To diagnose the implosion of a laser-driven-fusion target such as the symmetry, the hydrodynamic instability at the interface, a high-resolution, large field-of-view kilo-electron-volt X-ray imaging is required. A Kirkpatrick-Baez (K-B) microscope is commonly used, but its field of view is limited to a few hundred microns as the resolution decreases rapidly with the increase of the field of view. A higher resolution could be realized by using a Fresnel zone plate (FZP) for imaging. Presented in this work is a numerical study on the imaging properties of an FZP at Ti-Kα wavelength of 0.275 nm, and a comparison to a K-B imager. It is found that the FZP can realize not only a resolution better than 1 µm, but also a field-of-view larger than 20 mm when the FZP is illuminated by X-rays of spectral bandwidth less than 1.75%. These results indicate the feasibility of applying the FZP in high-resolution, large field-of-view X-ray imaging.

Optical Thomson scattering has been implemented as a diagnostic of laser ablated plumes generated with second harmonic Nd:YAG laser radiation at 532 nm. Thomson scattering data with both spatial and temporal resolution has been collected, giving both electron density, and temperature distributions within the plume as a function of time. Although the spatial profiles do not match very well for simple models assuming either isothermal or isentropic expansion, consideration of the measured ablated mass indicates an isothermal expansion fits better than an isentropic expansion and indeed, at late time, the spatial profile of temperature is almost consistent with an isothermal approximation.

Stimulated Raman forward scattering (SRFS) of an intense short pulse laser in a plasma channel formed by two pre-laser pulses is investigated. The density nonuniformity of a plasma channel increases the focusing of main laser pulse. Main laser pulse excites a plasma wave and two electromagnetic sideband waves. Laser and the sidebands exert an axial ponderomotive force on electrons driving the plasma wave. The nonlinear currents arise at sideband frequencies. The density perturbation due to plasma wave beats with the oscillatory velocity due to pump to drive the sidebands. The normalized growth rate of SRFS increases with the density nonuniformity of a plasma channel. However, in the presence of a deep plasma channel the focusing is ineffective to laser intensity, but the growth rate increases with the intensity of main laser pulse.

The paper presets the results of a study on a self-magnetically insulated ion diode with an explosive-emission potential electrode. The experiments have been carried out using the TEMP-4M accelerator, operating in a double-pulse mode: the first negative pulse (300–500 ns, 100–150 kV) followed by the second positive pulse (150 ns, 250–300 kV). The ion beam energy density was 0.3–2.5 J/cm2; the beam was composed from carbon ions (80–85%) and protons. We studied several geometries of the diode: planar and focusing strip arrangement, annular and spiral geometries. It was shown that during the second voltage pulse, a condition of magnetic insulation in the diode gap is fulfilled (B/Bcr ≥3). Using the new spiral geometry of the diode, it was possible to increase the efficiency of ion current generation due to the suppression of the electron component of the total diode current by increasing the electron transit time in the gap. We have increased the efficiency of carbon ion generation from 5–9% (in the planar strip diodes) up to 17–20% in the spiral diode. The spiral geometry of the diode makes it possible to increase the efficiency of C+ ion generation 25–30 times compared to the space-charge-limited current (Childe-Langmuir limit). This is more than two times higher than in other known geometries of self-magnetically insulated diodes. The spiral diode has a resource of more than 107 pulses.

We investigated generation of pre-formed plasma on plates and inside cone targets due to a pre-pulse before the arrival of the main ultra-intense laser pulse in the fast-ignition scheme of the inertial confinement fusion. We estimated the pre-pulse level to be 130 mJ for LFEX laser used in the 2009 FIREX experiment, and the density gradient scale length of the pre-formed plasma inside the cone target to be 27–47 microns between the critical and 1/10 of the critical density, based on the two-dimensional radiation hydrodynamic simulations. In order to reduce the generation of pre-formed plasma, we investigated a thin CH foil pre-pulse absorber, and proposed using a cone target with a pointed tip. We simulated CH plasma expansion to show that the CH foils works as a pre-pulse absorber. We also show the aluminum pointed tip of the cone target can delay the shock arrival time by 20 ps, much longer than the delay for the 10 micron thickness gold tip used in the typical implosion of GXII at Osaka University.

