Unexpected excess energy observed in fusion plasma

Laser-induced nuclear fusion

A mysterious excess of energy was measured during laser-induced nuclear fusion, which according to the Maxwell-Boltzmann distribution should not exist. The physicists have not yet been able to explain why the unexpectedly high-energy neutrons in the burning fusion plasma have more energy than they should have given the temperatures.


Livermore (USA). Nuclear fusion could cover the increasing energy demand of the people in the future. However, it is not yet clear on which fusion technology the necessary fusion power plants will be based. The most advanced is laser fusion, which physicists at the National Ignition Facility (NIF) recently used to achieve the burning plasma state .

In the experiment, deuterium-tritium ions in a tiny cavity were irradiated with a laser with a power of more than ten quadrillion watts for fractions of a second. This led to nuclear fusion in the heated and compressed plasma . The fusion energy reached 1.3 megajoules for the first time. So the plasma is almost reaching the point where nuclear fusion would be self-sustaining without external energy .


Laser fusion in the burning fusion plasma

Physicists around Edward Hartouni and Alastair Moore from the Lawrence Livermore National Laboratory (LLNL) have now published a study that examined what happens in laser-induced nuclear fusion in the burning fusion plasma. According to their publication in the journal Nature Physics , they analyzed measurement data on the amount and energy of the neutrons that were released in the plasma during fusion. During nuclear fusion, the trajectories and speeds of the neutrons were documented with a precision of up to five kilometers per second using special spectrometers from all directions in the reactor room.

Excess energy contradicts the Maxwell-Boltzmann distribution

According to the measurement data, many of the neutrons released by the burning fusion plasma had an energy of about 14 megaelectron volts. Their speed in the fusion reactor was over 51,000 kilometers per second.

The neutrons were thus significantly more energetic than they should be according to the Maxwell-Boltzmann distribution and other physics models. The Maxwell-Boltzmann distribution describes that the energy of the neutrons is directly related to the energy of the fusing atomic nuclei and the temperature of the fusion plasma. However, the analyzed measurement data of the laser-induced nuclear fusion from the NIF deviate significantly from this equation because, according to Moore, they release more energy than they should at the temperature of the plasma.


“Once the implosion caused the deuterium-tritium plasma to burn and ignite, the energies exceeded those expected for these reactions.”

According to the physics models, the plasma should have been about 2.5 times hotter at the documented particle energy.

No explanation for the excess energy in nuclear fusion

Using the known mechanisms, the scientists have so far not been able to explain why the measured energy surplus occurred during nuclear fusion. According to them, measurements of further laser fusions in the NIF reactor should help with the answer.

“This is an open-ended, experimental question. Here, more advanced simulations are needed to understand the effects.”

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