But when researchers gathered at Novosibirsk in Siberia for the third IAEA fusion conference in August 1968, all the talk was about tokamaks. While the results that Lev Artsimovich had reported in 1965 at Culham had been impressive, the latest readings from the T-3 and TM-3 tokamaks were sensational. Again, the temperatures were not measured directly but the Russians calculated them to be more than 10 million °C, ten times that of any other toroidal machine. The confinement showed a similar improvement. Artsimovich was rigorously grilled by sceptical US researchers, particularly those from Princeton. They argued that the Russians were probably measuring the temperature of a small group of electrons that had been accelerated to a high speed, and were separate from the rest of the plasma – the same problem that had led to false optimism about ZETA, Columbus and the Perhapsatron.
Throughout the 1960s, the Russians had developed a close collaboration with the British fusion effort at Culham. The British, then led by Sebastian Pease, were still working with ZETA, a pinch device, and the Russian tokamaks were also a variant of the pinch, so they had things in common. Meanwhile, the Culham researchers had also perfected a new technique to directly measure the temperature of a hot plasma. They would shine a bright laser beam into the plasma and by analysing the spectrum of light that is bounced out by the particles they could accurately calculate the plasma temperature. At Novosibirsk, Artsimovich made a bold proposal to Pease: send a British team to Moscow with their laser thermometer, measure the temperature in the T-3 tokamak and settle the issue once and for all.
Pease travelled home and won the agreement of the British government to send his staff, and technology, to the Soviet Union. At the height of the Cold War, this unprecedented East-West collaboration would decide whether the tokamak was another embarrassment, along the lines of ZETA or Juan Peron’s Thermotron, or whether it was the breakthrough fusion had been searching for.
CHAPTER 4
Russia:
Artsimovich and
the Tokamak
WIND BACK THE CLOCK AGAIN, THIS TIME TO 1949 AND Sakhalin, a cold, remote and inhospitable island off Russia’s far eastern coast. Soviet forces captured a large part of the island from the Japanese in the closing days of World War II and for the soldiers stationed there after the war it must have been a desolate posting. But to Red Army sergeant Oleg Aleksandrovich Lavrentyev it offered what he needed: time to study. Lavrentyev had not finished school when he joined the Red Army at the age of 18, but what he had read about the fission of uranium and the possibility of a nuclear chain reaction excited him and he was determined to study physics. A veteran of battles against the Germans in the Baltic States during 1944 and 1945, he was posted to the east after the war. Working as a radiotelegraph operator, he had plenty of time to read. He got hold of physics textbooks, monographs and even subscribed to the academic journal Soviet Physics-Uspekhi. He would give reports and lectures to his officers on scientific and technical subjects. In 1949 he completed his school exams, having covered three years’ study in twelve months.
In August that year, the Soviet Union exploded its first atomic bomb, much to the pride of its citizens and to the surprise of the United States. A nuclear arms race had begun and the following January US president Harry Truman announced to Congress that the country’s nuclear scientists would accelerate efforts to develop a more powerful fusion weapon, the H-bomb. Lavrentyev realised that it was time to act. He wrote a short letter to Comrade Stalin explaining that he had worked out how to make a hydrogen bomb and also a way to control fusion reactions to generate electricity for industry. He waited. Nothing happened.
A few months later Lavrentyev wrote another letter, this time addressed to the central committee of the Communist Party of the Soviet Union. Then things started happening very fast. An officer came to interrogate him. He was then put in a guarded room and given two weeks to put his ideas down in writing. These were sent to Moscow via the Communist Party’s secret courier service on 29th July, 1950. He was then demobilised and sent off to Moscow. Stopping en route in Yuzhno-Sakhalinsk, the island’s capital, Lavrentyev was warmly welcomed by the regional Communist Party committee. Following his arrival in Moscow on 8th August, he sat the entrance exam and was enrolled as a student at Moscow State University. He had gone, in just a few weeks, from lowly radio operator in the far east to a student at the Soviet Union’s elite research university in Moscow.
