Toshiro Ohtani

Numerical Simulation of Laser‐Driven In‐Tube Accelerator Operation

To achieve a higher thrust performance in the laser‐driven in‐tube accelerator operation, numerical analysises have been carried out. The computational code covers from the generation of the blast wave to its interactions with the projectile and the acceleration wall. The thrust history and the momentum coupling coefficient evaluated from the numerical simulation depend on the fill pressure and the projectile shape. The confinement effect can be clearly found using the projectile attached with a shroud.

Numerical Analysis of Laser-Driven In-Tube Accelerator Operation

A two-dimensional code to simulate the operation of laser-driven in-tube accelerator has been developed. The code includes laser ray-tracing and ionization non-equilibrium for an analysis of realistic operation. The feature of the blast wave can be reproduced with this code and the process of the generation of the laser-induced blast wave is analyzed. Moreover, our computational results show that the generated shock waves are repeatedly reflected on the tube wall and the projectile base. The quantitative comparisons with the experimental data are also presented.

Richtmyer-Meshkov instability in laser plasma-shock wave interaction

The interaction between a laser plasma bubble and a shock wave involving a Richtmyer-Meshkov instability was experimentally studied via framing Schlieren visualization with a new experimental arrangement. The plasma bubble was generated by irradiating a TEA (Transversely-Excited Atmospheric) CO2laser pulse onto a parabolic mirror made of aluminum. After the laser pulse, the plasma bubble expanded and drove a spherical shock wave. The shock wave was reflected against the parabola, and interacted with the plasma bubble itself. In the interaction, a sharp interface is generated without membrane so that undesired membrane-oriented disturbances were eliminated. The flow visualization was conducted with various ambient pressure and laser energy, thereby obtaining different jet formations patterns.

Physical Processes of the Interaction Between Laser‐Generated Plasma and Blast Wave Appearing in Laser‐Driven In‐Tube Accelerator Configuration

Flow visualizations of the interaction between a laser‐pulse‐generated plasma and a shock wave driven by it have been experimentally conducted. The configuration of the experimental set‐up corresponds to the laser‐driven, in‐tube accelerator. Primary‐mode deformation of the plasma is governed by Richtmyer‐Meshkov instability which is produced by the vector product between the pressure and density gradients, which in turn correspond to a reflected shock wave and to the plasma, respectively. Higher‐mode contact surface deformations are supposedly originated in Rayleigh‐Taylor instability in the shrinkage phase of the plasma, and is enhanced due to the passage of the reflected shock wave.

Toward the Optimal Operation of Laser-Driven In-Tube Accelerator

Axisymmetric numerical simulations of the operation of the laser-driven in-tube accelerator have been carried out to investigate the dependencies of the propulsion performance on various conditions. The computational code covers from the generation of the blast wave to its interactions with the projectile and the acceleration wall. The thrust history and the momentum coupling coefficient evaluated from the numerical simulation depend on the fill pressure of the propellant gas and the projectile shape. The confinement effect using the projectile attached with a shroud attributes to high momentum coupling coefficient. The higher momentum coupling coefficient is also found for the lower fill pressure with the LITA50 configuration.

Impulse Characteristics of Laser-driven In-Tube Accelerator (LITA)

In this study, impulse generation processes induced by a single laser pulse in the laser‐driven in‐tube accelerator are studied through pressure history measured at the center of the projectile base, which acts also as a parabolic mirror. The effects of the fill pressure, laser energy and length of a shroud are analyzed.

Impulse characteristics of laser-induced blast wave in monoatomic gases

The paper focuses on physical gas-dynamic characteristics of impulse generation by laser Induced blast wave (LIBW) in a laser-driven in tube accelerator (LITA). Propagation, reflection of blast wave and wave structure were intensively studied by using an ICCD camera system through shadowgraph.

Detailed Impulse Generation Mechanisms in the Laser‐Driven In‐Tube Accelerator

In this paper, we will report recent results of LITA 25 experiments, which include framing schlieren visualization and streak spectroscopy. The processes of laser energy absorption, laser plasma and blast wave generation, and their interactions are clearly observed.

In‐Tube Laser Propulsion; Performance and Application Prospects

This paper summaries the characteristics of in‐tube propulsion powered by laser energy. The thrust is enhanced due to confinement effect in a tube. This method has a large payload capability because the propellant does not need to be on board. Also, this has various advantages on application aspects. The performance and impulse production mechanisms are discussed based on results of laboratory experiments using 500‐W lasers.

Dependence of Initial Plasma Size on Laser‐driven In‐Tube Accelerator (LITA) Performance

At Tohoku University, experiments of Laser‐driven In‐Tube Accelerator (LITA) have been carried out. In order to observe the initial state of plasma and blast wave, the visualization experiment was carried out using the shadowgraph method. In this paper, dependency of initial plasma size on LITA performance is investigated numerically. The plasma size is estimated using shadowgraph images and the numerical results are compared with the experimental data of pressure measurement and results of previous modeling.