Читать книгу All sciences. №8, 2022. International Scientific Journal - Ibratjon Xatamovich Aliyev - Страница 7

Аннотация. История ускорительной техники берёт своё начало ещё во времена самых первых исследований в области изучения строения вещества, и, хотя вопрос о строении материи был поставлен ещё в глубокой древности, его активное развитие начинается лишь чуть ранее открытия радиоактивности Анри Беккерелем. Самые первые попытки в области увеличения энергии генерируемых частиц были приложены ещё во времена первых трубок Крукса, в которых обеспечивался высокий вакуум, что позволяло обеспечить вылет приличного потока электронов под действием термоэлектронной эмиссии.

Ключевые слова: история, ускорители заряженных частиц, линейные ускорители, циклотроны, опыты Резерфорда.

Annotation. The history of accelerator technology dates back to the time of the very first research in the field of studying the structure of matter, and although the question of the structure of matter was raised in ancient times, its active development begins only a little earlier than the discovery of radioactivity by Henri Becquerel. The very first attempts in the field of increasing the energy of the generated particles were made back in the days of the first Crookes tubes, in which a high vacuum was provided, which made it possible to ensure the departure of a decent flow of electrons under the influence of thermoelectronic emission.

Keywords: history, charged particle accelerators, linear accelerators, cyclotrons, Rutherford experiments.

But if we proceed from the very beginning, then in the history of accelerators we can find many outstanding inventions, new and bright physical ideas, in some cases, having the character of a scientific discovery. However, the development of methods for accelerating charged particles and the pursuit of higher energies has never been an end in itself and necessarily obeyed mainly the logic of the development of nuclear physics and the resulting high-energy physics.

Previously conducted research and construction in the field of accelerator physics can be depicted using a diagram, so the existence of objective laws of the development of accelerator technology is simply and clearly convinced by such a dependence on the time of the maximum energy achieved in laboratory conditions. On a logarithmic scale, this dependence is reflected by a straight line, which, with some reservations, both existing installations and projected machines fall into. That is, the energy of artificially accelerated elementary particles increases exponentially by an order of magnitude every seven to eight years, which reflects the objective regularity of the development of science and high-energy physics. With all the importance of new ideas in accelerator physics, it should not be noted that their appearance did not cause noticeable fractures on this line and did not lead to such a case, the presence of any obvious deviations.

Probably, the first considerations about obtaining artificially accelerated particles appeared together with the birth of experimental nuclear physics after the historical experiments of E. Rutherford in 1919, although by that time there were already high-voltage X-ray tubes and installations for producing "channel rays", to a certain extent, deserving the name accelerators. The capabilities of high-voltage technology of that time, and the energy of alpha particles of natural radioactive isotopes, with which the accelerators were designed to compete, determined the immediate goal – to obtain particles with an energy of the order of several MeV. However, of course, the fundamental advantages of accelerators were also clear – the possibility of accelerating protons and other elementary particles, as well as the directivity and high intensity of the beam, equivalent to tens and hundreds of kilograms of natural radioactive preparations. Interestingly, in the 20s, quite a lot of ideas of acceleration to high energy were expressed, which were ahead of their time and embodied in specific installations only after many years.

Nevertheless, the first artificial nuclear reaction – the splitting of the lithium nucleus by protons with an energy of 700 keV – was carried out by the staff of Rutherford J. By Cockcroft and E. Watson in 1931 and immediately repeated in several laboratories. This date can be considered the beginning of the history of accelerators.

The Cockcroft-Walton installation consisted of two main elements – a high voltage generator and an accelerator tube. Both of them technically underwent significant modifications in the future. One of the main stages in the development of electrostatic accelerators was the invention in 1929 by R. Van de Graaf from Preston University in the USA of a high voltage generator with mechanical charge transfer. The increase in energy in these machines was restrained mainly by the electrical strength of the support insulators and the accelerator tube, but the use of forced potential distribution soon allowed to obtain an energy of 2.5 MeV. In the USSR, in 1938, an electrostatic accelerator at 3.6 MeV was launched in Kharkov. It is also important to note that by the end of the 50s, the accelerator tube of a serial electrostatic accelerator could withstand an order of magnitude more, namely 16 MV.

