Research Profile

 by Luisa Bonolis

Pyotr Kapitsa

Nobel Prize for Physics 1978 "for his basic inventions and discoveries in the area of low-temperature physics".

From Petrograd to the Cavendish Laboratory in Cambridge
Pyotr Leonidovich Kapitsa was born in 1894 in Kronstadt, an island off the coast of St. Petersburg, into a family with strong intellectual traditions. After graduating from the Classical Gymnasium, he entered the Electromechanics Faculty of the St. Petersburg Polytechnic Institute. His studies were interrupted by the 1914 war, and for two years Kapitsa volunteered as ambulance driver at the Polish front. After the end of the war, he returned to the Petrograd Polytechnic Institute where he graduated in 1918 and was appointed to a teaching post. At that time, Abram F. Ioffe, a specialist in X-ray crystallography and physics of the solid state, was actively developing a school of physics with a more modern outlook and collected a group of young scientists around him who formed the nucleus of the enormous growth of Soviet physics in later years. Ioffe had recently established a seminar in which a number of future luminaries of Soviet physics participated. After some early research on the angular momentum associated with magnetisation of matter, Kapitsa studied atomic and molecular beams and together with his friend Nikolay Semenov, he proposed a technique for measuring the magnetic moment of an atom by observing the spread of an atomic beam after passing through a strongly inhomogeneous magnetic field. Such a technique was independently proposed and successfully applied by Stern and Gerlach to provide the demonstration of spatial quantisation. Many years later, Stern was awarded the Nobel Prize For this result. In this period, Kapitsa also proposed to focus a broad beam of X-rays by a bent crystal, anticipating an important practical technique realised in 1933 by T. Johannsson.
In the terrible conditions following the Russian Revolution and the Civil War, food and fuel were in short supply; famine and epidemics broke out. Kapitsa lost his young wife, whom he had married in 1916, and his two small children to scarlet fever and the Spanish influenza. Overwhelmed by these tragic losses, he was unable to work for a time. To help him in this difficult personal situation, Ioffe appointed Kapitsa to join a commission of the Russian Academy of Sciences for renewing scientific relations with other countries. At that time, as an ambassador of science who helped re-establish contacts with western scientists after World War I and the revolution, Ioffe journeyed abroad several times in order to obtain various apparatuses and reagents and renew subscriptions to foreign journals. However, travel abroad at that time was complicated because of lack of diplomatic relations with most of the outside world. Germany, France and Holland did not want to admit a young scientist from the young revolutionary Soviet regime, but eventually Ioffe succeeded in getting Kapitsa an English visa, and in June 1921 Kapitsa and Ioffe started a round of scientific visits, which culminated in a visit to Rutherford, the director of the Cavendish Laboratory in Cambridge. Kapitsa asked if he might work in the Cavendish for a few months, and eventually Rutherford admitted him even if he had initially turned down his request, saying his laboratory was already too crowded with thirty scientists.
Kapitsa joined the Cavendish in July 1921 and although the original plan was for him to stay only over the winter he remained for 13 years. From the start Rutherford was impressed by Kapitsa's ability to select research problems and always appreciated him for the unique combination of engineer and physicist in one person. After the usual initiation of practical work in the Cavendish attic - the so called “Nursery” - under James Chadwick's supervision, Rutherford suggested Kapitsa to study how the energy of an alpha-particle in a magnetic field falls off towards the end of its range. Research work led by Rutherford at Cavendish in those years was focusing on the transmutation of the lighter elements begun by Rutherford himself at Manchester and now continuing in close collaboration with James Chadwick. It was in 1919 that Rutherford had bombarded nitrogen with alpha particles from radium, carrying out the first artificial transmutation of a nucleus, and creating “atoms of hydrogen” which he named protons and, as was later proved by Patrick Blackett with his cloud chamber, oxygen nuclei. This was the first observation of an artificial nuclear reaction, obtained with a natural source.

