In order to establish a compact all-optical Thomson scattering source, experimental studies were conducted on the 45 TW Ti: sapphire laser facility. By including a steel wafer, mixed gas, and plasma mirror into a double-exit jet, several mechanisms, such as shock-assisted ionization injection, ionization injection, and driving laser reflection, were integrated into one source. So, the source of complexity was remarkably reduced. Electron bunches with central energy fluctuating from 90 to 160 MeV can be produced. Plasma mirrors were used to reflect the driving laser. The scattering of the reflected laser on the electron bunches led to the generation of X-ray photons. Through comparing the X-ray spots under different experimental conditions, it is confirmed that the X-ray photons are generated by Thomson scattering. For further application, the energy spectra and source size of the Thomson scattering source were measured. The unfolded spectrum contains a large amount of low-energy photons besides a peak near 67 keV. Through importing the electron energy spectrum into the Monte Carlo simulation code, the different contributions of the photons with small and large emitting angles can be used to explain the origin of the unfolded spectrum. The maximum photon energy extended to about 500 keV. The total photon production was 107/pulse. The FWHM source size was about 12 μm.

Short-pulse, ultrahigh-intensity lasers have opened new regimes for studying fusion plasmas and creating novel ultrashort ion beams and neutron sources. Diagnosing the plasma in these experiments is important for optimizing the fusion yield but difficult due to the picosecond time scales, 10 s of micron-cubed volumes, and high densities. We propose to use the yields of photons and neutrons produced by parallel reactions involving the same reactants to diagnose the plasma conditions and predict the yields of specific reactions of interest. In this work, we focus on verifying the yield of the high-interest aneutronic proton-boron fusion reaction ${}^{11}B{\left(p,2\alpha \right)}^{4}He$, which is difficult to measure directly due to the short stopping range of the produced αs in most materials. We identify promising photon-producing reactions for this purpose and compute the ratios of the photon yield to the α yield as a function of plasma parameters. In beam-fusion experiments, the 11C yield is an easily-measurable observable to verify the α yield. In light of our results, improving and extending measurements of the cross-sections for these parallel reactions are important steps to gain greater control over these laser-driven fusion plasmas.

Energy loss of protons with 90 and 100 keV energies penetrating through a hydrogen plasma target has been measured, where the electron density of the plasma is about 1016 cm−3 and the electron temperature is about 1-2 eV. It is found that the energy loss of protons in the plasma is obviously larger than that in cold gas and the experimental results based on the Bethe model calculations can be demonstrated by the variation of effective charge of protons in the hydrogen plasma. The effective charge remains 1 for 100 keV protons, while the value for 90 keV protons decreases to be about 0.92. Moreover, two empirical formulae are employed to extract the effective charge.

Based on the path encoding pulse compression teleology, a novel method for obtaining high-power microwave (HPM) pulse with ultrahigh repetition frequency is proposed in this paper. The mechanism of the path encoding pulse compression teleology is first introduced. And then, the obtained HPM pulse is analyzed. Theoretical analysis shows that the peak power of MW level and the repetition frequency of MHz level for the generated HPM pulse can be easily reached. To demonstrate the effectiveness of this method for obtaining HPM pulse with ultrahigh repetition frequency characteristic, a HPM-obtaining experiment was carried out based on an S-band microwave source. The HPM pulses with the width of 1 ns, 2 ns, and 3 ns are studied, respectively. The measured results show that the HPM pulse with the power higher than 100 kW and the repetition frequency of 250 kHz at the frequency of 2.856 GHz is easily obtained. The repetition frequency of the generated HPM pulse can be easily changed. Because the pulse with the power higher than 100 kW and the repetition frequency of several hundreds of kHz is obtained for the first time, this type of pulse will have a broad prospect of application in the communication, radar, and electronic countermeasure fields. In addition, the effect experiment of interfering communication and control links was carried out by utilizing the ultrahigh repetition frequency characteristic of the generated HPM pulse. Also, the experiment results show the feasibility of this pulse for interfering the communication and control links.