Nevertheless, the limited possibilities of the electrostatic acceleration method were obvious, and the development of nuclear physics urgently required a transition to energies of the order of ten MeV, comparable to the average binding energy of a nucleon in the nucleus. Therefore, the emergence of resonant methods that do not require high voltages should be considered a qualitatively new stage in the development of accelerators. The first ideas of this kind were expressed, as research shows, by the Swedish scientist Ising in 1924, but did not lead to the creation of a workable model. The linear version of the resonant accelerator was also studied by the Swedish physicist R. A video editor who also contributed to the development of betatron. There were no fundamental flaws in their schemes, but alas, only the absence of powerful short-wave generators in the late 20s did not allow them to be implemented in practice. It has already been mentioned above about the abundance of ideas that appeared at that time, which, unfortunately, did not find technical implementation. In this regard, it is worth mentioning the name of the American engineer J. Slepyan, whose patents contain prototypes of some future accelerators, including the well-known betatron and linear resonance accelerator.

Resonant acceleration was put on a real basis in the works of E. Lawrence, conducted in the laboratory of the University of California at Berkeley. Almost simultaneously, in 1930-1932, working models of a cyclotron appeared in this laboratory – the first cyclic accelerator, in the creation of which M. Livingston played an important role, and a linear resonant accelerator with drift tubes (D. Sloan). However, linear systems soon faded into the background due to the insufficient development of microwave technology compared to the cyclotron, which has already begun its truly great triumphal march.

Already in 1935, the energy of alpha particles equal to 11 MeV was obtained and for the first time exceeded the maximum energy of natural radioactive isotopes, and in 1938 a cyclotron with a pole diameter of 1.52 m was launched, on which alpha particles with an energy of 32 MeV were obtained. Before the outbreak of World War II, the construction of a cyclotron for deuterons with an energy of 100 MeV was started. The first cyclotron in Europe was launched in Leningrad in 1936 at the Radium Institute at an energy of 6 MeV.

Speaking about the general role of the cyclotron in the development of nuclear physics, it is difficult to overestimate it. A particularly important stage was the acceleration of deuterons in the cyclotron, first because of the interest that the deuteron represents as the simplest nuclear system, and then because of the opportunities that opened up for generating intense neutron fluxes using easy-going (d-n) type reactions, that is, deuteron-neutron reactions. The significance of the last mentioned circumstance does not require comments, since thanks to it, accurate quantitative information about the cross sections of the capture and fission reactions was subsequently obtained, because reactions with neutrons attracted great attention in the future due to uranium technology.

The problem of electron acceleration stood somewhat apart and could not be solved in the way of the development of the cyclotron, which is fundamentally unsuitable for the acceleration of relativistic particles. Linear accelerators experienced their real rebirth only after the Second World War due to the rapid development of microwave oscillation generation technology for radar purposes. However, in 1940, D. Kerst launched a cyclic induction accelerator in the USA, that is, a non—resonant 2.3 MeV betatron accelerator, the main idea of which was contained in Slepyan's patents. Videoroe came close to creating a betatron, who for the first time formulated the so-called betatron condition, which makes it possible to keep the radius of the orbit almost constant during acceleration, which turned out to be important from a practical point of view. In addition, in the early 40s, the conditions for the stability of electron motion in the betatron were clearly clarified, which was of fundamental importance. The fact is that the accelerating electric field in a betatron in practical conditions turns out to be very small and in order to achieve the same energy, a particle, instead of hundreds of meters, as in a cyclotron, must travel a full path of thousands of kilometers, which, of course, is strongly affected by even small perturbations of motion.

Kerst's work was repeated, although not immediately, in several laboratories, including in the USSR, and betatron soon became a reliable and simple source of bremsstrahlung used in photonuclear reaction physics and engineering. However, the main drawback of the cyclotron is a small accelerating field, which almost inevitably follows from the non—resonant nature of acceleration, and it determined the maximum energy at 100 MeV, when the largest betatron of the University of Illinois in the USA gave an energy of 300 MeV. The fundamental nature of this limitation is related to the magnetotormotic or, more precisely, synchrotron radiation of particles moving in a circle in the vacuum chamber itself.

The theory of synchrotron radiation, developed in the early 40s and well confirmed experimentally, indicated an inevitable increase in radiation losses with energy, which could not be compensated for by the relatively small accelerating field of the betatron. Thus, in the early 40s, an outwardly dead-end situation developed: it seemed that resonant methods had reached their ceiling associated with relativistic effects, and non-resonant ones faced insurmountable technical difficulties. At the same time, the transition to the energy range of the order of hundreds of MeV was necessary due to the emergence of a new branch of science – elementary particle physics and the requirements for the generation of recently discovered mesons, when the rest energy of the μ-meson is 106 MeV, and the π-meson is as much as 140 MeV. A new qualitative stage in the history of accelerators is associated with the name of V. I. Veksler, who then worked at the Lebedev FIAN.