電漿學分學程 暨 電漿所專題演講

演講者：Hideaki Takabe 講座教授

單 位：台大物理系

梁次震宇宙學與粒子天文物理學中心

地 點：綜合大樓2樓 48218教室

Talk 1：2022/12/21 19:00

The Laboratory Astrophysics with Intense Lasers

=Challenge the physics in the Universe in laboratory=

Thanks to a rapid progress of high-power lasers soon after the birth of laser by T. H. Maiman in 1960, intense lasers have been developed mainly for studying scientific feasibility of the laser fusion in the world wide. Inertial confinement fusion with intense laser has attracted attention as a new future energy after two oil crises from 1970s -1980s. From the beginning, the most challenging physics has been the physics of hydrodynamic instability to realize the spherical implosion to achieve more than 1000 times the solid density. During such activities in laboratory, the explosion of supernova SN1987A was observed in the sky on February 23, 1987. The x-ray satellites have revealed that the hydrodynamic instability is a key issue to understand the physics of supernova explosion. After strong interaction of laser plasma researchers and astrophysicists, the laboratory astrophysics with intense lasers has been proposed by the author and promoted around the end of 1990s as its image is shown in Figure below. The original subject was mainly related to hydrodynamic instabilities. However, after two decades of the laboratory astrophysics research, we can now find a diversity of its research topics. It has been demonstrated that a variety of nonlinear physics of collisionless plasmas can be studied in laser ablation plasmas in the last decade theoretically and experimentally. In my talk I focus on the recent topics intensively studied in laboratory experiments. After introducing the recent topics, I would like to talk about modeling cosmic-ray acceleration with lasers.

Talk 2：2022/12/22 19:00

Magnetic turbulence and fluid turbulence

Theory, experiment, simulations, and an intuitive model to reveal complex physics

The Universe is filled with magnetic turbulence and it plays important role in cosmic-ray generation, for example, by supernova remnants (SNRs) in our galaxy, and in AGN jets far in the Universe. How such magnetic turbulence is generated? It is a long-standing open question in astrophysics and cosmology.

We proposed to use the biggest laser NIF, LLNL ( https://lasers.llnl.gov/science/discovery-science ) for fundamental science to study the growth of magnetic field in counter-streaming collisionless plasma in astrophysical condition. We have found linear to nonlinear stage of magnetic field growth to demonstrate a structure formation of shock waves. The shock waves are an engine to accelerate the cosmic-ray in the Universe.

Stating from a simple theory to PIC simulations, we have proposed such an experiment with huge laser system. After approval, an international team has worked together for the experiment and demonstrated the generation of magnetic turbulence and the formation of collisionless shock. In addition, charged particle acceleration was also observed.

We are happy with the experimental demonstration of shocks in Universe, while I wished to find the physics more intuitively with use of the fact found in the simulations and laser experiments. After developing such mode theory, I found that the intuitive theory can explain not only the magnetic turbulence, but also the physics of turbulent mixing induced by hydrodynamic instabilities, which is the most important physics in laser fusion.

In the talk, after showing how this theory can explain the shock and acceleration in SNR (SN1006) as shown below, then, I hope to ley you share the happiness of finding a universal theory in different physics.