Laser Fusion Research Research Articles

Baseline design of laser fusion research reactor with MW class laser facility

We propose a sub-ignition/burning reactor which is named the Laser-fusion Subcritical Power Reactor Engineering Method (L-Supreme). The reliabilities of L-Supreme in a MW class laser facility are assessed with respect to the following points: a reactor core, a target chamber, a target delivery system, an Exhaust Detritiation System (EDS), and neutron shielding. The Japan Establishment for Power-laser Community Harvest (J-EPoCH) would be applied as a MW class laser facility. A non-cryogenic glass balloon target filled with gaseous deuterium-tritium (DT) is contained in a target capsule. A chain-type magazine system might be used for a mass supply of the target capsules. Each target capsule is delivered to the center of a reactor core at 1 Hz. A batch of 10 000 laser shots would realize 0.22 MJ fusion power. The amount of tritium per batch is 1.51 × 1012 Bq. During laser experiments, unburned tritium is evacuated and transferred into an Exhaust Detritiation System (EDS). An evacuation rate of more than 0.1 m3 s−1 is required in order to recover less than 5000 Bq m−3 of the threshold of tritium concentration within 1 h. For safety, emergency situations such as tritium leakage in facilities are examined. The EDS works by internal circulation processes. Assuming leakage of tritium for a batch, an air circulation flow rate of 4100 Nm3 h−1 is required in an experimental hall for recovering less than 5000 Bq m−3 within 48 h. A primary and secondary neutron shield concept are proposed and would provide full neutron shielding. We conclude that it is possible to construct the L-Supreme system by marshalling current technologies.

Optimization and application of shock wave measurement technology for shock-timing experiments on small-scale capsules

In laser fusion research, the precision of shock-timing technology is pivotal for attaining optimal adiabatic tuning during the compression phase of fusion capsules, which is crucial for ensuring the high-performance implosion. The current main technological approach for shock-timing experiments is to use keyhole targets and VISAR (velocity interferometer system for any reflector) diagnostics to measure the shock velocity history. Nonetheless, this approach encounters limitations when scaling down to smaller capsules, primarily due to the reduced effective reflection area available for VISAR diagnostics. In this work, a novel high-precision shock-timing experimental methodology is used to realize a double-step radiation-driven implosion of a 0.375 mm radius capsule on a 100 kJ laser facility. By calculating the intensity of VISAR images with spherical reflective surfaces, a new experimental technical route is proposed, i.e. using the keyhole cone reflection effect to enhance the VISAR diagnostic spatial area, which can effectively increase the effective data collection region by nearly threefold for small-scale capsules. The technique has been adeptly used to measure shock waves in cryogenic liquid-deuterium-filled capsules under shaped implosion experimental conditions, thus obtaining high-precision shock-timing experimental data. The experimental data reveal that the application of this technology can markedly enhance both the image quality and the precision of data analysis for shock wave velocity measurements in small-scale capsules. Furthermore, it is discovered that under similar laser conditions, there exist considerable variations in the shock velocity profiles. Simulation analysis shows that the difference in chasing behavior of the “<i>N</i>+1” reflected shock wave caused by small changes in laser intensity is the main reason for the significant difference in merging speed. It is demonstrated that small changes in laser parameters can significantly affect the transmission behavior of the shock wave. This experiment highlights the complex sensitivity of shock wave transmission in high-performance forming implosion physics process on a current small capsule scale, making it essential to conduct shock-timing experiments to accurately adjust actual shock wave behavior. This research not only lays a robust technical foundation for promoting adiabatic tuning experiments ofour 100 kJ laser facility but also has profound significance for the ultra-high pressure physics research based on the spherical convergence effect.

