卷 49, 编号 9 (2023)

This work is devoted to the project of a new-generation open trap, gas-dynamic multiple-mirror trap (GDMT), proposed at the Budker Institute of Nuclear Physics, Siberian Branch, Russian Academy of Sciences. The aim of the project is to substantiate the possibility of using open traps as thermonuclear systems: a source of neutrons and, in the future, a thermonuclear reactor. The main objectives of the project are to develop technologies for long-term plasma maintenance in an open trap, optimize neutron source parameters based on the gas-dynamic trap, and demonstrate methods for improving plasma confinement. The magnetic vacuum system of the facility consists of a central trap, multiple-mirror sections that improve the longitudinal plasma confinement, and expanders designed to accommodate plasma flux absorbers. The facility is to be built in several stages. The starting configuration is broadly similar to the GDT facility and includes a central trap with strong magnetic mirrors and expanders. It solves two main problems: optimization of the parameters of the neutron source based on the gas-dynamic trap and study of the physics of the transition to the configuration of a diamagnetic trap with a high relative pressure β ≈ 1, which significantly increases the efficiency of the system. This work describes the technical design of the starting configuration of the facility and outlines the physical principles on which the GDMT project is based.

The KINX and VENUS codes were used for simulation of the baseline inductive and steady-state scenarios of the ITER tokamak operation. The perturbations of plasma electron density and magnetic field caused by the Alfvén modes were calculated in the flux coordinates for these scenarios. The perturbation fields obtained were converted into the engineering coordinates in order to calculate the propagation of probe electromagnetic radiation of the reflectometer using the two-dimensional full-wave TAMIC RτX code in the expected geometry of the experiment. The calculations performed show that for the baseline inductive scenario, in the case of reflection of the extraordinary wave at the lower cutoff frequency from the high magnetic field side, the electric field relative perturbations of the reflected reflectometer signal correspond to the margin of linear range of the diagnostics operation or even go out of this range. It was found that in a number of scenarios, not only the electron density perturbations, but also the magnetic field perturbations significantly contribute to the total signal perturbations that makes even more difficult the further data interpretation. Another possible problem is the narrow frequency range of probing frequencies where the Alfvén mode can be observed. In addition to simulating the reflection of electromagnetic waves from plasma, it was analyzed also the possibility of measuring the Alfvén modes parameters when the extraordinary wave pass through the plasma in the transparency window between the upper and lower cutoff frequencies of the extraordinary wave (refractometry). It is shown that at the fundamental frequency, the phase perturbations range from 3 to 60 degrees, which makes it impossible to use the amplitude-modulated refractometer for analyzing signals. The “synthetic diagnostics” approach was used, which showed itself well for simulating the operation of reflectometers at plasma facilities.

Collective electromagnetic modes in weakly ionized plasma formed by multiphoton ionization of inert gas atoms, in which the Ramsauer–Townsend effect takes place, are studied. It is shown that at a relatively low energy of photoelectrons of the order of 1 eV, typical for multiphoton ionization, amplification of electromagnetic waves is possible. Amplification is possible both in the case of rare collisions of photoelectrons with neutral atoms and for collision frequencies higher than electron plasma frequency. At photoelectron energies somewhat higher than 1 eV, aperiodic instability can develop with growth rate whose value is comparable to electron plasma frequency. Detailed analytical and numerical analysis of the effect of collisions of photoelectrons with neutral atoms on the dispersion law of electromagnetic wave and the growth rates of instabilities is presented.

The effect of random forces, which are caused by fluctuations in a complex plasma, on the dynamics of charged dust grains is studied. Analytical dependences are obtained for the kinetic energy, the autocorrelation functions of velocities, the mass transfer functions, and the mean-square average displacements of the grains in the case of a grain moving under the effect of two random forces. A method is proposed for accounting for more than two random forces of different nature. The possibility is discussed of simulating the motion of dust grains in complex plasma by the Langevin equations with a temperature that is not equal to the temperature of the surrounding gas.

Исследован процесс электрического пробоя в разрядной трубке длиной 80 см и внутренним диаметром 1.5 см (так называемой “длинной разрядной трубке”) в ксеноне при давлении 1 Торр. Пробой осуществлялся положительными импульсами с линейно растущим передним фронтом крутизной dU/dt порядка 10^–1–10⁵ кВ/с. Измерялось напряжение пробоя в темноте и при освещении разрядной трубки люминесцентными лампами, светодиодами или диодным лазером. Воздействие освещения на напряжение пробоя зависит от крутизны фронта. При dU/dt > 100 кВ/с напряжение падает, при dU/dt < 100 кВ/с – растет. При 0.1–1 кВ/с этот рост достигает шести раз. Исследована зависимость наблюдаемого эффекта от интенсивности излучения, его длины волны и положения освещаемой области поверхности трубки. Предпробойная волна ионизации ведет себя в этих условиях необычно: ее скорость и интенсивность излучения фронта растут при ее движении. В качестве механизма наблюдаемых явлений рассматривается фотодесорбция электронов с поверхности трубки, в результате которой стенка вблизи анода приобретает положительный заряд. Это приводит к повышению пробойного напряжения и ускоренному движению волны ионизации. Проведены дополнительные эксперименты, подтверждающие наличие в этих условиях стеночного заряда в прианодной области.