A mini-reactor called CANDY that based on kJ-class diode-pumped solid-state laser (DPSSL) is proposed to perform feasibility studies of the power plant in fast ignition scheme fusion. In order to implement CANDY, we have adressed two issues. First is a repetitive operation of pellet injection and laser illumination, second is target physics related to inertial confinement fusion plasma. First is achieved using repetitive laser system, (i) succeeded in 10 Hz injection of CD beads longer than 2 minutes, which was demonstrated for the first time using inserter that works at the same frequency of laser toward the reactor. Second issue is achieved using a world-class ultra-intense laser LFEX at ILE, Osaka University, here we have demonstrated (ii) an efficient heating of a counter imploded core of a density of 2.8±0.3 g/cc with temperature upto 1 keV with efficiency evaluated to be 9±0.8%. These results are encouraging and gives hints on the fast ignition scheme as a candidate toward future compact reactor developments.
A laser-driven inertial fusion energy (IFE) reactor achieves the fusion of injected fuel pellets, which are continuously delivered into the reaction chamber and engaged by laser beams at 10’s Hz. The target physics developments are expected to obtain fusion gain and developments of pellet injection and engagement are indispensable to realize laser fusion reactor. The Graduate School for the Creation of New Photonics Industries (GPI) have conducted laser inertial fusion program since 2008 with corroboration with industries and academia. Our strategy is to demonstrate integrated repetitive operation that scalable for future laser fusion power plant. We proposed a mini-reactor CANDY (1) that utilizes a few kJ/10 Hz laser driver with ~100 W fusion power (figure 1.). Toward its development, three key issues are conducted; (1) Repetitive laser development (2, 3), (2) Target physics related on counter illuminating fast ignition scheme (4, 5) and (3) Pellet injection & engagement with fusion reactions (6-8). Figure 2 represents specifications of achieve values in Hamamatsu, designed values of laser fusion mini-Reactor CANDY (1) and inertial fusion Test Reactor LIFT (Phase-IIII) (9). Here we report the present status of R&D toward the CANDY.
Repetitive laser development
In the Hamamatsu area, several repetitive laser systems those utilizing DPSSL are under operation. The first high repetitive inertial confinement fusion experiment laser system called HAMA (2) is under operation since 2008. The HAMA consists of a Ti : sapphire laser pumped by a 10J/1-10 Hz DPSSL. The HAMA utilizes counter fuel assembling beam with pulse tailoring and counter heating beam since 2013. In 2018, Hamamatsu Photonics have issued a press release of a 100-Joule class DPSSL based facility “TERU” (Trek on fusion Energy Roadmap toward Ultimate SDGs). That is under operation at 50 J/0.5 Hz with potential upto 10 Hz (3). Toward the fabrication of kJ-class DPPSL required for the CANDY, repetitive laser research and developments are on-going in Hamamatsu.
Target physics related counter illuminating fast ignition scheme
We have demonstrated an efficient imploded core heating using a using a world-class ultra-intense laser LFEX at ILE, Osaka University by improving imploding laser beams from the previous experiments (4). Six green beams from GEKKO XII(GXII) laser (0.53 μm, 1.1 ns, 1.7 kJ) haveimploded a CD shell target to a density of 2.4 x solid density, that forms a 2.8±0.3 g/cc core. When two beams from LFEX laser (1.053 μm, 1.5 ps, 0.25 kJ) were axially illuminating to GXII symmetric axis, the bulk ion temperature increases beyond 1.0 keV from 0.6-0.7 keV evaluated using a multi-channel neutron spectrometer and the inferred heating efficiency was 9±0.8%. This result indicates that, as far as core density stays around a few g/cc, direct illuminating fast ignition scheme can expect a degree of core heating while the imploded core was surrounded by ablating corona plasma.
Pellet injection & engagement
We have demonstrated 10 Hz operatin of bead pellete injection and engagemnt. The injection machine is upgraded from the previous 1 Hz injection system by increasing number of holes on disk rotor from 20 to 200 (6-8). As the results, we have achieved 10 Hz pellet injection and laser engagement that last beyond 2 minutes. The repetition rate is now upgraded to 10 Hz, the same frequency with laser repetition. Figure 3 represents experiments history of hit ratio per second for bead pellet injection & engagement system. The hit ratio beyonds 40% resulting in 5 times incremental of laser hit ratio per second from the previous results which indicates the first demonstration that the pellet injection frequency equals to that of laser amplified frequency, an important step to increase fusion power in the future power plant.
In conclusion, toward the laser fusion mini-reactor CANDY, we have made advances both on (i) target phsyiscs that the imploded core with density 2.8±0.3 g/cc are heated upto 1keV with heating coupling efficiency 9±0.8% using the ultra-intense laser LFEX at ILE, Osaka University, and (ii) pellet injection & engagement demonstrating a 10 Hz beads injection and laser illumination beyond 2 minutes with hit ratio beyond 40%.
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(2) Y. Mori et al., Nucl. Fusion vol. 53, 073011 (2013).
(3) T. Watari et al., Proceedings of IAEA FEC2018 conference, IFE/P4-10 (2018).
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(5) Y. Mori et al., Phys. Rev. Lett. vol. 117, 005001 (2016), ibid. vol. 57, 116031 (2017).
(6) O. Komeda et al., Sci. Reports vol. 3, 2561 (2013).
(7) Y. Mori et al., Fusion Sci. & Technol. vol. 75, 36 (2019).
(8) Y. Mori et al., Nucl. Fusion vol. 59, 096022 (2019).
(9) T. Norimatsu et al., Nucl. Fusion vol. 57, 116040 (2017).
|Affiliation||The Graduated School for the Creation of New Photonics Industries|
|Country or International Organization||Japan|