Rutherford wanted to know everything about his beloved alpha particles; in particular he wanted to know exactly how the last fraction of the energy of alpha particles interacting with matter was expended. The dependence of alpha-particle energy loss on its speed and the structure of the atom had been examined by two methods. The first was that in which the alpha particle was projected through different thicknesses of material, its emergent velocity being measured by the deflection produced in a magnetic field. This was, a priori, the most exact method of attack, but in the experiment there was a weak point, in that the deflected beam must be observed, photographically, or by means of scintillations, and towards the end of the range, when the energy is small, these methods of detection lost their sensitiveness. The second method consisted in the study of the amount of the ionisation produced by the alpha particle in different parts of its range. The weak points of this method was a) that the assumption that all the energy of the particle is lost in the production of ions, and that each ionization requires the same amount of energy, has no definite theoretical or experimental foundation and b) that the method could not be applied to matter in the solid state. Up to that moment, no alpha-particle had been detected by those methods with a velocity less than 40 % of that of the alpha-particle from radium C. Consequently, it was not known how the last 16 per cent of the energy of the alpha-particle is expended, in spite of the fact that this energy is quite considerable.
Kapitsa's method was to measure the energy in a collimated beam of alpha-particles by the heating effect which it produced, after having travelled a certain portion of its range, in a plate attached to a Boys radiomicrometer, made sufficiently sensitive and modified to fulfil the requirements of small thermal capacity and the ability to reach a state of equilibrium rapidly.
He successfully constructed a sensitive micrometer and applied it to the measurement of the distribution of energy in an alpha-beam bringing this project to conclusion. Within nine months he drafted a paper for publication in the Proceedings of the Royal Society and wrote to his mother: “Only now have I really entered the Crocodile's school... which is certainly the most advanced school in the world and Rutherford is the greatest physicist and organiser. It is only now that I have felt my strength. Success gives me wings and I am carried away by my work.”
“Crocodile” was a nickname Kapitsa invented for Rutherford. Many years later he explained: “In Russia the crocodile is the symbol for the father of the family and is also regarded with awe and admiration because it has a stiff neck and cannot turn back. It just goes straight forward with gaping jaws - like science, like Rutherford.” In his letters Kapitsa always mentioned Rutherford with enthusiasm and their relationship was always built on mutual respect and deep friendship.
A real turning point in Kapitsa's career was the idea of producing very large magnetic fields, lasting only a very short time, to study how the alpha-particle velocity varied along its track by measuring the track curvature. Existing magnets at the time were not capable of producing large enough steady fields. Once large impulsive magnetic fields had been achieved, Kapitsa saw new perspectives for exploiting the technique that eventually led him into pioneering work in solid state and low temperature physic. That was also the beginning of the transition of the Cavendish from the string and sealing wax tradition to the age of large machine physics.

In order to store a large quantity of energy to be converted into electrical power and rapidly discharged through a coil, Kapitsa chose a chemical store, which he could build himself, instead of a much more expensive electrical condenser. The preliminary experiments were completely successful and Rutherford was enthusiastic, as Kapitsa wrote home: “My experiments are assuming a very broad scope... I shall remember my last conversation with Rutherford as long as I live. After a whole lot of compliments he said `I should be very happy if I could have the possibility of creating a special laboratory for you in which you could work with your own students...' Am I really such an able person? ... Will I be able to cope?”
The impulsive field method was a success. After a couple of months everybody could admire the first photographs of the curved tracks of alpha particles detected in a cloud chamber operated within the high field equipment. While all this work was progressing, Kapitsa was officially admitted as a research student for the Ph.D. degree, with backdating to October 1921, and he obtained a year's remission in view of his Russian Work. He thus completed his Ph.D. in the summer of 1923. Soon after he was awarded a Clerk Maxwell Scholarship and was also admitted as a member of Trinity College.
Kapitsa fully enjoyed the unique atmosphere of Cambridge and the Cavendish Laboratory, but he missed the lively discussions of Ioffe's seminars in Petrograd. So he soon started an informal discussion group of his own that held its first meeting in October 1922. He established certain strict rules according to which no one could remain a member after missing more than a small number of consecutive meetings, and members were regarded as permanent only after they had themselves given a talk. This weekly seminar soon came to be called the “Kapitsa Club”. A minute book was started and the tradition was established that the speaker should add his signature to the title of his talk. Many leading physicists outside Cambridge participated in the activities of the Club and presented key advances of the time that were eagerly discussed sometimes ahead of publication.
After publishing his last paper on alpha-tracks in a strong magnetic field, Kapitsa started an even more ambitious project for the production of hyperstrong impulsive fields. He conceived the idea of a new method in 1924, in the course of discussions with a Russian electrical engineer, M. P. Kostenko, who calculated that it should be practicable to design a large dynamo that on short circuit through a suitable coil could generate very high power for a very short time and so produce a field of order 106 G. The main difficulty stemmed from the overheating of the coils. Kapitsa proposed an original method for overcoming this obstacle - namely, by the creation of brief magnetic fields following the passage of a very strong current through the coil; during such brief intervals the coil does not overheat.
The stored energy would be the kinetic energy of rotation of the dynamo rather than the chemical energy of the accumulator, a method that was in practice limited to fields of little more than 100 kG, and required difficult repairs after comparatively few discharges.