A detailed study of Wakefield excitation in very dense quantum plasma is presented. Electric and magnetic Wakefields have been obtained for a particular profile of the laser pulse, using perturbative technique involving orders of the incident laser beam. The Wakefields can trap electrons and accelerate them to extremely high energies. It is observed that the quantum effects significantly change the classical nature of the Wakefield. The axial and radial forces acting on a test electron due to the Wakefields have been evaluated.

The low-impedance transit-time oscillator without foils is a new high-power microwave generator. In a previous report, a radiation power of 2.7 GW at 1.64 GHz has been achieved and the corresponding power conversion efficiency is 18.75%. Recently, the further experiments are continued in our laboratory. By increasing the cathode-anode gap properly, the operating voltage of device is enhanced to about 628 kV, and the corresponding radiation power reaches 3.6 GW. The device efficiency approaches 23%. In the newest experiments, because of the higher power level, the radiation power has been obviously influenced by RF breakdown in the vicinity of the dielectric window. By using a plastic bag filled with sulfur-hexafluoride (SF6), such an influence can be minimized.

Compressed ion beams are being studied as a driver for inertial confinement fusion energy and for the creation of matter in the high-energy-density regime. In order to facilitate compression of a positive ion charge bunch longitudinally and transversely beyond the limit determined by the space-charge field of the bunch, a source of charge-neutralizing electrons must be provided. Plasma sources have been developed for the NDCX-I and NDCX-II experimental facilities, both for the 2-m-long, field-free drift regions, and for the small-diameter interior of the multi-Tesla final focus solenoid. Barium titanate based cylinders with a high dielectric coefficient are used to line the wall of the 2-m-long drift region and by applying a 9 kV pulse between the inner and outer surfaces of the cylinders, plasma with a density in the 1010 cm−3 range is formed. Results are presented from experiments using this plasma source on NDCX-I. A compact plasma source 5.1 cm long and 3.8 cm in diameter, also made using the barium titanate based material, has been developed for use in the bore of the final focus solenoid. Plasma generated near the wall of the plasma source will follow the fringing magnetic field lines of the solenoid and help to fill the bore of the magnet with plasma. Improved designs for the barium titanate plasma sources are being considered that use different inner-surface electrode materials and structures, and also use a modified electrical driver employing a spark gap crowbar switch. In addition, plasma source designs using so-called flashboard technology have been developed. In the flashboard plasma source, high density plasma is formed when the applied high voltage pulse causes a series of breakdowns between isolated copper patches aligned in rows along the surface of the 0.2 mm thick flashboard.

This paper presents a simplified theoretical model for the study of emission from laser produced plasma to better understand the processes and the factors involved in the onset of saturation in plasma emission as well as in increasing emission due to plasma confinement. This model considers that plasma emission is directly proportional to the square of plasma density, its volume, and the fraction of laser pulse absorbed through inverse Bremsstrahlung in the pre-formed plasma plume produced by the initial part of the laser. This shows that plasma density and temperature (that means the electron-ion collision frequency νei) decide the threshold for saturation in emission, which occurs for νei ≥ 1013 s−1, beyond which plasma shielding effects become dominant. Any decrease in plasma sound (expansion) velocity shows drastic enhancement in emission supporting the results obtained by magnetic as well as spatial confinement of laser produced plasma. The temporal evolution of plasma emission in the absence and presence of plasma confinement along with the effect of laser pulse duration are also discussed in the light of this model.

