7th Asia-Pacific Conference on Plasma Physics, 12-17 Nov, 2023 at Port Messe Nagoya

Nuclear Fusion Study at GIST

Woosuk Bang1, *, Junho Won1, Jaehyun Song1, and Chiwan Song1
1
Department of Physics and Photon Science, GIST, Gwangju, South Korea*
e-mail (speaker): wbang@gist.ac.kr

Rapid heating of matter using high power lasers is anemerging research area in laser-plasma physics. This has
been motivated primarily by the interests in the exoticstates of matter achieved after heating. In theseexperiments, the interaction between intense light andmatter is sufficiently strong and fast for the atoms to beionized instantaneously, and the resulting electrons or ions(or both) attain large kinetic energies very quickly. By
directly illuminating a small solid target with an intenselaser beam, a target temperature on the order of 106 K has
been demonstrated. Using even smaller targets (~10 nm
radius spheres), an ion temperature exceeding 108 K has
been achieved in the laboratory,1 which is sufficiently highfor deuterium ions to produce nuclear fusion reactions
efficiently.
In a laser-cluster-fusion experiment, an intense (>1016W/cm2) laser beam irradiates ~10 nm radius spheres ofsolid density deuterium (called deuterium clusters).2 If theincident laser field is sufficiently strong, the laser-matterinteraction leads to an explosion of the individual spheres
generating energetic deuterium ions. The resulting
deuterium ions are so energetic (> 10 keV) that theygenerate nuclear fusion reactions as they collide with eachother within the plasma or with ions in the background gas.
These fusion reactions produce a ~1 ns burst of neutronsand protons.
At GIST, we have studied a scaling law (Y~Eβ) of thelaser pulse energy (E) for fusion neutron yields (Y) fromlaser-cluster fusion experiments, as shown in Fig. 1.3 We
find the scaling exponent β approaching 1.0 as the ion
temperature increases from 1 keV to 100 keV.
We have also built an experimental platform to study
fusion plasmas using high power lasers. We haveproduced high temperature deuterium fusion plasmas withion temperatures exceeding 300,000,000 K. We will showthat we can control the temperature of fusion plasmas byvarying the incident laser intensity. We have measured
fusion neutron yields at different plasma temperatures,and preliminary results will be presented.
High power lasers can also be used to produce intense
ion sources capable of heating a small sample to hightemperatures. When an energetic ion beam is incident on
a cold sample, the incident ions first transfer their kinetic
energy to target electrons via Coulomb collisions.
Subsequently, these electrons collide with ions within thesample, and electron-ion relaxation process begins. Sincelaser-driven ions travel very fast often exceeding several
percent of the speed of light, they can deliver a significant
portion of their kinetic energy to the sample very rapidly.
The whole heat transfer process takes less than ananosecond, and the heated sample does not have time toexpand hydrodynamically during heating and maintains
its initial density. Sometimes the heated sample near solid
density reaches temperatures far beyond those attainablethrough conventional heating sources, and scientists haveused it in research areas such as warm dense matter andion fast ignition.
At GIST, we have shown that a thick (> 1 cm) soliddensity aluminum sample can be heated rapidly, uniformly,
and efficiently all at the same time using an energetic
proton beam with a finite energy spread.4,5 We find that a
100 MeV proton beam with a Gaussian energy spread of∆E/E ~ 70% can transfer heat into a 32 mm thick soliddensity aluminum sample uniformly (temperature
nonuniformity < 2–6%) and efficiently (> 62% heattransfer efficiency) on a sub-nanosecond time scale.
This work was supported by NRF grant funded by theKorea government (MSIT) (No. 2023R1A2C1002912).

References[1] W. Bang et al., Phys. Rev. Lett. 111, 055002 (2013)[2] J. Song, J. Won, and W. Bang, PLOS ONE 16,e0261574 (2021)[3] J. Won, J. Song, S. Lee, C. Song, and W. Bang, Nucl.
Fusion 63, 066031 (2023)[4] C. Song, J. Won, J. Song, and W. Bang, Int. Commun.
Heat Mass Transf. 135, 106070 (2022)[5] C. Song, S. Lee, and W. Bang, Sci. Rep. 12, 15173(2022)

Figure 1. Fusion neutron yield is shown as a function of theincident laser pulse energy varying from 0.1 J to 200 J. The
scaling law for the neutron yields reported from previous
experiments is shown as a solid red line.