The eigenmode spectrum is a fundamental starting point for the analysis of plasma stability and the onset of turbulence. Quantum chaos theory provides tools for characterizing the spectrum statistically, from the regular spectrum of the separable case (integrable semiclassical dynamics) to that where the semiclassical ray dynamics is so chaotic that no simple classification of the individual eigenvalues is possible (quantum chaos). Using the CAS3D code, a data set of several hundred growth-rate eigenvalues has been calculated for a Mercier-unstable three-dimensional stellarator equilibrium with a rather flat, non-monotonic rotational transform profile. Statistical analysis of eigenvalue spacings for individual mode families shows evidence of quantum chaos, strongest for the N = 0 family, but to test this we compare it with the distribution of eigenvalue spacings in a similar separable case—ideal interchange modes in a Suydam-unstable plasma cylinder—using a similar rotational transform profile to the stellarator case. The statistics in the cylindrical model appear Poissonian, as expected for generic integrable systems and in clear contrast to the three-dimensional stellarator results.

The time evolution of the magnetic island formed at the tearing stable rational surface by the external magnetic flux perturbation in the plasma with poloidal flow is investigated numerically by using the resistive magnetohydrodynamic (MHD) model and the magnetic island is found to show rapid growth after the reduced growth phase due to the plasma rotation. It was also found that the onset condition of this rapid growth depends on the resistivity, but does not depend on the viscosity, in the parameter regime used in this study. On the other hand, the time constant of the rapid growth phase is almost independent of both the plasma resistivity and the viscosity. This rapid growth of magnetic island is the possible candidate for the trigger problem of the neoclassical tearing mode in a tokamak.

Marginal stability curves in ion/electron temperature gradient space are numerically obtained for the short wavelength ion temperature gradient instability, as well as the scaling of the critical gradient with respect to temperature ratio, toroidicity, magnetic shear and safety factor. Algebraic formulae for the critical gradient are presented.

In the two-dimensional simulation of the interaction of an ultrashort intense laser with droplet plasma, two hot electron jets generated by resonance absorption and emitted symmetrically with respect to the laser propagation direction are observed at a low laser field amplitude such as $a_0=0.1$. However, the emission angle of electron jets cannot be explained simply with the theory of resonance absorption for planar targets. When the laser amplitude is increased to $a_0=2$, electron bunches generated by the ponderomotive force separated by a laser period are superimposed into the hot electron jets. Accelerated ions have two groups at low laser intensities, one is anisotropic and associated with hot electron jets and the other is isotropic due to hydrodynamics expansion. At high light intensities, isotropic ion acceleration is found through Coulomb explosion.

A novel stimulated trapped electron-acoustic wave scattering instability by a linearly polarized laser interacting with a subcritical density plasma layer is observed by particle simulation. Its spectrum in the early stage is well-explained by a resonant three-wave parametric decay process and it takes place whether the ion dynamics are taken into account or not. When ion dynamics are considered, the excitation of the ion electrostatic wave, the generation of the electromagnetic (EM) soliton and the formation of ion vortices due to the large EM soliton, etc., are studied.

We have modelled the Ni-like and Co-like resonance lines emitted from Ni-like Silver X-ray laser media using a collisional radiative code. The code calculates intensities of Ni-like 1s$^2$2s$^2$2p$^6$3s$^2$3p$^6$3d$^{10}$$\longrightarrow$ 1s$^2$2s$^2$2p$^6$3s$^2$3p$^6$3d$^9nl$, Co-like 1s$^2$2s$^2$2p$^6$3s$^2$3p$^6$3d$^9$$\longrightarrow$ 1s$^2$2s$^2$2p$^6$3s$^2$3p$^6$3d$^8nl$ resonance lines emitted from silver. Intensities of photons emitted between Ni-like 1s$^2$2s$^2$2p$^6$3s$^2$3p$^6$3d$^9$$n^\prime l^\prime$$\longrightarrow$ 1s$^2$2s$^2$2p$^6$3s$^2$3p$^6$3d$^9$nl and Co-like 1s$^2$2s$^2$2p$^6$3s$^2$3p$^6$3d$^8$$n^\prime l^\prime$$\longrightarrow$ 1s$^2$2s$^2$2p$^6$3s$^2$3p$^6$3d$^8nl$ excited levels are also calculated. The optimum electron temperature and density for $J=0-1$ lasing at 13.9 nm is evaluated. The ratios of Co-like 3d–4p to Ni-like 3d–4p resonance lines are calculated with the aim that such ratios can serve as a diagnostic to measure electron temperatures.

Motivated by recent experimental observations of fast electron jets emitted along the target surface in intense laser–solid interactions with a large incident angle of the laser pulse, we simulate electron emissions by two-dimensional particle-in-cell simulations. When there is no preplasma in advance of the main laser pulse, electrons are emitted dominantly along the target surface. However, when there is preplasma, electron emission changes to the target normal. This difference originates from the different absorption mechanisms and different Coulomb electrostatic fields and self-generated magnetic fields induced in front of the target for the two cases.

