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Local plasma parameter measurements in colliding laser-produced plasmas for studying magnetic reconnection
摘要： We have implemented laser Thomson scattering for local plasma measurement of electron and ion temperatures, electron density, flow velocity, and charge state. The electron density increases by two times in the interaction of two plasma flows, indicating collisionless interaction. The density and velocity show fluctuations only at ns, and the density suddenly decreases, indicating the plasma ejection from the interaction region, which can be explained by a magnetic reconnection. The electron temperature in the double-flow is larger than that in the single flow. This may be explained by the energy transfer from the plasma kinetic energy to thermal energy. The ion temperature is much larger than electron temperature in the double-flow, and this may be explained by collisional effects between two plasmas, and/or possibly interpreted as a thermalization due to magnetic re-connection.
关键词： High energy density plasmas,Magnetic reconnection,Laser Thomson scattering
更新于2025-09-23 15:21:01
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[IEEE 2019 IEEE Pulsed Power & Plasma Science (PPPS) - Orlando, FL, USA (2019.6.23-2019.6.29)] 2019 IEEE Pulsed Power & Plasma Science (PPPS) - Laser Thomson Scattering Diagnostics for Streamer Discharge in HE Gas
摘要： Streamer discharge plasma, a type of non-thermal plasma, has received global attention as a source of reactive radicals, and is used for many applications such as ozone generation, decomposition of NOx and other gas pollutants, cleaning water, disinfection, deodorization, and medical applications. The tip of streamer discharge, known as the streamer head, in particular contributes to radical production. The peak electric field is located on the streamer head on the axis of symmetry of the discharge, likely resulting in many radical types. Very remarkable results in NO removal efficiency and superior ozone generation yield performed by streamer discharge have reported. Improving gas treatment methods requires understanding of physical characteristics of streamer discharge and streamer head, for example, electron temperature and electron density. This study investigates characteristics of streamer discharge by observing the propagation process of streamer head in a needle to conic electrode with positive voltage using a high speed gated emICCD camera. Then, incoherent laser Thomson scattering (LTS) diagnostic for streamer discharge and streamer head with positive voltage was performed. LTS diagnostic is considered to be the most reliable technique measuring electron temperature and density in plasma simultaneously. In addition, LTS diagnostic has high resolution temporally and spatially, therefore, LTS diagnostic can measure location dependence of electron temperature and density in streamer discharge including streamer head. The measurement point was 1 mm and 2 mm from tip of the high voltage needle electrode, and Thomson scattering signals were measured at the point of initial phase of streamer head propagation. In the results, electron temperature of streamer discharge was 4 to 6 eV, electron density of streamer discharge was 1021 m-3 order. This study has proven that LTS diagnostic can measure electron temperature and density in streamer discharge plasma.
关键词： Streamer discharge,Electron temperature,Laser Thomson scattering,Non-thermal plasma,Electron density
更新于2025-09-23 15:19:57
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Comparative study of electron temperature in cascaded arc Ar/N <sub/>2</sub> plasma using laser Thomson scattering combined optical emission spectroscopy approach
摘要： The expanding cascaded arc Ar/N2 plasma has been investigated by both the active and passive optical diagnostic technologies. In the investigation, the laser Thomson scattering (LTS) and optical emission spectroscopy (OES) have been adopted to measure electron temperature (Te) and electron excitation temperature (Texc), respectively. The LTS measurements show that a remarkable nonlinear behavior of Te as a function of the N2/(Ar + N2) ratio is found, which is caused by the collective interaction between the superelastic collision and the electron-impact excitation. The superelastic collisions by the highly excited vibrational nitrogen molecules can effectively heat the free electrons, while the electron kinetic energy can be transferred to N2 molecular internal energy via the electron impact with N2 in the ground state. The difference between Texc and Te demonstrates that the cascaded arc Ar/N2 plasma significantly deviates from the local thermodynamic equilibrium. This would be useful for improving our further understanding of nonequilibrium plasma and extending applications of the cascaded arc Ar/N2 plasma.
关键词： cascaded arc Ar/N2 plasma,local thermodynamic equilibrium,laser Thomson scattering,electron temperature,optical emission spectroscopy
更新于2025-09-19 17:13:59
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Investigation of picosecond thermodynamics in a laser-produced plasma using Thomson scattering
摘要： The picosecond evolution of the plasma conditions in a laser-produced plasma was measured using a Thomson-scattering diagnostic. The picosecond resolved Thomson spectra was enabled by a pulse-front-tilt-compensated spectrometer. The Thomson spectra revealed a transition in the plasma conditions from an initially cold evolving plasma to a quasi-stationary equilibrium plasma. The equilibrium temperature was found to match the generalized heat equation’s predicted scaling Te ∝ n2/5 and Te ∝ I 1/5. The plasma evolution was compared to Raman gain bandwidth calculations and showed a time-dependent resonance detuning that would limit the transfer e?ciency of a Raman plasma ampli?er in the linear regime.