Long-scale preformed plasmas are generated inside the cone by the pre-pulse of the heating laser in the cone-guided fast ignition scheme and it is found that coupling efficiency from the heating laser to fast electrons especially suitable for core heating is drastically reduced by the preformed plasmas. To mitigate this serious problem, an extremely thin film is suggested to cover the entrance of the cone. This method, however, introduces long rarefied plasmas around the entrance of the cone and the main pulse must propagate through these plasmas. Therefore, fast electron characteristics produced by the main pulse could be affected, and effects of long rarefied plasmas on fast electron generation are investigated. It is found that the electron beam intensity becomes larger than that without the rarefied plasma, but the energy coupling rate from the heating laser to the core decreases due to lack of appropriate electrons for core heating. To achieve less than 10% degradation of the core electron temperature, the thin film must be expanded by irradiation of the pre-pulse so that the length and the density of rarefied plasmas become less than 500 µm and one-tenth of the critical density. A thickness of the thin film can be determined by these criteria and the intensity of the pre-pulse.

Cyclotron resonance effects on electron acceleration by two lasers of different wavelengths in the presence of a magnetic field have been investigated. Beating of two high-intensity lasers of different wavelengths, propagating in opposite direction to each other, can produce a high accelerating field gradient. An electron can be accelerated by such accelerating field to a sufficiently higher energy level. Additional energy gain has been observed due to the applied magnetic field. The magnetic field turns down the electrons to the acceleration region to extract more energy from the accelerating field produced by the beating of the lasers. At resonance, when the Larmor frequency is comparable to the laser frequency, this effect becomes more pronounced. Using some reasonable experimental parameters, we estimate the electron energy gain for this mechanism.

Production of sharply collimated high velocity outflows – plasma jets from massive planar targets by a single laser beam at PALS facility is clarified via numerical simulations. Since only a few experimental data on the intensity distribution in the interaction beam near the focus are available for the PALS facility, the laser beam profile was calculated by a numerical model of the laser system and the interaction optics. The obtained intensity profiles are used as the input for plasma dynamic simulations by our cylindrical two-dimensional fluid code PALE. Jet formation due to laser intensity profile with a minimum on the axis is demonstrated. The outflow collimation improves significantly for heavier elements, even when radiative cooling is omitted. Using an optimized interaction beam profile, a homogeneous jet with a length exceeding its diameter by several times may be reliably generated for applications in laboratory astrophysics and impact ignition studies.

The new possibility of side-on laser ignition of p-11B with negligible radioactivity encouraged to study the fusion of solid state p-7Li fuel that again turns out to be only about 10 times more difficult than the side-on ignition of solid deuterium-tritium using petawatt-picosecond laser pulses at anomalous interaction conditions if very high contrast ratio. Updated cross sections of the nuclear reaction are included.

We explore the feasibility of accelerating electron beams up to energies much beyond 1 TeV in a realistic scale and evolution of the beam qualities such as emittance and energy spread at the final beam energy on the order of 100 TeV, using the newly formulated coupled equations describing the beam dynamics and radiative damping of electrons. As an example, we present a design for a 100 TeV laser-plasma accelerator in the operating plasma density np = 1015 cm−3 and numerical solutions for evolution of the normalized emittance as well as their analytical solutions. We show that the betatron radiative damping causes very small normalized emittance that promises future applications for the high-energy frontier physics.

The electromagnetic field structures and transport properties of laser produced relativistic beam electrons propagating through Au+25, Cu+20, Al+10, and C+5 plasma foils are investigated. Simulations show that high plasma resistivity as well as high collision rate of the beam electrons with gold and copper plasmas can hinder the forward motion of the beam electrons inside the targets. However, the beam electrons can propagate for a relatively long distance in aluminum and carbon plasma targets. They are well collimated by the strong self-generated resistive magnetic field, resulting in higher sheath electric fields behind the target. The use of low-Z target material is therefore more efficient for collimating beam electrons as well as generating higher-energy ions.