Once again Rutherford enthusiastically supported Kapitsa's project, which, however involved expenses of a bigger order of magnitude than could be provided from Cavendish funds. Rutherford turned to the Department of Scientific and Industrial Research and the big dynamo, the centrepiece of the scheme, was designed, built and successfully tested at Metropolitan-Vickers in Manchester in early summer 1925. After some difficult problems had been tackled, Kapitsa successfully used the high field machine to open up several new fields of research.
His main project was an extensive study of how the electrical resistance of metals increases with magnetic field. He was able to fit his results to a phenomenological theory of magnetoresistance at a time when the electronic theory of metals was still in its infancy. One of the most important results of Kapitsa's research into the physical properties of matter in strong magnetic fields was his discovery of a linear relationship between the magnetic field and the electric resistance of a number of metals subjected to very strong magnetic fields. He discovered that the electrical resistance of metal increases with magnetic field, a phenomenon known as Kapitsa's law of magnetoresistance. This law, discovered by Kapitsa in 1928, found its theoretical explanation much later, following the discovery of the properties of the structure of Fermi surfaces in metals. He also studied the magnetostriction of para-and diamagnetic substances in strong magnetic fields and discovered the abnormally high magnetostriction of bismuth monocrystals.
In 1925, he was appointed Assistant Director of Magnetic Research, an official University position, and was also elected to a Research Fellowship at Trinity College. He also married Anna Alekseyevna, daughter of the Admiral A. N. Krylov, a well-known naval engineer and applied mathematician, who had been an important member of the Commission of the Russian Academy of Sciences and had invited Kapitsa jointly with Ioffe to join the mission abroad.
In 1929, Kapitsa was elected to Fellowship of the Royal Society, a rare distinction, but even rarer at a time when the Royal Society was relatively closed to foreigners. He was simultaneously recognised in his own country by election to Corresponding Membership of the Soviet Academy of Sciences in 1929. During this time, he travelled widely in Europe and was a part of the international physics community. He also succeeded in finding short-term fellowships for several Soviet physicists, such as Aleksandr Leipunskii and the theoretician Lev Landau.
In 1930, Kapitsa discussed with Rutherford the possibility of setting up a new laboratory that could house not only the high field equipment, but also provide cryogenic facilities to extend his researches to much lower temperatures. As usual, Rutherford backed this idea enthusiastically and the money was found from a bequest to the Royal Society by Ludwig Mond. The building of the Royal Society Mond Laboratory started in 1931 in the courtyard of the Cavendish.

