Piece of the Sun : The Quest for Fusion Energy (9781468310412) Page 16

  Strachan tried again and found he could produce these shots – which his colleagues soon dubbed ‘supershots’ – on demand. The key seemed to be the preparatory cleaning shots using helium, so the TFTR team set up a protocol to prepare the machine that way before every shot. This conditioning took anywhere between two and sixteen hours for every supershot, but it was worth it. The plasma current had been low in Strachan’s initial efforts, but with further experiments researchers managed to push the plasma current up, until at last they were working with plasmas that were a lot more like the ones needed for a fusion reactor, with temperatures above 200 million °C. Finally, the TFTR team could again see a path to D-T shots and alpha-heating.

  JT-60 was the only one of the three giant reactors to have been built with a divertor, but it was positioned half way up the outside wall. When the Naka team tried to produce H-mode, they found that they just couldn’t get the right magnetic configuration with the divertor where it was. The Japanese researchers worked with the reactor for just four years and then in 1989 made a bold decision: they gave JT-60 a complete refit, installing a new divertor at the bottom and covering the whole interior with carbon tiles. The rebooted JT-60U began operating again in 1991 and the gamble paid off because it was soon operating in H-mode with properties as good as JET’s.

  By the beginning of the 1990s, TFTR and JET had refined supershots and H-mode to such an extent that they were getting fantastic results. TFTR could reach ion temperatures of 400 million °C. One measure of success is gain, the ratio of fusion power out over heating power in, denoted by Q. So break-even would be Q=1. At a conference in Washington in 1990, the two teams reported shots that, if they had been performed with D-T plasma, would have achieved Q=0.3 for TFTR and Q=0.8 for JET. Two years later the JET team announced that they had produced shots that would be Q=1.14 in D-T – more power out than in – but this record was soon bettered by JT-60U, which achieved Q=1.2. Although it had taken longer than expected for the big tokamaks to achieve this sort of performance, because of the problems with degraded confinement, they had got there. But just as the teams at Princeton and Culham were starting to think about tritium and burning plasmas something unbelievable happened: a pair of scientists declared that they had achieved fusion in a test tube.

  On 23rd March, 1989, Martin Fleischmann, a prominent electrochemist from Southampton University, and Stanley Pons of the University of Utah stood up in a press conference in Utah and described an experiment they had been performing in the basement of the university’s chemistry department. They took a glass cell – little more than a glorified test tube – and filled it with heavy water – made from deuterium and oxygen. They inserted two electrodes, one of platinum and one of palladium, and then they passed an electric current through it. Nothing much would happen in the cells for hours or even days but then they would start to generate heat; much more heat, Fleischmann and Pons said, than can be explained by the current passing through the cell or any chemical reactions that might be taking place. Their best cell, Pons said, produced 4.5 watts of heat from 1 watt of electrical input: Q=4.5. They didn’t believe that a chemical reaction could be producing such heat and so it had to be a nuclear process, in other words the fusion of deuterium nuclei into helium-3 and a neutron.

  Part of what was going on in the cells was an everyday process called electrolysis. When they passed a current through the cell, heavy water molecules were split apart and the oxygen ions migrated towards the positive, platinum electrode while the deuterium ions moved to the negative, palladium electrode. But the choice of electrodes was key because palladium is well known to have an affinity for hydrogen, and hence for deuterium too. It is able to absorb large quantities of hydrogen or deuterium into its crystal lattice structure. During the hours when the cells are first switched on, the palladium electrodes absorb more and more deuterium. Pons believed that eventually there would be twice as many deuterium ions in the lattice as there were palladium ones.

  The next part is where it all becomes strange. Pons and Fleischmann believed that some of these deuterium ions, crushed together in the palladium lattice, somehow overcame their mutual repulsion and fused. As evidence for fusion, Fleischmann and Pons said they had detected neutrons coming from the cells – which would be expected from such a fusion reaction – as well as both helium-3 and tritium – other possible fusion products. The two scientists were cautiously optimistic about the usefulness of their discovery. ‘Our indications are that the discovery will be relatively easy to make into a usable technology for generating heat and power,’ Fleischmann told the press conference. The Utah announcement caused a sensation around the world. Newspapers, TV and radio picked up the story. The idea that you could generate as much heat and electricity as you wanted using a simple glass cell filled with deuterium from seawater fired people’s imaginations. No longer would the world be dependent on coal, oil, natural gas and uranium.

  The initial reaction of fusion scientists was utter incredulity. It just didn’t make sense. As far as they had always understood it, deuterium ions are extremely reluctant to fuse because of their positive charges. Those charges make the ions strongly repel each other and it takes a huge amount of energy to force them close enough together to fuse. Inside a metal lattice, where was all the energy coming from to overcome the repulsion? But there were reasons for fusion scientists to pause for thought. The behaviour of ions inside a metal lattice is much stranger and harder to predict than in the near empty space inside a tokamak. Lattices do funny things to ions, affecting their apparent masses and how they interact with other ions. This was an environment that most plasma physicists had little knowledge of. Could it be that it was just something that they had missed? The two scientists were highly respected – Fleischmann was one of the world’s foremost electrochemists. And these two men must have been pretty sure of their results to stand up and make such bold claims in front of the world’s press, without the usual procedure of having published their results in a journal first and subjecting them to review by other experts.

