Hot Electron Spectra in Plain, Cone and Integrated Targets for FIREX-I using Electron Spectrometer

The traditional fast ignition scheme is that a compressed core created by an imploding laser is auxiliary heated and ignited by the hot electrons (produced by a short pulse laser guided through the cone). Here, the most suitable target design for fast ignition can be searched for by comparison of the spectra between varied targets using an electron spectrometer

Calibration of Compact Electron Spectrometer for the FIREX-I Project in Gekko XII

We have developed a compact electron spectrometer (ESM) to investigate ignition mechanism in the Fast Ignition Realization Experiment project. Hot electrons, produced by the irradiation of a gold target by using a compressed chirped pulse laser, are used for auxiliary heating of the imploded core. An imaging plate is used as the electron detector for medical purposes. However, the relationship between the beam intensity and the detector signal is not clear. The ESM should be calibrated because it is highly compact and has a complex magnetic field for bending caused by installation in a limited space. We have performed the calibration by using an L-band LINAC at the Institute of Scientific and Industrial Research, Osaka University, in order to obtain an accurate electron spectrum. The calibration used a single electron pulse at two different energies, 9.5 MeV and 27.1 MeV, with 0.1-10 pC. The energy spreads are 0.2 MeV at 9.5 MeV and 0.3 MeV at 27.1 MeV. The analyzer has been tested to measure energetic electrons from plain and integrated targets irradiated by the Laser or Fast Ignition Experiment (maximum energy of 10 kJ) up to 800 J

Ultrahigh-contrast kilojoule-class petawatt LFEX laser using a plasma mirror

Laser pulse contrast exceeding 10^11 was demonstrated on a kilojoule-class petawatt laser for fast ignition experiments (LFEX) laser system [J. Phys. IV France 133, 81 (2006)] by implementing a 2 in. plasma mirror. Laser beams of up to 1.2 kJ striking the plasma mirror with a pulse duration of 1.5 ps were reflected and focused onto a target without significant distortions in the focal spot. Transmitted light from the plasma mirror reveals that it has a high reflectivity 2 ps before the main peak. The estimated laser pulse contrast at the target was 10^11 at 1 ns before the main peak. No preformed plasma was observed with optical interferometry diagnostics, but in the experiment without a plasma mirror a preplasma was clearly observed. The energetic proton was generated from a 0.1μm thick CH film showing excellent pulse contrast. This technique constitutes a promising method to enhance the LFEX laser system performance in fast ignition experiments