The 2018 upgrade of LUE-75 linear accelerator facility and prospects

Until 2005, the linear accelerator LUE-75 has been the injector unit for ARUS synchrotron, Yerevan, Armenia. After the suspension of the ARUS synchrotron in 2008, the LUE-75 operated as the only base station of the experimental department used to solve the topical issues of the low-energy nuclear physics.
In recent years, the linear accelerator was being reconstructed and adapted to make it more reliable. Due to the special parallel-beam-extraction unit and magnetic optics set up in the synchrotron hall, it became possible to carry out various experiments on the investigation of electron and (photo-) nuclear phenomena and electron radiation in monocrystals as well as on the study of the possibilities to obtain the radioisotopes 99mTc for medical diagnostic purposes by means of an electron accelerator, etc.

Fig.1. General view of linear accelerator.

In 2015-2018, jointly with JINR (Dubna, Russia), the beams of the linear accelerator operated under the specially worked out low-intensity regimes (10-20 e-/s, 10-50 MeV) were used to calibrate the CsI crystals to be used in the Mu2e experiment (FNAL, USA).
The measurements made with a step of every 5 MeV in the 15-50 MeV energy range using a (3 × 3) matrix of nine CsI crystals (fig.3) completed the results obtained by the Mu2e collaboration with the active participation of the JINR group on BTF (Frascati, Italy) in the energy range of 80-120 MeV.

Fig.2. A group photo of staff members of JINR and ANSL (YerPhI) during the 2018 summer beam sessions.

Fig. 3.Histogram of the distribution of the number of events in the ADC channels (left panel); energy resolution of
the (3 × 3) matrix of nine CsI crystals (right panel).
In these experiments, the maximum electron beam energy did not exceed 50 MeV, as only two of the three accelerating units of LUE-75 were employed.
Fig.4.  In the control room of synchrotron. From left to right: A. Babayan, G. Torosyan, Yu. Davydov, K. Davtyan.
Recently, the Department of Experimental Physics carried out the following works related to the complex created on the basis of the LUE-75 linear accelerator.
⦁    After upgrading, in particular, after launching the third accelerating unit of LUE-75, a stabilized up to 75 MeV electron beam at an average current of 0.5 μA was obtained.
⦁    The 75 MeV beam was successfully shifted to the end of the magnetic optics for parallel transport (fig.5).

Fig. 5.The trace of the 75 MeV electron beam on the phosphor screen at the end of the parallel path.
The works on ensuring the thermal regime of the parallel transfer magnets are carried on. For this purpose, new additional coils are being prepared, the installation of which will ensure safe and long-lasting beam extraction sessions.
Jointly with JINR (Dubna, Russia), YerPhI will continue to calibrate the crystals to be used in the prototype electromagnetic calorimeter of the Mu2e experiment (FNAL, USA). To this end, there will be worked out very low intensity (10-20 e-/sec) test beam modes in the LUE-75 linear accelerator complex in the energy range of 50-75 MeV.
Such experiments were made with the 15-50 MeV test beams in 2015-2018, the results of which have been sent for publication.


Fig.6. Beam tuning.

⦁    The upgrade of the linear accelerator in October-November 2018 gave a chance to two different groups to use the 30 MeV and 0.5-0.8 μA mean current electron beam in their experiments.
Fig.7. Experimenters and employees of the accelerator in the control room of LUE-75.
⦁    One of them was the joint experiment of some researchers from the Yerevan State University and the Department of Experimental Physics on the investigation of alpha particle production in photonuclear reactions.  They used 51V, 65Cu, 92Mo, 115In и 207Pb targets in their experiments for investigation of A (γ, α) A’ type processes.
Fig.8. The joint experiment of YSU and ANSL; placing of the sample.

⦁    The other was the experiment suggested by one of the Experimental Physics Department research groups for the search for multineutron systems in the bremsstrahlung photon induced processes, in particular, in the exotic 209Bi(γ, mn)209-mBi channels of nuclear fission. It is expected that the sub-threshold 30 MeV radiation is a more favorable for the search for systems of two, three, and four neutrons bound together. The target material was BGO (Bi4Ge3O12).

Fig. 9. Placing of the sample in an experiment of a research group from Experimental Physics Department.

The experiments were successfully conducted, the results are processed.
Тhe 50–75 MeV electron beams of linear accelerator complex LUE-75 will allow the JINR (Dubna, RF) group to carry out measurements for calibration of the matrix consisting of CsI crystals in the range below 80 MeV. Increasing the energy of the LUE-75 linear accelerator facility up to 75 MeV provides the conditions for the JINR (Dubna) – ANSL (YerPhI, Yerevan) joint researches of crystals in the energy range below 80 MeV.
In addition, it will give an opportunity to explore the photonuclear processes in higher-threshold reactions included in the research plans of the Yerevan State University and Department of Experimental Physics of the Alikhanyan National Science Laboratory Foundation (Yerevan Physics Institute).
The availability of such beams will create greater opportunities for studying fundamental and applied problems in the low-energy nuclear physics.
We congratulate the experimental physics department and especially the accelerator staff, whose hard work has resulted in achieving such a success. On this occasion, we congratulate all the employees of the ANSL as well.
Department of Experimental Physics
22 November 2018

Updated: 12/10/18