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Fusion Energy Breakthrough: Scientists Extract Net Energy from Fuel

On September 27th, 2013, Professor Omar Hurricane and his team at the Lawrence Livermore National Laboratory made a breakthrough in inertial confinement fusion science: the researchers, for the first time, extracted more energy from controlled nuclear fusion than was absorbed by the fuel to trigger it, meaning they extracted net energy from fuel. This is a critical step to achieve inertial confinement fusion and the findings have been published in Nature on February 12th.

The working mechanism of inertial confinement fusion (ICF) is to heat the fuel and trigger the implosion and compression of the fuel. The unique advantage of ICF is that the emitter and blanket are separate, thus it becomes safe and convenient to do maintenance for emitter and blanket.

Fusion reactor

A schematic of the fusion reactor. *Image source: Nuclear Lecture Notes


The experiment adjusts the way laser beam enters the reactor and the stability of implosion has been improved. In the latest experiment on November 19th, 2013, the NIF laser beam carried 1.9 megajoules worth of energy into the hohlraum and generated a high temperature of around one hundred million degree Celsius (50% higher than the past) and ten million atmospheric pressure. The energy release from the fusion fuel was 17.3 kilojoules, which is ten times of the previous record.


An image of the hohlraum containing hydrogen isotopes. *Image source: NIF.


Compared with previous studies, the alpha particles released by fusion are retained in the fusion fuel, leading to self-heating and hence providing extremely large amount of energy, which is close to half of the total net energy. The research team believe that this self-heating plays a vital role in “ignition” (stable process of releasing fusion energy equal to or greater than the amount of energy used to confine the fuel). NIF’s experiment successfully proved their previous hypothesis – the unstable plastic shell caused by implosion is the root of why the net energy is lower than that predicted by computer models.

However, the current achievement is still not sufficient to accomplish real “ignition”: The November 2013 experiment only reached half of the Lawson criterion (An important general measure of a system that defines the conditions needed for a fusion reactor to reach ignition). In addition, it remains unclear about how to control the shape of implosion by controlling the wavelength of incident laser beams and the experiment mode comes from practical experience. Professor Hurricane says, the further understanding of incident wavelength and the improvement of physical properties of hohlraum will both be beneficial for getting ideal results.

Can new lasing mode realize stable fusion reaction? Maybe time is the only answer.
Source: Nature
Image source: Damien Jemison/LLNL