In September he was summoned to see I. D. Serbin, head of the Communist Party’s department of heavy engineering industry. Serbin again asked Lavrentyev to write down his ideas about thermonuclear electricity generation, which he did in a classified security-protected room. Lavrentyev settled into the life of a Moscow university student but one evening the following January, as he arrived back at his room in the student hostel, he was told to ring a certain phone number. The person who answered was V. A. Makhnev, the Minister of Measuring Instrument Industry (the codename for the Soviet nuclear industry). Makhnev told him to come immediately to his office in the Kremlin. A man met Lavrentyev at the security gate and walked with him to Makhnev’s office. The minister then introduced Lavrentyev to his guide, Andrei Sakharov, father of the Russian H-bomb and, much later, a prominent Soviet dissident.
The previous summer, while working at Arzamas-16, one of the Soviet Union’s secret nuclear cities, Sakharov had been asked to look at the paper Lavrentyev had written in Sakhalin. In his report, Sakharov dismissed Lavrentyev’s idea for an H-bomb with a single sentence. Lavrentyev had proposed fusing hydrogen and lithium but Sakharov pointed out that this combination was not reactive enough to work in an atomic explosive (something that Lavrentyev would not have known from his readings on Sakhalin). The second suggestion, of using controlled fusion reactions to generate electricity, Sakharov found much more interesting. ‘I believe the author has formulated an extremely important and not necessarily hopeless problem,’ he wrote.
Lavrentyev’s scheme used electric fields to confine a plasma so that it would fuse. He described having two concentric spheres: the outer one would act as an ion source while the inner one, made of a metallic grid, would be put at a large negative voltage with respect to the outer one. This creates an electric field that will accelerate deuterium ions from the outer sphere towards the centre, where they form a hot plasma and fuse. The field also prevents the ions from escaping from the sphere. Sakharov pointed out a couple of reasons why the device, known as an electromagnetic trap, wouldn’t work. First, while the electric field would indeed propel ions towards the centre of the sphere, it works in the opposite direction for electrons, so they would be ejected from the device. As a result the plasma in the centre would be dominated by a positive electric charge which would stop the nuclei getting close enough together to fuse. Sakharov also thought that the low density of the plasma would mean that not enough collisions would take place. He didn’t exclude the possibility that improvements to the design could overcome these problems, but he concluded by saying, ‘It is necessary at this point not to overlook the creative initiative of the author.’ Lavrentyev, he thought, was worth cultivating.
Makhanev told the two of them that they would need to meet the chairman of the Special Committee on atomic weapons. Some days later they were again ushered into the Kremlin and to the chairman’s office. Sitting behind the desk was Lavrentiy Beria, the most feared man in the Soviet Union. Beria was in charge of Soviet security and the notorious secret police of the NKVD, the forerunner of the KGB. During the war he coordinated anti-partisan operations and ordered the execution of thousands of deserters and ‘suspected malingerers.’ He hugely expanded the Gulag slave labour camps and ordered the Katyn massacre of 22,000 Polish army and police officers. After the war he was elevated to deputy premier and took personal control of the crash programme to develop nuclear weapons. With Lavrentyev and Sakharov he was polite and formal, asking them about their families, including relatives who were in prison. Nothing nuclear was discussed. Lavrentyev got the impression that Beria was siz
ing them up, assessing what sort of people they were. As they left, Sakharov said to Lavrentyev that from then on everything would go smoothly and they would work together.