Experimental study of medical isotopes 62,64Cu and 68Ga production using intense picosecond laser pulse

Radioisotopes are indispensable agents in medical diagnosis and treatment, among which copper-62, 64 (62,64Cu) and gallium-68 (68Ga) are medical isotopes widely used in positron emission tomography (PET) imaging. Experiments that generate these radioisotopes via laser-induced photonuclear reactions were performed on the XingGuangIII laser facility of the Laser Fusion Research Center in Mianyang. High-charge ( ∼ 40 nC) MeV electron (e− ) beams were generated with 100 terawatts, picosecond laser pulses. The e− beams were then impinged on a metal stack composed of Ta foil and activation plates (natural Cu and Ga2O3), producing high-energy bremsstrahlung x-rays and medical isotopes 62,64Cu and 68Ga, respectively. The characteristic emissions of the produced 62,64Cu and 68Ga were detected off-line , and the production yields of 62,64Cu and 68Ga were obtained to be of the order of 106 per laser shot. For electrons with energy higher than 8 MeV, the dependence of isotope production efficiency (per e− ) on electron temperature () is investigated through Geant4 simulations. It is found that the production efficiency increases with the . At ∼ 10 MeV, the values are 10−4 for 62Cu and 2 × 10 − 5 for 68Ga, respectively. The prospect of producing the medical isotopes 62,64Cu and 68Ga are further evaluated using a table-top femtosecond laser system of high repetition. With a repetition rate of 100 Hz, their activity is expected to reach 0.2 GBq for 62Cu, 0.1 GBq for 64Cu and 0.05 GBq for 68Ga, respectively. Such activity would meet the required dose for clinical PET imaging, indicating the great potential to produce medical isotopes with an all-optical, high-repetition laser system.

An active dose-measuring device for X-rays generated by ultra-short, ultra-intense laser pulses

Ultra-short, ultra-intense laser pulses can create extreme physical conditions for a wide range of applications in atomic and molecular physics, materials chemistry, and inertial-confinement fusion. However, laser-matter interactions can be accompanied by significant X-ray emission that introduces radiation risks to the nearby environment and personnel. It is usually to monitor the radiation dose during in high-intensity laser-target interactions with optically stimulated luminescence and thermo-luminescence devices. However, these passive methods cannot measure the radiation dose in real time, while most active dosimeters cannot accurately measure pulsed radiation doses. Here, transient pulse X-ray radiation doses are converted by CdWO4 crystals into slow signals. Because the crystals have a 14-μs luminescence decay time, they can absorb sub-nanosecond X-ray pulses and release the energy at a 100-μs rate, thus reducing the linear-response pressure of subsequent devices. A pulse detector based on a CdWO4 crystal, a phototube, and a custom signal-processing circuit was developed. Experiments were performed at the 45-TW femtosecond laser facility of the Laser Fusion Research Center. The detector deviation was less than ±20% relative to that of an ionization-chamber detector. This initially verified its feasibility for real-time pulsed X-ray radiation detection.

First optical Thomson scattering measurements made in Z-pinch fusion devices

Approach provides a new look into temperature and electron diagnostics for Z-pinch devices and can be ported to laser and tokamak fusion research machines.

Application of low flow rate micro gas cell nozzle in laser wakefield acceleration

After forty-year tremendous advances, laser wakefield acceleration (LWFA), in which an ultra-intense femtosecond laser interacts with a gas target to produce energetic electrons, is becoming more and more mature. Acceleration with a high repetition rate will be an important topic in the near future. When operating at a high repetition rate, the influence of the gas load on the vacuum system cannot be neglected. Among the widely used gas targets, gas cells have a lower flow rate than supersonic gas nozzles. However, most of gas cells are several centimeters long, unsuitable for a moderate-size laser facility. In this work, we design a kind of micro gas cell with a sub-centimeter length. The flow rate of the micro gas cell and the supersonic nozzle are compared by hydromechanics simulations. Comparing with the supersonic nozzle, the flow rate of the micro gas cell is reduced by 97%. Moreover, the gas cell sustains a longer flattop region. The reduced flow rate is attributed to two reasons. The first reason is that the area of the nozzle exit decreases significantly. In the case of the supersonic nozzle, the laser interacts with the gas jet outside the nozzle exit. Therefore, the exit size is determined by the interaction length. In the case of the micro gas cell, the laser interacts with the gas inside the gas cell. The exit only needs to be larger than the laser focal, which is much smaller than the interaction length. The second reason is that the velocity of the gas jet decreases. When using a supersonic nozzle, the velocity at the nozzle exit must be high enough to generate a flattop density distribution, which is required by LWFA. As a comparison, in the micro gas cell, the gas is confined by the cell wall. As a consequence, the gas velocity has little influence on the density distribution inside the cell. By changing the inner radius of the cell, 1–4 mm-long flattop regions can be generated while keeping a low flow rate. Experiments using the micro gas cell are conducted on a 45 TW femtosecond laser facility at the Laser Fusion Research Center. The stable electron beams with maximum energy of 250 MeV are generated. This study will contribute to the investigation of stable and high-frequency laser wakefield acceleration.