Two-dimensional particle-in-cell (PIC) simulations of fast particles produced by a short laser pulse with a duration of 40 fs and an intensity of $10^{20}$ W cm$^{-2}$ interacting with a foil target are performed. The dependence of the energy of the generated fast protons on the target geometry is examined. The absorbed laser energy is transferred to fast electrons, which interact with the foil and are partially ejected from the foil surfaces. These electrons produce an electric field that causes a proton beam to be emitted from the rear surface of the foil. Various kinds of target are considered. The optimum target plasma conditions for the maximum proton acceleration are determined.

Three-dimensional electron motion in a linearly polarized tightly focused laser field is numerically calculated. A high-intensity laser pulse focused on the free electrons in vacuum generates relativistic electron bunches whose length is shorter than the laser wavelength. The extremely short electron bunches with low-energy spread less than 1% are generated for a wide range of the laser parameters.

We observed a preformed plasma of an aluminum slab target produced by a high-intensity Ti:sapphire laser. The expansion length of the preformed plasma at the electron density of 3 × 1018 cm−3, which was the detection limit, was around 100 μm measured with a laser interferometer. In order to characterize quantitatively and to control the preformed plasmas, we perform a two-dimensional hydrodynamic simulation. The expansion length of the preformed plasma was almost the same as the experimental result, if we assumed that the amplified spontaneous emission lasted 3.5 ns before the main pulse arrived.

The propagation of intense laser pulses and the generation of high-energy electrons from underdense plasmas are investigated using two-dimensional particle-in-cell simulations. It is shown that quasi-monoenergetic electron beams are generated in the regime where the laser pulse length is much longer than the plasma wavelength, when the condition of the focusing is appropriately controlled.

By using a particle code including atomic and relaxation processes, we investigated the ionization dynamics of a carbon film irradiated by an intense laser pulse. We found two types of ionization dynamics, namely, a fast time scale convective propagation of the ionization front with C4+ triggered by induced plasma waves, and a slow front with C5+ and C6+ triggered by heated electrons due to non-local thermal conduction. Thus, ionization dynamics in solids are found to evolve through multiple stages.

The nonlinear evolution of ion acoustic fluctuations in the presence of a uniform electron drift which exceeds the sound speed and electron–ion collisions is investigated using a collisional particle simulation model for parameters relevant to laser-heated plasmas. The results indicate that for the one-dimensional case, strong electron–ion collisionality can lead to a significantly higher saturation level of the fluctuations, which is comparable to the saturation level in the two-dimensional collisionless regime. This relatively high turbulence level can act to enhance heat flux inhibition and strongly influence the absorption and transport properties of laser-produced plasmas.

We study stimulated Raman scattering (SRS) in laser-fusion plasmas with the Eulerian Vlasov code ELVIS. Backward SRS occurs in sub-picosecond bursts and far exceeds linear theory. Forward SRS and re-scatter of backward SRS are also observed. The plasma wave frequency downshifts from the linear dispersion curve, and the electron distribution flattens. This is consistent with trapping and reduces Landau damping. There is some acoustic ($\omega\propto k$) activity and possibly stimulated electron acoustic scatter. Kinetic ions do not affect SRS for early times but suppress it later on. SRS from inhomogeneous plasmas exhibits a kinetic enhancement for long density scale lengths. More scattering results when the pump propagates towards a higher as opposed to towards a lower density.

The generation of low-frequency radiation at around the terahertz frequency, caused by a linearly polarized intense laser pulse passing through a low-density homogeneous plasma, is studied by one-dimensional particle simulations. The excited transverse current component with its frequency at the electron plasma frequency serves as a radiation source to generate electromagnetic waves both in the front and the rear side vacuum regions of the plasma layer. It is found that the electromagnetic radiation fields increase with both increasing plasma density and increasing laser amplitude.

Moving one-dimensional electromagnetic solitons formed in a weakly relativistic laser-plasma are studied in the generalized nonlinear Schroedinger equation model. Conserved quantities and moving soliton solutions are analytically derived in a closed form. Stability studies reveal a transition at maximum amplitude to an unstable cusp-soliton. Simulations of two interacting electromagnetic (EM) solitons show a critical dependence on the solitons' amplitude, velocity and mutual phase; resulting in either elastic collisions or a break up of the soliton pair.

With the advent of high-intensity short pulse lasers it has become possible to achieve extremely high intensities. When such laser pulses interact with plasmas or high-energy electron beams, radiation damping, which is usually small, can become large. We examine the effects of radiation damping on the backscattered Thomson radiation numerically and analytically. Using parameters comparable to the laser and microtron at the Advanced Photon Research Center we find that the overall spectrum is down-shifted and that the overall amplitude of the radiation is smaller than in the case with no damping.