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For the most advanced multi-frame camera in the world, the shortest response time between two frames is no shorter than 1.5 ns. Thus, there is no effective way to diagnose the ultrafast sub-nanosecond dynamic of a microwave-driven plasma discharge in a single pulse. Different-length multi-sub-beam optical fibers, together with a spectrometer and an EMICCD camera, are proposed and designed to detect the nanosecond discharge spectra in a single pulse, like a real-time multi-frame spectral camera. This novel method could realize a time interval between two consecutive frames shorter than 0.1 ns by a length difference of 2 cm for sub-fibers, achieving the measurement of ultrafast plasma dynamics. Temporal evolution of electron density as well as energy of electrons and ions during nanosecond microwave discharge is further studied by de-convolving the Stark broadening and thermal Doppler broadening and by calculating the ratio of emission coefficients. [ABSTRACT FROM AUTHOR]

Experiments have been conducted on Constance B to study transport properties in electron cyclotron resonance (ECR) heated plasmas of high-charge-state neon ions. Measurements were made of confinement parallel and perpendicular to the magnetic field at heating frequencies of 10.5 and 14 GHz, and corresponding ECR magnetic field strengths. Although radial ion losses scaled approximately as B[sup -2], the total particle confinement time was independent of magnetic field. Thus, higher current densities of multicharged neon ions were extracted at higher ECR heating frequency and magnetic field. [ABSTRACT FROM AUTHOR]

Abstract: In order to quantify the surface charging of a plasma actuator using surface Dielectric Barrier Discharge, we propose a new equivalent circuit for this surface DBD and a new simple method allowing the measurement of the surface charging during the first half cycle and the discharging during the other half cycle. Using this method, we observed the temporal evolution of the total charge on the dielectric surface during an operation of a SDBD starting with positive cycle. We also observed the same phenomenon during an operation starting with a negative cycle. The comparison between these two observations suggests that the high electro-negativity of oxygen plays an important role in these discharges. Finally, we compare the total amount of charge transferred over a cycle under different experimental conditions and we find that the transfer is the lowest in oxygen and the highest in nitrogen. [Copyright &y& Elsevier]

The linear and quasilinear theory of the collisionless trapped electron mode (also called the ‘‘ubiquitous’’ mode) is analyzed, in order to illustrate its possible role in the electron thermal energy transport observed in magnetically confined plasmas. This instability is driven by the combined effects of the plasma pressure gradient (which includes the contributions from the temperature gradients of ions and electrons) and of the local magnetic curvature drift of trapped electrons and of circulating and trapped ions. Depending on the value of its wavelength across the magnetic field, this mode can connect with a branch of the ion temperature gradient instability, provided the ion temperature gradient is sufficiently strong. Also, under certain conditions, it can be driven unstable solely by a combination of electron temperature gradient and Landau damping by trapped electrons. The relevant modes are found to be robust against variation of parameters such as the electron collisionality, and to be consistent candidates in order to explain the experimentally observed rate of electron thermal energy transport from the center of the plasma column. [ABSTRACT FROM AUTHOR]

In this paper, a method for simultaneously acquiring the temporal and spatial evolution of characteristic plasma spectra in a single microwave pulse is proposed and studied. By using multi-sub-beam fiber bundles coupled with a spectrometer and EMICCD (Electron-multiplying intensified charge-coupled device), the spatial distribution and time evolution of characteristic spectra of desorbed gases at the dielectric/vacuum interface during nanosecond microwave-driven plasma discharge are observed. Arrays of small align tubes punctured with metal walls of feed horn are filled with separate fibers of matched sizes and equal lengths. The output ends of fibers arranged in a single longitudinal column are connected to the entrance slit of a spectrometer, where the optical spectrum inputs to a high-speed EMICCD, to detect the rapid-varying time and space spectra of nanosecond giga-watt microwave discharges. The evolution of spectral clusters of N2 (C-B), N2+ (B-X), and the hydrogen atoms is discovered and monitored. The whole duration of light emission is much longer than the microwave pulse, and the intensities of ion N2+ (B-X) spectra increase after microwave pulses with rise times of 25–50 ns. The brightness distribution of plasma spectra in different space is observed and approximately consistent with the simulated E-field distribution. [ABSTRACT FROM AUTHOR]

A simple one-dimensional ion dynamic model with charge exchange collisions as the predominant ion-neutral reactions in the sheath is used to obtain the ion energy distribution function (IEDF) in a single-frequency collisional capacitive argon discharge. The shape of IEDF strongly depends on the electron density in this model. IEDFs predicted by this model can be in good agreement with those measured by adjusting the electron density at the ion sheath boundary. The electron densities obtained in this way are in good agreement with those from optical emission spectroscopy measurement, which also indicates the validity of the model. [ABSTRACT FROM AUTHOR]