Cross-Section Measurements of the 11B(p,α)2α Reaction near the First Resonant Energy

In preparation for an experiment with a laser-generated intense proton beam at the Laser Fusion Research Center at Mianyang to investigate the 11B(p,α)2α reaction, we performed a measurement at very low proton energy between 140 keV and 172 keV using the high-voltage platform at the Institute of Modern Physics, Lanzhou. The aim of the experiment was to test the ability to use CR-39 track detectors for cross-section measurements and to remeasure the cross-section of this reaction close to the first resonance using the thick target approach. We obtained the cross-section σ = 45.6 ± 12.5 mb near 156 keV. Our result confirms the feasibility of CR-39 type track detector for nuclear reaction measurement also in low-energy regions.

A single long electron bunch detect electromagnetic field evolution in laser plasma

Laser fusion research needs much more high-time-resolved diagnostic technologies to study the dynamic process in laser plasma. We develop a special method and setup a device to measure the electromagnetic field in the plasma by using a single electron bunch. The measurement covers the whole-time window of the plasma process driven by a 3.6 ns laser pulse. An electron source can generate a single electron bunch with 0–100 keV energy and 10ns bunch length. A laser pulse with 1 J energy and 532 nm wavelength irradiates on the edge of a silver target, the target nearby the irradiated spot is ionized into plasma. At the beginning of plasma generation, the head of the electron beam begins to pass through the plasma. Electromagnetic field in plasma pushes the electrons transversely. A high voltage pulse at a good time is used to deflect the electrons linearly in the transverse direction to avoid overlapping of the different electrons on the scintillator downstream. By analyzing the deflection distances of the different electrons in this single bunch, we succesfully achieve an average electronic field along the trajectory in the plasma in the whole plasma process. The maximum value of this electronic field is <inline-formula> <tex-math id="M2">\begin{document}$ 7.74\times {10}^{5}\;\mathrm{V}/\mathrm{m} $\end{document}</tex-math> <alternatives> <graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="1-20211374_M2.jpg"/> <graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="1-20211374_M2.png"/> </alternatives> </inline-formula>.

Probing ultrafast laser plasma processes inside solids with resonant small-angle x-ray scattering

Extreme states of matter exist throughout the universe e.g. inside planetary cores, stars or astrophysical jets. Such conditions are generated in the laboratory in the interaction of powerful lasers with solids, and their evolution can be probed with femtosecond precision using ultra-short X-ray pulses to study laboratory astrophysics, laser-fusion research or compact particle acceleration. X-ray scattering (SAXS) patterns and their asymmetries occurring at X-ray energies of atomic bound-bound transitions contain information on the volumetric nanoscopic distribution of density, ionization and temperature. Buried heavy ion structures in high intensity laser irradiated solids expand on the nanometer scale following heat diffusion, and are heated to more than 2 million Kelvin. These experiments demonstrate resonant SAXS with the aim to better characterize dynamic processes in extreme laboratory plasmas.

Research on Self-Aligning Flanges Based on Piezoelectric Actuators Applied to Precision Grinding Machines.

Laser fusion research requires a large number of high-precision large-diameter aspherical components. To improve the grinding efficiency in the component production process, the manual operation time during the grinding process needs to be reduced. The grinding process requires the installation of the dressed grinding wheel onto the grinding machine spindle, and the off-line dressing results in installation errors during the loading and unloading process, which requires more time for manual alignment. To achieve self-aligning, the circumferential contour of the grinding wheel was first restored by the reversal method, then noise reduction and circle fitting were performed to obtain the eccentricity value and eccentricity position between the flange and the spindle, and finally, the flange was adjusted finely by three piezoelectric actuators installed inside the flange to reduce the eccentricity. Three repetitive experiments were conducted to verify that the self-aligning flange can reduce the eccentricity value by retracting the piezoelectric actuators so that the proper alignment between the flange and the spindle could meet the requirements; the average eccentricity value of the three experiments decreased by 74%, which greatly improved the efficiency of the grinding wheel alignment.

