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A highly energetic photon is emitted via nonlinear inverse Compton scattering after an electron undergoes scattering with an ultra-intense relativistic laser pulse. In the laser-nanostructured interaction, gamma photons are emitted in different directions due to different electron heating mechanisms. However, the physics that leads to such gamma-photon emission directionality still requires further understanding. This paper shows that ∼ 53 % of the photons emitted from the nanowires fall into the forward-directed cone, with ∼ 21 % of the backward-emitted photons. Using the two-dimensional particle-in-cell simulations, we found that the backward-emitted photons are mainly ascribed to the j × B heating and reflux electrons. The direction of photon emission from the nanowire tip is in the direction of the ponderomotive force. Furthermore, we also demonstrate that the nanowire target attached to the supporting substrate helps to enhance forward photon emission and reduce emission from reflux electrons. Understanding the correlation between the laser heating mechanisms and the directionality of photon emission could provide insights into the generation of collimated gamma rays using nanowire targets for various applications. [ABSTRACT FROM AUTHOR]

Here, we developed a high-resolution, dual-channel toroidal-crystal x-ray imager for time-framed x-ray backlit imaging diagnostics using the 4.727 keV helium-like Ti line. We also presented a method for adjusting the dual-channel imager through the self-imaging of a two-dimensional periodic object. Offline x-ray experiments achieved a spatial resolution of ∼5.0 μm in the center and better than 8.0 μm within a field of view (FOV) of ∼2 mm. At the ShenGuang-III prototype laser facility, we obtained imaging results with a spatial resolution of better than 5 μm within an FOV of ±40 µm. This imager thus provides a way of observing with high spatial, temporal, and spectral resolutions to diagnose the behavior of laser-produced plasma. [ABSTRACT FROM AUTHOR]

Efficient generation of 13.5 nm light with increased conversion efficiency and output power is important for Extreme Ultraviolet (EUV) lithography applications. In this study, we present a computational investigation of plasma dynamics and EUV generation from laser-driven plasma, with specific focus on the influence of magnetic fields, ranging up to 50 T. Simulations show that the plasma expansion is restricted based on the direction and strength of the magnetic field, resulting in an anisotropic plasma confinement, which in turn allows for radiation escape with a reduced loss. Moreover, angle-dependent measurements show an increase in in-band EUV (2% bandwidth around 13.5 nm) yield, reaching a peak enhancement of up to 40% when a magnetic field is applied, particularly when it is oriented perpendicular to the laser axis. The ability to control plasma dynamics by magnetic field offers exciting prospects for optimizing EUV radiation sources. [ABSTRACT FROM AUTHOR]

Collective Thomson scattering (TS) is a powerful technique to accurately diagnose the parameters of laser-produced plasmas. However, when the scattering parameter α, which is inverse to the product of electron Debye length and wavenumber of plasma fluctuations, is significantly larger than 1, which of the conditions is easily satisfied in the experiment, the accuracy of electron density measurement is usually poor just with the single-wavenumber ion-acoustic wave feature of the TS spectrum. This situation can be greatly improved in the imaging TS experiment because the signal intensity is proportional to electron density. A novel algorithm is developed and validated for the data analysis of imaging TS through the combination of signal intensity and spectral profile. The results show that we can obtain the electron density with high confidence, as well as other plasma parameters like electron and ion temperatures. [ABSTRACT FROM AUTHOR]

