere is interpreted as evidence for localized ionospheric O+ outflow at the outer edge of the geospace plume with subsequent O+ acceleration to >50 keV in

Proton acceleration can be induced by non‐equilibrium plasma developed by high‐intensity laser pulses, at 1016 W/cm2, irradiating different types of thin polyethylene targets. The process of proton acceleration and directive yield emission was investigated, optimizing the laser parameters, the irradiation conditions, and the target properties. The use of 600 J pulse energy, a laser focalization inducing self‐focusing effects and advanced targets with embedded nanoparticles and optimal thicknesses, has permitted to accelerate forward protons up to the energies of about 6 MeV and amount of the order of 1015 H+/pulse. High proton energy is obtained using thin foils enriched with gold nanoparticles, whereas high proton yield is obtained using targets with a thickness of about 10 μm. The plasma diagnostics using SiC semiconductor detectors in time‐of‐flight configuration was fundamental to monitor the optimal conditions to improve the plasma processes concerning the ion acceleration and the X‐ray and relativistic electron emission. [ABSTRACT FROM AUTHOR]

Multi‐point measurements on kinetic scales through Earth's magnetosheath have revealed a spectrum of filamentary currents and vortical flows advected with the shocked plasmas outside the magnetopause. The spectral energy density in these structures is correlated with enhanced ion temperatures. Using an empirically derived statistical model based on fluid‐kinetic theory for these structures we demonstrate how they act to scatter magnetosheath ions. Through the combined action of energization in the direction perpendicular to the background magnetic field along chaotic orbits, and pitch‐angle scattering into the parallel direction appreciable ion energization occurs. These dynamics drive heating while generating non‐thermal energetic tails similar to that observed. It is shown how the operation of this process depends on the field topology with deviations from planar form and counter‐propagation required to drive significant energization. This process will modulate ion anisotropies through the magnetosheath independent of both adiabatic effects and the action of anisotropy instabilities. Plain Language Summary: Multi‐point measurements from the Magnetospheric Multi‐Scale Mission have been used to create a three‐dimensional dynamic model for broadband electromagnetic fluctuations in the region downstream of the shock‐wave caused by the impact of the Solar wind on the Earth's magnetic field (the magnetosheath). This model has been employed to investigate the interaction between these fields and the positively charged particles (ions) populating this region of space. It has been shown that these fluctuations, because of their morphology and propagation characteristics, efficiently scatter and energize magnetosheath ions. The operation of this process is supported by the similarity of the observed distribution of ions as a function of velocity with that returned via numerical simulations in the model fields. Because these energized ions can penetrate the outer boundary of Earth's magnetic field, this processing has basic importance in defining the nature of matter populating near‐Earth space with significant implications for its internal dynamics. Key Points: Multi‐scale filamentary EM magnetosheath structures drive ion energization and pitch‐angle scatteringMulti‐scale filamentary EM magnetosheath structures modulate magnetosheath ion temperature anisotropyField topology and wave propagation characteristics are essential elements in defining the observed energization [ABSTRACT FROM AUTHOR]

Recent observations in the quasi‐parallel bow shock by the Magnetospheric Multiscale spacecraft show rapid heating and acceleration of ions up to an energy of about 100 keV. It is demonstrated that a prominent acceleration mechanism is the nonlinear interaction with a spectrum of waves produced by gradient‐driven instabilities, including the lower hybrid drift (LHD) instability, modified two‐stream (MTS) instability, and electron cyclotron drift (ECD) instability. Test‐particle simulations show that the observed spectrum of waves can rapidly accelerate protons up to a few hundreds of keV by the ExB mechanism. The ExB wave mechanism is related to the surfatron mechanism at shocks, but through the coupling with the stochastic heating condition, it produces significant acceleration on much shorter temporal and spatial scales by the interaction with bursts of waves within a cyclotron period. The results of this study are built on the heritage of four‐point measurement techniques developed for the Cluster mission and imply that the concepts of Fermi acceleration, diffusive shock acceleration, and shock drift acceleration are not needed to explain proton acceleration to hundreds of keV at the Earth's bow shock. Plain Language Summary: The acceleration, or energization, of particles is a common and fundamental process throughout the universe. In particular, particle acceleration is a common occurrence at collisionless shocks that occur in plasmas in our solar system and beyond. This study presents new observations of the acceleration of protons to high energies (hundreds of keV) by waves at the bow shock upstream of the Earth, where the solar wind first encounters Earth's magnetic field. The observations by NASA's Magnetospheric Multiscale (MMS) mission show a specific event where energized protons are measured, along with wave activity that is consistent with theoretical expectations for a certain type of interaction between the waves and particles that allows the waves to transfer energy to the protons. Numerical simulations are also performed and the results agree with what was observed in real life by the spacecraft. The results are important because they provide insight into potential processes that can create high‐energy particles both near the Earth and at other astrophysical systems. Key Points: At quasi‐parallel shocks, ions are rapidly accelerated from 10 eV to 100 keV by the ExB mechanism of electrostatic wavesThe waves are produced by current‐driven instabilities with frequencies between the proton and the electron cyclotron frequenciesThe acceleration occurs locally within a few gyroperiods [ABSTRACT FROM AUTHOR]

