Stabilization of radiation reaction with vacuum polarization

Seto, Keita*; Zhang, S.*; Koga, J. K.; Nagatomo, Hideo*; Nakai, Mitsuo*; Mima, Kunioki*

Progress of Theoretical and Experimental Physics (Internet), 2014(4), p.043A01_1 - 043A01_10, 2014/04

https://doi.org/10.1093/ptep/ptu031

Radiation reaction in ultrarelativistic laser-spinning electron interactions

Seto, Keita*; Nagatomo, Hideo*; Koga, J. K.; Mima, Kunioki*

Progress of Theoretical and Experimental Physics (Internet), 2013(5), p.053A01_1 - 053A01_10, 2013/05

https://doi.org/10.1093/ptep/ptt023

Equation of motion with radiation reaction in ultrarelativistic laser-electron interactions

Seto, Keita*; Nagatomo, Hideo*; Koga, J. K.; Mima, Kunioki*

Physics of Plasmas, 18(12), p.123101_1 - 123101_8, 2011/12

https://doi.org/10.1063/1.3663843

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

Mima, Kunioki*; Sunahara, Atsushi*; Shiraga, Hiroyuki*; Nishimura, Hiroaki*; Azechi, Hiroshi*; Nakamura, Tatsufumi; Jozaki, Tomoyuki*; Nagatomo, Hideo*; Garcia, C.*; Veralde, P.*

Plasma Physics and Controlled Fusion, 52(12), p.124047_1 - 124047_6, 2010/12

https://doi.org/10.1088/0741-3335/52/12/124047

Fast ignition is a new scheme in laser fusion, in which higher energy gain with a smaller laser pulse energy is expected. At 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. Furthermore, the distance between the hot electron source and the core plasma is large. 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.

Control of laser-accelerated proton beams by modifying the target density with ASE

Yogo, Akifumi; Kiriyama, Hiromitsu; Mori, Michiaki; Esirkepov, T. Z.; Ogura, Koichi; Sagisaka, Akito; Orimo, Satoshi; Nishiuchi, Mamiko; Pirozhkov, A. S.; Nagatomo, Hideo*; et al.

European Physical Journal D, 55(2), p.421 - 425, 2009/11

https://doi.org/10.1140/epjd/e2009-00045-5

We demonstrate the laser-ion acceleration from a near-critical density plasma, when amplified spontaneous emission (ASE) was used to convert a solid foil target into the lower-density target. In this work, a direct comparison is made by changing the ASE intensity by factor 3 in order to investigate the target density-dependency of the laser-ion acceleration. The beam direction of high-energy component is successfully controlled by modifying the target density. The near-critical density plasma can be a favorable target to control the beam direction to be dependent on its energy.

Experimental and computational characterization of hydrodynamic expansion of a preformed plasma from thin-foil target for laser-driven proton acceleration

Sagisaka, Akito; Nagatomo, Hideo*; Daido, Hiroyuki; Pirozhkov, A. S.; Ogura, Koichi; Orimo, Satoshi; Mori, Michiaki; Nishiuchi, Mamiko; Yogo, Akifumi; Kado, Masataka

Journal of Plasma Physics, 75(5), p.609 - 617, 2009/06

https://doi.org/10.1017/S0022377809990043

We characterize the electron density distributions of preformed plasma for laser-accelerated proton generation. The preformed plasma of a thin-foil target is generated by prepulse and ASE of a high-intensity Ti:sapphire laser and is measured with an interferometer using a second harmonic probe beam. High-energy protons are obtained by reducing the size of the preformed plasma by changing the ASE duration before main pulse at the front side of the target. Simulation results with two-dimensional radiation hydrodynamic code are close to the experimental results for low-density region 410 cm at the front side.