关键词： laser-produced plasma,Thomson scattering,picosecond thermodynamics,Raman plasma amplifier,plasma conditions
更新于2025-09-19 17:13:59
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Spatial Characteristics of Thomson Scattering Spectra in Laser and Magnetic Fields
摘要： Spatial characteristics of Thomson scattering spectra are studied for an electron moving in the circularly polarized laser field in the presence of a strong uniform magnetic field. The results show that the angular distributions of the spectra with respect to the azimuthal and polar angles exhibit different symmetries, respectively, which depend on the fields and electron parameters sensitively and significantly. Moreover, for relatively large parameters such as high laser intensity, high magnetic resonance parameter as well as large initial momentum of electron, the two lobes in spectra tend to the laser-propagating direction so that the radiation can be collimated in the forward direction. Furthermore, an important finding is that by choosing the appropriate fields and initial momentum of electron, the high frequency part of the Thomson scattering spectra can reach the frequency range of soft x-ray, in which a high radiation power per solid angle as ～1011 a.u. can be obtained.
关键词： Thomson scattering,magnetic field,spatial characteristics,laser field,soft x-ray
更新于2025-09-12 10:27:22
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[IEEE 2018 43rd International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz2018) - Nagoya, Japan (2018.9.9-2018.9.14)] 2018 43rd International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz) - Developments of Equipment for sub- THz Collective Thomson Scattering in LHD
摘要： Equipment for collective Thomson scattering diagnostics in the Large Helical Device has been developed. The probe beam source is a 303 GHz Gyrotron. It operates in a pulse mode. No parasitic mode is excited during the whole pulse width including the turn-on and turn-off phases. Single mode oscillation at several frequencies has been confirmed. For power transmission, a 3.5 inch corrugated waveguide line installed for electron heating with lower frequency gyrotrons will be used. The test with the 303 GHz gyrotron has shown a sufficiently low transmission loss.
关键词： Gyrotron,collective Thomson scattering,corrugated waveguide,sub-THz,Large Helical Device
更新于2025-09-10 09:29:36
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Application of portable near-infrared spectrometer to Heliotron J plasma diagnostics
摘要： A simple near-infrared (NIR) spectrometer with a wavelength range of 898–2130 nm has recently been applied to diagnose Heliotron J plasmas. It adopts a symmetrical crossed Czerny–Turner mount equipped with a thermoelectrically cooled 512 channel InGaAs linear sensor. Reciprocal linear dispersion was deduced to 96.37 nm/mm at the center of the detector. External ?lters can be inserted into the path of the collection optics to reject second-order spectra, as needed. Absolute intensity calibration was performed together with a visible spectrometer using a tungsten halogen lamp, and the effect of the transmittance fringe in the visible region of the applied long-pass ?lter on the NIR calibration was investigated. The intended application of the NIR spectrometer includes extending the wavelength region of a spectral monitor to less contaminated regions for Heliotron J plasma studies. In preliminary measurements, we observed the Paschen series for the hydrogen pellet injection plasma and two atomic helium lines, i.e., 2S-2P singlet and triplet lines, in helium gas puf?ng experiments. A continuum spectrum in this regime that is attributable to black-body radiation from hot spots on the plasma-facing components was identi?ed. In addition, this may also be used to monitor background radiation in the YAG-Thomson scattering signals near 1064 nm.
关键词： near-infrared spectrometer,YAG-Thomson scattering,plasma diagnostics,helium lines,black-body radiation,Paschen series,Heliotron J
更新于2025-09-10 09:29:36
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The Measuring System for the Thomson Scattering Diagnostics of the GOL-3 and GDT Facilities
摘要： The measuring system for Thomson scattering diagnostics of the GOL-3 and GDT facilities at the Budker Institute of Nuclear Physics is described. The system has a modular architecture and is based on eight-channel measuring subsystems, including photodetectors, two-channel recorders (ADC12500), synchronization modules, and the Ethernet/UART communication channel adapter. The photodetectors are based on avalanche photodiodes and are operable in the frequency range of 0–50 MHz. The ADC12500 recorders are used to measure scattering signals with a duration of ~20–30 ns at a sampling rate of to 500 MHz and an amplitude resolution of 12 bits and accumulate data in a buffer memory with a capacity as large as 2 MB.
关键词： ADC12500,avalanche photodiodes,GDT,measuring system,Thomson scattering diagnostics,GOL-3
更新于2025-09-04 15:30:14