In the course of devising unique equipment to measure the temperature-dependent effects of high-strength magnetic fields on the properties of matter, Kapitsa was drawn into the field of low-temperature physics. This work involved the use of liquefied gases, which were not readily available in large quantities, to attain very low temperatures. This soon became one of the main motivations for developing a more efficient and safer way of producing large quantities of liquid helium for use as a cryogenic fluid. The liquefaction of helium had first been achieved in 1908 by the Dutch physicist Heike Kamerlingh Onnes at the University of Leiden, by using several stages through with he lowered the temperature to the boiling point of helium, 4.2 K. By reducing the pressure of the liquid helium he achieved a temperature near 1.5 K. These were the coldest temperatures achieved on earth at the time. His production of extreme cryogenic temperatures led to his discovery of superconductivity in 1911: Onnes found that at 4.2 K the resistance in a solid mercury wire immersed in liquid helium suddenly vanished. He was awarded the Nobel Prize in 1913 for his low temperature researches “which led, inter alia, to the production of liquid helium”. Subsequently, Onnes and others discovered that liquid helium exhibits odd behaviour. By 1924, Onnes had measured liquid helium's density and determined that as the temperature decreases, the density goes through a sharp maximum at about 2.2 K.
Kapitsa applied his considerable physics and engineering skills in the design of a remarkably efficient apparatus for liquefying helium, which was capable of producing 2 litres per hour, compared with Kamerlingh Onnes's method, which took several days to produce only small amounts of impure liquid helium. Before the new laboratory was ready, Kapitsa and John Cockcroft had already completed a hydrogen liquefier, the first step in the advance towards lower temperatures. At that time, Cockcroft was already working at the problem of accelerating protons by high voltages, in collaboration with E. T. S. Walton. In 1932, Cockcroft and Walton successfully disintegrated the nuclei of lithium and other light elements by protons entirely artificially accelerated by high-energy potentials. For this achievement they shared the Nobel Prize in physics for 1951. Kapitsa and Cockcroft always remained close friends, and the latter eventually became head of the Mond Laboratory in 1934.
In constructing a helium liquefier, Kapitsa chose a completely original method, achieving the main cooling by adiabatic expansion in a piston and cylinder engine and solving the problem of lubricating the piston - never solved before - by the ingenious expedient of using the helium gas itself as the lubricant. The machine was completed in 1934 and provided liquid helium for over 10 years of Cambridge research. For the first time, a machine had been made which could produce liquid helium in large quantities without previous cooling with liquid hydrogen. This heralded a new epoch in the field of low-temperature physics. It also supplied the basic idea for a factory-built helium liquefier designed by S. C. Collins at the Massachusetts Institute of Technology, which revolutionised low temperature physics by making liquid helium easily accessible all over the world.
At Cambridge, Kapitsa's reputation and career had advanced rapidly, and in 1933 he became the director of the new Mond Laboratory, whose formal opening was a great occasion, announced in the February issue of Nature. A life-size crocodile, carved on the wall just outside the main entrance, and a bas-relief of Rutherford himself, inside the foyer, both by Kapitsa's friend, the sculptor Eric Gill, were revealed. Kapitsa, however, was to work there for only one year.

