Volume 49, Nº 4 (2023)

NBI-assisted plasma heating with one or two injectors of fast neutral atoms was studied at the Globus-M2 spherical tokamak at the toroidal magnetic fields of 0.8–0.9 T and plasma currents of 0.35–0.4 MA. Measurements of the spatial temperature and electron density distributions, performed using the Thomson scattering diagnostics, showed a twofold increase in heating of plasma electrons during the injection of neutral particles with energies of up to 45 keV at the beam power of 0.75 MW, as compared to the ohmic heating regime. Switching on the second additional beam with the particle energy of up to 30 keV and power of up to 0.5 MW resulted in obtaining the hot ion mode in the range of mean plasma densities of (1.6–10) × 1019 m−3. According to the data of active spectroscopy and neutral particle analyzer diagnostics, in the hot zone, the ion temperature reached 4 keV at the plasma density of 8 × 1019 m−3, which is more than 2.5 times higher than the electron temperature.

The paper presents a computational estimate of the DT-to-DD neutron yield ratio for a spherical plasma-focus chamber PF9. The computations were carried out by the MHD modelling using the beam–target mechanism for neutron production. The charging voltage of the capacitor bank was varied in the range from 15 to 25 kV, and the initial pressure of the working gas was varied in the range from 4 to 30 Torr. The computations showed that the ratio of the DT and DD neutron yields varies in a wide range from 2 to 120, while the ratio of the DT and DD reaction cross sections for the typical ion energies in the beam varies in the range from 95 to 122. An analysis of the computational results showed that the difference in the estimates of the neutron yield is due to the features in the ion energy distributions.

The propagation of longitudinal harmonic plasma oscillations in monolayer graphene under an external magnetic field is analyzed analytically on the basis of the Boltzmann kinetic equation. Simple analytical formulas are presented for the positions of cyclotron resonances in the spectrum of magneto-plasma oscillations.

Acceleration of laser-induced plasma created as a result of three-step photoionization of atomic vapor by pulsed radiation of dye lasers pumped by copper-vapor lasers is studied experimentally. The acceleration was achieved due to the alternating magnetic field appearing upon propagation of a current pulse through an inductor located in direct proximity from the area of laser protoionization of atomic lutetium vapor.

The energy distribution of hot electrons escaping from the plasma of the ion source based on the discharge ignited under conditions of electron cyclotron resonance (ECR) was studied experimentally. The measurements were performed in wide ranges of microwave heating powers and neutral gas pressures. The facility under study is capable of providing uniquely high unit energy input into the plasma confined in the quasi-gas-dynamic (collisional) regime. In the course of the experiments, the diagnostics was performed of microwave radiation generated by the hot fraction of electrons escaping from the plasma. The regimes were discovered, in which the conditions are satisfied for the development of kinetic instabilities in the ECR discharge plasma. The energies are determined of electrons that cause the development of instabilities of this type, which are characterized by bursts of microwave radiation.

The effect is theoretically studied of nonreciprocity of interparticle forces on the energy exchange between the linear chain of dust particles and the ambient medium. It is shown that the energy exchange between the dust component and ion flow is important. When approaching the threshold for developing the instability of coupled waves, the considerable deviation occurs of the kinetic energy distribution from the law of equipartition of kinetic energy over degrees of freedom. In the case of inhomogeneous heating of the chain, the heat conduction coefficient does not depend on the number of particles and is determined by the parameters of the ambient plasma

Experimental and computational-theoretical studies of the electron energy distribution function (EEDF) at the afterglow stage of a glow discharge in a mixture of helium (content of 98.5% He) and xenon (content of 1.5% Xe) for pressures of 1, 2, and 3 Torr and a discharge current of 10 mA are carried out. The discharge is ignited in a tube with a radius of 1.25 cm. According to the measurements, the electron energy distribution function (EEDF) has a form close to the Maxwellian function in the low-energy region. A characteristic feature of the measured distribution functions is also a plateau in the energy range of 1–4 eV. The formation of this plateau is associated with fast electrons (4.5 eV) formed during chemionization with the participation of metastable xenon atoms. The calculations are performed within the nonstationary Boltzmann equation in the local approximation for the EEDF, taking into account the source of fast electrons. Experimental and calculated results are compared.

The results of measuring the lifetime of negative molecular ions @ and HD─ were refined by repeated processing: the lifetime of the @ ion is 3.9 ± 0.1 µs and that of the HD─ ion is 4.6 ± 0.1 µs. The values of the beam energy at which the measurements were carried out were refined. It is shown that the measurement results are divided into two groups in which the lifetimes of the @ and HD─ ions are equal with good accuracy.