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Dynamics of albumin agglomeration and dissolution induced by a helium plasma jet using the Schlieren visualization technique were demonstrated. The Schlieren technique enabled us to visualize the plasma-induced agglomeration of albumin on the albumin solution and dissolution from the agglomerate. Through the dissolution, a high-density albumin region moved downward, forming downward flows. During the plasma treatment, the downward flows were observed with a flow velocity of around 0.2 mm/s, while the flow velocity was 0.7 mm/s–0.9 mm/s without the plasma treatment. It was found that the plasma treatment decelerates the downward flows.

Striation phenomena in a plasma flare produced by an atmospheric pressure plasma jet had been observed. In this study, we measured the striation structure in a neon plasma flare by optical emission spectroscopy. As a result, it shows that the emission from the plasma flare is synchronized with the plasma current. We discuss the temperature estimated from the Boltzmann plot using the two emission lines of Ne I at 692.9 and 724.5 nm whose upper levels are Ne [3p (2p6)] and Ne [3p (2p10)], respectively. This temperature has peaks with a spatial interval of about 0.5 mm, and the peak positions correspond to the spatial variation of the emission intensity. We also discuss the mechanism of the striation phenomena with the estimated temperature, and collisional relaxation between excited and neutral atoms.

The effect of viscosity on the destabilization of the Rayleigh–Taylor (RT) instability by thermal conductivity has been investigated as an extension of the Ryutov analysis [D. D. Ryutov, Phys. Plasmas 7, 4797 (2000)]. The viscosity stabilizes the RT instability for short wavelength perturbations when gradients of a molecular weight and a gravitational acceleration are in the same direction. It only reduces the growth rate for short wavelength perturbations when they are in the opposite directions. The growth rates have been quantitatively evaluated as functions of a normalized wavelength for various Prandtl numbers in the case when adiabatic perturbations are neutrally stable.

A stochastic acceleration mechanism which is a direct acceleration mechanism effective for the intense laser case is studied by the Fokker–Planck approach. The Fokker–Planck equation of the electron distribution function is derived from the equation of motion of electrons which interact with filamented laser fields. The Fokker–Planck equation contains nonlinear coefficients and gives an anisotropic distribution in momentum space. The strong directionality of the acceleration is explained. The accelerated electrons tend to be collimated towards the direction of the wave vector. The effective temperature scales as T∝tβ with β≃1.

By using a particle-in-cell simulation code which includes tunneling ionization, it is found that strong wake fields are excited and amplified due to the modulation of an intense laser pulse induced by an ionizing plasma in the regime where the matching condition between laser pulse length (LLaser) and plasma wavelength (λp), i.e. LLaser⩽λp is not satisfied. The modulation is characterized by a gradual steepening of the pulse front where there is a copropagating density gradient which is due to the rapid plasma formation from ionization there. Accordingly, the wake field is convectively amplified to a significant level. This amplification of plasma waves always occurs, more or less, for laser propagation in ionizing plasmas.

Monoenergetic electron beams were generated in the self-modulated laser wakefield acceleration regime using a 2–6TW, 50fs Ti:sapphire laser system. The monoenergetic electron beams of energies up to 15MeV and 30MeV, with a plasma density around 1.5×1020cm−3 and 3.5×1019cm−3, respectively, were observed. The monoenergetic energy was found to be inversely proportional to the plasma density. The monoenergetic electron beam was generated at only specific plasma densities for each experimental condition. The plasma density dependence of the electron energy spectrum, the forward scattered light spectrum, and the side scattered light image of the laser pulse was studied in detail. The conditions for monoenergetic electron beam generation are discussed based on the results of the plasma diagnostics.

The generation of a quasi-monoenergetic electron beam in laser-driven plasma acceleration is reported. A monoenergetic electron beam with an energy of 7 MeV was emitted from a high-density plasma (electron density >1020cm−3) produced by a 2 TW 50 fs laser pulse. The divergence of the monoenergetic beam was ±1.2°. The first Stokes satellite peak of stimulated forward Raman scattering was observed in the spectrum of the light transmitted through the plasma. The plasma wave was excited in the region of which electron density was around 1.3×1020cm−3. The acceleration length was estimated to be 500μm from the length of the side-scattered light image. It is considered that the monoenergetic beam generation is due to the matching of the acceleration length to the dephasing length determined by the velocity difference between the accelerated electrons and the plasma wave.