Return to the Soviet Union
While remaining a Soviet citizen, he had always been able to go in an out of the Soviet Union at will, visiting his native country nearly every summer. He always had his permission to return underwritten, but his friends wondered whether his exclusive status could continue indefinitely. At that time, Georgii Antonovich Gamow, the famous Soviet theorist who proposed the quantum theory of nuclear decay, had applied for permission to stay abroad longer. He actually decided not to return to the Soviet Union after the Solvay Conference in October 1933 and advised Kapitsa not to return to the Soviet Union in 1934. But in August 1934, Kapitsa made his usual summer trip accompanied by his wife and after attending a congress in Leningrad he was preparing to return to England early in October when he was told that his permission to return was no longer valid and that he would have to stay in the Soviet Union. Anna was allowed to return to Cambridge and she personally told Rutherford what had happened.
A series of reasons probably influenced this decision. In particular, owing to the great expansion of the Soviet economy and the concomitant need for a rapid growth of science, Kapitsa was viewed as a key person for the building of an Institute in Moscow on the lines of the Mond Laboratory in Cambridge. Soviet officials responsible for Kapitsa's fate may have also been influenced by their experience with Gamow. They may reasonably have suspected that Kapitsa, too, would remain outside his homeland permanently.
Meanwhile, Soviet officials made it almost impossible for scientists to travel abroad for any length of time. They suspended international conferences scheduled in the Soviet Union. No one was to publish in a foreign journal; private correspondence with foreigners became exceedingly dangerous. Kapitsa was but one scientist affected by this new isolationist trend in the Soviet Union.
Kapitsa was devastated by his inability to return to Cambridge. At the same time Rutherford made diplomatic attempts to convince the Soviet establishment figures to let him go back to his laboratory in England. Eventually the affair leaked to the Press and became public. During all those months, Kapitsa felt very frustrated, lonely and depressed, surrounded by hostility and suspicion, missing his family and his work. He even thought of leaving physics for physiology, so that he could collaborate with I. P. Pavlov. By the end of 1934, very unhappy with the situation, Kapitsa began to cooperate in planning the new Institute for Physical Problems of which he was appointed director. He gradually convinced the authorities that he couldn't do anything useful unless he had facilities similar to those in Cambridge. Difficult negotiations started with Rutherford for transferring Kapitsa's special equipment from the Mond Laboratory to the new Institute in Moscow. The agreement provided that, in return for the payment of 30000 pounds, the University would transfer to Moscow the high field equipment and duplicates of equipment needed in Cambridge to continue the activities. In addition, the University would give a year's leave of absence to Kapitsa's key assistants, Laurmann and Pearson, so that they could help him set up all the equipment in the new Institute as quickly as possible.
In the meantime, his wife Anna and his two children rejoined him, and all the equipment, including the big dynamo were sent to Moscow. Kapitsa had worked hard to get everything ready to install the equipment as soon as it arrived. In October 1936, when the institute was in a state of being finished, he wrote to Bohr: “ I am trying my best to help the people here ... organize science, and it is my conviction that the injustice done to me must not blind me ... to this world. During great historical moments there are always victims, such is life, and the worst in my case is over. I feel the responsibility of my position, especially having the experience which I gained in Cambridge. Besides just resuming my work here, I think I must try to organize my Institute in such a way as to show people here all the healthy and powerful methods of the work in the Cavendish. I will try to follow Rutherford's methods as far as I am capable.” By the end of 1936, everything was completed, and Kapitsa was able to carry on his scientific work. But his forced exile from science had lasted for two very long years.
The Institute was in part a copy of the Mond laboratory, with a long magnet hall and adjacent research room, but on a much larger scale. It was very well equipped and provided a high standard of technical assistance. The institute became known for weekly seminars, built on the model of the Kapitsa Club in Cambridge, which became a scientific and cultural institution of the physics community and drew leading scholars from around Moscow.

The Institute for Physical Problems in Moscow
In parallel with high field experiments, Kapitsa opened two new lines of research, which became his main preoccupation for the next ten years: the study of the transport properties of helium II and the development of a new and more efficient method of liquefying air and of manufacturing oxygen on an industrial scale. By 1938, he had perfected a small turbine that liquefied air more efficiently than any previous method. Kapitsa's interest in liquid helium was stimulated by experiments performed in 1927 by Willem Keesom - Onnes' student and successor at Leiden University - and Mieczyslaw Wolfke who had concluded that liquid helium-4 undergoes a phase transition at a temperature of roughly 2.2. K. This temperature is called the lambda point because the graph of specific heat versus temperature resembles the Greek letter lambda. The two phases are called helium I and helium II.
Kapitsa measured the extraordinary drop in viscosity of helium II, which allows it to pass through the tiniest openings and even to climb the walls of a container in apparent defiance of gravity. The liquid flowed with such great ease that Kapitsa drew an analogy with superconductors. It was a liquid of zero viscosity. The phenomenon was also accompanied by an increase in heat conductivity. In the paper announcing the discovery in January 1938, Kapitsa wrote that, by analogy with superconductivity, “The helium below the lambda point enters a special state that might be called a ‘superfluid'.”
Similar work had been independently done by two of his former colleagues at the Cavendish Laboratory, J. F Allen and A. D. Misener. They published their papers in the same issue of Nature. This paper and two others published in 1941 are considered among Kapitsa's most important contributions to low-temperature physics. During the short period remaining before the interruption of the war, fundamental contributions both in Moscow and in the West led to a better understanding of the behaviour of helium-4 below the lambda point. Decisive results were obtained in a series of ingenious experiments by Kapitsa, displaying the spectacular behaviour of liquid helium. But perhaps the most dramatic manifestation of anomalous flow behaviour was the so-called fountain effect discovered by Allen and Jones. Observations were being made on the flow of liquid helium II through a tube packed tightly with fine emery powder and partially immersed in a helium-4 bath. The top of the tube was allowed to project several centimetres above the level of the liquid helium bath, and an electric pocket torch was flashed on the lower part of the tube containing the powder. A steady stream of liquid helium was observed to flow out of the top of the tube, rising high above the level of the surrounding helium bath as long as the powder was irradiated.