Although foreshock transients can generate strong magnetospheric Pc5 ultralow‐frequency (ULF) waves, whether they can modulate the energy of magnetospheric ions is still poorly understood. In this study, we analyze the strong magnetospheric ion energy modulations in a foreshock transient event on October 30, 2008, based on the magnetospheric observations by the time history of events and macroscale interactions during substorms A and D in the prenoon sector. ULF wave‐induced E×B drift accelerated the cold ions up to ∼10 keV and the enhanced ion fluxes have wave‐like patterns. There is another portion of enhanced ion fluxes from ∼0.8 to ∼10 keV but with strong energy dispersions in this event. By comparing the observations and the theoretical prediction, we for the first time found that the drift‐bounce resonances played a major role in modulating the energy of those ions with energy dispersions, during the interactions between the ions and the foreshock transient‐driven Pc5 ULF wave with growing and damping effects. Plain Language Summary: Foreshock transients are generated in front of the Earth's bow shock. Those transient structures are always associated with strong dynamic pressure variations, which enables them to strongly compress and inflate the Earth's magnetosphere. However, according to the past studies on foreshock transients, whether they can modulate the energy of magnetospheric ions is still poorly understood. In this study, we analyze the strong magnetospheric ion energy modulations in a foreshock transient event on October 30, 2008, based on the magnetospheric observations by the time history of events and macroscale interactions during substorms A and D in the prenoon sector. We found two mechanisms of modulating ion energies in this event. First, the ultralow frequency (ULF) wave‐induced electric field accelerated the cold ions, of which the ion fluxes have wave‐like patterns. However, it had a limited contribution to the enhanced ion fluxes with strong energy dispersions. Second, by comparing the observations and the theoretical prediction, we for the first time found that the drift‐bounce resonances played a major role in modulating the energy of those ions with energy dispersions, during the interactions between the ions and the foreshock transient‐driven ULF wave with growing and damping effects. Key Points: We show that the foreshock transient‐induced ultralow‐frequency (ULF) wave electric field contributes to the ion acceleration in the outer magnetosphereWe for the first time found that the foreshock transient‐induced ULF waves can modulate magnetospheric ions through drift‐bounce resonanceThe comparison between observations and theory shows that growing/damping stages of waves contribute to broadband ion energy modulations [ABSTRACT FROM AUTHOR]

Foreshock bubbles (FBs) form as a result of the interaction between solar wind discontinuities and backstreaming ion beams in the foreshock. They are carried by the solar wind in the anti‐sunward direction and are associated with high energy ions. We employ electromagnetic hybrid (kinetic ions, fluid electrons) simulations and test particle calculations to investigate ion acceleration by FBs. Simulation results show that the maximum energies which the ions attain are not sensitive to the topology of the FBs, which varies from spherical to planar limits. However, the solar wind velocity does control the maximum energies reached by FB acceleration. Test particle calculations show that ion energization takes place through reflection of sunward moving ions from FBs through one or more collisions consistent with second‐order Fermi acceleration. The results also indicate that energy gain does not reach that expected for elastic reflections. Examination of ion energy spectra within different FBs shows a self‐similar pattern consisting of distribution peaked at the solar wind ram energy Esw with a distribution tail that reaches energies of ∼5.6 Esw. This behavior is consistent with second‐order Fermi acceleration and the inherent limitations on energy gain in this process. We also discuss the role of nonlinear structures called foreshock cavitons in the acceleration process. Key Points: Ions are accelerated by foreshock bubbles through second‐order Fermi processMaximum energies attained are determined by solar wind velocityIon energy spectra within foreshock bubbles exhibit self‐similarity [ABSTRACT FROM AUTHOR]

In order to accelerate ions by a laser, we go back to the original and the fundamental idea of how longitudinal field structure generation can be carried out in an ionized media and how particles may be trapped by the created wakefield. The latter condition is characterized by the phase velocity of the longitudinal structure vph be equal to the particle trapping width vtr. Since the trapping width is inversely proportional to the square-root of the mass of the accelerated particles, this width is much shorter for ions than for electrons. Thus, our dictum for laser ion acceleration is to impose a near critical density trap to decelerate laser group velocity, vg and subsequently to generate longitudinal wakefield to be able to trap ions under the condition of vtr = vph. We demonstrate this concept by PIC simulation and find that this method is effective, and the efficiency of laser ion acceleration is enhanced by a couple of orders of magnitude toward unity.