This study is the further research of the path encoding pulse compression technique. In this study, the regularity of pulse compression gain is studied by adopting the numerical simulation and experiment measurement methods. For the lossless cavity, the power gain has the characteristic of equal pulse length with equal compression gain contribution according to the numerical simulation results. It means that the pulse compression gain is increased linearly along with the time length of the input pulse. The obtained pulse power gains are equal for the two subpulses intercepted arbitrarily form the input pulse with equal time length for the pulse compression. For the lossy cavity, the power gain usually does not increase significantly after the length of input pulse reaches to a certain value. The gain contribution decreases gradually along with the increase of time length of input pulse until the growth rate of gain contribution equals to zero. Assuming two subpulses with equal time length were intercepted from the input pulse, the gain contribution of the earlier subpulse is lower than that of the later subpulse. The measured results verified the simulated gain contribution regularity according to the established experimental system.

A 3D verification and validation suite of test problems is presented and used to evaluate hydrodynamic methods within a radiation hydrodynamics code, xRAGE. These test problems exercise different levels of complexity, building towards ICF problems which in addition to hydrodynamics also include three temperature plasma physics, thermal conduction, and radiation diffusion. Among the problems in the test suite are the Kidder ball problem, the Verney shell problem, and a 5-material compression problem, which exercise different purely hydrodynamic methods implemented within xRAGE. There is excellent agreement between 2D and 3D XRAGE simulation results and between the xRAGE results and the benchmark solutions. Two 3D ICF test problems are also presented, based on an OMEGA direct drive capsule experiment and on a NIF indirect drive capsule experiment. It is demonstrated that the newer unsplit hydrodynamic method in xRAGE produces more vorticity relative to the older default method. For the indirect drive capsule, the 3D simulations are in reasonable agreement with the experimental values of ion temperature and neutron production.

Porous materials have peculiar characteristics that are relevant for inertial confinement fusion (ICF). Among them, chemically produced foams are proved to be able to smooth the laser inhomogeneities and to increase the coupling of the laser with the target. Foams realized with other elements and techniques may prove useful as well for ICF applications. In this work, we explore the potential of a novel class of porous materials for ICF, namely, carbon nanofoams produced with the pulsed laser deposition (PLD) technique, by means of hydrodynamic numerical simulations. By comparison with a simulation of solid-density carbon, PLD nanofoams show a higher pressure at the shock front, which could make them potential good candidates as ablators for a capsule for direct-drive fusion.

Effects of solid nanolayers embedded in a near-critical density plasma on the laser-driven collisionless shock acceleration are investigated by using two-dimensional particle-in-cell simulations. Due to the interaction of nanolayers and the incident laser, an additional number of hot electrons are generated and an inhomogeneous magnetic field is induced. As a result, the collisionless shock is reinforced within the nanolayer gaps compared to the target without the structured nanolayers. When the laser intensity is 9.8 × 1019 W/cm2, the amplitude of the electrostatic field is increased by 30% and the shock velocity is increased from 0.079c to 0.091c, leading to an enhancement of the peak energy and the cutoff energy of accelerated protons, from 6.9 MeV to 9.1 MeV and 12.2 MeV to 20.0 MeV, respectively. Furthermore, the effects of the width of the nanolayer gaps are studied, by adjusting the gap width of nanolayers, and optimal nanolayer setups for collisionless shock acceleration can be acquired.

Laser-induced damage threshold is the main limitation for fused silica optics in high-power laser applications. The existence of various defects near the surface is the key factor for the degradation of the threshold. In this work, the photoluminescence spectra at different regions of the damaged and recovered fused silica samples are recorded to analyze the correlation between photoluminescence of surface defects and laser-induced damage threshold. The experimental data concluded the inverse proportional correlation between fluorescence and laser-induced damage threshold value. The weak photoluminescence is the guarantee of the high laser-induced damage threshold, and then the higher local Si nanocluster concentration corresponds with the higher laser-induced damage threshold value for the fused silica optics after CO2 laser treatment. The investigation reveals that photoluminescence measurement can be employed to check the quality of pristine fused silica and evaluate the tendency of the laser-induced damage threshold value. The current results are helpful for understanding the evolution of interaction from CO2 laser treatment and fused silica optics and can provide the guide of process technology for the high quality of fused silica optics.

