A compact accelerator-based neutron source has been proposed and created at the Budker Institute of Nuclear Physics in Novosibirsk, Russia. An original design tandem accelerator is used to provide a proton beam. The proton beam energy can be varied within a range of 0.6–2.3 MeV, keeping a high-energy stability of 0.1%. The beam current can also be varied in a wide range (from 0.3 mA to 10 mA) with high current stability (0.4%). In the device, neutron flux is generated as a result of the ⁷Li(p,n)⁷Be threshold reaction. A beam-shaping assembly is applied to convert this flux into a beam of epithermal neutrons with characteristics suitable for BNCT. A lot of scientific research has been carried out at the facility, including the study of blistering and its effect on the neutron yield. The BNCT technique is being tested in in vitro and in vivo studies, and the methods of dosimetry are being developed. It is planned to certify the neutron source next year and conduct clinical trials on it. The neutron source served as a prototype for a facility created for a clinic in Xiamen (China).

It is found that multi-cycle pulses of high-power coherent terahertz radiation can be efficiently generated in a plasma by counterstreaming long-pulse electron beams driving potential plasma waves via the two-stream instability. Instead of the well-known three-wave interaction processes between oblique beam-driven modes, we propose to generate electromagnetic radiation near the doubled plasma frequency due to the novel and much more efficient mechanism based on the head-on collision of longitudinal plasma waves with mismatching potential profiles. It is shown that this radiation mechanism can be implemented experimentally either by the collision of low-density electron beams with different transverse sizes or by the counter injection of denser equal-size beams unstable against filamentation perturbations. Particle-in-cell simulations for kiloampere electron beams capable of focusing into millimeter-scale sizes demonstrate the possibility to reach the high efficiency of beams-to-THz power conversion (3%–7%), which opens the path to gigawatt-class THz sources with a narrow spectral line.

In this paper, the theoretically predicted possibility to increase the efficiency of electromagnetic radiation generated by a thin beam-plasma system in the regime of oblique emission, when a plasma column becomes transparent to radiation near the plasma frequency, is investigated using particle-in-cell simulations. If a finite-size plasma column has a longitudinal density modulation, such a system is able to radiate electromagnetic waves as a dipole antenna. This radiation mechanism is based on the conversion of an electron beam-driven potential plasma wave on the periodic perturbation of plasma density. In this case, the frequency of radiated waves appears to be slightly lower than the plasma frequency. That is why their fields enable the penetration into the plasma only to the skin-depth. This case is realized when the period of density modulation coincides with the wavelength of the most unstable beam-driven mode, and the produced radiation escapes from the plasma in the purely transverse direction. In the recent theoretical paper [I. V. Timofeev et al. Phys. Plasmas 23, 083119 (2016)], however, it has been found that the magnetized plasma can be transparent to this radiation at certain emission angles. It means that the beam-to-radiation power conversion can be highly efficient even in a relatively thick plasma since not only boundary layers but also the whole plasma volume can be involved in the generation of electromagnetic waves. Simulations of steady-state beam injection into a pre-modulated plasma channel confirm the existence of this effect and show limits of validity for the simplified theoretical model.

Generation of electromagnetic (EM) radiation near the second harmonic of the plasma frequency during the injection of an electron beam into a rippled-density plasma channel is investigated using both analytical theory and particle-in-cell simulations. The generating scheme is based on nonlinear interaction of the most unstable beam-driven potential plasma wave with its satellite arising due to scattering on the longitudinal modulation of plasma density. Resulting superluminal oscillations of electric current in a finite-size plasma channel radiate EM waves via the same mechanism which has been recently studied for the fundamental harmonic emission and reffered as a beam-driven plasma antenna. It is shown that theoretical predictions for the optimal plasma width and modulation period are confirmed by simulation results and the power conversion efficiency of the second harmonic emission reaches several percent. Such an efficient mechanism opens the path to explanation of laboratory experiments with a thin electron beam at the GOL-3 mirror trap as well as to developing the scheme of terahertz generation at the gigawatt power level.

High-beta plasma equilibria are realized in a number of physical systems, from planetary magnetospheres, sunspots, and magnetic holes to fusion laboratory experiments. When plasma pressure becomes large enough to completely expel the magnetic field from its volume, the particle trajectories cannot be considered any more as circular gyro-orbits, and plasma pressure ceases to be gyrotropic. These non-gyrotropic effects require kinetic description and are actively studied for a long time in the magnetic reconnection problem. In this paper, we will show that non-gyrotropy of plasma pressure makes it possible to markedly exceed the limit β=1 dictated by the magnetohydrodynamics for finite-size plasmas, which may be attractive for some fusion schemes such as mirror and cusp configurations. As a first step, we study how these effects manifest themselves in a simple classical problem of confining a cylindrical plasma column by a uniform vacuum magnetic field. Using particle-in-cell simulations, we show that the equilibrium of the diamagnetic bubble type with zero internal magnetic field is formed with an electron-produced current layer of sub-ion scale and found that the gas-kinetic pressure of the central plasma exceeds the pressure of the vacuum magnetic field by 15%.