古賀 麻由子

Gas target injection system is newly fabricated to observe behaviors of injected fast ignition targets. It can eject a mimic fast ignition target by pressured nitrogen gas and magnetic separator. The flight attitude of injected target is observed by high-speed cameras. Analysis of high-speed camera images indicates that the target velocity is increased with the injection gas pressure up to around 100 m/s which meets the demanded specification of a reactor and the target flight angle is varied in wide range shot by shot. The technical problem how to control flight angle is recognized for a fast ignition reactor. (c) 2022 The Japan Society of Plasma Science and Nuclear Fusion Research

We perform the principal verification of reconstructing object surface images by using deep learning. Using the deep learning neural network based on convolutional neural networks, simple object surface images with 128 x 128 pixels are reasonably reconstructed with up-converting from rough microwave signal images with 16 x 16 pixels. The model captures large structural features of the object surface images even with small number of training data. As the number of training data increases, it captures small structures of objects. It is also found that noises of input signal images affect reconstructions of small structures of objects. (C) 2022 The Japan Society of Plasma Science and Nuclear Fusion Research

The lens-less technique of microwave holography is expected to provide information of three-dimensional structures of plasma with a wide field of view. From the complex amplitudes of waves, which are observed on a single planar array of antennas, we will be able to obtain an imaging of the three-dimensional object. With a geometry of back-scattering observation, the feasibility is examined with a numerical tool of electromagnetic analysis on dielectric objects. With respect to the variety of the dielectric constant and shape of object, it is shown that useful information can be acquired in regarding the complex amplitude distribution at planar detector. (C) 2021 The Japan Society of Plasma Science and Nuclear Fusion Research

© 2019 Elsevier B.V. We have developed a novel method to fabricate an aluminum cone tip to attach the conventional gold cone for fast ignition. An aluminum cone tip is fabricated by laser thermal chemical vapor deposition. Trimethylaluminum (TMA) is used as a chemical precursor of aluminum. TMA is introduced into a vacuum chamber with argon gas and heated on a substrate by using a heater and a laser. Aluminum products are measured by using digital zoom microscope. It is found that the deposition rate is increased with the increase of the substrate temperature, argon gas flow, and the laser intensity. However, the increase of the laser intensity increases the temperature of the deposit, and also causes the melt of the deposit. Under suitable conditions, we succeeded in making desired aluminum conical shape with 32 μm height, whose size is difficult by conventional cutting technology. Therefore, this method will be important not only to the fusion experiments but also to many other industrial applications.

© 1973-2012 IEEE. We have employed an exploding-wire compression method to measure the electrical conductivity of diamond-like carbon (DLC) in a warm dense matter (WDM) state. We generated a DLC in the WDM state using shock compression driven by an exploding-wire discharge within a rigid capillary. To elucidate the generation of DLC in WDM, we performed a 1-D magnetohydrodynamic simulation. Using the numerical results, we estimated the electrical conductivity of the DLC plasma. By comparing the time-evolutions of the voltage and current for gold and gold + DLC samples, we demonstrated that the voltage-current evolution is different in the two cases. From the absorption spectroscopy, we estimated the DLC temperature to be 8000-9000 K. By comparing the results of the experiment with those of the numerical simulation, we determined the electrical conductivity of the DLC plasma to be 10 6 S/m. This is relatively high compared with the electrical conductivity of the conventional carbon plasma, but the experimental results are similar to the theoretical values for diamond at solid density.

Microwave, unlike visible light, can be measured directly on the phase of the wave. The measurement of complex amplitude suggests a possibility of holographic plasma imaging with a single view-field of planar array of detectors. In this paper, an inverse problem of holography is formulated with respect to reflection and scattering wave observations. Against the restricted view-field and few detectors, a solution of Tikhonov type is proposed and examined by numerical simulations. The first result of feasibility study is presented. (C) 2019 The Japan Society of Plasma Science and Nuclear Fusion Research

© 2017 Elsevier B.V. In fast ignition research, a divergence of laser-generated hot electrons is a serious problem. Using diamond like carbon (DLC) cones is one of the realistic solutions to this problem. However, it is difficult to make a stand-alone DLC cone because it needs a thick DLC layer. In this paper, we report survey findings of preparation conditions for a thick DLC layer. DLC layers were prepared by using plasma–based ion implantation and deposition system. Acetylene gas or toluene vapor was used as a source. After trials of many deposition conditions, it is found that low gas pressure and low RF power condition is suitable for a thick DLC deposition. Properties of the made DLC layers were measured by near edge X-ray absorption fine structures (NEXAFS) and elastic recoil detection analysis (ERDA). It is found that these DLC layers have typical hydrogenated amorphous DLC properties. Based on these results, we succeeded in making stand-alone DLC cones.

