December 25, 2022

Lasers for Fusion Breakthrough and Its Nuclear Bomb Connection

Prabir Purkayastha

LAWRENCE Livermore Laboratory's advance in achieving fusion energy using lasers has been splashed worldwide as a huge success. So what was the success all about? The joint press release of the US Department of Energy and the National Nuclear Security Administration states that this experiment "...will pave the way for advancements in national defense and the future of clean power." In other words, there was also a weapons component to the fusion experiment. The Department of Defence is the Department of War.

Talking to the Bulletin of Atomic Scientists, Professor Richard Rosner of the University of Chicago and a former director of the Argonne National Laboratory explained (The Energy Department’s fusion breakthrough: It’s not really about generating electricity, John Mecklin, December 16, 2022) that this experiment's main purpose was to test the health of the stockpile of nuclear weapons without conducting an actual explosion. The controlled fusion experiment was a real-life test of the laser system. It showed that using lasers, it is possible to ignite hydrogen (in this experiment, a mixture of hydrogen isotopes deuterium and tritium), producing a little more energy – therefore a net gain – than what the lasers supplied. However, if we take the energy to produce the 192 laser beams into account, then alas, we are still very far away from a net gain out of the experiment. The possibility of viable fusion energy production using lasers is at least a few decades away. It is as good as saying we do not know when; or if at all.

Why is such an experiment required, as the press release states, for the advancements in national defence? 

The Comprehensive Test Ban Treaty was originally thought to be an intermediate step towards total disarmament. Maintaining complex equipment – a thermonuclear nuclear warhead – was initially done by replacing faulty parts from the other disassembled bombs. It may still be possible to continue on this path if all the disassembled bomb parts are maintained in the inventory or if a few parts continue to be manufactured, even at a high cost. The question still remained: what about the health of the fissile material itself? How long would it remain stable and usable?

Ensuring the "health" of the bombs without conducting physical tests was the task of the "stockpile stewardship" program of the US National Nuclear Security Administration. The major test that the Lawrence Livermore Laboratories just conducted ensures that the nuclear materials are still functional: take a few samples from the stockpiled bombs, and ignite them using the complex 192 laser system that the Lawrence Livermore Laboratories has built. See whether the outputs are as expected. If so, the stockpile is still of "healthy" hydrogen bombs. So no physical tests are necessary, and the "crown jewels" – this is what Colin Powell called them – of the US weapons are still as potent as ever! And it also ensures that the people handling such complex tests really know what they are doing.

The National Nuclear Security Administration of the US government funds the team that worked on the laser project. Lawrence Livermore Laboratory itself, along with Los Alamos Laboratory, are the two biggest weapons research laboratories in the United States. In this particular case, the funding came from the stewardship program of the National Nuclear Security Administration, which looks after the health of the nuclear bomb stockpile that the US maintains.

How much does the ageing stockpile of nuclear weapons cost the US? Daniel Gross tells us in an article on this subject (An Ageing Army, May 28, 2016, that the upkeep of the stockpile – store, protect, and maintain – requires about $20 billion annually, almost three times that of the National Science Foundation budget.

While the primary purpose of the Lawrence Livermore Laboratories laser experiment was checking out the health of the hydrogen bomb stockpile, does it also have a major spin-off in terms of fusion energy? After all, there have been a number of such military-to-civilian transfers in the past. So why does this not herald a possibility of plentiful fusion energy? And therefore moving away from fossil fuels and global warming due to the emission of greenhouse gases? A simple issue of time is important here. If we do not cut our emissions drastically in the next 10-20 years, our window of reducing greenhouse gas emissions such that temperature rise can be limited to 2 Deg C will be over. We no longer have the luxury of time. So anything which is at least two decades away is no longer of importance in limiting global warming.

So let us forget global warming with respect to fusion energy. Can fusion energy be a source of grid energy, if not to stop or slow down global warming, but as a long-term, plentiful source?

Leaving out the easy answer – we already use fusion energy: the solar energy we use is actually from the fusion in the sun – yes, it is a possible source. The two questions we then need to address are: a) the science-technology question, what processes to use to produce as output more energy than we have to spend as input, and b) what is it going to cost us? The second question is always what technologists have to answer, ok it works but at what cost? Is it cheaper or at least comparable to other technologies?

The science component is the easy one to answer. As Professor Richard Rosner, in his interview with Bulletin of Atomic Scientists, said, we have solved this problem long back. In the hydrogen bomb, we use a fission device (a miniature atom bomb) as the trigger, and it causes fusion in the hydrogen envelope surrounding the trigger and initiating nuclear fusion. To quote Rosner, "So we have known how to fuse hydrogen and release energy for a long time – in 1952, we exploded the first thermonuclear device, whose detonation was largely the result of hydrogen fusion. So we've known how to do that for a very, very long time." What is different here is that it has been done under controlled conditions.

Is it the first example of controlled fusion? No, it has been done in other facilities as well and using electromagnetic compression of hydrogen in what are called Tokamaks. And in a few cases, the fusion lasted for much longer. What is new in the Lawrence Livermore Laboratories experiment is that there was more energy output than input from the lasers, which is why the term net gain. But if we take the amount of energy required to produce the 192 laser bombs used in compressing the tiny capsule containing the mixture of deuterium and tritium, that would be about a hundred times more than what the lasers supplied to the capsule.

Let us leave the question of the energy involved in firing the lasers out of the equation. To make the laser-firing of hydrogen a viable energy source, what is the scaling up that we need to do? The answer is quite depressing. Again quoting Rosner, we will need to fire such laser beams ten times a second and a million pellets/capsules per day before we can say such a process is viable. This is without taking into account the other key question, what will it cost and, therefore, will such a process be economically viable?

Are there better alternatives to fusion energy than using laser beams? The Tokamaks, where the mixture of various hydrogen isotopes as fuel are compressed by electromagnetic forces that lead to fusion. These have been tried out in various institutions. At the moment, the lead appears to be with the Chinese one called EAST, followed by the European Tokamak called JET. The ITER tokamak, an international project in which India is also a partner, is scheduled to come on stream by 2025. But it plans to produce sustained fusion energy using deuterium and tritium only by 2035, with an output 10 times that of the input. But it will still not produce electricity as that is a well-known technology with no new research component.

Why is it that we find it so difficult to produce fusion energy when all the stars, including our sun, can do it so easily? The answer is that the enormous gravitational force of the sun, which is, of course, a star, compresses the hydrogen far more easily than we can. Compressing hydrogen isotopes here on earth without such a gravitational force is the problem. That is why we are using lasers and electromagnetic forces to achieve what gravitational force does far more easily in the stars. We need alternates to fossil energy here and now. As I have written in these columns earlier, the challenge is storing the energy from renewable sources like the sun for the grid and switching to mass public transport for the energy transition we urgently need to make. Rather than solving the far more difficult problem of creating mini-suns here on earth.