Probing of nonlinear evolution of laser wakefield by Raman scattering of laser light

Zhou, W.*; Mima, Kunioki*; Nakamura, Tatsufumi; Nagatomo, Hideo*

Physics of Plasmas, 15(9), p.093107_1 - 093107_6, 2008/09

https://doi.org/10.1063/1.2983150

When a weak probe laser pulse is injected into a wakefield excited by a short high-intensity pump laser pulse, the probe pulse will be Raman scattered by the wakefield. It is possible to determine the density profile from the spectrum of this forward Raman scattered probe laser. In previous research, an analytical solution for the multiple sidebands of the forward Raman scattering of the probe laser pulse was presented. These multiple sidebands are connected with the steepening of density perturbation of the wakefield. More detailed information of the probe pulse in wakefield is studied with one-dimensional particle-in-cell simulations. The analytical solution and the results of simulation are consistent with each other and other experiments.

Efficient production of a collimated MeV proton beam from a Polyimide target driven by an intense femtosecond laser pulse

Nishiuchi, Mamiko; Daido, Hiroyuki; Yogo, Akifumi; Orimo, Satoshi; Ogura, Koichi; Ma, J.-L.; Sagisaka, Akito; Mori, Michiaki; Pirozhkov, A. S.; Kiriyama, Hiromitsu; et al.

Physics of Plasmas, 15(5), p.053104_1 - 053104_10, 2008/05

https://doi.org/10.1063/1.2928161

High-flux energetic protons whose maximum energies are up to 4 MeV are generated by an intense femtosecond Titanium Sapphire laser pulse interacting with a 7.5, 12.5, and 25m thick Polyimide tape targets. The laser pulse energy is 1.7 J, duration is 34 fs, and intensity is 310Wcm. The amplified spontaneous emission (ASE) has the intensity contrast ratio of 410. The conversion efficiency from laser energy into proton kinetic energies of 3% is achieved, which is comparable or even higher than those achieved in the previous works with nanometer-thick targets and the ultrahigh contrast laser pulses (10).

Laser-driven proton acceleration from a near-critical density target

Yogo, Akifumi; Daido, Hiroyuki; Bulanov, S. V.; Esirkepov, T. Z.; Nemoto, Koshichi*; Oishi, Yuji*; Nayuki, Takuya*; Fujii, Takashi*; Ogura, Koichi; Orimo, Satoshi; et al.

Journal of Physics; Conference Series, 112, p.042034_1 - 042034_4, 2008/00

https://doi.org/10.1088/1742-6596/112/4/042034

In this work, we present a new method to enhance the proton generation by a 10-contrast laser. High-energy protons up to 3.8 MeV are observed with 7.5-m-thick insulator (Polyimide) target irradiated by a laser pulse having energy of 0.8 J and an intensity of 10-W/cm. Using two time-of-flight (TOF) spectrometers simultaneously in different directions, we measure the direction dependency of proton-energy spectra. As a result, we find that high-energy component of proton beam is shifted away from the target normal toward the laser-propagation direction, when the laser is focused with 45 incident angle. The TOF measurements over 130 laser shots confirm that the generation of the high-energy protons, which are steered away from the target normal, depends strongly on the laser-focusing condition.

High energy electron generation by laser-cone interaction

Nakamura, Tatsufumi*; Sakagami, Hitoshi*; Jozaki, Tomoyuki*; Nagatomo, Hideo*; Mima, Kunioki*; Koga, J. K.

Plasma and Fusion Research (Internet), 2, p.018_1 - 018_6, 2007/05

https://doi.org/10.1585/pfr.2.018

Electron acceleration processes taking place in the interaction of ultra-intense laser pulses with cone targets are studied by using two-dimensional Particle-in-Cell (PIC) simulations to understand the characteristics of electrons generated from cone targets. It is explained that there are two dominant acceleration processes which are distinctive in the laser-cone interaction. One is the acceleration and transport along the side wall of the cone target, where electrons are guided along the side wall surface towards the cone tip by surface magnetic and electric fields. The second is the ponderomotive acceleration at the cone tip by the laser field which is intensified by cone focusing. The understanding of these acceleration processes helps to design cone targets to control the electron energy characteristics.