© 2017 Author(s). X-ray imaging is very useful to investigate imploded core plasma in inertial fusion experiments. We can obtain information from X-ray images, such as shape, density, and temperature. An X-ray framing camera (XFC) capable of taking two-dimensional, time-resolved X-ray images is used to capture the images. In previous work, we developed a numerical model of an XFC to analyze its X-ray image. The calculated results agreed qualitatively with experimental results. However, it was not accurate enough to determine the absolute value of the signal. We thought this discrepancy was caused by gain depletion. In high energy laser experiments, high photon flux may cause gain depletion. This is a problem for accurate X-ray measurement. In this paper, we report our new model, including gain depletion. The new model is evaluated by tabletop laser experiments and high energy laser experiments. The results calculated using the new model agree quantitatively with our experimental results. Furthermore, we confirmed that gain depletion occurs in our high energy laser experiments. For quantitatively accurate X-ray intensity measurements, the XFC should be used with limited incident photon flux such that the gain linearity is guaranteed.

© 2017 SPIE. X-ray imaging is very useful to investigate a imploded core plasma in inertial fusion experiment. We can obtain many information from X-ray images, such as shape, density and temperature of a plasma. X-ray framing camera (XFC) is capable of taking two dimensional time resolved X-ray images. In previous work, we developed a numerical model of XFC to analyze its X-ray image. Calculated results agreed qualitatively with experimental results. However, it is not enough when we discuss absolute value of the signal. Moreover, in high energy laser experiment, high photon flux may cause signal depletion of XFC. This is a problem for accurate X-ray measurement. In this paper, we report our improved calculation model including signal depletion. Results using the new model shows signal depletion at high applied voltage range. The new model are evaluated by tabletop laser experiments. Calculated results using the new model agree quantitatively with experimental results.

© Published under licence by IOP Publishing Ltd. We proposed the new laser arrangement to implode a target, a 12-beam implosion, and tried it in a fast ignition integration experiments. The concept of the 12-beam implosion is as follows. The three laser beams near a cone are shifted not to irradiate a cone and a long gold cone is used to prevent the irradiation of those three laser beams with fundamental frequency. In experiments, time-resolved two-dimensional X-ray images of an imploded core plasma were obtained by an X-ray framing camera. It is found that the spherical symmetry of the imploded core plasma is improved and the motion of the imploded core plasma towards the cone is suppressed in half in the 12-beam implosion. We believe that the 12-beam implosion will become a useful concept in controlling the imploded core plasma.

© 2016 The Japan Society of Plasma Science and Nuclear Fusion Research. This paper reports characteristic evaluations of perforated metal sheet type high pass filters for milli- or microwave by numerical analysis and the guiding principle of designing broad-band high pass filters. The broadband filters will be used for the microwave plasma diagnostics such as ECE, interferometer and reflectometer. We used 3D-modeling electromagnetic field calculation code to take complex interferences into account. The validity of the numerical analysis is guaranteed by a good agreement between calculated results and measured results. It is found that the frequency characteristic over the cut-off frequency depends on the filter thickness and that a thin filter is desirable for the ideal broad-band frequency filter.

Copyright © Cambridge University Press 2015. The transport of relativistic electron beam in compressed cylindrical targets was studied from a numerical and experimental point of view. In the experiment, cylindrical targets were imploded using the Gekko XII laser facility of the Institute of Laser Engineering. Then the fast electron beam was created by shooting the LFEX laser beam. The penetration of fast electrons was studied by observing Kα emission from tracer layers in the target.

The ability to measure the injection time of a heating laser synchronized to the imploded core plasma is very important in fast-ignition experiments. In this research, we demonstrate the successful measurement of the injection time using a new x-ray framing camera design. Thermal x-rays for imploded core measurement and hard x-rays for measurement of the heating laser injection time were discriminated using x-ray reflectors made of platinum. The measured hard x-ray signal was evaluated with numerical calculations and found to agree well with the calculated values. We have established a technique for estimating the heating laser injection time from the position of the peak intensity of the hard x-ray signal. © 2014 IOP Publishing Ltd.

