Fabrication of disk-shaped, deuterated resorcinol/formaldehyde foam target for laser–plasma experiments

Resorcinol/formaldehyde (RF) foam resin is an attractive material as a low-density target in high-power laser–plasma experiments because of its fine network structure, transparency in the visible region, and low-Z element (hydrogen, carbon, and oxygen) composition. In this study, we developed disk-shaped RF foam and deuterated RF foam targets with 40–200 µm thickness and approximately 100 mg/cm3 density having a network structure from 100 nm to a few micrometers cell size. By deuteration, the polymerization rate was drastically slowed down owing to kinetic isotope effects. These targets were used in high-power laser experiments where a megaelectronvolt proton beam was successfully generated.Kaneyasu Y., Nagai K., Cadatal-Raduban M., et al. Fabrication of disk-shaped, deuterated resorcinol/formaldehyde foam target for laser–plasma experiments. High Power Laser Science and Engineering 9, e31 (2022); https://doi.org/10.1017/hpl.2021.15

Magnetized Fast Isochoric Laser Heating for Efficient Creation of Ultra-High-Energy-Density States

The quest for the inertial confinement fusion (ICF) ignition is a grand challenge, as exemplified by extraordinary large laser facilities. Fast isochoric heating of a pre-compressed plasma core with a high-intensity short-pulse laser is an attractive and alternative approach to create ultra-high-energy-density states like those found in ICF ignition sparks. This avoids the ignition quench caused by the hot spark mixing with the surrounding cold fuel, which is the crucial problem of the currently pursued ignition scheme. High-intensity lasers efficiently produce relativistic electron beams (REB). A part of the REB kinetic energy is deposited in the core, and then the heated region becomes the hot spark to trigger the ignition. However, only a small portion of the REB collides with the core because of its large divergence. Here we have demonstrated enhanced laser-to-core energy coupling with the magnetized fast isochoric heating. The method employs a kilo-tesla-level magnetic field that is applied to the transport region from the REB generation point to the core which results in guiding the REB along the magnetic field lines to the core. 7.7 $\pm$ 1.3 % of the maximum coupling was achieved even with a relatively small radial area density core ($\rho R$ $\sim$ 0.1 g/cm$^2$). The guided REB transport was clearly visualized in a pre-compressed core by using Cu-$K_\alpha$ imaging technique. A simplified model coupled with the comprehensive diagnostics yields 6.2\% of the coupling that agrees fairly with the measured coupling. This model also reveals that an ignition-scale areal density core ($\rho R$ $\sim$ 0.4 g/cm$^2$) leads to much higher laser-to-core coupling ($>$ 15%), this is much higher than that achieved by the current scheme

Direct fast heating efficiency of a counter-imploded core plasma employing a laser for fast ignition experiments (LFEX)

Fast heating efficiency when a pre-imploded core is directly heated with an ultraintense laser (heating laser) was investigated. \u27Direct heating\u27 means that a heating laser hits a pre-imploded core without applying either a laser guiding cone or an external field. The efficiency, η, is defined as the increase in the internal core energy divided by the energy of the heating laser. Six beams (output of 1.6 kJ) from the GEKKO XII (GXII) green laser system at the Institute of Laser Engineering (ILE), Osaka University were applied to implode a spherical deuterated polystyrene (CD) shell target to form a dense core. The DD-reacted protons and the core x-ray emissions showed a core density of 2.8 ± 0.7 g cm−3, or 2.6 times the solid density. Furthermore, DD-reacted thermal neutrons were utilized to estimate the core temperature between 600 and 750 eV. Thereafter, the core was directly heated by a laser for fast-ignition experiments (LFEX, an extremely energetic ultrashort pulse laser) at ILE with its axis lying along or perpendicular to the GXII bundle axis, respectively. The former and latter laser configurations were termed \u27axial\u27 and \u27transverse modes\u27, respectively. The η was estimated from three independent methods: (1) the core x-ray emission, (2) the thermal neutron yield, and (3) the runaway hot electron spectra. For the axial mode, 0.8%< η <2.1% at low power (low LFEX energy) and 0.4%< η <2.5% at high power (high LFEX energy). For the transverse mode, 2.6%< η <7% at low power and 1.5%< η <7.7% at high power. Their efficiencies were compared with that in the uniform implosion mode using 12 GXII beams, 6% < η <12%, which appeared near to the η for the transverse mode, except that the error bar is very large

Properties of fast carbon cluster microbeams produced with a tapered capillary

We study the transmission properties of fast cluster ions (Cn^+ (n = 2–4) with velocities ranging from 0.89 to 1.79 a.u.) through a single tapered capillary with an outlet diameter of 13.7 μm. We investigate the projectile-velocity dependence of the transmission fraction from the measurements of transmitted particle energy spectra. It is found that the non-fragmentation fraction of C2^+ projectiles increases with decreasing velocity, indicating that fragmentation occurs mainly via close collisions with the surfaces of the capillary wall. For Cn^+ (n = 2–4) ions with the same incident velocity, the cluster-size dependence of the non-fragmentation fraction shows even–odd alternation, implying that the fraction includes contributions from stable clusters surviving the grazing scattering process at the capillary surface. We also find that the angular distribution of transmitted particles is narrower for cluster projectiles compared with atomic projectiles

Thermal neutron fluence measurement by Cadmium differential method at laser-driven neutron source

We generated high-energy neutrons by (d, n) and (p, n) reactions on a Be target with protons and deuterons that were accelerated up to 30 and 10 MeV/u, respectively, by laser-plasma interactions. Thermal neutrons were subsequently generated through deceleration by a small moderator with conjunction on the Be target. Here we report the measurements on the thermal neutron fluence using the activation method with/without Cd filters. The unstable isotopes of 198Au, 56Mn, 60Co, and 181Hf were produced through (n, γ) reactions by a single laser shot. The nuclear reaction rates were evaluated by measurring the γ-rays emitted from these unstable isotopes. The thermal neutron fluences from the four nuclides are consistent within their experimental uncertainties. The fluence is evaluated to be (2.2±0.4)×105 neutrons/cm2 at the distance of approximately 9-mm at 90◦ against the laser axis. The present result shows that the method to generate thermal neutrons from a compact neutron source with a diamater of 44 mm and length of 46 mm is expected to be a useful tool for various nuclear experiments

High Flux Neutrons Provided by a Laser driven Neutron Source and its Application to Nuclear Astrophysics

We demonstrated that (n, 2n) and (n, gamma) reactions are induced by a high-flux pulse of fast neutrons provided from a Laser-driven Neutron Source (LDNS). Several kinds of metal targets are exposed to the fast neutrons with energies of approximately 10-20 MeV. As a result, 180Hfm,181Hf, 56Mn, 198Au, and 60Co are produced by (n, gamma) reactions. Furthermore, unstable isotopes such as 54Mn, 58Co, 175Hf, and 196Au are produced by (n, 2n) reactions. We evaluate the neutron fluence and energy spectrum using the activation method in conjunction with a time-of-flight (TOF) method.The 16th international symposium on nculei in cosmo