Miscellany

Fusion Energy

A new step forward Fusion energy!
'Thanks to Lasers'

Salamanca, 25th of August, 2021

Introduction and main result

Reaching potential infinite amount of clean energy is one of the human dreams since the beginning of the modern society and nowadays is an urgency due to the climate changes that are becoming more and more frequents in the last decades. Fusion energy is one of the more credible candidates to satisfy such a dream and scientists are working on it for the last 60 years. Nuclear fusion is the most natural way to produce energy in the universe but not on the Earth where nuclear energy is obtained by using Fission, the opposite process where atoms are broken instead of fused. Indeed, what is a natural process in the stars, in which plasma is confined by gravity, seem to be very hard to reproduce in the Earth.

This summer scientists from the Livermore National Laboratory went very close to demonstrate nuclear fusion on the Earth. Indeed, at the National Ignition Facility (NIF) they were able to convert more than 70% of laser energy into nuclear energy, result never reached so far. This step forward renews the hope in the laser-fusion community to finally reach one of the more ambitious dreams of our society: 'the establishment of the first nuclear reactor for civil energy'. The path for reach such goal is still long and full of scientific and technological milestones to be fulfilled but it is a matter of fact that on of the more relevant milestones has been reached this summer.

The hope is flaring up again.

What is laser-fusion?

Confining plasma to reach nuclear fusion can be done in several ways but the most trustable approaches are based on magnetic fields and/or laser pulses confinement schemes. Both approaches aim to reproduce the Sun interior conditions which fix the value of plasma density and time of confinement, necessary in order to start nuclear fusion reaction. In the magnetic confinement fusion approach (Wikipedia description) confinement time is of the order of tens of seconds with plasma densities up to 1E+14 particles per cubic centimetres while in laser fusion approach (Wikipedia description) the confinement time is extremely short, around few nano seconds (one nanosecond is equal to one billionth of seconds) and plasma densities are extremely high, around 1E+23 particles per cubic centimetres.

Laser-Fusion approach can be represented as made by three steps:

  • Firstly, 192 laser pulses are focused in the internal wall of a cylindrical cavity in order to produce soft X-rays distribution converging toward the centre of the geometrical centre if the cavity
  • Then, the X-rays distribution irradiates a millimetric spherical plastic ball filled with a mixture of Deuterium and Tritium (isotopes of Hydrogen) by inducing the explosion of the internal fuel according to the action-reaction Newton principle
  • Finally, during the implosion the radius of the sphere reduces and consequently the fuel density and temperature increase up to thousands of time the solid density and up to hundreds-millions degrees of temperature. These are the necessary conditions for nuclear fusion. The laser induced micrometric nuclear fusion reaction that is supposed to produce an amount of energy greater than the one used for the process

Such laser-fusion experiments are possible in principle only in two laboratories in the world: the NIF in Livermore (USA) and the Laser Mega Joules -LMJ- in Bordeaux (France); both laboratories depend on the ministries of Defense with a small percentage, around 20%, of experimental access for civil applications. The NIF is in operation mode since 2009 and the LMJ started partial operation the last years and will be fully operative in a couple of years.

Laser-fusion research made a relevant step forward this summer with the fantastic experimental results communicated by our US colleagues working at the NIF in Livermore. Indeed, Sunday the 8th of August, 2021 an impressive result has been obtained with a final energy gain of more than 1.3 MJ of energy obtained as the result of nuclear fusion. Considering and inertial laser energy of 1.8 MJ this means a final gain of around 0.70, very close to 1 with an improvement from the last best result by a factor of x8. Waiting for a more detailed report it is clear that, if confirmed, such results demonstrate that nuclear fusion called on the Earth has been obtained without any doubts.

Why this result is important for CLPU?

Demonstration of nuclear fusion induced by lasers was a driving force for the development of high-power laser technology in the last decades. The PW VEGA system at CLPU is currently the most powerful laser in Spain and among the first in EU. Extreme state of matter and particle beam are routinely generated with VEGA and several experiments has been performed in the last years since the laser has been operating. Laser-fusion research is part of the scientific programme at CLPU where a dedicated experiment led by L. Volpe was performed in 2020 with the aim to study the ion stopping power in Warm Dense Matter (WDM). The excellent results of the experiments are important to understand how the ions deposit their energy in the plasma which is a key process in the nuclear fusion reaction. In addition, the high repetition-rate of VEGA is important to study diagnostic and targetry related to laser-fusion in view of a necessary extension of the mode of working from single shot (At NIF they can do one shot per day now) to several shots per seconds which is the requirement for building a nuclear reactor.

 

Luca Volpe
Director of the CLPU Laser-Plasma Chair at USAL