In the realm of high-energy-density laboratory plasma experiments, ion radiography is a vital tool for measuring electromagnetic fields. Leveraging the deflection of injected protons, ion imaging can reveal the intricate patterns of electromagnetic fields within the plasma. However, the complex task of reconstructing electromagnetic fields within the plasma system from ion images presents a formidable challenge. In response, we propose the application of neural network techniques to facilitate electromagnetic field reconstructions. For the training data, we generate corresponding particle data on ion radiography with diverse field profiles in the plasma system, drawing from analytical solutions of charged particle motions and test-particle simulations. With these training data, our expectation is that the developed neural network can assimilate information from ion radiography and accurately predict the corresponding field profiles. In this study, our primary emphasis is on developing these techniques within the context of the simplest setups, specifically uniform (single-layer) or two-layer systems. We begin by examining systems with only electric or magnetic fields and subsequently extend our exploration to systems with combined electromagnetic fields. Our findings demonstrate the viability of employing neural networks for electromagnetic field reconstructions. In all the presented scenarios, the correlation coefficients between the actual and neural network-predicted values consistently reach 0.99. We have also learned that physics concepts can help us understand the weaknesses in neural network performance and identify directions for improvement. [ABSTRACT FROM AUTHOR]

Ultrahigh-energy density (UHED) states greater than 1 Gbar pressure are typically observed under extreme conditions, such as in the core of an inertial confinement fusion implosion. A novel alternative approach for generating volumetric UHED states is to use nanowire arrays irradiated with a femtosecond ultrahigh-intensity laser. In this paper, we present an experimental investigation on laser absorption and energy transport in nanowire arrays irradiated with a picosecond kilojoule petawatt laser. The laser–target interactions were studied by measuring the x-ray emission and escaping hot electrons from a bare Cu foil and a foil with a nanowire array grown on its surface. The measured Cu-Kα and He-α emissions from the nanowire array were higher than those from the flat foil. In addition, hot electrons observed from the front surface of the nanowire array were enhanced. On the other hand, despite the stronger Kα emission from the nanowire array and the enhancement of hot electrons escaping from the front surface of the nanowire array, the number of hot electrons observed from the rear side of the flat foil target was slightly lower than that of the flat foil. A comparison of the experimental results with the results of a two-dimensional particle-in-cell simulation code suggested that the magnetic fields generated around the periodic nanowire array trap hot electrons, improving the electron-to-target energy coupling and efficiently producing UHED states. [ABSTRACT FROM AUTHOR]

We study the propagation of a relativistic ultrashort laser pulse in two-dimensional inhomogeneous plasma with a density ripple based on the theoretical analysis and the particle-in-cell simulation. An analytical solution of the laser pulse propagating in the homogeneous plasma is completely obtained. It is found that the stable propagation of the relativistic ultrashort laser pulse in homogeneous plasma can be realized, and the propagation distance and intensity of the laser pulse and the spatial distribution of electron density can be effectively modulated by adjusting the pulsewidth of the incident laser and the plasma frequency. More interestingly, in the inhomogeneous plasma with a density ripple, when the wave amplitude of the density ripple is less than a critical value, the intensity of the ultrashort laser pulse is almost unchanged and the propagation characteristics of the laser in the inhomogeneous plasma are basically consistent with those in the homogeneous plasma. However, when the wave amplitude of the density ripple is larger than the critical value, the inhomogeneity of the plasma has an obvious effect on the laser characteristics, and the intensity and the spatial distribution of the laser pulse will be modulated by the plasma density ripple. The influence of the laser pulsewidth, plasma density, and plasma density ripple on the laser characteristics is discussed in detail. [ABSTRACT FROM AUTHOR]

This work presents a study on laser wakefield electron acceleration in the self-modulated regime (SM-LWFA) using 50-fs laser pulses with energy on the mJ scale, at λ = 0.8 µm, impinging on a thin H2 gas jet. Particle-in-cell simulations were performed using laser peak powers ranging from sub-terawatt to a few terawatts and plasma densities varying from the relativistic self-focusing threshold up to values close to the critical density. The differences in the obtained acceleration processes are discussed. Results show that bunched electron beams with full charge on the nC scale and kinetic energy in the MeV range can be produced and configurations with peak density in the range 0.5–5 × 1020 atoms/cm3 generate electrons with maximum energies. In this range, some simulations generated quasimonoenergetic bunches with ∼0.5% of the total accelerated charge and we show that the beam characteristics, process dynamics, and operational parameters are close to those expected for the blowout regime. The configurations that led to quasimonoenergetic bunches from the sub-TW SM-LWFA regime allow the use of laser systems with repetition rates in the kHz range, which can be beneficial for practical applications. [ABSTRACT FROM AUTHOR]

