A great step toward laser nuclear fusion with fast laser heating technique
High-pressure (20 billion bar) plasma for triggering nuclear fusion generated
A group of researchers from Osaka University, Hiroshima University, University of Nevada, Reno, the Institute for Laser Technology, Purdue University, the National Institute for Fusion Science, and the Graduate School for the Creation of New Photonics Industries has generated high-pressure plasma (20 billion bar, 1/10 of the pressure of the center of the sun) with the highest efficiency, using a device known as LFEX (Laser for Fast Ignition Experiment), which can deliver up to 2,000 trillion watts, or 2 petawatts (PW), in one trillionth of a second.
The researchers achieved a temperature of 20 million degrees Celsius in plasmas by using a magnetic field of 1 kilotesla (1,000 times the magnetic field strength of a typical magnet) and heat laser-driven heat waves.
Inertial confinement fusion (ICF) research in Japan has been exploring efficient methods that can be achieved by a small laser projector in anticipation of the realization of fusion energy in the future.
In the central ignition (isobaric hot-spot ignition) scheme, a prevailing scheme for ICF, has the problem of ignition quench, which is caused by the hot spark mixing with the surrounding cold fuel. On the other hand, in the fast ignition scheme (fast isochoric heating) in ICF, a small pellet that contains nuclear fuel should be compressed to the high density by lasers of multinanoseconds and ignite fusion reactions by a separate multi petawatt laser of a very short duration (fast ignition). Nuclear fusion releases a large amount of energy by burning the majority of the fuel. In 2018, this group demonstrated the effectiveness of “magnetized fast isochoric heating,” increasing heating efficiency. ( https://resou.osaka-u.ac.jp/en/research/2018/20180926_1 )
In this study, the researchers heated plasmas up to 22 million degrees C, generating high-pressure plasma of 2.2 PPa (20 billion bar). They clarified physical mechanisms of fast laser heating, making laser-based nuclear fusion a real possibility.
In the process of plasma heating in this study, a portion of high-density nuclear fusion fuel is directly heated by laser, and heat waves propagate with high velocity in a dense plasma. In order to diffuse the heat waves into a plasma, it is necessary to continue to heat the plasma by laser. Using a two-dimensional particle-in-cell simulation, this group confirmed that diffusive heating from a laser-plasma interaction zone to the dense plasma plays an essential role in the efficient creation of an ultrahigh-energy-density (UHED) state.
LFEX at Osaka University can heat for a relatively long period of time, specifically a picosecond, or one trillionth of a second. IFC research using fast ignition technique is one of Japan's priority plans for nuclear fusion. This group’s achievement is a great step toward efficient plasma heating, which is essential for realizing economical electricity generation by nuclear fusion. Moving forward, this group will work on nuclear fusion energy by increasing the heating laser irradiation time by more than 10 times than what was achieved in this study and producing high-density and high-temperature plasmas.
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The article, " Peta-Pascal Pressure Driven by Fast Isochoric Heating with Multi-Picosecond Intense Laser Pulse ," was published in Physical Review Letters at DOI: https://doi.org/10.1103/PhysRevLett.124.035001 .
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