For Lavrentyev things did go smoothly. One evening, much to the alarm of his fellow students, darkly dressed men came and took him and his belongings away in a black limousine. His classmates feared the worst but he was back in lectures the next day having been installed in his own furnished room near the city centre. He was also given a generous scholarship, delivery of any scientific literature he asked for, and the university’s professors of physics, chemistry and mathematics tutored him personally. Soon after his interview with Beria he was visited by another official who took him to a government building where, after many security checks, he was introduced to two generals and a civilian with a copious dark beard. This time the conversation was much more technical but when it moved on to his H-bomb design Lavrentyev was unsure whether he should be talking about it. He told the three men that he had recently been to see Beria and the talk veered towards more practical matters. The bearded civilian was Igor Kurchatov, the head of the Soviet nuclear weapons programme. During the war, Kurchatov had vowed not to cut off his beard until his programme to develop a nuclear bomb for the Soviet Union had succeeded. After the first bomb was tested in 1949, Kurchatov decided to keep the beard and he often wore it trimmed into eccentric shapes. To his loyal staff, he was known simply as ‘The Beard.’
In May 1951 Lavrentyev was granted clearance to work at the Laboratory of Measuring Instruments (LIPAN), the Soviet Union’s secret nuclear research laboratory, alongside his university studies. When he arrived there, he found that a high-powered team was already working on a fusion device. To his dismay, it was not his electromagnetic trap but a magnetic design devised by Sakharov and his colleague and mentor Igor Tamm.
Despite now being at the very heart of the Soviet Union’s nuclear research effort, a place he could only have dreamed about a year earlier, Lavrentyev never fitted in there. His connection with the hated Beria made him an object of suspicion, while at the university his privileged status set him apart from the other students.
After the death of Stalin in March 1953, there was a brief struggle for power among members of the Politburo. Most of them feared and distrusted Beria and in June they had him arrested, moving a tank division and a rifle division into the city to prevent security forces loyal to Beria from rescuing him. Six months later Beria and six accomplices were accused of being in the pay of foreign intelligence agencies and of wanting to restore capitalism. They were executed days later. With his sponsor gone, Lavrentyev’s privileges evaporated and he was barred from LIPAN. Nevertheless, he finished his physics degree and went on to complete a doctorate, even without access to a laboratory. He got a job at the Physical-Technical Institute in Kharkov, Ukraine, where he continued, without success, to work on plasma confinement with an electromagnetic trap. Sakharov stayed in contact with Lavrentyev and always insisted that it was Lavrentyev’s paper written on Sakhalin that provided the spark for Russia’s controlled fusion research.
When Sakharov received that paper in the summer of 1950, he had already been thinking about controlled nuclear fusion but couldn’t figure out a way to achieve it. Although he didn’t think Lavrentyev’s electromagnetic trap would work, it did get him wondering about a magnetic trap instead. He discussed the problem with Igor Tamm. Although the two of them were working frantically on the H-bomb, they took some time out to consider the problem of controlled fusion. Following the same thought processes that Lyman Spitzer would work through in a few months’ time, they realised that charged particles could be held in place by a magnetic field because they would be forced to move in tight circles around the magnetic field lines. And by making the field lines go around in a circle inside a toroidal tube they could avoid the particles escaping off the end of the field lines – the lines would have no end. Like Spitzer, Sakharov and Tamm realised that the fact that the magnetic field was stronger on the inside of the curve than the outside would push particles towards the outer wall. But while Spitzer got around this by twisting the tube into a figure-of-8, the Russians instead twisted the magnetic field. They added a second magnetic field that did a vertical loop around the inside of the tube, and the combination of the two fields led to field lines that wound around the torus in a helical pattern. So a particle travelling around the ring would move in a tight spiral around a field line, and that field line would curve down the outer wall, say, at an angle and then across the bottom and up the inner wall. Hence the tendency of particles to drift towards the outer wall would be cancelled out by visits close to the inner wall.
In a tokamak, plasma particles still gyrate around the magnetic field lines but the lines also follow a helical path around the torus.
(Courtesy of EFDA JET)
Sakharov and Tamm enlisted the help of some theoreticians from the Lebedev Physics Institute in Moscow to flesh out the idea and then presented it to Kurchatov. Their boss was enthusiastic about the idea and began assembling a group of physicists to work on it at LIPAN. To lead the scientific effort, Kurchatov appointed one of his most able deputies: Lev Artsimovich. On 5th May, 1951 – as Spitzer was drawing up plans for his stellarator and a few months after Thonemann moved from Oxford to Harwell – the USSR Council of Ministers, with the approval of Stalin, passed a resolution launching Russia’s fusion research programme.