© Springer-Verlag Berlin Heidelberg 2013. Extreme ultraviolet (EUV) spectrum emitted from laser-sustained oxygen plasma in a laser detonation atomic oxygen beam source was investigated. In order to measure EUV spectra, specially designed flat-field grazing-incidence EUV spectrometer was designed. The EUV spectra were recorded on an imaging plate which provides quantitative analysis capability. It was confirmed that EUV emission in the range of 20 –50 nm was included in the emission from laser-sustained oxygen plasma in a laser detonation source. The experimental results clearly indicated that the EUV intensity depends strongly on the translational energy of atomic oxygen. Even though the effect of EUV on the material erosion has not been confirmed, presence of high-energy photon need to be considered for better understanding of the reaction of hyperthermal atomic oxygen in the ground-based facility.

Absolute K. α line spectroscopy is proposed for studying laser-plasma interactions taking place in the Au cone-guided fast ignition targets. X-ray spectra ranging from 20 to 100keV were quantitatively measured with a Laue spectrometer composed of a cylindrically curved crystal and a filter-absorption method for Bremsstrahlung continuum emission. The absolute sensitivities of the Laue spectrometer systems were calibrated using pre-characterized laser-produced X-ray sources and radioisotopes. The integrated reflectivity for the crystal is in good agreement with predictions by an X-ray diffraction code. The energy transfer efficiency from incident laser beams to hot electrons, as the energy transfer mechanism, is derived from this work. The absolute yield of Au and Ta K. α lines were measured in the fast ignition experimental campaign performed at Institute of Laser Engineering, Osaka University. Applying the hot electron spectrum information from electron spectrometer and scaling laws, the energy transfer efficiency from the incident LFEX, a kJ-class PW laser, to hot electrons was derived for the first time. © 2013 Elsevier B.V.

One of the most advanced fast ignition programmes is the fast ignition realization experiment (FIREX). The goal of its first phase is to demonstrate ignition temperature of 5 keV, followed by the second phase to demonstrate ignition-and-burn. The second series experiment of FIREX-I, from late 2010 to early 2011, has demonstrated a high (>10%) coupling efficiency from laser to thermal energy of the compressed core, suggesting that the ignition temperature can be achieved at laser energy below 10 kJ. Further improvement of the coupling efficiency is expected by introducing laser-driven magnetic fields. © 2013 IAEA, Vienna.

The FIREX-1 project, the goal of which is to demonstrate fuel heating up to 5 keV by fast ignition scheme, has been carried out since 2003 including construction and tuning of LFEX laser and integrated experiments. Implosion and heating experiment of Fast Ignition targets have been performed since 2009 with Gekko-XII and LFEX lasers. A deuterated polystyrene shell target was imploded with the 0.53- μm Gekko-XII, and the 1.053- μm beam of the LFEX laser was injected through a gold cone attached to the shell to generate hot electrons to heat the imploded fuel plasma. Pulse contrast ratio of the LFEX beam was significantly improved. Also a variety of plasma diagnostic instruments were developed to be compatible with harsh environment of intense hard x-rays (γ rays) and electromagnetic pulses due to the intense LFEX beam on the target. Large background signals around the DD neutron signal in time-of-flight record of neutron detector were found to consist of neutrons via (γ,n) reactions and scattered gamma rays. Enhanced neutron yield was confirmed by carefully eliminating such backgrounds. Neutron enhancement up to 3.5 × 107 was observed. Heating efficiency was estimated to be 10-20% assuming a uniform temperature rise model. © Owned by the authors, published by EDP Sciences, 2013.

Absolute Kα line spectroscopy is proposed to study laser-plasma interactions taking place in cone-guided fast ignition targets. A transmission-type spectrometer was developed, and its absolute sensitivity was measured with laser-generated x-rays and radioisotopes, showing good agreement with theoretical predictions. The absolute yield of Au Kα line was mesured in the fast ignition experimental campaign perfomed at ILE, Osaka University. Assuming a single Maxwellian electron spectrum and one-way travel of hot electrons through the cone, energy transfer efficiency of incident LFEX laser to hot electrons was derived. © Owned by the authors, published by EDP Sciences, 2013.

