Development of Thomson Scattering Measurement System for Upstream Plasmas in the NAGDIS-II Device

Takano, Hiroki; Ohshima, Hiroshi; Kajita, Shin; Tanaka, Hirohiko; Ohno, Noriyasu

doi:10.1585/pfr.14.2405031

Cited by 6 publications

(3 citation statements)

References 15 publications

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“…An electrostatic probe was positioned at 16 cm upstream from the LTS location and was used to measure the ion saturation current, which was used as a reference signal for CA. The radial position of the electrostatic probe was several mm away from the center considering the disturbance of the probe, which was revealed recently from a comparison to LTS in an upstream region of the NAGDIS-II device [23].…”

Section: Methodsmentioning

confidence: 84%

Spatial and temporal measurement of recombining detached plasmas by laser Thomson scattering

Kajita

Ohshima

Tanaka

et al. 2019

Plasma Sources Sci. Technol.

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Elucidation and control of the low temperature recombining plasmas under fusion relevant conditions are crucial issues. In this study, we applied a conditional average for laser Thomson scattering technique to measure the temporal evolution of the plasma instability in detached recombining plasmas in the divertor simulator NAGDIS-II. In recombining plasmas, it is shown that the electron energy distribution function has a non-Maxwellian component, and the fraction of the low electron temperature component increases with the gas pressure. It is found that one of the major reasons to cause the non-Maxwellian distribution function is in the temporal variations of the electron temperature. By using the conditional averaging method, the temporal evolutions of the spatial (vertical and radial) profiles of the electron density and temperature are revealed for different frequency ranges.

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Section: Methodsmentioning

confidence: 84%

Spatial and temporal measurement of recombining detached plasmas by laser Thomson scattering

Kajita

Ohshima

Tanaka

et al. 2019

Plasma Sources Sci. Technol.

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“…The electron density and temperature of the plasma were measured along the radial direction of the upstream (x = 0.4 m) and downstream (x = 1.88 m) regions by using the LTS [17][18][19]. The radial resolution of the upstream and downstream LTS is 1.4 mm and 1.25 mm, respectively.…”

Section: Diagnostic Results Of Ltsmentioning

confidence: 99%

Hydrogen isotope effects on recombination dominant plasmas in NAGDIS-II

Shi,

Kaizawa,

Uematsu

et al. 2024

Plasma Phys. Control. Fusion

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The detachment processes of the hydrogen (H) and deuterium (D) plasmas are comparatively investigated in the linear plasma device NAGDIS-II. The laser Thomson scattering measurements demonstrate that the recombination rate of the H plasma is greater than that of the D plasma as the neutral pressure increases in the molecular activated recombination (MAR) dominant detachment phase. As the recombination process by MAR is strongly dependent on the vibrational and rotationally excited states of the molecule, the rovibrational quantum state populations of the H and D molecules are measured using the Fulcher-α band spectroscopy. The results indicate that the vibrational temperature in the electronic ground state is considerably higher than the rotational temperature during detachment. The reaction rate coefficients for MARs due to charge exchange chains (CX-MAR) and dissociative attachment chains (DA-MAR) are calculated by the collision-radiation model under the measured temperature conditions. It can be observed that the CX-MAR is larger than the DA-MAR for both H and D, and that the CX-MAR of H is larger than the CX-MAR of D at electron temperatures T e above 1 eV. In consideration of the experimentally observed vibrational and rotational excitation temperatures, the reaction rate coefficients of CX-MAR and DA-MAR are increasing in the low T e region. These calculations are in accordance with the experimental results, which indicate that recombination processes due to MAR are more predominant in the H plasma compared to the D plasma. Furthermore, a transition from MAR to electron–ion recombination processes is observed in the D plasma at T e below 0.5 eV.

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“…LTS diagnostic systems were mounted 0.40 m upstream and 1.88 m downstream of the divertor test region, with the same laser and spectrometer used for both the upstream and downstream measurements [28]. The LTS system used a double frequency (wavelength 532 nm) Nd:YAG laser (Surelite II-10, Continuum) for the light source, with a pulse width of 5 ns, a repeat frequency of 10 Hz and a pulse energy of ∼0.3 J and a half-wave plate and a polarizing beamsplitter cube were adopted to change the laser polarization to switch the laser paths of upstream and downstream.…”

Section: Laser Thomson Scattering Diagnosticmentioning

confidence: 99%

Transition from MAR to EIR of deuterium plasma detachment in NAGDIS-II

Shi,

Kaizawa,

Tanaka

et al. 2023

Phys. Scr.

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Volumetric plasma recombination in a detached deuterium (D) plasma was experimentally studied in the linear plasma device NAGDIS-II. The radial distributions of the electron temperature (T e ) and the electron density (n e ) were measured by upstream and downstream laser Thomson scattering (LTS) systems and D-atom excited states of the Balmer series (n = 3–7) were measured by optical emission spectroscopy (OES). The results indicated that the electron static pressure, particle flux and heat flux present a two-step reduction with an increasing neutral pressure, suggesting that molecule activated recombination (MAR) and electron–ion recombination (EIR) were activated, respectively. The difference in the distributions of the atomic state population densities was observed to be a feature of the transition from the MAR-dominant phase to the EIR-dominant phase. The transition between the two phases had a distinct boundary at T e ∼0.7 eV, which was considered a transition point between the phases. The ratios of the atomic state population densities showed different features in the two phases, and are expected to be useful in characterizing the phase and degree of plasma detachment.

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Development of Thomson Scattering Measurement System for Upstream Plasmas in the NAGDIS-II Device

Cited by 6 publications

References 15 publications

Spatial and temporal measurement of recombining detached plasmas by laser Thomson scattering

Spatial and temporal measurement of recombining detached plasmas by laser Thomson scattering

Hydrogen isotope effects on recombination dominant plasmas in NAGDIS-II

Transition from MAR to EIR of deuterium plasma detachment in NAGDIS-II

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