The Multiphase Buoyancy-Drag model recently formulated in Balakrishnan & Menon, Laser and Particle Beams, 2011 is applied to investigate the (1) rise of dusty gas Rayleigh-Taylor bubbles into a pure gas and (2) fall of pure gas Rayleigh-Taylor spikes into a region of particles. It is demonstrated that for these two scenarios, the bubble or spike amplitude oscillates about the dusty gas/pure gas interface. The ratio of the bubble or spike amplitudes on the pure gas side to the dusty gas side, asymptotes to a constant that depends only on the initial Atwood number, A, the multiphase Atwood number, Am, and the initial wavelength of the perturbation, λo. For the same Am, the ratio decreases with A for oscillating bubbles, and vice versa for oscillating spikes.

The goal of this theory is to study the conversion of a fraction of a laser beam to its phase-mismatch second and third harmonics. This conversion takes place by focusing an intense laser beam into a transversely magnetized plasma, as a nonlinear medium. The influence of the polarization field is considered, however, the plasma density is below the critical density. It has already been revealed that for dense plasma, the second and third harmonics efficiencies decreased with density increasing in the presence of a sufficiently strong magnetic field. This result is in contrast to the under dense and weakly magnetized plasma, which the harmonics efficiencies increased with density increasing. It is shown that the harmonics radiation cut-off, when the magnetic field increases up until the saturation strength Bsat. In addition, the results indicated that the average phase-mismatch third harmonic conversion efficiency is a little smaller than the phase-match case reported for non-magnetized plasma.

In this paper, the characteristic impedance matching of the inner line and outer line of the multi-filar tape-helix Blumlein pulse forming line (BPFL) is analyzed in detail by dispersion theory of tape helix. Analysis of the spatial harmonics of multi-filar tape-helix BPFL shows that the integer harmonic numbers of the excited spatial harmonics are not continuous. In addition, the basic harmonic component still dominates the dispersion characteristics of the multi-filar tape-helix BPFL at low frequency band. The impedance mismatching phenomenon caused by the discontinuity of filling dielectrics in the inner line of BPFL is studied as an important issue. Effects of dielectric discontinuity on the coupled electromagnetic fields and the parameters of the outer line are also analyzed. The impedance matching conditions are both obtained under the situations of continuous filling dielectric and discontinuous dielectrics, respectively. Impedance characteristics of these two situations are analyzed by comparison, and effects of the thickness of support dielectric on the impedance are also presented. When the 6 mm-thickness nylon support of the multi-filar tape helix is used in the filling dielectric of de-ionized water, the characteristic impedances of the inner line and outer line of BPFL are 53 Ω and 14.7 Ω, respectively. After the improvement about substituting de-ionized water by castor oil, the relative permittivities of the support dielectric and filling dielectric are almost the same, and the impedances of the inner and outer line of BPFL become 80 Ω and 79 Ω, respectively. That is to say, the impedance mismatching problem caused by dielectric discontinuity is solved. Circuit simulation and experimental results basically correspond to the theoretical results, and the fact demonstrates that impedance analysis of the multi-filar tape-helix BPFL based on dispersion theory is correct.

We investigated a dynamic procedure for relativistic channeling by a linearly polarized ultraintense laser pulse in overdense plasma, subsequently determining a phenomenological formula for the channel-digging speed. Channeling of the linearly polarized pulse usually results in a sharp-cut (non-adiabatic) pulse front, since the pulse is continuously reflected on the transparency-opacity interface during the channeling process. Using the novel formula for the channel-digging speed, it was possible to analytically predict where such a sharp-cut occurs longitudinally.

The current trends in stimulated Brillouin scattering and optical phase conjugation are overviewed. This report is formed by the selected papers presented in the “Fifth International Workshop on stimulated Brillouin scattering and phase conjugation 2010” in Japan. The nonlinear properties of phase conjugation based on stimulated Brillouin scattering and photo-refraction can compensate phase distortions in the high power laser systems, and they will also open up potentially novel laser technologies, e.g., phase stabilization, beam combination, pulse compression, ultrafast pulse shaping, and arbitrary waveform generation.