Laser-driven wakefield acceleration (LWFA) has attracted lots of attention in recent years. However, few writers have been able to make systematic research into the bow waves generated along with the wake waves. Research about the bow waves will help to improve the understanding about the motion of the electrons near the wake waves. In addition, the relativistic energetic electron density peaks have great potential in electron acceleration and reflecting flying mirrors. In this paper, the bow waves generated in laser-plasma interactions as well as the effects of different laser and plasma parameters are investigated. Multidimensional particle-in-cell simulations are made to present the wake waves and bow waves by showing the electron density and momentum distribution as well as the electric field along x and y directions. The evolution of the bow wave structure is investigated by measuring the open angle between the bow wave and the wake wave cavity. The angle as well as the peak electron density and transverse momentum is demonstrated with respect to different laser intensities, spot sizes, plasma densities, and preplasma lengths. The density peak emits high-order harmonics up to 150 orders and can be a new kind of “flying mirror” to generate higher order harmonics. The study on the bow waves is important for further investigation on the electron motion around the wake waves, generation of dense electron beams, generation of high-order harmonics, and other research and applications based on the bow waves.

We investigate the production of intense ү-rays following the interaction of ultraintense laser pulse with a hybrid combination of under-dense plasma associated with a thin foil of fully ionized Al or Cu or Au at the rear side. Relativistic electrons are accelerated following the interaction of high intensity laser pulses with an under-dense plasma. These electrons are then stopped by the thin foils attached to the rear side of the under-dense plasma. This results in the production of intense-ray bursts. So, the enhancement of photon generation is due to the under-dense plasma electrons interacting with different over-dense plasma. Using open-source PIC code EPOCH, we study the effect of different electron densities in the under-plasma on photon emission. Photon emission enhancement is observed by increasing the target Z in the hybrid structure. Hybrid structure can enhance photon emission; it can increase the photon energy and yield and improve photon beam divergence. Simulations were also performed to find the optimal under-dense plasma density for ү-ray production.

The two-dimensional snake scanning of the CCD method provides an effective solution to measure small-scale light spots which are smaller than one CCD pixel. The influences of the A/D conversion digits and response uniformity of the CCD on the measurement error are studied. When the A/D conversion digit is 20, the measurement error can be ignored. The maximum error value of the nonuniform response of the CCD pixel when the order of the super-Gaussian function is 10 is 0.7 μm. The research results can be used to guide the experiment.

The topic of proton-boron fusion has recently attracted considerable interest in the scientific community, both for its future perspectives for energy production and for nearer-term possibilities to realize high-brightness α-particle sources. Very interesting experimental results have been obtained, in particular in laser-driven experiments but also using other experimental approaches. The goal of this special issue is to collect the most recent developments in experiments, theory, advanced targetry, diagnostics, and numerical simulation codes.

A transmission line circuit model was conducted to compare the performances of the two-level 2.5 Ω magnetically insulated transmission lines (MITLs) system of a 5-MA linear-transformer-driver (LTD) accelerator for two kinds of typical loads, including bremsstrahlung electron beam diodes and Z-pinch loads. Both the electron current loss in the pulse front during the magnetic insulation setup process and the electron flow distribution in the magnetic insulation steady state were analyzed. When the accelerator drives an electron beam diode load with impedance of 1.20 Ω (a single level), the duration of the magnetic insulation setup is about 12 ns, the current loss is about 130 kA in a single MITL level, the maximum electron flow current is about 50 kA in the end of MITL, and its amplitude decreases gradually after the steady magnetic insulation is established. When the accelerator drives a Z-pinch load with length of 1.5 cm, radius of 1.2 cm, and mass of 0.3 mg/cm, the duration of the magnetic insulation setup is almost zero, the maximum electron flow current in the end of MITL can reach about 55 kA (a single level), and the waveform of the electron flow resembles a saddle shape, which reaches the peak at the pinch stagnation time.

Here, we report the generation of MeV alpha-particles from H-11B fusion initiated by laser-accelerated boron ions. Boron ions with maximum energy of 6 MeV and fluence of 109/MeV/sr@5 MeV were generated from 60 nm-thick self-supporting boron nanofoils irradiated by 1 J femtosecond pulses at an intensity of 1019 W/cm2. By bombarding secondary hydrogenous targets with the boron ions, 3 × 105/sr alpha-particles from H-11B fusion were registered, which is consistent with the theoretical yield calculated from the measured boron energy spectra. Our results demonstrated an alternative way toward ultrashort MeV alpha-particle sources employing compact femtosecond lasers. The ion acceleration and product measurement scheme are referential for the studies on the ion stopping power and cross section of the H-11B reaction in solid or plasma.