  In the days that followed the press conference, it also emerged that another group at a different Utah institution – Brigham Young University – had been doing similar experiments and had also detected neutrons and heat, but much less heat than Fleischmann and Pons found. Also fusion researchers found themselves called upon in the media to explain what fusion is all about, and to justify why they needed such huge complex tokamaks to achieve it. All of a sudden these machines seemed a wasteful extravagance.

  One of the benefits of such a simple experimental setup as the one in Utah is that it is very easy for other scientists to carry out similar tests to verify or refute it. Within days researchers the world over had current flowing through heavy water and were waiting to see the same signs of fusion taking place. It took a few weeks for the first results to come in. A team at Texas A&M University also detected excess heat in their cells, which were modelled on Pons and Fleischmann’s, but they hadn’t yet tested for neutrons. Other results came in from labs all over the world in the following weeks, but they didn’t make things any clearer: some saw neutrons but not heat, others got heat but no neutrons, and some found nothing at all. Researchers at Georgia Tech announced they had found neutrons, only to withdraw the claim three days later when they realised their neutron detector gave false positives in response to heat.

  That didn’t stop Pons being greeted as a hero when he appeared at a meeting of the American Chemical Society in Dallas on 12th April. Chemists were enjoying their moment in the Sun. There was a recent precedent of a miraculous discovery by a pair of researchers working on their own. Three years previously physicists had been stunned when two researchers in a lab in Switzerland announced the discovery of high-temperature superconductivity. That led to a now legendary session at the March 1987 meeting of the American Physical Society in New York City. Thousands of scientists crammed into a hastily arranged session – now referred to as the ‘Woodstock of physics’ – to hear
all the latest results about these wondrous new materials. For the 7,000 chemists who gathered in Dallas to hear about cold fusion, it was their turn to make history.

  The president of the Chemical Society, Clayton Callis, introduced the session by saying what a boon fusion would be to society and commiserated with physicists over what a hard time they were having achieving it. ‘Now it appears that chemists have come to the rescue,’ he said, to rapturous applause. Harold Furth, director of the Princeton fusion lab, came to make the case for conventional fusion. He didn’t think nuclear reactions were happening in the Utah pair’s cells. Certain key measurements hadn’t been done so the proof for fusion just wasn’t there. But that wasn’t what the chemists wanted to hear. During his presentation, Furth had shown a slide of his lab’s giant tokamak, TFTR – the size of a house, bristling with diagnostic instruments and sprouting pipes and wires. When Pons came on afterwards he flashed up a slide of his own setup: a glass cell the size of a beer bottle held by a rusty lab clamp in a plastic washing-up bowl. ‘This is the U-1 Utah tokamak,’ he said, and the crowd went wild.

  Despite the enthusiasm of the chemists, people were starting to ask hard questions about cold fusion. One was over the shortage of neutrons. Those labs that did see them never found very many. If the cells in Fleischmann and Pons’ experiments were really producing as much heat as they claimed via conventional fusion reactions, they should be producing enough neutrons to kill the experimenters. In fact researchers were detecting one-billionth the number that would be expected. Some suggested that this was a new form of fusion that produces heat but no neutrons. More results came in from other labs, but they were still contradictory. One troubling observation was the erratic nature of the heat produced: sometimes cells would run for days producing nothing, then put out a burst of heat, continue for a while then stop.

  Fleischmann and Pons didn’t help the situation by being reluctant to give out too much information about their experiment. The paper that they submitted to Nature just after the March press conference was returned with questions from the reviewers – a standard procedure – but Fleischmann withdrew it from publication saying he was too busy to make the asked-for revisions. In public, their responses to questions were often evasive and sometimes downright cryptic. At the Dallas chemistry conference Pons was asked why he hadn’t done a control experiment using normal water. Although normal water and heavy water have different nuclei, they are chemically identical so if the effect they were seeing was a chemical reaction then a cell filled with normal water should behave in exactly the same way. Such a control experiment would be an obvious thing for any experienced scientist to do. But Pons said using normal water was not a good control. Asked why not, Pons suggested that they had done it and had seen fusion. ‘We do not get the total blank experiment we expected,’ he said.

  On 1st May the American Physical Society had its meeting in Baltimore. It also scheduled a special session on cold fusion but this was no Woodstock. By this time, and with this audience, the mood was very different. Neither Fleischmann nor Pons attended the Baltimore meeting but a seventeen-strong team of chemists and physicists from the California Institute of Technology described their attempts to replicate the Utah experiments. They found many places where mistakes could have been made and concluded that you could explain the results without resorting to fusion. ‘We’re suffering from the incompetence and delusions of Professors Pons and Fleischmann,’ said Caltech theoretical physicist Steven Koonin. ‘The experiment is just wrong.’ At the end of the session the nine main speakers were polled and eight declared they thought cold fusion was dead, the ninth abstained.

