Projects of the XXI century

Record particle cooling parameters

Electron cooling systems are designed to compress beams of heavy charged particles in ion accelerators. Cooling is necessary to increase the efficiency of the experiment: the cooler is the beam, the higher the density of particles is and the more interesting events physicists will see by colliding them with each other or as a result of directing the beam at a static target. In the joint work of specialists from the G.I.Budker Institute of Nuclear Physics SB RAS (INP SB RAS) and the Joint Institute for Nuclear Research, record particle cooling parameters have been obtained. As a result, the rate of the set of events in the experiment and hence its efficiency has been doubled.

The strong interaction of charged particles has been well studied in high energy. At the same time, experimental data in low and average energies, important for understanding the internal structure and dynamics of hadrons, are insufficient and often contradictory. Therefore, precision investigation of these ranges is an interesting and urgent task for researchers. In particular, physicists at the NICA heavy ion collider at JINR work on such issues. The technique of electron cooling proposed at the Institute of Nuclear Physics SB RAS by Academician G.I.Budker, concerning a decrease in the scatter of particles in momentum, turned out to be one of the most important tools for improving the quality of ion beams and studying dense quark-gluon plasma.

The basic principle of experiments in high energy physics is that the higher is the particle density, the higher the quality of the research is. Experiments can be held in a collider, where beams of particles collide with each other, or as a result of a collision - with a static target. But in both cases, the efficiency depends on the ion flux density: the more the beams are compressed, the more statistical data physicists will accumulate.

"The electron cooling technique allows to reduce the phase volumes of cooled beams by thousands of times. To do this, cold electrons are directed using a magnetic field from an electron gun into an accelerator ring; in the case of the experiment in Dubna, this is a superconducting booster synchrotron. Here, they combine with hot ions, move along the ring together for some time and cool the ions due to collisions. An uncooled ion beam occupies most of the transverse space of the chamber and adding new particles to it is inefficient. If the ions are cooled, they will shrink into a thin cord, making room for another injection. The energy density of such beams is significantly higher than that of uncooled beams. Due to this, it is possible to accumulate tens of times more particles. No scientific organization in the world can make equipment of this class. Electronic cooling systems have opened up such broad prospects that at present, ion storage devices without them are practically not used," Deputy Director of the BINP SB RAS for research Evgeny Levichev explained.

The electronic cooling system of the NICA booster is designed to accumulate an ion beam during injection (at an ion energy of 3.2 MeV/n), as well as to prepare it for efficient transfer into the Nuclotron ring at intermediate energy ~65 MeV/n). In the 2023 session, at the JINR heavy ion storage complex, as part of the synchrotron rings of the booster and Nuclotron, the first electronic cooling of heavy ions in Russia was obtained that was used to increase the efficiency of the BM@N research facility.

Deputy Head for Research of the Accelerator Department of VBLHEP Anatoly Sidorin noted that in the last session, held in 2022-2023, as a result of optimization of the operation of all systems, a record intensity for the Nuclotron was achieved for a beam of xenon nuclei (over 10⁷ nuclei per cycle), accelerated to energy 3.9 GeV/nucleon. For more than a month, the accelerator complex has operated stably for the BM@N experiment; about 500 million events have been registered at an energy of 3.9 GeV/nucleon and another about 50 million - at an energy of 3 GeV/nucleon.

"A wide range of applied research has been carried out under the ARIADNA collaboration programme," VBLHEP Acting Director Andrey Butenko explained. "The protective properties, radiation resistance and radio modification of new composite materials for the space industry, radiation modifications in sapphires (Al₂O₃), polytetrafluoroethylene, polyethylene terephthalate, polyethylene and polyimide films have been consistently studied. Irradiation of HTSC (high temperature superconductor) tapes have been carried out in order to study the possibility of increasing the critical current. As part of the Programme "Plants and vegetation in space", 16 containers with seeds of various plants have been irradiated. An activation analysis of materials under irradiation with relativistic heavy ions has been carried out. At the SOCHi facility (Station Of Chip Irradiation, positioned at the output of the linear accelerator), thermal radiation-modified polytetrafluoroethylene (TRM-PTFE) films have been irradiated with xenon ions. Investigations of the interaction of a xenon beam with internal targets of the Nuclotron made of tungsten and silver have been carried out at two energies."

Electronic cooling of a beam of heavy ions, obtained through the joint efforts of specialists from the Institute of Nuclear Physics SB RAS and JINR allowed to double the rate of data acquisition during experiments on the research of dense baryonic matter on a fixed target and to obtain new interesting experimental data.

"The successful operation of the electron cooling system allowed to formulate a concept for further increase of the intensity of accelerated heavy ion beams that consists of accumulating the beam at the injection energy in the longitudinal phase plane with electron cooling. Increasing the intensity of accelerated beams is fundamental for the operation of the heavy ion collider and putting it into operation is scheduled for 2025," Anatoly Sidorin commented.

The electron cooling technique, proposed and first implemented at the G.I.Budker Institute of Nuclear Physics SB RAS, has found application in many foreign scientific centres. In the Russian Federation, electron cooling was used in a nuclear physics experiment for the first time.

"The idea of the electron cooling technique was proposed by the organizer and first director of the BINP SB RAS Academician G.I.Budker in 1966. Here, it was implemented on a model accelerator - the APA-M facility (Antiproton Accumulator, model)," the chief researcher of the BINP SB RAS Academician of the RAS Vasily Parkhomchuk commented. "The whole world came to us to see how the technique works and to learn from us. Over the years, we have made several similar systems for various world scientific centres - this is enough to talk about the world leadership of the BINP SB RAS in this field. Although the technology is the same for all systems, we develop unique equipment for each individual project. Our facilities operate in Russia, China and Europe, including at CERN and JINR."

Based on the information from BINP SB RAS