These discoveries opened a new trend in physical research - namely, the quantum physics of the condensed state. A model called the two-fluid model was developed by Landau, Fritz London and Laszlo Tisza to describe these phenomena. According to this model, liquid helium-4 below lambda point can be thought of as two interpenetrating fluids, the normal and the superfluid components. The latter component is involved in superflow through pores and cracks and does not carry entropy. Furthermore, it does not interact with the walls of the vessel containing the fluid in a dissipative fashion. The normal fluid carries heat away from the heat source and is replaced by the superfluid component, so one has a countercurrent heat flow. The flow of the superfluid component toward a source of heat is spectacularly manifested in the fountain effect. Landau's fundamental quantum theory of liquid helium that provided a rigorous basis for the two-fluid idea also led to important new predictions.
The discovery of the superfluidity of helium certainly helped strengthen the position of Kapitsa during the great pre-war purges, a dangerous time in the Soviet Union. In 1938, when Lev Landau, the leading theoretician of the Institute, was arrested by the KGB secret police on charges of being a Nazi spy, Kapitsa showed great courage by intervening on his behalf. He wrote to Stalin saying that his work on superfluidity could hardly go on without Landau and later sent a reminder to Molotov. Threatening to resign as director of the Institute, he obtained Landau's release and also defended another persecuted scientist, the leading Soviet physicist Vladimir Fock, saving him from almost certain death during the Great Terror. In a tribute for Kapitsa's 70th birthday, Landau wrote: “I spent a year in prison and it was clear that I couldn't last another 6 months - I was simply dying... It is hardly necessary to say that such an action in those years required no little courage, great humanity and crystal-clear honesty.”
Kapitsa’s work was broken off in 1941, when the Soviet Union was invaded by Nazi troops, and Kapitsa himself did not continue it after the war. However, he actively encouraged further work and two of the most striking new predictions of Landau's theory were convincingly confirmed in his Institute. For his pioneering theories for condensed matter, and especially for developing the quantum theory of superfluidity, Landau was awarded the Nobel Prize for Physics 1962.

