JINR basic facilities

Acceleration in the second wind

One can talk about this equipment as about an employee of the Institute: it is of foreign origin, arrived to Dubna a quarter of a century ago, has survived with us the years of crisis for science and today, it ranks high among the JINR basic facilities. We are talking about the LINAC-800 accelerator. On 12 February, a successful test run of the first stage (LINAC-200) of the new facility was held and the next day, a solemn opening ceremony was held with the participation of members of the 137th session of the Scientific Council and representatives of JINR Directorate.

The beginning of history

The accelerator (then called MEA - Medium Energy Accelerator) was constructed in 1975-1978 for the Dutch National Institute for Subatomic Physics (NIKHEF) and was used first for independent research and later, as part of the AmPS (Amsterdam Pulse Stretcher) complex - as an injector for the storage ring. At the end of the 1990s, the Amsterdam Institute moved all experimental research to CERN and decided to put the equipment that had been left behind into good hands.

On 12 March, 1999, a ceremony of handing over the symbolic key from the AmPS accelerator complex to JINR Chief Engineer, Corresponding Member of the Russian Academy of Sciences I.N.Meshkov was held at NIKHEF. An explanation was published in our newspaper (No.11, 1999): "The decision to donate the accelerator complex was dictated, first of all, by the desire to prolong the life of this perfectly operating research instrument".

At a new place

"The transportation of the accelerator from Amsterdam started in 1999 and finished in 2000," Head of Sector of VBLHEP Valery Kobets, whose group members immediately began assembling the accelerator at the new place, says. "They started assembling the accelerator in building No.118 that used to house the LIU-30 accelerator of the Laboratory of Neutron Physics. It was impossible to build such a room anew in those days: the area is more than 1200 square meters each - modulator and accelerator halls, the building is 250 meters long and almost 20 meters wide."

Assembly of the accelerator after cleaning of the accelerator hall started in 2002 and in 2010, the first, cosmetic, repair of the building was made. In August 2017, the physical launch of LINAC-200 (200 MeV energy) was carried out. And after the facility was transferred from VBLHEP to DLNP in 2017-2018, a more thorough reconstruction of the premises was carried out over a period of three years. In particular, due to changes in radiation safety regulations, the ventilation system had to be completely changed. The old one that took up a lot of space, was dismantled and the freed space was equipped for users - windows were cut through, partitions were put up and three rooms were prepared. In addition, new electricity and water supply systems were put into operation and modern radiation control and interlocking and alarm systems were developed and installed.

Second birth

The accelerator itself has also undergone great changes. The control system of klystron modulators was completely renewed. New electronics have been developed, new control systems (work is underway on a new accelerator control system that will unite all separate control systems into one global one) and many failed or obsolete components have been replaced. In addition, four beam outlets were developed for users with maximum energies of 24, 60, 130 and 200 MeV. The fact that the precision of the work was jewel-like can be evidenced by the following fact: the accelerator sections (LINAC-200 includes 7 sections, LINAC 800 will consist of 24) are installed strictly in a straight line, relative to each other they should be aligned with an accuracy of about 50 microns.

"A year and a half ago, the licensed organization LLC "Spetsatomservis" developed design documentation for radiation control, interlocking and alarm systems for our accelerator, with implementation of these systems to be completed in early 2025," Head of Research and Innovation Department of DLNP Vladimir Glagolev says. The stages of putting the accelerator into operation have been defined. Currently, we are talking about the first stage - we have entered the commissioning mode at an energy of 200 MeV.

All design modes of operation are to be tested and to make sure that the accelerator is reliable and safe. The sequence of testing to be implemented is as follows: to complete the commissioning mode for LINAC-200, to prepare the relevant set of documents, to submit it to the Federal Medical and Biological Agency and to obtain a permit for pilot operation. Next, the 400 MeV stage begins. When this part of the accelerator is assembled, the cycle will start again: documents, testing, operating permit... "I think that this can be done, including preparation of documentation and waiting for approvals, by the end of 2027," V.V.Glagolev comments. "As for 800 MeV, additional resources will be required. We are going to complete this work by 2030 if funding is available."

As you can see, there is a lot of work and paperwork to be done and how much has already been done! And a legitimate issue arises - maybe it would be cheaper to buy a new accelerator?

"A new one costs hundreds of millions of dollars and at the moment, it is basically impossible to buy it because of the sanctions," V.V.Kobets says. "In Russia, such accelerators can only be constructed at the Institute of Nuclear Physics in Novosibirsk but today, their staff is busy with the SKIF project. There are only five accelerators like ours in the world. Usually, they operate in conjunction with large facilities and it is very difficult to allocate time for users. Our accelerator operates specifically for users and in this sense, it is the only one".

"There are only two such accelerators in the country," Deputy Head of Department of DLNP Karen Bunyatov adds. "One was launched in 2024 at the Institute of Nuclear Physics of the Siberian Branch of the Russian Academy of Sciences in Novosibirsk and the other - here, in Dubna. The Novosibirsk one is set up for a specific task - to use the SKIF accelerator complex as an injector, while our facility is equipped with experimental channels and there is an opportunity to implement a wide range of applied research in radiation materials science, radiobiology and radiochemistry and to carry out experiments in the field of nuclear physics."

In addition, the LINAC-200 extracted beams will be used to test prototypes of electromagnetic calorimeters and to coordinate detectors for MPD and SPD experiments at the NICA collider.