Two-dimensional time- and space-resolved diagnostic method for an integrated implosion process.

To precisely measure and evaluate X-ray generation and evolution in a hohlraum during an implosion process, we present a two-dimensional (2D) time- and space-resolved diagnostic method by combining a compressed ultrafast photography (CUP) system and a simplified version of space-resolving flux detector (SSRFD). Numerical experiment results showed that the reconstruction quality of the conventional CUP significantly improved owing to the addition of the external SSRFD, especially when a coded mask with a large pixel size was used in the CUP. Further, the performance of the CUP cooperation with the SSRFD was better than that of adding an external charge-coupled device or streak camera. Compared with existing ultrafast imaging techniques in laser fusion, the proposed method has a prominent advantage of measuring the 2D evolution of implosion by combining high temporal resolution of streak camera and high spatial resolution of SSRFD; moreover, it can provide guidance for designing diagnostic experiments in laser fusion research.

Overview of Laser Fusion Research and Development

Overview of Laser Fusion Research and Development

Progress of X-ray high-speed photography technology used in laser driven inertial confinement fusion

In the study of laser driven inertial confinement fusion (ICF), the image data obtained through X-ray high-speed photography technology can be used to analyze the spatial and temporal evolution of the plasma with fluid state produced by work and energy transport. The research of X-ray high-speed photography technology has always been an important part of the development of ICF diagnostics. The Laser Fusion Research Center of China Academy of Engineering Physics has made important progresses in the research of X-ray high-speed photography technology in recent years. These advances include: (1) making a success in developing the X-ray camera with 100ps exposure time for Shenguang laser facilities, which has reached the international advanced level as a whole, and is characterised in such aspects as high sensitivity, transmission-type band-pass filtering and miniaturized design; (2) proposing new types of X-ray high-speed photography technologies with 10 ps exposure time such as the micro-sweep gating technology to break the bottleneck of temporal resolution; (3) taking the lead in carrying out theoretical design, technical verification and engineering design of the radiation-hardened X-ray high-speed camera in China; (4) making the efforts on modeling and simulation on target debris and carrying out the special experiments for the first time in China to verify the simulation results.

Kα X-ray Emission from Nanowire Cu Targets Driven by Femtosecond Laser Pulses for X-ray Conversion and Backlight Imaging.

A high-quality X-ray source was proposed by modifying the target material structure characteristics driven by ultrahigh laser energy. The experiments were performed on the Ti:sapphire femtosecond laser beam device (4.3–6 J, 30 fs), one of the three XG-III lasers in Laser Fusion Research Center of China Academy of Engineering Physics. The femtosecond laser beam drove the nanowire copper material with an average length of 18–50 μm and a diameter of about 260 nm. A single-photon counting charge-coupled device was employed to measure the copper Kα X-ray emission of the nanowire and foil targets. A clear maximum photon yield of the nanowire target was calculated to be 3.6 × 108 photons sr–1 s–1, the conversion efficiency was up to 0.0087%, and the average yield was 2.5 times that of the copper foil targets. In addition, by using a pinhole imaging method of φ10 μm, the minimum full width at half maximum spot size of the X-ray source was calculated in the range of 85–240 μm, which was similar to that of the copper foil material with a long radius of 170 μm and a short radius of 63 μm. The experimental data illustrate that the nanowire has the potential to enhance the energy absorption of femtosecond laser for X-ray conversion and backlight imaging.

XingGuang III laser facility and its experimental ability to drive high-energy particle beams

The XingGuang III (XGIII) laser facility at the Science and Technology on Plasma Physics Laboratory at the Laser Fusion Research Center is unique in the world and consists of one 0.7 PW picosecond beam, one 0.6 PW femtosecond beam and one 1 kJ nanosecond laser beam. The three laser beams with different wavelengths and durations can converge in the target chamber with high spatial and temporal synchronization. Because of its smart beam configurations, XGIII providesunique opportunities for multi-beam pump–probe experiments in research fields such as high-energy density physics, plasma physics and laboratory astrophysics. Laser-driven high-energy particle beams were experimentally investigated, and found to play an important role in pump–probe schemes. High-energy electrons, protons, positrons and their experimental scalings were obtained using the picosecond laser beam with an intensity of 1019 W cm−2. A two-beam pump–probe experiment was demonstrated in which the plasma channel of the femtosecond laser pulse propagating in underdense plasma was imaged by a proton beam driven by the picosecond laser. Furthermore, a three-dimensional reconstruction of the plasma structure may be achieved in multi-beam pump–probe experiments with XGIII.