The experiments to simulate astrophysical jet generation are performed using Gekko XII (GXII) HIPER laser system at the Institute of Laser Engineering. In the experiments a fast plasma flow generated by shooting a CH plane (10 μm thickness) is observed at the rear side of the plane. By separating the focal spot of the main beams, a non-uniform plasma is generated. The non-uniform plasma flow in an external magnetic field (0.2∼0.3 T) perpendicular to the plasma is more collimated than that without the external magnetic field. The plasma β, the ratio between the plasma and magnetic pressure, is ≠1, and the magnetic Reynolds number is ∼150 in the collimated plasma. It is considered that the magnetic field is distorted by the plasma flow and enhances the jet collimation. © Owned by the authors, published by EDP Sciences, 2013.

We improved diagnostic instruments to measure X-ray images in a hard X-ray harsh environment and succeeded in obtaining clear images with X-ray framing camera and X-ray streak camera in fast ignition experiment conducted in 2011 (FG-02 Experimental Campaign). We found that high-energy X-ray signals could be used as an indicator of the LFEX laser injection time relative to the imploded core. The LFEX laser injection time was estimated with better than 10 ps accuracy. Time-resolved 2D X-ray images suggested that shapes and motions of imploded core plasmas were improved by changing the configuration of the implosion lasers. © Owned by the authors, published by EDP Sciences, 2013.

Ground-based tests involving atomic-oxygen-induced erosion, which are intended to simulate the neutral gas environment in low Earth orbit, often result in disagreement between ground-based data and space data for certain materials. This disagreement is due to differences in the atomic oxygen test environments in space and in the laboratory. The imaging plate was a position-sensitive detector such that the EUV spectrum was obtained by converting the position on the imaging plate to a wavelength. Its calibration was carried out using Ar as a source gas. The EUV spectrum emitted from laser-induced oxygen plasma in a laser-detonation atomic oxygen beam source was measured using a grazing-angle flat-field spectrometer. EUV spectrum from oxygen plasma and time-of-flight distribution of the atomic oxygen beam were simultaneously measured. The experimental results clearly indicated that many spectral lines between 30 and 50nm were present in the photon emission from the laser-induced oxygen plasma.

Implosion and heating experiments at the Institute of Laser Engineering, Osaka University on Fast Ignition (FI) targets for the FIREX-1 project have been performed with Gekko-XII laser for implosions and LFEX laser for heating. We tried to reduce the prepulse level in the LFEX laser system and have improved the plasma diagnostics to observe the plasma in the harsh hard X-ray environment. A plastic (CD) shell target, 7-μm thick and 500 μm in diameter with a hollow gold cone was used in this experiment to guide the short-pulse laser at the time of the maximum compression. The shell target was imploded with 9 or 12 beams of Gekko-XII laser (527 nm) with energy of 300 J/beam in a 1.5 ns pulse. Two of the four LFEX laser (1053 nm) beams were injected into the inside bottom of the cone with an energy up to 0.7 kJ/beam in a 1.5 ps pulse at the time around the maximum implosion. We have observed neutron enhancement up to 3.5 × 10 7 with total heating energy of 300 J, which is higher than the yield obtained in the previous experiment in 2002 [R. Kodama et al. Nature 418, 933 (2002)]. We found the estimated heating efficiency is at a level of 10-20%. Fuel heating to 5 keV is expected when the full output of LFEX is used. © 2012 Elsevier B.V.

The fast ignition realization experiment (FIREX) project is progressing. The new short pulse laser system, LFEX laser, has been completely assembled and one of the four beamlets is now in operation. A fast-ignition experiment was performed using this single short pulse combined with the Gekko XII implosion laser. The energy of the GXII implosion laser was about 2 kJ and the pulse width was 1.5 ns. The energy of the LFEX laser was increased upto 800 J and two pulse durations 5 and 1.6 ps were compared. Targets were deuterated plastic shells with gold cones. It was found that the neutron yield was increased by a factor of 30 as a result of the fast electron-induced heating in LFEX 1.6 ps shot. The estimated coupling efficiency between the LFEX laser pulse and the compressed fuel was low (less than 5%). This may be due to pre-plasma formed by light arriving at the target before the main laser pulse. Further investigations and attempts to overcome these problems are now in progress. © 2011 Elsevier B.V.

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. © 2011 The Japan Society of Applied Physics.

