In the summer of 2022, Dr Károly Osvay’s team demonstrated that neutron radiation can be generated even with low-energy laser pulses. Last year’s experiments were carried out on ELI ALPS’ SYLOS Alignment laser providing ultrashort pulses. Since then, the team has further improved the technique: in a recent experiment–which was also the first "sealed" experiment at the research institute, remotely controlled from a so called control room–the number of neutrons produced per second was increased by a factor of 100.
Last year, using a self-developed, rotating target system the Szeged-based physicists could produce a beam of 1,200–1,500 neutrons per pulse by operating the laser at a rate of one pulse per second for a sustained period of time.
To further improve the neutron yield, the team developed a new primary target at the TeWaTi laboratory of the University of Szeged for the 2023 experiments. As a result, they were able to increase the number of laser pulses per second by an order of magnitude, and sustain the process for 6–8 hours gross (4–5 hours net) a day in a pilot project conducted this past June. Consequently, the total number of fast neutrons in the beam has increased by a factor of 100, making it suitable for various applications, including research on biological samples.
“Three weeks ago, a pilot campaign ended on ELI ALPS’ SYLOS Alignment laser, which operates at a frequency of 10 Hz (10 shots per second). Compared to last year, we have made a big leap forward: in the new experimental setup, we fired at a liquid-jet target in vacuum,” Dr. Osvay said. “The research team has thus demonstrated that it is not only possible to generate neutrons with a low-energy laser, but also that the resulting neutron radiation can be sustained for a period of 4–5 hours.”
Neutrons from less energy
“Our results provide a proof of principle showing that a continuous neutron beam can be obtained with lower energy pulses. The experiments on ELI ALPS’ laser delivering 20 mJ pulses breaks through the previous research paradigm according to which sustained neutron production requires lasers with the highest possible energy,” the researcher added.
Dr. Károly Osvay Photo: Ádám Kovács-Jerney
The long-term goal of the National Laser-Initiated Transmutation Laboratory is to reduce the decay half-life of spent nuclear fuel from power plants using lasers. The first step is to develop its laser technology to produce a safe neutron source. In chemistry, transmutation is the transformation of one element into another; in this sense, a technology based on laser-initiated neutron generation can be useful to reduce the proportion of long-lived isotopes. In fact, irradiated neutrons cause the actinide isotopes in spent uranium fuel, which can radiate for hundreds of thousands of years, to decompose into elements with a radiation lifetime of a few hundred years.
Dr. Károly Osvay confirmed that direct irradiation of spent reactor fuel would not be economically viable for the nuclear industry. He believes that a laser-based neutron source would be able to drive a so-called subcritical reactor. Compared to a conventional reactor, it represents a much safer technology, because it requires additional neutrons from an external source. Without a stable external neutron source, the reactor will never start up, and will shut down immediately if the neutron supply is disrupted. According to the researcher, the lack of a stable and safe external neutron source is one of the reasons why such a reactor has not yet been built. Currently, neutrons in industrial quantities are produced either from the nuclear reactors themselves or by cyclotrons and linear accelerators, which need to be shut down from time to time due to their technology.
Dr. Károly Osvay hopes that they will be able to further improve the neutron yield (to 108 to 1010 neutrons per second) in experiments planned for the end of the year, when they will use ELI ALPS’ SYLOS2 laser operating at a repetition rate of 1 kHz instead of 10 Hz. As a result, the neutron doses could reach several Gy and supportserious industrial and medical applications. The experimental neutron source at ELI ALPS has already been used for a radiobiology experiment by the institute’s Biomedical Applications Group.
Neutron generation experiment at ELI ALPS Laser Research Institute in June 2023
The members of the research group at the University of Szeged are Előd Buzás, Dr. Miklós Füle, Péter Gaál, Tibor Gilinger, Máté Karnok, Dr. Attila Pál Kovács, Dr. Árpád Mohácsi, Bence Nagy, Dr. Sargis Ter-Avetisyan and Dr. Parvin Varmazyar.
Dr. Károly Osvay pointed out that the experimental results could not have been achieved without the contribution of ELI ALPS’ staff and management. especially that of SYLOS Laser Group, the Vacuum Engineering Group, the Scientific Engineering Group, the Radiation Protection Group, the General IT Group, as well as Dr. Ádám Börzsönyi, Head of Laser Department, Dr. Katalin Varjú, Science Director and Dr. Gábor Szabó, Managing Director.
Dr. Károly Osvay graduated from the Physics Department of József Attila University of Sciences, the predecessor of the University of Szeged, in 1990. He was awarded the degree of Candidate of Physical Sciences of the Hungarian Academy of Sciences in 1995 for his research results in laser physics. He habilitated at the University of Szeged in 2011. He is the founder (1998) and head of the first terawatt laser laboratory in Hungary (SZTE TeWaTi). He spent 8 years in leading international research institutes (RAL UK; University of Lund, Sweden; MBI, Germany). Between 2008 and 2011, he was the scientific project manager of the ELI Preparatory Phase, from 2011 he headed the ELI ALPS Scientific Working Group, and between 2013 and 2019 he filled the post of Research Technology Director. His main research interests include ultrafast laser pulse generation and applications, laser-matter interactions, nonlinear optics, and laser particle acceleration.
Written by Judit Zelena based on Sándor Panek’s interview