The phenomenon of superfluidity is probably the most spectacular example of quantum behaviour in bulk matter that research at low temperatures has yet uncovered. Quantum mechanics is of great importance in determining the macroscopic properties of the liquid form of helium-4, the most abundant isotope of helium, whose atoms contain even numbers of elementary particles. For this reason helium-4 is termed a boson, obeying Bose-Einstein statistics, which means that any number of atoms can aggregate in a single quantum state in the non-interacting particle approximation. In fact, macroscopic numbers of atoms in a quantum fluid can fall into the lowest energy state even at finite temperatures. This phenomenon is called Bose-Einstein condensation. On the other hand, helium-3 atoms, the lighter and much rarer of the two nonradioactive helium isotopes, each of which contains an odd number of elementary particles, is therefore a fermion and obeys Fermi-Dirac statistics: only one atom can occupy a given quantum state. Therefore one should expect a very large difference between the behaviour of liquid helium-4 and that of liquid helium-3 for low temperatures, where they both belong to the class of quantum fluids - as distinct from classical fluids - for which quantum statistics has important consequences. Since the two isotopes of helium are built up of different numbers of particles, dramatic differences in their behaviour arise when they are cooled to temperatures near absolute zero. Fermions such as helium-3 should not actually be condensable in the lowest energy state. For this reason superfluidity should not be possible in helium-3 which, like helium-4, can be liquidised at a temperature of some degrees above absolute zero. Fermions can in fact be condensed, but in a more complicated manner. According to the theory for superconductivity in metals, formulated in 1956 by John Bardeen, Leon Cooper and Robert Schrieffer (who were awarded the Nobel Prize in Physics 1972), electrons in greatly cooled metals can combine in twos to form what are termed Cooper pairs and then behave as bosons. These pairs can undergo Bose-Einstein condensation to form a Bose-Einstein condensate. Starting with the experience of superfluidity in helium-4 and superconductivity in metals, it was expected that the fermions in liquid helium-3 should be capable of forming bosonic pairs and that superfluidity should be obtainable in very cold samples of the isotope helium-3. In the 1950s, it was established that no transition to a superfluid took place in helium-3 anywhere near 2.2 K. Although many research groups worked with the problem for years, particularly during the 1960s, none had succeeded and many considered that it would never be possible to achieve superfluidity in helium-3. In spite of these failures to discover a superfluid transition in helium-3, the substance remained of considerable interest as a system of fermions that remains in the liquid state even at absolute zero. However, David Lee, Robert Richardson and their graduate student Douglas Osheroff discovered at the beginning of the 1970s, in the low-temperature laboratory at Cornell University, that helium-3 can be made superfluid at a temperature only about two thousandths of a degree above absolute zero. This superfluid quantum liquid differs greatly from helium-4. The new quantum liquid helium-3 has very special characteristics. One thing all this shows is that the quantum laws of microphysics sometimes directly govern the behaviour of macroscopic bodies also. For this achievement Lee, Richardson and Osheroff shared the Nobel Prize in Physics 1996.
Shortly after Russia entered the war, the Institute for Physical Problems, together with many other Academy institutions, was evacuated to Kazan, on the Volga. There, an old University served as the seat for the many evacuated institutes of the Academy of Sciences. Scientific research shifted to the war effort: Kapitsa's oxygen helped the air force to fly and the army to produce explosives. One of his main efforts was the rapid development of the industrial-scale plant for oxygen production. In 1942, he constructed a larger device capable of producing nearly 200 kilograms of liquid oxygen per hour and a pilot plant was successfully completed during the two years that the evacuation lasted. His design of the expansion turbine method for oxygen production proved to be the basis of much of the world's industrial production of oxygen. Since the beginning of his scientific career, Kapitsa was a pioneer of what has become today a characteristic trait of the recent scientific-technological revolution, being among the first who applied large technical installations in the laboratory and at the same time making direct practical use of some of the latest achievements of physics.

During those years, Kapitsa received many official recognitions of his achievements, such as the Stalin prize in 1941 and 1943, as well as the Order of Lenin in 1943, 1944 and 1945. He was also elected as a full academician and received the title of Hero of Socialist Labour after the approval of the Balashikha plant that starting from the fall of 1944 produced forty tons of liquid oxygen per day, about one-sixth of the total Soviet output at the time.
The Special Atomic Committee established by Stalin in August 1945 included only two physicists - Igor Kurchatov and Pyotr Kapitsa. However, tensions soon developed between him and the committee's political chairman Lavrenty Beria. Kapitsa was critical of Beria's administration. In his letters to officials in the commissariats of Education and of Heavy Industry, the Supreme Economic Council, and other bureaucracies, and to such leaders as Stalin and Molotov, Kapitsa had always described at length his view of how science ought to be funded and organised and criticized the way that the Soviet government saw things. He continued his extensive letter-writing campaign concerning what he perceived as organisational and directional problems, and subjected Beria to hostile comments. As a result, Kapitsa fell out of favour with Stalin, to whom he wrote long and often daring personal letters. Since the spring of 1946, commissions investigating the activities of the Institute and his oxygen project kept arriving and began to speak badly of the factory built at Balashikha near Moscow, condemning his methods and criticising its activity as not productive enough, uneconomical, or late in meeting its targets. Stalin signed an official decision that said that Kapitsa had failed to fulfil government orders for the construction of more efficient apparatuses for the production of gaseous and liquid oxygen. He was accused of being more occupied with experiments than with industrial applications. After a few months, a short announcement stated that Kapitsa was relieved of his duties as Director of the Institute for Physical Problems. Although dismissed, Kapitsa retained his position - and salary - as an Academician. He chose to live at his country house where he built up a laboratory aided by his sons and continued experimental work, writing theoretical papers on various topics. Considering the limited resources available, what Kapitsa achieved in his domestic laboratory was really impressive, again demonstrating his ability and intellectual power. At first he undertook a series of elegant studies in mechanics and hydrodynamics. In the late 1940s his interest turned to the prospects for the creation of powerful continuous-action UHF oscillators. He was able to solve the intricate mathematical problem of electron movement in UHF oscillators of the magnetron type. On the basis of these calculations he built very powerful UHF oscillators of a new type. During these studies, Kapitsa discovered an unexpected phenomenon: when a helium-filled flask was placed in the beam of electromagnetic waves emitted by the generator, the helium developed a very bright discharge and the quartz walls of the flask melted. On these grounds he assumed that plasma can be heated to a very high temperature by the use of powerful UHF electromagnetic waves.
In 1955, when Beria lost his power after Stalin's death, Kapitsa was reinstated as director of the Institute for Physical Problems and it was acknowledged that the unfavourable report on his oxygen work was mistaken. He became the editor of the leading Soviet physical journal, the Journal of Theoretical and Experimental Physics. Having done original work on ball lightning while he was out of favour with the government, Kapitsa switched from low-temperature physics to high-power microwave generators and later he also contributed to controlled thermonuclear fusion research.

