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A concept of achieving trifocal terahertz (THz) radiation is discussed based on the application of a periodic electric field in addition to two dark hollow laser beams impinging into collisional plasma. Nonlinear plasma medium is engineered for altering the dynamics of electrons under such a periodic electric field and obtaining an additional transverse component of nonlinear current. This additional component modifies the optics associated with the emitted radiation, leading to trifocal THz radiation. The parameters associated with the doughnut intensity of dark hollow laser beams, such as beamwidth and beam order, control the position and peak of the emitted THz field. Interestingly, the efficiency of the emitted THz field can also be tuned by appropriate combinations of the laser beam orders. [ABSTRACT FROM AUTHOR]

In order to reconstruct the plasma boundary directly and independently, a new method based on visible imaging diagnostics is developed for experimental advanced superconducting tokamak (EAST); its effectiveness has been verified by conducting offline experiments based on EAST’s historical data. The offline boundary reconstruction results, including X-points, are compared to offline equilibrium fitting code (offline EFIT), which is a commonly used reconstruction method. With an average error of 1.5 cm, the total processing time for one frame is less than 2 ms by current software and hardware. When the camera sensor is not saturated, the algorithm is robust for different image intensities of the plasma discharge. The results of the boundary reconstruction by visible imaging diagnostics also show potential for real-time plasma control in a tokamak. [ABSTRACT FROM AUTHOR]

High-resolution optical emission spectroscopy and automated Langmuir probe are applied to examine the production of active species in the pure nitrogen plasma excited by single (40.68 MHz) and dual high-frequency (HF) radio frequency (RF) power sources (40.68/2.1 MHz). The emission intensities of the spectral bands correspond to the (0, 2) transition of the second positive system (SPS) of N2 ( \(\lambda =380.50\) nm) and ( \(0, 0\) ) transition of the first negative systems (FNSs) of N2+ ( \( \lambda =391.40\) and 427.81 nm) have been measured and compared with plasma parameters using the Langmuir probe to investigate the dependence of their radiative states on operating conditions for both single and dual HF RF capacitively coupled plasma (CCP) discharge. It was found that the high power of the low-frequency (LF) source and the gas pressures are the most effective parameters in dual RF CCP discharge system. Thus, both SPS intensity decreases and FNS intensity increases with the increasing LF power at constant pressure. Furthermore, the emission intensity of the first negative band heads increases at least four times in dual RF mode in comparing with the single RF CCP discharge. In contrast, the intensity of the second band heads decreases dramatically to its half values. Likewise, it was found that the transition pressures for the electron heating mode (with increasing the gas pressure) and the transition from \(\alpha \) to \(\gamma \) mode (with increasing the RF power) is close to 0.3 torr in single RF mode, but these transitions are about 0.5 torr for dual RF CCP mode. [ABSTRACT FROM PUBLISHER]

An optical tomographic diagnostic instrument has been fielded at the Dual-Axis Radiographic Hydrodynamic Test Facility at Los Alamos National Laboratory. Four optical lines of sight create projections of an image of an electron beam on a Cerenkov target, which are relayed via optical fiber to streak cameras. From these projections, a reconstruction algorithm creates time histories of the beam’s cross section. The instrument was fielded during and after facility commissioning, and tomographic reconstructions reported beam parameters. Results from reconstructions and analysis are noted. [ABSTRACT FROM PUBLISHER]

We present time-resolved laser-induced breakdown spectroscopy (LIBS) spectra of atomic (In I) and ionic (In II) indium lines recorded in time ranges from 500 ns to \(20~\mu \) s. Optical spectra have been acquired using a streak camera. Since it is assumed that the available supply of indium will slowly but inevitably diminish, the recycling of indium and finding the new natural sources are more and more important as the price of indium rises. The study of indium lines showed in this paper could be useful for making the LIBS detecting devices less expensive and more portable. [ABSTRACT FROM PUBLISHER]

Rotating gliding arc plasma reactor performs two operation modes according to supply power (dc and ac modes). According to the images of operating states and the emission spectrum of the two modes, the characteristics of dc mode and ac mode are well distinguished and investigated. The dc mode owns platform-type plasma region, high temperature, and energy consumption, suitable for fuel conversion field. The ac mode has a few advantages in gaseous organic pollutants treatment field, because of its relatively low gas atmosphere temperature, little by-products (NOx) production, and low energy consumption. [ABSTRACT FROM PUBLISHER]