Evaluation of axial decay length of plasma pressure in detached plasma

Tanaka, Hirohiko; Ohno, Noriyasu; Kajita, Shin; Takano, Hiroki; Hattori, Shuzo; Imaeda, Yuya

doi:10.1016/j.nme.2020.100812

Cited by 3 publications

(4 citation statements)

References 20 publications

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“…The optical emission spectra of the plasma were collected by a 23-channel fiber bundle at the same downstream location as the LTS measurements [20]. The OES spectra are measured along the radial direction with a spectral resolution of 2.4 mm.…”

Section: Diagnostic Results Of Oesmentioning

confidence: 99%

“…Although the particle loss rate caused by D 2 -DA is not evaluated, it is anticipated that the contribution of DA-MAR would be consistently minimal or constrained in the deuterium plasma. As P down increases, the recombination front gradually shifts towards the upstream [20,36], resulting in an extended recombination path. Although the particle loss rates in the hydrogen plasma are slightly higher than those in the deuterium plasma at the downstream, there is a greater volume MAR in the hydrogen plasma from upstream to downstream.…”

Section: The Isotope Effects On Plasma Detachmentmentioning

confidence: 99%

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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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Section: Diagnostic Results Of Oesmentioning

confidence: 99%

Section: The Isotope Effects On Plasma Detachmentmentioning

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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show abstract

“…Experimental conditions of deuterium plasma discharges in NAGDIS-II NAGDIS-II is a linear divertor plasma simulator with length (z) 2.5 m and radius (r) 0.09 m, consisting of a direct current (DC) plasma discharge region and a divertor test region [24], as shown in figure 1. This device can easily generate detached helium plasmas in the steady state, and has been investigated in prior research studies [25][26][27]. However, previous tests indicated that for a deuterium gas discharge plasma, the discharge voltage tended to be high (∼200 V) and the plasma became unstable.…”

Section: Experimental Setup and Conditionsmentioning

confidence: 99%

“…The optical emission spectrum of deuterium plasma at the same downstream location as the LTS was collected via a fiber bundle [27], transmitted to a C-T structured spectrometer (SPEX, 750M) with a grating of 1200 l mm −1 and a focal length of 750 mm, and detected by a CCD camera. The detection region of OES was slightly wider in the radial direction than that of LTS, due to the different focusing systems.…”

Section: Optical Emission Spectroscopymentioning

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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Four-dimensional conditional averaging tomography of rotating plasma ejection from cylindrical detached plasma

Tanaka,

Kajita,

Natsume

et al. 2024

Sci Rep

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Detached plasma formation is a way to reduce the heat load on the wall in magnetic fusion devices. This study proposes a novel analysis technique consisting of the conditional averaging, sliding window, and tomography to reveal the spatiotemporal behavior of the rotating radial ejection event of detached plasma, which further contributes to local heat load reduction. The used equipment is a high-speed camera and an electrostatic probe located at the periphery of the linear plasma device NAGDIS-II. By applying this method, four-dimensional (4D) behavior of the emission structure along time (1D) and space perpendicular and parallel to the magnetic field (3D) was clarified; a rotating distorted structure appears as a precursor, which is then scraped and transported radially and axially. The proposed method is widely applicable to short-term rigid-body rotating structures, especially in linear plasmas.

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Evaluation of axial decay length of plasma pressure in detached plasma

Cited by 3 publications

References 20 publications

Hydrogen isotope effects on recombination dominant plasmas in NAGDIS-II

Hydrogen isotope effects on recombination dominant plasmas in NAGDIS-II

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

Four-dimensional conditional averaging tomography of rotating plasma ejection from cylindrical detached plasma

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