The Lawson criterion for proton-boron (p-11B) thermonuclear fusion is substantially higher than that for deuterium-tritium (DT) because the fusion cross section is lower and peaks at higher ion energies. The Maxwellian averaged p-11B reactivity peaks at several hundred keV, where bremsstrahlung radiation emission may dominate over fusion reactions if electrons and ions are in thermal equilibrium and the losses are unrestricted. Nonequilibrium burn has often been suggested to realize the benefits of this aneutronic reaction, but the predominance of elastic scattering over fusion reactivity makes this difficult to achieve. The development of ultrashort pulse lasers (USPL) has opened new possibilities for initiating nonequilibrium thermonuclear burns and significant numbers of p-11B alpha particles have been reported from several experiments. We present an analysis that shows that these significant alpha yields are the result of beam fusion reactions that do not scale to net energy gain. We further find that the yields can be explained by experimental parameters and recently updated cross sections such that a postulated avalanche mechanism is not required. We use this analysis to understand the underlying physics of USPL-driven nonequilibrium fusion reactions and whether they can be used to initiate fusion burns. We conclude by outlining a path to increasing the p-11B reactivity towards the goal of achieving ignition and describing the design principles that we will use to develop a computational point design.

A compact high-power ultra-wideband bipolar pulse generator based on a modified Marx circuit is designed, which is mainly composed of a primary power supply, Marx generator, sharpening and cutoff subnanosecond spark gap switches, and coaxial transmission lines. The Marx generator with modified circuit structure has thirty-two stages and is composed of eight disk-like modules. Each module consists of four capacitors, two spark gap switches, four charging inductors, and a mechanical support. To simplify the design of the charging structure and reduce the number of switches, four groups of inductors are used to charge the capacitors of the Marx generator, two of which are used for positive voltage charging and the other two for negative voltage charging. When the capacitor of each stage is charged to 35 kV, the maximum output peak voltage can reach 1 MV when the Marx generator is open circuit. The high-voltage pulse generated by the Marx generator charges the transmission line and forms a bipolar pulse through sharpening and cutoff switches. All transmission lines used for bipolar pulse generation have an impedance of 10 Ω. When the 950 kV pulse voltage generated by the Marx generator is fed into the transmission line, the bipolar pulse peak voltage can reach 390 kV, the center frequency of the pulse is about 400 MHz, and the output peak power is about 15.2 GW.

We present a novel method that we call FAINE, fast artificial intelligence neutron detection system. FAINE automatically classifies tracks of fast neutrons on CR-39 detectors using a deep learning model. This method was demonstrated using a LANDAUER Neutrak® fast neutron dosimetry system, which is installed in the External Dosimetry Laboratory (EDL) at Soreq Nuclear Research Center (SNRC). In modern fast neutron dosimetry systems, after the preliminary stages of etching and imaging of the CR-39 detectors, the third stage uses various types of computer vision systems combined with a manual revision to count the CR-39 tracks and then convert them to a dose in mSv units. Our method enhances these modern systems by introducing an innovative algorithm, which uses deep learning to classify all CR-39 tracks as either real neutron tracks or any other sign such as dirt, scratches, or even cleaning remainders. This new algorithm makes the third stage of manual CR-39 tracks revision superfluous and provides a completely repeatable and accurate way of measuring either neutrons flux or dose. The experimental results show a total accuracy rate of 96.7% for the true positive tracks and true negative tracks detected by our new algorithm against the current method, which uses computer vision followed by manual revision. This algorithm is now in the process of calibration for both alpha-particles detection and fast neutron spectrometry classification and is expected to be very useful in analyzing results of proton-boron11 fusion experiments. Being fully automatic, the new algorithm will enhance the quality assurance and effectiveness of external dosimetry, will lower the uncertainty for the reported dose measurements, and might also enable lowering the system’s detection threshold.

Transient electromagnetic field plays very important roles in the evolution of high-energy-density matter or laser plasma. Now, a new design is proposed in this paper to diagnose the transient magnetic field, using relativistic electron bunch as a probe based on high-energy electron radiography. And based on this scheme, the continuous distribution of magnetic strength field can be snapshotted. For 1 mm thick quadrupole magnet model measured by 50 MeV probe electron beams, the simulation result indicates that this diagnosis has spatial resolution better than 4 microns and high measurement accuracy for strong magnetic strength and high magnetic gradient field no matter whether the magnetic interaction is focusing or defocusing for the range from -510 T∗ μm to 510 T∗ μm.