Based on the successful result of fast heating of a shell target with a cone for heating beam injection at Osaka University in 2002 using the PW laser (Kodama et al 2002 Nature 418 933), the FIREX-1 project was started in 2004. Its goal is to demonstrate fuel heating up to 5 keV using an upgraded heating laser beam. For this purpose, the LFEX laser, which can deliver an energy up to10 kJ in a 0.5-20 ps pulse at its full spec, has been constructed in addition to the Gekko-XII laser system at the Institute of Laser Engineering, Osaka University. It has been activated and became operational since 2009. Following the previous experiment with the PW laser, upgraded integrated experiments of fast ignition have been started using the LFEX laser with an energy up to 1 kJ in 2009 and 2 kJ in 2010 in a 1-5 ps 1.053 μm pulse. Experimental results including implosion of the shell target by Gekko-XII, heating of the imploded fuel core by LFEX laser injection, and increase of the neutron yield due to fast heating compared with no heating have been achieved. Results in the 2009 experiment indicated that the heating efficiency was 3-5%, much lower than the 20-30% expected from the previous 2002 data. It was attributed to the very hot electrons generated in a long scale length plasma in the cone preformed with a prepulse in the LFEX beam. The prepulse level was significantly reduced in the 2010 experiment to improve the heating efficiency. Also we have improved the plasma diagnostics significantly which enabled us to observe the plasma even in the hard x-ray harsh environment. In the 2010 experiment, we have observed neutron enhancement up to 3.5 × 10 7 with total heating energy of 300 J on the target, which is higher than the yield obtained in the 2009 experiment and the previous data in 2002. We found the estimated heating efficiency to be at a level of 10-20%. 5 keV heating is expected at the full output of the LFEX laser by controlling the heating efficiency. © 2011 IOP Publishing Ltd.

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.

The high energetic electron measurement is one of the most important issues to research the ignition mechanism in the Fast Ignition Realization EXperiment Project. It is also important for the energy spectra with angular distribution because the electron spread is different by the target design. Therefore we have been developed the compact Electron SpectroMeter so as to be installed on different angular potions. We have performed the calibration using L-band LINAC in the Institute of Scientific and Industrial Research, Osaka University. The analyzer has been tested to measure energetic electrons from the aluminum and gold plain targets irradiated by LFEX laser (maximum energy of 10 kJ) up to 800 J. The electron measurement has been performed at the integrated experiments using CD-shell with Au cone. The non-Maxwellian spectrum can be observed when the effective core heating by the electron is occurred. © 2010 IOP Publishing Ltd.

Thermonuclear ignition and subsequent burn are key physics for achieving laser fusion. In fast ignition, a highly compressed fusion fuel generated with multiple ns-laser beams is rapidly heated with a large energy, ps-laser pulse in prior to core disassembly. This scheme has a high potential to achieve ignition and burn since driver energy required for high fusion gain is predicted to be about one tenth of that needed for the central ignition scheme. In Japan, Fast Ignition Realization Experiment (FIREX) project has been started to clarify the physics of energy transport and deposition in the core plasma and to demonstrate fuel temperature of above 5 keV. After the success, FIREX-I will be followed by the second phase of the project (FIREX-II) to demonstrate ignition and burn. LFEX laser, designed to deliver a laser pulse of 10 kJ in 10 ps, are operational and the first phase of FIREX experiments has been stated. A new target is proposed to attain dense compression of fuel and improve laser-core coupling efficiency by adopting double-cone structure, a low-density inner liner, low-Z outer coating, and Br-doped fuel shell. In this paper, present status and near term prospects of the FIREX-I project will be reported together with activities on target designing, laser development, and plasma diagnostics. © 2010 American Institute of Physics.

Cryogenically cooled foam shells with deuterium and tritium fuels are expected to be utilized in the fast ignition realization experiment project of ILE, Osaka University, to demonstrate efficient heating of properly compressed fuel plasmas. These targets consist of a foam shell with solid fuel and a conical light guide for additional heating with an ultra-high intensity laser beam, in accordance with previous preliminary experiments [R. Kodama et al., Nature 412, 798 (2001).] Recent theoretical predictions and elemental experiments have suggested some advanced modifications to enhance the coupling efficiency of fast heating and improve implosion performance. The five major points of these improvements are as follows: 1) use of a low-Z foam layer on the inner surface of the cone; 2) use of a double-layered cone as a light guide; 3) use of a low-Z plastic layer on the outer surface of the cone; 4) adding a Br-doped plastic ablator to the fuel capsule; and 5) evacuation of the target center.

