Plasma Physics Reports

The characteristics of poloidal correlation fluctuation reflectometry diagnostics for a small-sized tokamak were studied using numerical simulations. The simulations were conducted using the method of fast synthetic diagnostics based on the linear (Born) scattering theory and including full-wave calculations of electric fields of microwaves in unperturbed plasma. The signal of microwaves scattering by density fluctuations was calculated in accordance with the reciprocity theorem using the data from gyrokinetic calculations of the space-time distribution of these fluctuations in plasma of the FT-2 tokamak. The frequency spectra of the synthetic scattering signals were compared with the spectra of density fluctuations in the scattering region obtained from gyrokinetic calculations. From synthetic scattering signals, radial profiles of the poloidal phase velocity of fluctuations were calculated and compared with similar profiles calculated directly from the gyrokinetic distributions of density fluctuations, as well as with the profiles of the poloidal E × B drift velocity of plasma.

Modern trends in tokamak design include the use of strong magnetic fields, whose generation produces Lorentz forces, which can damage the electromagnetic system (EMS) of the tokamak. A concept for the tokamak EMS is proposed that ensures reduced loads in the central region. Results of numerical simulations are presented, which substantiate the possibility of a significant reduction in mechanical stresses on the tokamak inductor through the use of quasi-force-free windings.

A thermal atmospheric plasma generated by an electrodeless microwave torch in an argon jet, which is placed within a protective nitrogen environment, is used to produce plasma-activated water (PAW). The aim is to prepare hydrogen peroxide and nitrous acid-based solutions for application in cancer and skin-disease therapy via indirect treatment methods. In these approaches, the activated water or the medium (PAM) prepared from it, which contains controlled concentrations of long-lived reactive oxygen and nitrogen species (RONS), can selectively affect transformed cells without injuring healthy ones. PAW produced by well-known non-thermal (cold) atmospheric plasma (CAP) sources based on electrode discharges typically contains metal impurities originating from the electrodes and moreover is produced only in limited quantities because of the low plasma density of such discharges. By contrast, PAW obtained using thermal atmospheric plasma has high purity and offers controlled levels of long-lived species, namely hydrogen peroxide (H₂O₂) and nitrite ions (NO₂^-), with concentrations exceeding 1mM at pH≈3. Batch volumes of 0.1-2 L can be produced with activation times up to 20 min.

A self-consistent model describing a glow discharge in argon with a liquid-phase (distilled water) anode is presented. The model is based on an extended hydrodynamic description of plasma and takes into account the heating of the metal cathode and liquid-phase anode, as well as the equilibrium evaporation of water molecules into the discharge gap and the kinetics of elementary processes involving them. A numerical study is performed for two key cases: the discharge initiation in a pure argon atmosphere and that with the initial presence of water molecules at a concentration corresponding to the saturated vapor pressure at an initial liquid-phase anode temperature of 293 K. For the first case, it is shown that a change in the plasma-forming ion from Ar⁺₂ to the hydrated cluster ion H₂O⁺₄ and also a change in the dominant negatively charged particle from the electron to the OH⁻ ion are observed during the evaporation of water molecules. For the second case, it is shown that is the dominant positive ion H₂O⁺₄ over the entire time interval. The competition between electrons and OH⁻ ions on times up to ~0.01 s was detected for negatively charged particles. The OH⁻ ion becomes the dominant negatively charged particle at times larger than 1 s but the electron density remains comparable by the order of magnitude, which is critical for maintaining plasma conductivity.