The researchers at LIPAN first turned their attention to how to produce a current around the torus. Starting off with a high-frequency alternating current, they soon switched to a unidirectional current pulse. In fact they found that the current moving around the torus created such a strong pinch effect that they began to wonder if the toroidal magnetic field that Sakharov had started out with was needed at all. So they began experimenting with straightforward pinch machines akin to Thonemann’s Mark I to Mark IV and Tuck’s Perhapsatron. But the researchers were having trouble getting higher temperatures from the pinch machines and although they produced some neutrons in July 1952 these turned out to be spuriously produced by instabilities.
As a result, their approach swung back towards using a combination of toroidal and poloidal magnetic fields, just as Sakharov had suggested. In 1955 they built their first tokamak-like device, although they hadn’t yet given it that name. However, like its predecessors, the new machine was not producing high temperatures. They didn’t realise it until later, but the problem was that the Russians were making their reactor vessels out of ceramics. Atoms knocked out of the vessel’s walls were polluting the plasma and radiating energy out of the plasma as UV light, so preventing it from getting hot. The Russian effort was not making progress and they were running out of ideas.
Partly as a way of injecting some new blood into his fusion teams, Kurchatov decided in 1955 that he needed to get the field declassified. He started by organising a conference of scientists from all over the Soviet Union and revealed LIPAN’s work on controlled fusion. Delegates, who didn’t even know that the programme existed, were stunned by the scale and quantity of the work already done. The following April, Kurchatov surprised western scientists by describing Soviet fusion research in his famous speech at Harwell. Now that the ice was broken, discreet connections between East and West were made at scientific conferences, even though the topic had not been officially declassified. In the autumn of 1956, for example, Artsimovich and a colleague attended an astrophysics conference in Sweden where they made the acquaintance of Princeton’s Lyman Spitzer and Harwell’s Sebastian Pease.
With their own research stalled, the Russian team was astonished to read in British newspapers in January 1958 about the success of ZETA. From the scant details and photographs in the media reports, theorists at LIPAN scrambled to figure out what sort of a machine ZETA was. From the pictures, they realised that it had to be a compact torus – more like a doughnut than a hula-hoop – but the only way they could see to contain the plasma in such a vessel was with tokamak-like magnet
ic fields. Once the issue of Nature arrived with the articles by the ZETA team and their US colleagues, the Russians realised they were wrong. Although the ZETA results turned out to be false, the theoretical work that the LIPAN team did trying to understand it helped them in the plans for the first large tokamak, T-3.
In Russia just as in the West, nuclear authorities decided to completely declassify Soviet fusion research just before the 1958 Geneva conference, so the Russian researchers arrived there with all their papers recently published in hefty four-volume sets, ready to share with their new-found Western colleagues. Spitzer’s stellarators were the surprise of the conference for the Russians. It was an approach, with its steady-state operation and long figure-of-8 or racetrack-shaped vessels, that had not occurred to them. Kurchatov was so taken with the idea that he ordered construction of the T-3 to stop so that a stellarator could be built in Moscow instead. LIPAN theorists compared the two approaches and argued forcefully in favour of the tokamak. Kurchatov relented and they left the stellarator to the Americans.
Russian fusion research was still having problems, but at least they were problems that could now be shared with like-minded colleagues in the West. The challenges they all faced included short confinement times, low plasma temperatures and Bohm diffusion. Following the ZETA debacle, researchers everywhere were going back to basic plasma physics and trying to understand better how plasmas work. The Soviet authorities considered the pursuit of fusion a high priority so there was no shortage of money for experiments at LIPAN. Because their understanding of plasma was poor and their instruments were rudimentary, the team of mostly young researchers there would simply build one device after another with slight variations of design to try out different ideas in the hope that one might show some improvement in performance.
Piece of the Sun : The Quest for Fusion Energy (9781468310412) Page 10