Implosion and heating experiments of Fast Ignition (FI) targets for FIREX-1 laser fusion project have been performed with Gekko-XII and PW/LFEX lasers at the Institute of Laser Engineering, Osaka University. Typical FI target has a hollow cone for guiding the short-pulse heating laser beam at the time of the maximum compression. The cone is mounted so as to in one-side penetrate the shell target. Detailed implosion hydrodynamics, FI heating and core plasma formation of plastic (CD) shell target with gold cone have been clarified by observing those with ultra high-speed imaging x-ray spectroscopy as well as neutron diagnostics. Multi-channel Multi-Imaging X-Ray Streak Camera (McMIXS) was improved for observation of time-resolved x-ray images and time-resolved two dimensional temperature distributions with spatial and temporal resolutions of 20 microns and 24 ps (42 Gfps), respectively. With this instrument, one can observe heating properties of the imploded core such as spatial distribution of the heated region and its temporal evolution. Also 2D-SIXS (Two-Dimensional Sampling Image X-ray Streak camera) coupled with an x-ray imager was improved for time resolved x-ray imaging of the imploded core. Synchronization of the heating beam injection to the implosion dynamics has been monitored with an x-ray framing camera. It was found that the shape of the core is neither spherical nor uniform mainly because of the existence of the cone and moving toward the tip of the cone and interacting with it. Experimental results are compared with two-dimensional hydrodynamic simulations. Target design taking into account of these phenomena is quite important because such core movement and jet formation can affect the condition of the cone. © 2009 SPIE.

Since the approval of the first phase of the Fast-Ignition Realization Experiment (FIREX-I), we have devoted our efforts to designing advanced targets and constructing a petawatt laser, which will be the most energetic petawatt laser in the world. Scientific and technological improvements are required to efficiently heat the core plasma. There are two methods that can be used to enhance the coupling efficiency of the heating laser to the thermal energy of the compressed core plasma: adding a low-Z foam layer to the inner surface of the cone and employing a double cone. The implosion performance can be improved in three ways: adding a low-Z plastic layer to the outer surface of the cone, using a Br-doped plastic ablator and evacuating the target centre. An advanced target for FIREX-I was introduced to suit these requirements. A new heating laser (LFEX) has been constructed that is capable of delivering an energy of 10 kJ in 10 ps with a 1 ps rise time. A fully integrated fast-ignition experiment is scheduled for 2009. © 2009 IAEA, Vienna.

Fast ignition scheme on laser nuclear fusion has a potential to achieve ignition and burn with about one tenth of laser energy required for these programs compared to conventional ignition scheme. The recent fast heating of a compressed core to 0.8-1 keV temperature has provided proof-of-principle of the fast ignition (FI) concept. We have launched the FI Realization EXperiment (FIREX) project at Institute of Laser Engineering. The goal of the first phase of FIREX is to demonstrate fast heating of a fusion fuel up to the ignition temperature of 5-10 keV. Several nuclear diagnostics has been developed to diagnose the heated temperature and the density of the imploded core plasma. We have developed an advanced design for a time-of-flight (TOF) neutron spectrometer and applied a wave-coincidence method to the neutron detection process to improve the signal-to-noise ratio (S/N) by a factor of 7-8 compared to the conventional TOF method was achieved. We have also developed new lithium glass scintillation material. Decay time of the material is 2-3 times faster than that of conventional Li glass detector.

© 2008 IOP Publishing Ltd. Measurement of PW laser injection time relative to the imploded core plasma by using X-ray framing camera was successfully achieved. The core plasma radii estimated from the X-ray framing camera are consistent with those estimated from X-ray streak camera and well agree with the results of 1D hydrodynamic simulation (ILESTA-1D). This means that the spatial resolution of X-ray framing camera is high enough and reliable to monitor implosion processes. PW laser injection time was observed as the bright zone on the stripline of X-ray framing camera. The measured X-ray intensity peak is consistent with that observed with X-ray streak camera. It is concluded that one can estimate PW laser injection time with a few tens of ps resolution from the peak position of X-ray intensity recorded by X-ray framing camera.