Conceptual design of a subcritical research reactor for inertial fusion energy with the J-EPoCH facility

The Japan Establishment for a Power-laser Community Harvest (J-EPoCH) is proposed as a next generation laser facility having multi-purpose high repetition laser beams at the maximum rate of 100 Hz. One of the experimental areas is assigned for laser fusion research. The omnidirectional 12 laser beams with 8 kJ and a 5 PW heating laser are arranged. A Large High Aspect Ratio Target (LHART) with the laser beams would yield ~1013 neutrons. The fusion energy corresponds to ~22 J/shot. As one of the J-EPoCH applications, a laser fusion subcritical research reactor with replaceable cores has been conceptually designed based on existing technologies. Moreover,we can conduct a variety of fusion engineering studies: energy conversion, tritium breeding, neutron irradiation effects and other subjects. The feasibility of tritium breeding and preliminary energy conversion studies are proven according to calculations by the Particle and Heavy Ion Transport code System (PHITS).

Research on Laser Fusion and its Applications

In the last half century, laser fusion research has been intensively pursued to achieve energy production. The fuel for laser fusion, deuterium, can be abundantly found in sea water. Compared to fission scheme, fusion is much more benign to our environment. Along with the remarkable progress of laser technology, the laser fusion research has reached a crucial phase, and many applications in terms of such advanced laser technology are now under quick development in different fields such as medical treatment, energy, and industry.

Design of Neutron Imaging Aperture for Inertial Confinement Fusion in Laser Fusion Research Center

Neutron Imaging System (NIS) has been used to image the burn volume and cold fuel volume of imploding fusion capsules. In this work, we present a design of neutron imaging aperture for inertial confinement fusion in Laser Fusion Research Center. Since the total neutron yield should be less than 1014, the penumbral aperture has been chosen. A geometric model has been developed to assess the performance of the neutron imaging system, including the spatial resolution, the field of view and the signal-to-noise ratio. This model reproduces the performances of neutron image systems on OMEGA. The spatial resolution of designed NIS is about 22 μm for a field of view of 250 μm. The signal-to-noise ratio can be better than 10, if the neutron yield is higher than 1013.

Energy band alignment at Cu2O/ZnO heterojunctions characterized by in situ x-ray photoelectron spectroscopy**Project supported by the National Natural Science Foundation of China (Grant No. 11404302) and the Laser Fusion Research Center Funds for Young Talents, China (Grant No. RCFPD1-2017-9).

With the increasing interest in Cu2O-based devices for photovoltaic applications, the energy band alignment at the Cu2O/ZnO heterojunction has received more and more attention. In this work, a high-quality Cu2O/ZnO heterojunction is fabricated on a c-Al2O3 substrate by laser-molecular beam epitaxy, and the energy band alignment is determined by x-ray photoelectron spectroscopy. The valence band of ZnO is found to be 1.97 eV below that of Cu2O. A type-II band alignment exists at the Cu2O/ZnO heterojunction with a resulting conduction band offset of 0.77 eV, which is especially favorable for enhancing the efficiency of Cu2O/ZnO solar cells.

A ten-inch manipulator (TIM) based fast-electron spectrometer with multiple viewing angles (OU-ESM).

The measurement of angularly resolved energy distributions of mega-electron-volt electrons is important for gaining a better understanding of the interaction of ultra-intense laser pulses with plasma, especially for fast-ignition laser-fusion research. It is also crucial when evaluating the production of suprathermal (several 10-keV) electrons through laser-plasma instabilities in conventional hot-spot-ignition and shock-ignition research. For these purposes, we developed a 10-in. manipulator-based multichannel electron spectrometer-the Osaka University electron spectrometer (OU-ESM)-that combines angular resolution with high-energy resolution. The OU-ESM consists of five small electron spectrometers set at every 5°, with an energy range from ∼40 keV to ∼40 MeV. A low-magnetic-field option provides a higher spectral resolution for an energy range of up to ∼5 MeV. We successfully obtained angularly resolved electron spectra for various experiments on the OMEGA and OMEGA EP laser systems.