Proton acceleration using high‐intensity laser pulses, at 1016 W/cm2 was studied irradiating different types of thin metal and plastic targets having 1‐micron thickness. The maximization of the proton energy process was investigated optimizing the laser parameters, the irradiation conditions and the target properties. Employing 600–700 J laser pulse energy, a focalization inducing self‐focusing effects and using targets with optimized thickness, it was possible to accelerate protons up to energies of above 8 MeV. The time‐of‐flight diagnostics has allowed to monitor the plasma properties and to control the ion acceleration process. [ABSTRACT FROM AUTHOR]

Fast solid target delivery and plasma-ion detection systems have been designed and developed to be used in high intensity laser-matter interaction experiments. We report on recent progress in the development and testing of automated systems to refresh solid targets at a high repetition rate during high peak power laser operation (>1 Hz), along with ion diagnostics and corresponding data collection and real-time analysis methods implemented for future use in a plasma-based ion acceleration beamline for multidisciplinary user applications. [ABSTRACT FROM AUTHOR]

In this work, we investigate the application of the plasma shutters for heavy ion acceleration driven by a high-intensity laser pulse. We use particle-in-cell and hydrodynamic simulations. The laser pulse, transmitted through the opaque shutter, gains a steep-rising front and its peak intensity is locally increased at the cost of losing part of its energy. These effects have a direct influence on subsequent ion acceleration from the ultrathin target behind the shutter. In our 3D simulations of silicon nitride plasma shutter and a silver target, the maximal energy of high- Z ions increases significantly when the shutter is included for both linearly and circularly polarized laser pulses. Moreover, application of the plasma shutter for linearly polarized pulse results in focusing of ions toward the laser axis in the plane perpendicular to the laser polarization. The generated high energy ion beam has significantly lower divergence compared to the broad ion cloud, generated without the shutter. The effects of prepulses are also investigated assuming a double plasma shutter. The first shutter can withstand the assumed sub-ns prepulse (treatment of ns and ps prepulses by other techniques is assumed) and the pulse shaping occurs via interaction with the second shutter. On the basis of our theoretical findings, we formulated an approach toward designing a double plasma shutter for high-intensity and high-power laser pulses and built a prototype.

We analyze multipoint measurements in magnetosheath plasmas, just upstream of the Earth's magnetopause, to investigate the morphology of the turbulent fields and coincident 3‐D ion distributions observed. Using interferometric and generalized wave polarization analyses, we show how the fields comprise a multiscale spectrum of Alfvénic structures composed of flow shears and vortices, and current sheets and filaments advected over the spacecraft with the magnetosheath flow. It is shown how these features are correlated with intervals of enhanced ion energy, temperature anisotropy, and impulsive variations in the agyrotropy of ion velocity space distributions. It is demonstrated that the observed variation in ion properties is inconsistent with an adiabatic response but is instead correlated with the spectral energy density of nonplanar structures at ion gyroradii scales. The capacity of these field structures to scatter ions is considered. Plain Language Summary: The region of space just beyond the outer reaches of Earth's magnetic field is pervaded by electromagnetic structures on a variety of scales. In this letter we examine the toplogy of these structures on scales similar to that of the orbits of the positively charged particles (ions) in which they are immersed. Measurements of the distributions of these ions in concert with the field structure topology suggest that the structured fields drive ion scattering and energization. Because these particles are the source for much of the matter populating near‐Earth space, this research contributes to understanding of our local environment in the solar system and how it is in part defined by the exchange of energy between particles and electromagnetic fields. Key Points: Broadband EM magnetosheath fluctuations have properties of a k‐spectrum of nonplanar Alfvénic structures on ion kinetic scalesBroadband EM magnetosheath fluctuations comprise a multiscale mixture of flow shears and vortices, current sheets, and filamentsSpectral energy densities in kinetic filamentary and vortical structures through the magnetosheath are correlated with ion energization [ABSTRACT FROM AUTHOR]

X‐rays and forward ion emission from laser‐generated plasma in the Target Normal Sheath Acceleration regime of different targets with 10‐μm thickness, irradiated at Prague Asterix Laser System (PALS) laboratory at about 1016 W/cm2 intensity, employing a 1,315 nm‐wavelength laser with a 300‐ps pulse duration, are investigated. The photon and ion emissions were mainly measured using Silicon Carbide (SiC) detectors in time‐of‐flight configuration and X‐ray streak camera imaging. The results show that the maximum proton acceleration value and the X‐ray emission yield growth are proportional to the atomic number of the irradiated targets. The X‐ray emission is not isotropic, with energies increasing from 1 keV for light atomic targets to about 2.5 keV for heavy atomic targets. The laser focal position significantly influences the X‐ray emission from light and heavy irradiated targets, indicating the possible induction of self‐focusing effects when the laser beam is focalized in front of the light target surface and of electron density enhancement for focalization inside the target. [ABSTRACT FROM AUTHOR]