Kapitsa actively worked to permit Soviet scholars to travel abroad for conferences, while inviting foreign scientists to the USSR and cooperated with such centres as Bohr's Institute for Theoretical Physics. But only in 1965 he was finally allowed to travel outside the Soviet Union. He visited Copenhagen, where he was awarded the Niels Bohr International Gold Medal of the Danish Engineering Society, and in 1966 he returned to Cambridge after a lapse of 32 years to receive the Rutherford Medal of the Institute of Physics. On that occasion a special meeting was arranged on 10 May with quite a few present who had been members when Kapitsa was in charge more than 30 years earlier. In subsequent years he was able to visit Canada, USA, India, Switzerland and many other countries to receive honorary degrees.
Although the discovery of superfluidity stands as one of the most significant in physics in the 20th century, it was to be 40 years before the Royal Swedish Academy of Sciences honoured this seminal discovery with a Nobel prize - an exceptionally long interval. In 1978 Kapitsa, by then 84, was awarded half of that year’s Nobel Prize for Physics. In his Nobel address, Kapitsa broke with tradition and chose not to address his work on the physics of low temperatures, a field he acknowledged having left thirty years earlier. Instead, on the grounds that he had abandoned work on low-temperature physics decades earlier, he reviewed his most recent research on thermonuclear reactions. Kapitsa saw nuclear power as a solution to eventual shortages of fossil fuels, and believed that wind, solar, and hydroelectric power were also possibilities. He worried about waste and proliferation problems associated with nuclear fission, and thus pursued fusion. He was also active in the international Pugwash Conferences on Science and World Affairs, founded in 1957 to provide a forum for influential scientists and public figures concerned with reducing the danger of armed conflict. The movement was initiated by Albert Einstein and Bertrand Russell to seek cooperative solutions to global problems at a time when many scientists were worried about the Cold War and the threat of a thermonuclear conflict. Joseph Rotblatt, a Polish physicist British-naturalised, the youngest signatory of the Russell-Einstein Manifesto in 1955, was the only physicist to leave the Manhattan Project on the grounds of conscience. He became one of the most prominent critics of the nuclear arms race and his work on nuclear fallout was a major contribution toward the ratification of the 1963 Partial Nuclear Test Ban Treaty. Rotblatt was secretary-general of the Pugwash Conferences on Science and World Affairs from their founding until 1973 and despite the Iron Curtain and the Cold War, he always advocated establishing links between scientists from the West and East. Since its founding, Pugwash has continued to create opportunities for dialogue, fostering creative discussions on the steps needed to free the world from nuclear weapons and other weapons of mass destruction. In 1995, the Nobel Peace Prize was awarded jointly to Joseph Rotblat and the Pugwash Conferences on Science and World Affairs “for their efforts to diminish the part played by nuclear arms in international politics and, in the longer run, to eliminate such arms.”

Boag J. W. et al. (1990) Kapitsa in Cambridge and Moscow. Life and letters of a Russian Physicist. Elsevier Science Publishers.
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