Characterization of Oscillations in Closed Drift Thrusters

The nature of oscillations in the 1 kHz-60 MHz fre-quency range that have been observed during opera-tion of closed drift thrusters (CDT), such as the sta-tionary plasma thruster (SPT) and the anode layer thruster (ALT), is quantitatively discussed. We use contours of various plasma parameters measured in-side the accelerating channel of an SPT[1, 2] as the starting point of our investigation and calculate the magnitude and spatial distribution of various asso-ciated natural and collision frequencies, characteris-tic lengths and velocities. This leads to a thorough characterization of the plasma in the channel under typical operation. This detailed picture is then used to evaluate the stability criteria and dispersion rela-tions of oscillations that are suspected to occur. Us-ing various dispersion relations, we present a band by band overview of the oscillations with a description of their observed behavior and discuss their nature and dependencies through comparison of the calcu-lated contours to reported observations. In particular we discuss the excitation of low frequency azimuthal drift waves that can form a rotating spoke at lower values of B∗r, axially propagating “transit-time ” os-cillations, high frequency azimuthal drift waves, ion-ization instability-type waves, and wave emission pe-culiar to weakly ionized inhomogeneous plasma in crossed electric and magnetic fields

Investigations of the development of thunderstorm with hail. Part 3. Numerical simulation of cloud evolution

The three-dimensional nonstationary model of a convective cloud is used for investigating a thunderstorm with hail which developed over Pyatigorsk on May 29, 2012 and produced a severe hailstorm. The values of cloud characteristics (liquid water content, ice content, vertical velocity, etc.) are obtained. The importance ofconsidering wind shear is noted. The simulation results are used to analyze the transformation of precipitation field and the electric charge structure of the analyzed cloud during its development