Ran Hai

High spatial resolution mapping of deposition layers on plasma facing materials by laser ablation microprobe time-of-flight mass spectroscopy

A laser ablation microprobe time-of-flight mass spectroscopy (LAM-TOF-MS) system with high spatial resolution, ~20 nm in depth and ~500 μm or better on the surface, is developed to analyze the composition distributions of deposition layers on the first wall materials or first mirrors in tokamak. The LAM-TOF-MS system consists of a laser ablation microprobe combined with a TOF-MS and a data acquisition system based on a LabVIEW program software package. Laser induced ablation combined with TOF-MS is an attractive method to analyze the depth profile of deposited layer with successive laser shots, therefore, it can provide information for composition reconstruction of the plasma wall interaction process. In this work, we demonstrate that the LAM-TOF-MS system is capable of characterizing the depth profile as well as mapping 2D composition of deposited film on the molybdenum first mirror retrieved from HL-2A tokamak, with particular emphasis on some of the species produced during the ablation process. The presented LAM-TOF-MS system provides not only the 3D characterization of deposition but also the removal efficiency of species of concern.

Enhancement of Laser-Induced Breakdown Spectroscopic Signals in a Liquid Jet with Glow Discharge:

In this work, emission signals of laser-induced breakdown (LIBS) plasma of a flowing liquid jet in the absence and presence of an air-supported glow discharge have been investigated. In combination with a needle-to-needle glow discharge, a Q-switched neodymium-doped yttrium aluminum garnet (Nd:YAG) laser (1064 nm, 5 ns) with power density ∼1010 W/cm2 was used to generate a plasma from a liquid jet. Emission lines of Mg, Ca, Al, Li, Na, and K all showed significant enhancements in the presence of the glow discharge. Lower continuum background was also observed. Mechanisms of the line emission enhancement and continuum radiation reduction were discussed.

Molecular Dynamics Simulation on Terahertz Spectra of Methamphetamine Hydrochloride

Methamphetamine hydrochloride crystal (trade name Methedrine) that is one of the illegal drugs used as a stimulant to the nervous system has been considered to be detected by T-ray via the terahertz time-domain spectroscopy (THz-TDS). In this research, we simulated the THz spectra of Methedrine by molecular dynamics methods for the first time. The terahertz spectra at temperatures 78.4K, 200K, 294K and 400K in the frequency range of 10-100cm-1 were investigated, which exhibited the variation of spectra position and intensity with increasing temperature. Firstly, we used DL_POLY simulation package to obtain the instantaneous values of the dipole moment. Subsequently, the intensities of THz vibrational modes were obtained by the Fourier transform of the autocorrelation function of the dipole moment. The results showed our theoretical calculation by molecular dynamics simulations got a good consistency with available experimental spectroscopy. These are useful to determine the best conditions of temperature at which the terahertz time-domain spectroscopy of Methedrine results a highly informative spectrum.

Remote in situ laser-induced breakdown spectroscopic approach for diagnosis of the plasma facing components on experimental advanced superconducting tokamak

The diagnosis of the fuel retention and impurity deposition on the plasma facing components (PFCs) is very important for monitoring plasma-wall interactions and improving the performance of long-pulse operation for tokamak devices. In this study, a remote in situ laser-induced breakdown spectroscopic (RIS-LIBS) system has been developed to be an effective and routine method for the diagnosis of the composition of the PFCs on Experimental Advanced Superconducting Tokamak (EAST). The RIS-LIBS system can be operated between EAST discharges via a remote network control system. This allows a flexible diagnosis for the PFCs at a specific EAST discharge operation or under planned plasma scenarios according to the experimental requirement. Measurements on the fuel retention and impurity deposition of the PFCs have been performed for the test of the RIS-LIBS system, and the depth resolution and the lateral resolution of the RIS-LIBS system have been achieved to be ∼100 nm and ∼3.0 mm, respectively. For the test of detectable elements, the fuel (deuterium) and impurities have been detected and identified clearly. In addition, the measurement of fuel abundance on the first wall as a function of the days of EAST deuterium plasma discharges has been carried out for the first time. These results well manifest a significant prospect of the RIS-LIBS for the diagnosis of the PFCs in the upcoming fusion devices like China Fusion Engineering Test Reactor (CFETR) and ITER.

Study of Spark Discharge Assisted to Enhancement of Laser-Induced Breakdown Spectroscopic Detection for Metal Materials

In this work, laser triggered spark discharge was combined with laser-ablation under Air and Ar gases to investigate the characteristics of laser-ablated plasma emission. The experimental results show that the optical emission intensity is significantly enhanced by electric discharge compared to without discharge and the spectral emission time of plasma is much longer than that without discharge. The enhancement effect is more apparent in the presence of Ar ambient. In addition, the plasma temperature and electron density as well as limits of detections (LOD) have been determined. The better LOD can be attributed to the improvement of plasma. The higher plasma temperature and electron density indicate that the enhanced mechanism in emission intensity is predominated by the further excitation/ionization of the laser-ablated material by the spark discharge due to the energy deposition in the plasma.

Preliminary study of identifying trench oil based on laser-induced breakdown spectroscopy

In order to distinguish edible oil and trench oil (which is called di-gou-you in Chinese), spectral features of the samples were investigated by laser-induced breakdown spectroscopy (LIBS) in this paper. Artificial neural network (ANN) model was also built and tested for spectral data analysis, and the research results showed that the ANN model was reasonably efficient. Two kinds of common edible oil and a kind of typical trench oil were chosen for experimental investigations. Totally, we tested four kinds of samples, including filter paper as sample-matrix for laser ablation, soybean oil, blend oil and trench oil. One hundred and forty LIBS spectra for each sample were collected, and the extracted 24 characteristic spectral lines have been adopted for the principal component analysis (PCA). The resulting data showed that each kind of sample tied together in principal components space and the four samples were separated well. For ANN statistical analysis, the observed 100 LIBS spectra for each sample were chosen as training set to build ANN model. And the other 40 LIBS spectra of each sample were used as the experimental data analysis. The achieved identification accuracy based on PCA and ANN was 94.2%, 98.1%, respectively. This indicates that LIBS detecting technique based on PCA and ANN statistical analysis brings a new possible approach to identify trench oil efficiently and quickly.