A simultaneous measurement of imploded core plasma and injection time of heating laser is conducted by using an x-ray framing camera (XFC). The experiments are performed using Gekko XII laser system for implosion of the deuterated polystyrene (CD) plastic shell target and Peta Watt (PW) laser system for heating. The time of PW laser injection is observed as the bright zone in the XFC image. The measured x-ray intensity profiles fit the Gaussian profiles well. The calculations of microchannel plate by using dynode model explain these broadened temporal profiles qualitatively. The peak position of fitted x-ray intensity profile is almost in agreement with the time when the high energy x ray is observed by x-ray streak camera. Moreover, the peak position is delayed corresponding to the delayed setting of PW laser injection time. From these results, it is concluded that we can estimate the heating laser injection time with resolution of the order of 10 ps by using XFC. © 2008 American Institute of Physics.

The ion temperature in a large diameter plasma is measured with the high-resolution optical emission spectroscopy. It is found that the ion temperature is low when the radial distribution of the plasma is flat profile compared with that in the case of peaked profile. The results of numerical calculation carried out by using the hybrid model validate the assumption of Boltzmann distribution in plasma and agree well with the experimental results. Thus, it is concluded that the decrease of the ion temperature is caused by the decrease of the radial electric field. © 2005 Elsevier Ltd. All rights reserved.

A large diameter plasma over 300 mm in diameter is produced by electron cyclotron resonance (ECR) discharges using a cylindrical vacuum chamber of 400 mm in inner diameter. It is found that the plasma uniformity is improved by adding the nitrogen gas to pure Ar plasma. The electron temperature is decreased by adding the nitrogen gas. It is considered that the electron energy is absorbed in the vibrational energy of nitrogen molecules and the electron temperature decreases. Therefore, the adjunction of the nitrogen gas is considered to be effective for producing uniform and low electron temperature plasma. © 2005 Elsevier B.V. All rights reserved.

The ion temperature in a large diameter plasma is measured with the high-resolution optical emission spectroscopy. It is found that the ion temperature is low when the radial distribution of the plasma is flat profile compared with that in the case of peaked profile. The results of numerical calculation carried out by using the hybrid model agree well with the experimental results. It is found that the calculated ion temperature increases as the radial electric field increases. Thus, it is concluded that the decrease of the ion temperature is due to the decrease of the radial electric field. © 2005 Elsevier B.V. All rights reserved.

The temporal evolution of nano-structures in mixing the aqueous solutions of anionic and cationic surfactants was investigated by measuring time-resolved SAXS spectra. It is found that vesicles formed just after mixing annihilate to be followed by the lamella formation. The peak intensity due to the vesicle structure decays exponentially with an elapsing time. The peak intensity assigned to the lamella structure grows with a power law of time. The decay time of vesicle and the exponent of power function of time describing the lamella growth increase with NaCl concentration. These results indicate that the electrostatic interaction affects the stability of nano-structures. © 2006 American Institute of Physics.

Time-resolved SAXS spectra emerged from the nano-structure formed after mixing of cationic dodecyltrimethylammonium chloride (DTAC) and anionic sodium dodecylsulfate (SDS) solutions were investigated. The catanionics with equal length tails are known to exhibit a lamella structure at equilibrium. In the present investigation, however, we found that a vesicle structure formed immediately after mixing (t=0.038 see) and a lamella structure grew later with time elapsed after mixing. It is found that the peak intensity identified with vesicle exponentially decays with time. The decay time T increases with NaCl concentration of the mixture. This result indicates that the vesicles are stabilized by the shielding of the electrostatic interaction due to the added salt. On the other hand, the peak intensity identified with lamella is described by a power law of time and the exponent of the power function is found to increase with NaCl concentration.

The ion temperature in N2/Ar and O2/Ar electron cyclotron resonance (ECR) plasma is measured by high-resolution optical emission spectroscopy for pressure of 0.27 Pa and microwave power of 2.4 kW. It is found that as the nitrogen gas concentration is increased, the ion temperature in N2/Ar ECR plasma decreases drastically and the uniformity of the radial electron density distribution improves. It is considered that the decrease of the ion temperature in N2 /Ar ECR plasma is caused by the decrease of the radial electric field. In the case of O2/Ar ECR plasma, the ion temperature increases as the oxygen gas concentration is increased. It is considered that the increase of the ion temperature in O2/Ar ECR plasma is caused by energy exchange between electrons and ions because the electron temperature considerably increases with increasing of the oxygen concentration. © 2004 Elsevier B.V. All rights reserved.