Time-resolved spectra are often recorded in optical Thomson scattering experiments of laser-produced plasmas. In this article, the meaning of time-resolved spectrum output from a grating spectrometer is examined. Our results show that the recorded signal is indeed a convolution of the response function of the dispersion element and the product of the instant local dynamic form factor and electron density when the plasma evolves slowly; the plasma varies very little in the time duration of the scattering light passing through the scattering volume. [ABSTRACT FROM AUTHOR]

A summary of closed-form expressions for the magnetic fields produced by rectangular- and circular-shaped finite-length solenoids and current loops is provided altogether for easy reference. Each expression provides the magnetic field in all space, except locations where a current of infinitesimal thickness is considered to exist. The closed-form expression for the magnetic field of a rectangular-shaped finite-length solenoid is derived using the Biot–Savart law. Closed-form expressions for the magnetic fields of solenoids and current loops can be used to avoid approximations in analytical models and may reduce computation time in computer simulations. [ABSTRACT FROM AUTHOR]

Measurement of the matched spot size in the hydrogen-filled capillary discharge waveguide based on the spot size oscillation of a collimated laser is presented in this paper. The spot size oscillation trace is retrieved from the laser modes measured at the exits of discharged capillaries of different lengths under the same discharge conditions. With the gas pressure, peak discharge electric current and capillary radius fixed, the radial density profiles are identical in all the discharged capillaries. The measured laser modes are equivalent to the evolution at discrete positions in a long plasma channel. Compared to former researches based on the spot size at the capillary exit, this method is not affected by the multiple solution problem. The use of a collimated laser eliminates the influences of the divergence angle on the fitting accuracy. By this means, the matched spot sizes of hydrogen-filled capillary discharge waveguides under different gas pressures (5-20mbar) are measured. The results can provide a spot size reference for the laser wakefield accelerator guided in a plasma channel. [ABSTRACT FROM AUTHOR]

We present experimental results of two head-on colliding plasma sheaths accelerated by pulsed-power-driven coaxial plasma accelerators. The measurements have been performed in a small vacuum chamber with a neutral-gas prefill of ArH2 at gas pressures between 17 Pa and 400 Pa and load voltages between 4 kV and 9 kV. As the plasma sheaths collide, the electron density is significantly increased. The electron density reaches maximum values of ≈8.1015 cm-3 for a single accelerated plasma and a maximum value of ≈2.6 . 1016 cm-3 for the plasma collision. Overall a raise of the plasma density by a factor of 1.3 to 3.8 has been achieved. A scaling behavior has been derived from the values of the electron density which shows a disproportionately high increase of the electron density of the collisional case for higher applied voltages in comparison to a single accelerated plasma. Sequences of the plasma collision have been taken, using a fast framing camera to study the plasma dynamics. These sequences indicate a maximum collision velocity of 34 km/s. [ABSTRACT FROM AUTHOR]

A coil-capacitor target is modeled using FEM simulations and analytical calculations, which allow to explain the time evolution of such complex target during magnetic field production driven by the flow of an extremely high current generated through the interaction with a high power laser. The numerical model includes a detailed study of the magnetic field produced by the coil-capacitor target, both in the static and transient cases, as well as magnetic force and Joule heating. The model is validated by experimental data reported in literature and can be of interest for several applications. As an example, the combination of two synchronized nanosecond lasers with the purpose of producing a plasma responsible of the proton-boron (p+ + 11B → 8.5 MeV + 3α) fusion reaction, and energizing two multi-turn coils with the main purpose of confining such a plasma could enhance the reaction rate. The preliminary conceptual design of a magnetic mirror configuration to be used for confining protons and boron ions up to a few MeV/u in a region of less than 1 mm2 is briefly reported. [ABSTRACT FROM AUTHOR]