Theoretical and experimental studies of large scale modes in Hall thrusters and methods of their control

Partially-magnetized plasmas with magnetized electrons and weakly-magnetized ions in crossed electric and magnetic fields are common in the nature and industrial devices, such as magnetrons, MHD generators, electric propulsion (ion/Hall thrusters, helicon thrusters), and Penning discharges. Such plasmas are usually in a strongly non-equilibrium state, exhibiting a variety of turbulent fluctuations. These fluctuations are responsible for anomalous transport phenomena and large-scale plasma structures. This study investigates one of the most known and pervasive examples: rotating spokes and breathing modes, in Hall thrusters. Breathing mode is an m=0 mode (where m is the azimuthal mode number), propagating in the axial direction, and leading to strong oscillations of the discharge current, up to 100 % in amplitude. Spoke is an m=1,2,… mode, rotating in an azimuthal direction and is thought to be responsible for a large part of the anomalous current in a system. These large-scale perturbations can critically affect the performance of Hall thrusters, but the exact nature of these modes is unknown. Both types of oscillations are believed to be induced and strongly affected by the equilibrium electron current due to ExB drift, plasma density gradients, and ionization. This thesis is devoted to theoretical and experimental studies of spoke and breathing mode mechanisms, their coupling, and methods of their control

A confocal laser-induced fluorescence diagnostic with a ring-shaped laser beam

In this work, we report a confocal laser induced fluorescence (LIF) configuration, which allows for high spatial resolution measurements of plasma properties in plasma setups and sources with a limited optical access. The proposed LIF configuration utilizes a ring-shaped laser beam generated by a pair of diffractive axicons. LIF signal is collected along the main optical axis within the ring region. It is shown experimentally that at the focal distance of 300 mm, the spatial resolution of approximately 5.3 mm can be achieved. More than that, theoretical estimations predict the possibility of achieving ~1 mm resolution at the same focal distance by adjusting laser beam parameters. This is approaching the localization accuracy of conventional LIF collection methods (with crossing laser beam injection and fluorescence collection optical paths). Measurements of the ion velocity distribution function in an argon plasma using both the confocal LIF with ring shaped laser beam and conventional LIF demonstrate a satisfactory agreement. The proposed LIF setup has potential applications for diagnostics in various plasma processing equipment, and plasma sources such as hollow cathodes, microplasmas, electric propulsion, etc

Formation of a high energy density field reversed configuration for compact toroid applications

Formation of a compact toroid (CT) or field reversed configuration (FRC) with a maximum input of energy and the capture of the magnetic field into plasma is an important scientific and technical challenge. The new method of CT formation is proposed and applications of CT/FRC are presented.Рассмотрен новый принцип создания системы удержания плазмы высокой плотности на основе обращенной магнитной конфигурации (FRC), как наиболее перспективной для малорадиоактивных/безнейтронных реакций синтеза. Рассчитан баланс мощностей реактора на основе D-T и D⁻³Не топлива. Обсуждается применение D⁻³Не топлива в качестве источника энергии для перспективных двигательных установок, представлены основные параметры (тяга, импульс) для такой системы.Розглянуто новий принцип створення системи утримання плазми високої густини на основі зверненої магнітної конфігурації (FRC), як найбільш перспективної для малорадіоактивних/безнейтронних реакцій синтезу. Розраховано баланс потужностей реактора на основі D-T і D⁻³Не палива. Обговорюється застосування D⁻³Не палива в якості джерела енергії для перспективних двигунових установок, представлені основні параметри (тяга, імпульс) для такої системи

Stability of Ion Flow and Role of Boundary Conditions in a Simplified Model of the E × B Plasma Accelerator with a Uniform Electron Mobility

Abstract: Resistive oscillations of axial plasma with ionization effects are analyzed in configuration similar to the Hall effect thrusters. From analysis of stationary equations we have identified different types of the steady-state plasma flow profiles and use these solutions as initial conditions in time-dependent initial value simulations. We have identified unstable regimes with intrinsic oscillations, as well as stable regions without oscillations. It was found that nonlinear oscillations may exist in different form depending on the range of plasma parameters. Single mode coherent, multi-mode with nonlinear harmonics, and incoherent (stochastic) mode regimes were identified. We have further investigated the role of boundary conditions on the characteristics of nonlinear oscillations. © 2020, Pleiades Publishing, Ltd