The effect of the boundary condition on chaotic behavior of the fluctuation observed in an electron cyclotron resonance plasma is investigated by chaos analysis using measured time series data. It is found that when a stainless cage of 290mm in diameter and 500mm in length is introduced in the chamber, the fluctuation changes from turbulent state to chaotic state in high microwave power region while it changes from chaotic state to periodic state in low microwave power region. This result suggests that the geometry of the cage affects the state of the instability. Moreover, it is found that the superposition of multicusped fields created by small permanent magnets reduces the chaotic dimension of the instability. ©2005 The Physical Society of Japan.

The experiments and simulations on the control of the plasma parameters are performed using large diameter electron cyclotron resonance (ECR) plasmas. It is found that the plasma parameters are controlled by diluting with N2 gas in the mirror magnetic field. The electron temperature (Te) decreases down to 40% and the electron density (ne) increases up to 80%, respectively, that is, a low Te ECR plasma with high ne is realized. Furthermore, the Te control is attempted by changing the spatial profile of the microwave power absorption. It is observed that Te decreases with changing the power absorption profile that is achieved by changing the external conditions such as incident microwave power, magnetic field configuration, and incident microwave frequency. The production mechanism of an ECR plasma with plasma parameter variable is also discussed. © 2004 Elsevier B.V. All rights reserved.

Ion temperatures in N2/Ar and O2/Ar electron cyclotron resonance (ECR) plasmas have been measured with high-resolution optical emission spectroscopy. It was found that the Ar ion temperature in N2/Ar plasma decreased drastically as the nitrogen gas concentration was increased, while the electron temperature slightly increased. The uniformity of the radial electron density distribution also increased with increasing the nitrogen gas concentration. These results suggest that the radial electric field decreased with increasing the nitrogen gas concentration, and as a result, the transverse ion temperature in N2/Ar plasma decreased. On the other hand, the ion temperature in O2/Ar ECR plasma increased as the oxygen gas concentration was increased and the electron temperature considerably increased. This increase in the electron temperature may be caused by generation of negative ions. As the negative ion generation affects the electron density and hence the electron temperature, the ion temperature in O2/Ar plasma is increased with increasing the oxygen gas concentration. © 2004 Elsevier Ltd. All rights reserved.

The ion temperature in 2.45 GHz electron cyclotron resonance (ECR) Ar/N2 plasma was measured with a high-resolution optical emission spectroscopy. It was found that the ion temperature decreased from 0.6 to 0.03 eV as the nitrogen gas concentration was increased. It was also found that the uniformity of the electron density was improved by adding the nitrogen gas. Furthermore, the ion temperature in 915 MHz ECR plasma was measured and the similar result was obtained. In this case, the ion temperature was low compared with that in 2.45 GHz ECR plasma. © 2003 Elsevier Science B.V. All rights reserved.

The behavior of the fluctuation observed in an electron cyclotron resonance plasma was presented. It was found that the amplitude of the fluctuation increased with increasing the incident microwave power and decreasing the gas pressure. The choas analysis using time series data showed that the fluctuation was in turbulent state in the high microwave power region and chaotic state in the low microwave power region.

The mechanism to generate a low-electron-temperature electron cyclotron resonance plasma using magnetic filed and mixture ratio was investigated by means of simulation and experiment. As the working gas, a mixture of argon and nitrogen was used under the assumption of plasma nitriding. The results showed that the application of the magnetic mirror was valid for decreasing the electron temperature due to both effects of plasma confinement and temperature anisotropy. Furthermore, the addition of nitrogen was found to be effective to decrease the electron temperature approximately 2 eV due to the vibrational excitation of nitrogen molecules by electron impact. © 2003 Elsevier Science B.V. All rights reserved.

In general, electron temperature is an important plasma parameter which has much influence in the film property. In this paper, the mechanism for decreasing the electron temperature in an electron cyclotron resonance plasma is numerically investigated using a fluid model. A mixture of argon and nitrogen is used as the working gas under the assumption of plasma nitridation. The simulation was carried out with typical magnetic field configurations and various mixture ratios. As a result, it was found that the application of magnetic mirror was suitable for the production of a low-electron-temperature plasma. Besides, the calculation results indicated that the addition of nitrogen was effective to decrease the electron temperature approximately 2 eV due to the vibrational excitation of nitrogen molecules by electron impact. © 2003 Elsevier Science B.V. All rights reserved.