Anomalous Relativistic Emission from Self-Modulated Plasma Mirrors

The interaction of relativistically intense laser pulse with a plasma mirror produces harmonics of the incident frequency co-propagating in the direction of specular reflection due to the plasma mirror surface oscillating with velocity close to the speed of light. This mechanism has shown its potential for realization of a bright source of extreme ultraviolet radiation and attosecond pulses. Here, we reveal an unexpected transition of this well-known process into a new regime of efficient extreme ultraviolet radiation generation. A novel mechanism of relativistic emission of radiation from plasma mirrors is identified with an extraordinary property that instead of following specular reflection, the radiation is emitted in the direction along the plasma mirror surface. With analytical calculations and numerical particle-in-cell simulations, we show that this radiation originates from laser-driven non-linear oscillations of relativistic electron nanobunches that are generated by a plasma surface instability and propagate along the plasma mirror surface.Comment: 6 pages, 3 figure

Industrial Applications of Laser Neutron Source

The industrial applications of the intense neutron source have been widely explored because of the unique features of the neutron-matter interaction. Usually, intense neutron sources are assembled with fission reactors or high energy ion accelerators. The big size and high cost of these systems are the bottle neck to promote the industrial applications of intense neutrons. In this paper, we propose the compact laser driven neutron source for the industrial application. As the first step of our project for the versatile applications of laser driven neutron source, Li-neutron and/or Li-proton interactions have been investigated for the application to the development of Li battery

Key paramaters in the design of HiPER reaction chamber

The future chamber reactor of HiPER will have to withstand short energy pulses (3 μs long) of up to 5 MJ of charged particles and X-rays with different repetition rates. Nowadays, tungsten has been selected as first wall material for a 5m radius reaction chamber. From the thermo-mechanical point of view, experiments have demonstrated that tungsten can withstand heat flux parameters up to 28 MJm-2 s -1/2 without roughening and 40 MJm-2 s -1/2 without undergoing melting. From the atomic point of view, He retention and bubble formation represents the biggest threat to its survivability, being doses of ~10 17 He/cm2 the upper limit for safe operation. Comparison of these limiting values with those proposed for a 48 MJ shock ignition target in HiPER reveals that, under a reasonable plan of 1000 fusion shots during the chamber lifetime, tungsten should guarantee a proper performance of the first wall

Stopping of α particles from the core in corona plasmas

In the laser fusion reactor design, the protection of first wall and the final optics from high energy ions is the key issue. So, it is necessary to predict the precise energy spectra of ions.In the previous reactor designs, the ion energy spectra were provided by the classical ion transport codes. However, this poster shows that the α particle spectrum is significantly modified by the anomalous process in ablated plasmas

FIREX project and effects of self-generated electric and magnetic fields on electron-driven fast ignition.

Fast ignition is a new scheme in laser fusion, in which higher energy gain with a smaller laser pulse energy is expected. A cone target has been introduced for realizing higher coupling efficiency. At ILE, Osaka University, a laser with four beams and a total output of 10 kJ ps−1, laser for fast ignition experiment (LFEX), has been constructed and we have carried out an integrated experiment with one beam of the LFEX. Through experiments it was found that the coupling efficiency is degraded when the laser pre-pulse is not sufficiently small. Namely, the main pulse is absorbed in the long-scale pre-plasma produced by the pre-pulse and the hot electron energy is higher than that for a clean pulse. Furthermore, the distance between the hot electron source and the core plasma is large. Hence, we are exploring how to overcome the pre-pulse effects on the cone target. In this paper it is proposed that a thin foil covers the laser entrance of the cone to mitigate the pre-plasma and a double cone reduces the loss of high-energy electrons from the side wall of the cone. The simulations indicate that a higher coupling efficiency is expected for the double cone target with a thin foil at the laser entrance. Namely, the pre-pulse will be absorbed by the foil and the electromagnetic fields generated on the surface of the inner cone will confine high-energy electrons