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In laser-driven inertial fusion energy reactors, injected fuel pellets are continuously delivered into the reaction chamber and irradiated by laser beams injected at a frequency of tens of hertz. Thus far, a spherical shell pellet has been confirmed as the most conventional target design to achieve high-energy-density state thorough an implosion process that is required for fusion burn. To demonstrate repetitive fuel implosion with a 1 Hz joule-class laser system, a testbed of a shell injection system delivering a spherical shell (500 m diameter and 7 m thickness) was developed. The developed testbed demonstrated that (i) repetitive implosion (maximum frequency: 0.5 Hz) of shell injection was possible for more than ten shells at a shell speed of 191 mm s−1, and (ii) the distribution of the injected shell after 18 cm free-fall was within a circular region, 6.4 mm in diameter. The estimated laser-hit-ratio to the pellet was on the order of 10%. [ABSTRACT FROM AUTHOR]

Fast heating is a method of heating an assembled high-density plasma into a hot state by irradiating it with short-duration (sub-picosecond), high-intensity ( W ) laser pulses before the plasma expands and dissolves hydrodynamically. In this paper, we present detailed experimental results of fast heating fuel assembled in a spherical deuterated polystyrene shell target of 500 m diameter and 7 μm thickness with counterbeam illumination by using a HAMA 1 Hz, 5.9 J inertial confinement fusion laser driver with pulse tailoring. These tailored pulses contain three pulses in sequence: a ‘foot’ pulse of 2.4 J/25 ns, a ‘spike’ pulse of 0.5 J/300 ps and a ‘heater’ pulse of 0.4 J/110 fs; these pulses are designed to assemble the fuel and heat it. By varying the energy of the foot pulse, we find that fast heating the fuel is achieved only if the fuel is weakly ablated by the foot pulse and then shock-assembled by the spike pulse into the target centre so that the heater pulse can access the fuel with a focal intensity greater than W . Without a foot pulse, the heater pulse contributes to assembling the fuel. For higher foot-pulse energies, the heater pulse drives a hydrodynamic motion with speeds of the order 107 cm with intensities of the order W , resulting in re-assembling and additional heating of the pre-assembled fuel. Once a shock-assembled core is achieved at the target centre, we succeed qualitatively in fast heating the core for shots in sequence with variations of laser energy within 18%. The coupling efficiency from the heating laser to the core is inferred to be % in total: % for the ionized bulk electrons and % for the bulk ions. The fusion neutron spectrum detected on the laser axis exhibits peaks at 1.0 MeV, 1.7 MeV and 3.8 MeV. These peaks are attributed to the N and He reactions induced by counterpropagating fast deuterons accelerated by the photon pressure of the heating pulses. [ABSTRACT FROM AUTHOR]

A CD shell was preimploded by two counter-propagating green beams from the GEKKO laser system GXII (based at the Institute of Laser Engineering, Osaka University), forming a dense core. The core was predominantly heated by energetic ions driven by the laser for fast-ignition-fusion experiment, an extremely energetic ultrashort pulse laser, that is illuminated perpendicularly to the GXII axis. Consequently, we observed the D(d, n)3 He-reacted neutrons (DD beam-fusion neutrons) at a yield of n sr. The beam-fusion neutrons verified that the ions directly collided with the core plasma. Whereas the hot electrons heated the whole core volume, the energetic ions deposited their energies locally in the core. As evidenced in the spectrum, the process simultaneously excited thermal neutrons with a yield of n sr, raising the local core temperature from 0.8 to 1.8 keV. The shell-implosion dynamics (including the beam fusion and thermal fusion initiated by fast deuterons and carbon ions) can be explained by the one-dimensional hydrocode STAR 1D. Meanwhile, the core heating due to resistive processes driven by hot electrons, and also the generation of fast ions were well-predicted by the two-dimensional collisional particle-in-cell code. Together with hot electrons, the ion contribution to fast ignition is indispensable for realizing high-gain fusion. By virtue of its core heating and ignition, the proposed scheme can potentially achieve high-gain fusion. [ABSTRACT FROM AUTHOR]

The concept of a novel approach to make a compact SMES unit composed of a stack of Si wafers using a well-established MEMS process was proposed. The concept was backed up by pilot estimations for energy storage capacity and mechanical strength to endure electromagnetic stress. The estimated volume density of the storable energy is comparable to that of rechargeable batteries and the mechanical strength of Si wafer endures the electromagnetic stress imposed on it. These estimations support the feasibility of this novel concept, although there needs to be more detailed design of the system for its practical realization. Furthermore, there are a lot of challenges to overcome. The first step of the experimental proof of this new concept was successfully performed through several repeated test fabrications. In one of these test fabrications, the theoretically estimated upper limit value of the energy storage corresponding to a pilot design of a spiral superconducting NbN coil in the spiral trench formed on a Si wafer 10.15 cm in diameter was attained. [ABSTRACT FROM AUTHOR]