User policy

The quality of accelerator operation is determined by the minimum possible beam size, the energy range at the output and the stability of the beam parameters. The narrower the beam and the lower the energy range, the better. Although much depends on the application that users will be investigating with this facility. For example, for testing radiation resistance, to observe how material or electronics behaves under radiation, you need the same beam parameters. And for testing of detectors, calorimeter elements, a mode close to the flight of single electrons is needed to know what area the electron hit and what energy it released. The uniqueness of LINAC-200 also lies in the fact that it can produce fluxes from units to 4 ·10¹³ electrons per second. This is indispensable equipment for developing detectors.

"We are going to be in commissioning mode until autumn," V.V.Glagolev says. "The beam with various targets and converters on all four leads is to be tested. Specialists from the Radiation Safety Department should measure the background at all modes of accelerator operation, reflect these readings in test reports and protocols and prepare the relevant documents. And after that, we can enter the pilot operation mode. An Organizational and Programme Committee has already been established that will consider applications from users. At the moment, six applications have been obtained and their number will increase over time. Some of the first users will be our colleagues from Nuclear Spectroscopy and Radiochemistry Department of DLNP, as well as employees from Vietnam. Three Vietnamese physicists under the supervision of former Plenipotentiary Representative of Vietnam at JINR Le Hong Khiem are to start working with us in the near future. Currently, they are engaged in simulation and preparation of the experiment on the investigation of photonuclear reactions, development of equipment for subsequent research at the 130 and 200 MeV beam exit channels."

In addition, interest in LINAC has been expressed by the staff members of LRB for biological research. A group of physicists that have previously worked at the synchrocyclotron also have plans for accelerator time.

An application form for users has been approved. It should specify how and when the scientists are going to work with the beam: what energy, what current, how long it will take to prepare and clean the equipment, for radiation, whether they have everything they need for the beam or whether they need some help. Applications will be reviewed based on the importance of the work, feasibility, time requested and compatibility with other users' plans. Priority is given to JINR laboratories and research groups of the Member States.

"In addition, an important task of the accelerator is education," Head of Linear Accelerator Sector of DLNP Mikhail Nozdrin that also heads the Science and Engineering Group of the UC responsible for educational tasks at the accelerator highlights. "One of the outputs is set aside for students. Not entirely, but a significant part of the time on this output will be spent by trainees and interns in the field of accelerator technology and particle detectors."

FLAP collaboration

FLAP international collaboration (Fundamental & Applied Linear Accelerator Physics collaboration) has been established for research at LINAC-200. It is aimed at both applied and fundamental research. "In broad strokes, the objectives of the collaboration can be described as the search for new mechanisms and an investigation of the fundamentals of the interaction of accelerated electron beams with matter and external fields," Head of the Collaboration Anton Baldin said in an interview. "These investigations are interesting both for the development of new science-intensive devices and instruments and for meeting fundamental tasks of modern physics, such as the search for "Higgs-like" particles (H17) in the mass range of about tens of MeV". The plans for the collaboration were approved by the members of the Programme Advisory Committee for Particle Physics last year.

Prospects

In addition to the mentioned above, there are plans for research in the field of particle accelerators and radiation generation to obtain qualitatively new opportunities.

"Development of the facility can be related to the development of a photon source with a wide spectrum of ranges on its basis," M.A.Nozdrin explains. "There are ideas to develop a free-electron laser and a source of high-energy Compton gamma-quanta, but the realization requires a high-quality beam. As part of the work to improve the quality of the beam, a special photoinjector stand is currently designed, where electron generation occurs as a result of interaction with the cathode of the laser beam, rather than heating the cathode, as it is at the accelerator today. Replacing the LINAC-800 thermal injector with a photoinjector will significantly improve the beam emittance and its temporal profiling capabilities. The free electron laser, for example, will allow specific applied research. These facilities produce a series of very short pulses in a wide range of spectra (the higher the electron energy, the higher the photon energy; the energies of our accelerator allow us to produce photons up to soft X-rays) that allows one to study very fast chemical and biological processes - in fact, "to shoot a movie", to register successive stages of fast processes".

"In 2011-2013, an ondulator (a device for generating coherent synchrotron radiation - Editor's note) was positioned on the beam," Kobets adds. "We carried out a beam of 17 MeV energy through it and obtained infrared radiation with a wavelength of about 13.7 microns that roughly corresponds to the radiation of the human body. No one needed it at the time. But if you set the ondulator to a 200 MeV channel, you can use it to make an ultraviolet free electron laser."

"Also, the linac can be considered as a neutron source," K.S.Bunyatov adds. "Neutrons are selected by their time of flight and a beryllium neutron converter will be put on the 200 MeV channel for various experiments. Short pulses are important here, so that we can allocate neutrons of a certain energy according to the time of flight."

Last question

"Is the new facility safe for the environment?" a citizen that has learned that a new accelerator has started to operate outside the JINR fence probably will ask. "Absolutely safe," V.V.Glagolev answers. "The protection systems ensure that any employee can safely stay near Building No. 118 and in its corridor. The accelerator hall is surrounded by two-meter-thick concrete walls and the concrete used was special, so-called heavy (that is, of high density - Editor's note). In addition, each experimental channel is equipped with a beam absorber. Accordingly, our accelerator is no danger to the city or the laboratory.

Galina MYALKOVSKAYA,
photo by Igor LAPENKO