Hideaki Takabe

School of Science Osaka University

Time: 10:45 am, April 17, 2013

Place: Lecture room 111, physics building

Title1：Physics of vacuum breakdown with ultra-intense lasers

Title2：Collisionless shock formation with big lasers modeling supernova remnant shocks

Abstract1: The progress of laser technology is going to make it possible to demonstrate the focused laser intensity of 1023-24 W/cm2 in the near future. In such high intensity, it is possible to change laser energy efficiently to highly-relativistic electron positron plasmas, very new high-energy plasma in laboratory, although they can be thought to play important role in high-energy astrophysics such as gamma-ray bursts, AGN jets, and so on.

This physics is directly related to the long-standing fundamental physics question of the vacuum breakdown. Swinger predicted if electric field of 1016V/cm is imposed in the vacuum, electrons predominantly appear from the so-called “Dirac sea” and electron-positron pair plasmas will fill up the vacuum . The laser can provide ultra-high electric field, but this Schwinger limit value can be achieved with the intensity of 1029 W/cm2. It would be impossible to be technically achieved in the near future.

So, we are looking for the way using the induced pair production process to obtain enough energy conversion from laser to pair-plasmas. In this case, seed electrons emits high-energy gamma rays via radiation damping physics in ultra intense laser field and the gamma-rays interact with laser photon to crate pairs via Briet-Wheeler process and direct pair production by high energy gamma-ray. We are now developing computational code based on PIC simulation with such QED effects.

In the presentation, we also discuss about the enhancement of pair production on Non-linear QED effects on Breit-Wheeler effects. 

Abstract2: The origin of ultra-high-energy cosmic rays is still open question. It is said that the cosmic-ray particles of proton whose energy is less that 1015eV are accelerated in our Galaxy and they are mainly accelerated by the supernova remnants (SNRs). The standard model is the stochastic diffusive acceleration around the shock surface of SNR. It is, however, still open question how the shock waves are generated and how the electro-magnetic turbulence is generated following the collisionless shock front (see Figure).

We have proposed a new physics for the generation of the collisionless shock formation through Weibel instability. We demonstrate the physics by PIC simulations; however, it is necessary to proof experimentally in order to persuade the most of opinion makers in Astrophysics, who are still skeptical about the simulation after the experience that simulation can reproduce observation data but it has many of adjustable parameters.

I would like to explain the physics scenario and also pointed out that magnetic reconnection should also couples with this phenomenon when currents filaments coalescence in the nonlinear stage of the Weibel instability in 3D PIC simulation. I will explain the experiments carried out so far with Gekko, LULI2000, Vulcan, Shingang-II, and OMEGA regarding mainly the shock formation in counter-streaming ablating plasmas. We found that in early time the electrostatic collisionless shock is observed. It is very exciting data showing physics scenario from Chaos to Structure formation.