[Show abstract][Hide abstract] ABSTRACT: A series of experiments were carried out to evaluate the energy-coupling efficiency from heating laser to a fuel core in the fast-ignition scheme of laser-driven inertial confinement fusion. Although the efficiency is determined by a wide variety of complex physics, from intense laser plasma interactions to the properties of high-energy density plasmas and the transport of relativistic electron beams (REB), here we simplify the physics by breaking down the efficiency into three measurable parameters: (i) energy conversion ratio from laser to REB, (ii) probability of collision between the REB and the fusion fuel core, and (iii) fraction of energy deposited in the fuel core from the REB. These three parameters were measured with the newly developed experimental platform designed for mimicking the plasma conditions of a realistic integrated fast-ignition experiment. The experimental results indicate that the high-energy tail of REB must be suppressed to heat the fuel core efficiently.
Full-text · Article · Jun 2015 · Physical Review E
[Show abstract][Hide abstract] ABSTRACT: A Compton-scattering-based X-ray spectrometer is developed to obtain the energy distribution of fast electrons produced by intense laser and matter interactions. Bremsstrahlung X-rays generated by fast electrons in a material are used to measure fast electrons' energy distribution in matter. In the Compton X-ray spectrometer, X-rays are converted into recoil electrons by Compton scattering in a converter made from fused silica glass, and a magnet-based electron energy analyzer is used to measure the energy distribution of the electrons that recoil in the direction of the incident X-rays. The spectrum of the incident X-rays is reconstructed from the energy distribution of the recoil electrons. The accuracy of this spectrometer is evaluated using a quasi-monoenergetic 6 MeV electron bunch that emanates from a linear accelerator. An electron bunch is injected into a 1.5 mm thick tungsten plate to produce bremsstrahlung X-rays. The spectrum of these bremsstrahlung X-rays is obtained in the range from 1 to 9 MeV. The energy of the electrons in the bunch is estimated using a Monte Carlo simulation of particle-matter interactions. The result shows that the spectrometer's energy accuracy is ±0.5 MeV for 6.0 MeV electrons.
No preview · Article · Nov 2014 · Review of Scientific Instruments
[Show abstract][Hide abstract] ABSTRACT: We explore the potential of Pr- or Ce-doped 20Al(PO3)(3)-80LiF (APLF80+3Pr or +3Ce) scintillator to observe the lower edge of down-scattered neutron and discriminate fusion originated neutron from strong X-ray signals. APLF80+3Pr or +3Ce scintillator exhibits considerably fast decay profiles and negligible slow-decay components. Using these newly developed APLF80+3Pr or +3Ce scintillators, we have successfully observed fusion-originated neutron signal in the midst of strong X-ray-excited fluorescence in an integrated experiment using our 10 kJ class GEKKO XII Nd-glass laser system. A sophisticated neutron detection system using APLF80+3Pr or 3Ce will be used for the first fast ignition experiment. (C) 2011 Elsevier BY. All rights reserved.
No preview · Article · Jan 2013 · Journal of Crystal Growth
[Show abstract][Hide abstract] ABSTRACT: 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.
Preview · Article · Jan 2013 · Plasma and Fusion Research
[Show abstract][Hide abstract] ABSTRACT: In the fast ignitor experiment the neutron diagnostics is very
challenging due to too large backgrounds originated from hard X ray. In
the Fast Ignition integrated experimental campaign held in 2010 in GEKKO
XII and LFEX facility in Institute of Laser Engineering Osaka (ILE), the
Xylen based new liquid scintillator coupled with the gated
photomultiplier tube has successfully recorded neutron signal with
heating the energy of up to 400 J. However there was significant large
background in the signal originated from neutrons via (γ,n)
reaction from the target chamber wall. The neutron collimator was
developed and implemented to suppress these neutron backgrounds. We
succeeded to record a very clear neutron signals in every shot in the
fast ignitor experimental campaign held in July 2012 with the heating
laser energy of around 1000 J with the pulse width of 2.2 ps. The
details of the detector and the result of the fast ignition experiment
will be presented.
[Show abstract][Hide abstract] ABSTRACT: Scintillation properties of Ce3+-doped 20Al(PO3)(3)-80LiF glasses were investigated in order to seek a candidate for down-scattered neutron scintillator in nuclear fusion diagnostics. The decay constant of APLF80+3Ce with 5.5 MeV alpha particles from Am-241 radioisotope excitation was measured to be 32.1 ns. Moreover, sufficiently low afterglow decay profile and improved light output of APLF80+3Ce were experimentally demonstrated.
Full-text · Article · Oct 2012 · IEEE Transactions on Nuclear Science
[Show abstract][Hide abstract] ABSTRACT: The fast ignition integrated experiment was conducted on GEKKO-XII laser
facility by using LFEX laser with the energy up to 1.4 kJ in a 1.2 ps
pulse in 2010. Neutron yield enhancement was observed by a developed
liquid scintillation detector . DD fusion neutron signal was
correctly separated from intense background signals originated from 1)
γ rays from the targets and scattered by experimental bay wall,
and 2) neutrons by (γ-n) reaction in the target vacuum chamber or
diagnostics instruments. The DD fusion neutron yield up to
(3.5±1.3)x10^7 was obtained with 300J of the additional heating
laser energy, whereas 1x10^6 was obtained in without heating case. The
neutron yield was higher than that reported in the previous work .
[4pt]  T. Nagai, et. al., Japanese Journals of Applied Physics, (to
be published) [0pt]  R. Kodama, et. al., Nature, 418, 933-934 (2002)
[Show abstract][Hide abstract] ABSTRACT: 4,4'''-Bis[(2-butyloctyl)oxy]-1,1':4',1'':4'',1'''-quaterphenyl (BBQ) dye dissolved in xylene and enriched with oxygen is shown to exhibit the characteristics of an ideal neutron scintillator for time-of-flight (TOF) measurement in a laser fusion experiment. Initial results from excitation with 290-nm pulses show that it has a 0.76-ns fast decay component and a negligible slow decay component or afterglow. By using this scintillator for TOF measurement, we have successfully discriminated between nuclear fusion-generated neutrons and X-rays. This would dramatically improve neutron diagnostics in fast ignition experiments where neutrons have to be detected in the presence of an intense X-ray burst.
No preview · Article · Aug 2011 · Japanese Journal of Applied Physics
[Show abstract][Hide abstract] ABSTRACT: The characteristics of an APLF80+3Ce scintillator are presented. Its sufficiently fast decay profile, low afterglow, and an improved light output compared to the recently developed APLF80+3Pr, were experimentally demonstrated. This scintillator material holds promise for applications in neutron imaging diagnostics at the energy regions of 0.27 MeV of DD fusion down-scattered neutron peak at the world's largest inertial confinement fusion facilities such as the National Ignition Facility and the Laser Mégajoule.
No preview · Article · Oct 2010 · The Review of scientific instruments