Том 44, № 12 (2018)

Results are presented from experimental studies of fast electrons in modes with disruption instability in the T-10 tokamak. The spatiotemporal dynamics of electron beams is investigated using two sets of cadmium telluride detectors and tomographic recovery of the intensity of suprathermal X-ray emission (E_γ ~ 15–300 keV). Generation of fast electron beams in the central zone of the plasma column in the initial stage of disruption in the T-10 tokamak is established. Analysis of suprathermal X-ray bursts during the development of disruption indicates spatial inhomogeneity of fast electron beams. The characteristic repetition frequency and duration of X-ray bursts are f ~ 2.5–3 kHz and Δt ~ 5 ms, respectively. Analysis of the experimental results shows that oscillations of the X-ray intensity may be related to the filamentation of fast electron beams.

The paper continues studies of the capabilities of plasma treatment of spent nuclear fuel and radioactive waste. The study is devoted to the problem of integration of the plasma source and separator, while the initial conditions of the substance input are considered by taking into account the possibilities of the process implementation. The results of calculations are presented in the one-particle approximation of 3D trajectories of the substance ions simulating the components of spent nuclear fuel. The calculations have been performed for the magnetic field generated by the coils and for the model configurations of the electric field approximated for the experimental capabilities. The electric potential configurations and the initial conditions pertinent to plasma injection along the magnetic field have been proposed, which allow efficiently separating singly charged ions of model substances characterized by masses of 150 and 240 amu, energies in the range of 0.02–20 eV, and an initial angular spread in velocities of 60°. The distance between the separated beams with different masses is found to be 10 cm for the characteristic separator size of 1 m.

A solution to the Boltzmann equation is obtained for a magnetized plasma with strongly degenerate nonrelativistic electrons and nondegenerate nuclei. The components of the diffusion, thermal diffusion, and diffusion thermoeffect tensors in a nonquantizing magnetic field are calculated in the Lorentz approximation without allowance for electron−electron collisions, which is asymptotically accurate for plasma with strongly degenerate electrons. Asymptotically accurate analytical expressions for the electron diffusion, thermal diffusion, and diffusion thermoeffect tensors in the presence of a magnetic field are obtained for the first time. The expressions reveal a considerably more complicated dependence on magnetic field than analogous dependences derived in the previous publications on this subject.

The process of charging of a spherical body absorbing plasma electrons and ions is modeled by directly solving the Vlasov–Poisson equations. The main goal of the numerical experiment is to determine the sphere charge in a stable steady state established on long times in perturbed plasma. Special attention is paid to the contribution of trapped ions moving in finite orbits to the screening of a charged body. The charge of the trapped particle cloud is determined as a function of the body size in a wide parameter range of an initially unperturbed plasma.

The propagation characteristics and physical nature of low-frequency waves observed in the ionosphere during heating of the near-Earth plasma by a powerful short-wavelength radiation are investigated using the singular value decomposition method. The experimental results obtained with the Sura midlatitude heating facility and detected by the onboard equipment of the DEMETER satellite were used. The ion composition of the near-Earth plasma is estimated from the spectral characteristics of the observed radio waves. The method is verified using results of full-scale measurements performed at altitudes corresponding to the Earth’s outer ionosphere.

Ionization−overheating instability of a non-self-sustained discharge in air in a subthreshold microwave field creates a self-sustained discharge with a fine cellular structure, whose UV radiation, in turn, generates a new non-self-sustained discharge on the microwave beam path, where ionization−overheating instability arises again. It is shown that, at microwave intensities in the range of 3–18 kW/cm², the propagation velocity of the ionization wave, including the region of the self-sustained discharge and the forward region of the non-self-sustained discharge developing in its UV halo, is proportional to the third power of the microwave field strength, while the maximum temperature in the discharge is inversely proportional to the microwave field strength.

Results of particle-in-cell simulation of the formation of a near-wall plasma layer produced by an ionization source remote from the chamber walls are verified experimentally. The measured profiles of the density and temperature of the plasma produced by an electron beam in two modes are compared: (i) gas is ionized by a low-density electron beam, while collective interactions are almost absent (beam-induced plasma), and (ii) gas is mainly ionized by plasma electrons heated due to the development of two-stream instability (beam−plasma discharge). The measured spatial profiles of the parameters of the beam-induced plasma are found to qualitatively agree with the model ones.

Radiological methods of treatment of malignant tumors are widespread in medical practice. In addition to the type of radiation and dose and fractionation of the radiation regime, the dose rate is one of the factors that affects the effectiveness of treatment. The therapeutic dose rate lies in the range of tens of mGy/s. At modern high-current accelerators of relativistic electron beams, a significant increase in the dose rate to hundreds of MGy/s is achievable, which is more than 10⁸ times greater than the therapeutic dose rate. It is difficult to predict the nature of processes in tissues and its cells at such radiation intensities. To determine the effect of extreme dose rate on the radiosensitivity of tissues at the Angara-5-1 facility, experiments were conducted to determine the lethal dose (LD50/30) for laboratory mice. Our result on the study of the LD50/30 dose (~100 MGy/s) allows us to make a conclusion about a possible higher lethal dose than the power range of the doses used for medical purposes.