  Meanwhile, Fleischmann and Pons were in Washington demonstrating their apparatus to members of Congress while officials from the University of Utah tried to persuade the politicians to provide as much as $40 million for a $100-million cold fusion research centre in Utah. Congress declined but the Department of Energy was asked to investigate cold fusion. The DoE report, published in July, said that it doubted the Utah results were the signs of a new nuclear process and, in any event, whatever was going on in the cells wasn’t going to provide a useful source of energy. So there would be no federal cold fusion research programme, but the report said that enough questions remained for the Department of Energy to fund a few studies through normal channels.

  By now, only a few months since it was born, cold fusion was running out of friends. The major US newspapers had long since stopped running stories. Most labs had quietly given up on their cold fusion studies but there remained a determined few groups who were convinced that, whether or not it was fusion, there was something interesting going on in these cells that deserved investigating. The state of Utah agreed and put up $4.5 million in August to set up the National Cold Fusion Institute. But for most of the scientific world, the cold fusion saga was over. Many now consider it an example of ‘pathological science,’ where a combination of wishful thinking and misinterpretation of complex results causes researchers to hold fiercely to an idea that most have dismissed. Fleischmann and Pons left the US in January 1991 and set up a lab in France funded by the Toyota car company. The lab was closed in 1998 having still not achieved fusion in a bottle. The National Cold Fusion Institute closed in June 1991 when it ran out of money.

  Although the whirlwind of excitement around cold fusion did not last long, it cast an uncomfortable spotlight on the state of conventional, hot fusion. Scientists had been working on it for more than four decades and had spent billions on increasingly complex machines, but still they had generated no excess heat. But by the early 1990s, most felt that they were close. The big tokamaks had shown, using deuterium alone, they could get plasmas dense enough and hot enough that – if there had been tritium in there – a large number of fusion reactions would take place and the alpha particles generated would start to heat the plasma themselves. The researchers at Princeton and Culham, however, were in no hurry to move to D-T operation. They were learning a lot with their machines about how to get good confinement, how to create long stable pulses, and how to control instabilities. Moving to D-T would make everything more difficult: the reactors would need more shielding to protect people from neutrons; every scrap of radioactive tritium would have to be accounted for; and the bombardment of neutrons would make the reactor itself moderately radioactive – or ‘activated’ – so any later modifications inside the vessel would be much more complicated.

  The Culham researchers were coming under some pressure from the JET council to move ahead with D-T experiments. The reactor was working well; the tritium handling facilities were built; the council wanted to see some energy. But Rebut and his team had another good reason to delay D-T: they wanted to refit the interior of JET with a divertor, which was now thought to be essential for a future power-producing reactor. Apart from the role it plays in H-mode, a divertor would be able to extract the fusion exhaust – the alpha particles – and stop the plasma getting clogged up with them. Getting experience using a divertor would pay dividends when planning future reactors. Here was the dilemma: installing the divertor first would delay D-T experiments for too long; doing D-T first would make the interior activated so the whole refit would have to be done with remote handling, a slow and laborious process. So they came up with a compromise plan: they would do some shots with a plasma of 90% deuterium and 10% tritium. This would provide real evidence of plasma burning, but would keep the rate of neutron production at a low level so the vessel interior wouldn’t get too activated.

  The interior of JET, showing limiters on the central column, radio antennas on the outside wall and a divertor at the bottom.

  (Courtesy of EFDA JET)

  There was much to be done to get the reactor ready for D-T operation. The shielding had to be checked, the tritium handling tested, two of JET’s sixteen neutral beam sources had to be set up to fire tritium instead of deuterium, and the researchers had to work out what was the best kind of pulse to get the plasma to burn. They settled on a
plasma current of 3 MA, a toroidal magnetic field of 2.8 tesla and 14 MW of neutral beam heating – experiments with deuterium showed that as soon as the heating beams kicked in this plasma swiftly went into H-mode and the number of neutrons produced from D-D fusions continued to grow. It was a time of high excitement: many of those who worked on JET had spent their entire working lives trying to make a plasma that would burn; now they were going to see if it was all worthwhile. Media organisations got a whiff that something was going on and asked if they could be present at the first burning plasma. Rebut thought about it and decided that the public had paid for it and so the public had a right to know what was going on. It was a potentially risky strategy, however, because it could fail to work. Fusion researchers had been burned before with ZETA and didn’t want the same thing to happen again.

  On the appointed day, 9th November, 1991, hundreds of people crowded into the JET control room – researchers, officials, journalists. Getting the machine ready wasn’t a quick process. First the researchers did some shots with just deuterium to check they were still getting the plasma performance they wanted. Then they carried out some shots containing a trace of tritium, less than 1%, to test the diagnostics. Then the moment of truth arrived. The crowds in the control room craned to see screens that showed an image of what was going on inside the vessel. As the shot started they could see the diaphanous plasma form inside the vessel and when controllers switched on the neutral beams, including those firing tritium, the screens whited-out as neutrons flooded the camera. The control room erupted into applause. They had achieved the first controlled release of significant amounts of fusion energy.