As fusion fans no doubt have heard, on December 5th the National Ignition facility (NIF) at Lawrence Livermore National Laboratory in California achieved a major fusion advance with its giant laser. We at LPPFusion join in congratulating the three thousand researchers and staff at NIF on their achievement.
What exactly has been achieved? The December 5th shot for the first time achieved plasma net energy: more fusion energy out of the plasma than was put into the plasma by the laser. The laser focused 2.1 MJ (megajoules) of energy onto a tiny pellet of deuterium-tritium fusion fuel. The fusion yield was 3.1 MJ, a doubling of NIF’s previous best yield, achieved last year, of 1.6 MJ. This is certainly a significant advance, as getting more energy out of the plasma that goes into it is a necessary step toward practical fusion energy generation.
However, as much reporting has correctly emphasized, this achievement is quite different from the ultimate goal of the fusion energy research effort: device net energy. This is when more energy comes out of the fusion generator than is drawn into it from the grid. So, device net energy is thus the ratio of the total system energy out divided by total energy in, not just the plasma net energy. We at LPPFusion refer to it as “net energy” or “wall-plug efficiency” and we strive to deliver a device where a total energy out of the device is larger than the total energy in. However, the language in media uses unclear terms such as Q for total fusion yield where Q is often just a plasma net energy, and not a total wall-plug efficiency measure. For NIF’s latest shot, 300 MJ was used to run the lasers, almost 100 times more than the fusion energy produced. This 1% “wall-plug efficiency” is still a record, surpassing the previous record of 0.6% set by the JET tokamak device, located in the UK.
NIF’s giant laser approach is not likely to close the gap in wall-plug efficiency any time soon. Lawrence Livermore’s own leadership estimated that it will take 30 years for their approach to produce commercial fusion energy.
However, we at LPPFusion join the rest of the fusion research community in viewing the NIF announcement as helping the whole field, mainly in public perception. The new advance, despite its limitations, drills through the popular narrative that there is no progress in fusion energy and that records set 20 years ago never get surpassed. The US government’s trumpeting of the NIF’s results help to ensure that fusion energy will from now on be included in the options available to shift from fossil fuels’ energy sources. Overall, this will certainly aid LPPFusion as well as others in getting the needed funding.
Interestingly, this advance may prove to be a “last hurrah” for the purely inertial confinement approach that NIF has used. In this approach, no magnetic fields confine the plasma, which just does not have time to expand during the fusion burn. But NIF was unable to replicate its record shot of 2021 and may not be able to replicate the December 5th shot as well. To overcome this super-sensitivity to nanometer flaws in the fuel pellet, NIF researchers have done initial experiments using a hybrid laser- magnetic confinement approach. They run current through a thin coil of wire around the pellet (see Fig.3) and then use the laser to compress the resulting magnetic field. This hybrid approach has promised to be more repeatable than the pure inertial confinement and may well be NIF’s future.
At LPPFusion, we hope to catch up with and surpass NIF’s achievement of 1% wall plug efficiency. To do so, we will transition from deuterium to our final pB11 fuel, and we hope to do that soon. Stay tuned!
Figure 3. In recent experiments (not the Dec. 5th record one) NIF researchers used this hybrid pellet with a solenoidal coil to supply an initial magnetic field. When hit with laser light (purple) the pellet contracted rapidly, intensifying the magnetic field and briefly helping to contain the hot fusion plasma.