Behavior of 23S metastable state He atoms in low-temperature recombining plasmas

Kajita, Shin; Tsujihara, T.; Aramaki, Mitsutoshi; Meiden, H. van der; Oda, Hiroshi; Ohno, Noriyasu; Tanaka, Hirohiko; Yasuhara, Ryo; Akiyama, Tsuyoshi; Fujii, Keisuke; Shikama, T.

doi:10.1063/1.4990077

Cited by 22 publications

(24 citation statements)

References 29 publications

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“…In order to reduce the stray light, baffles are equipped on the laser path, and a viewing dump is placed at the end of the field of view (detailed setup was described in Ref. [5]). Detachment was induced by controlling the neutral gas pressure, P, via the amount of injected gas near the end target.A typical LTS spectrum and fitting curve in attached He plasma (P = 5 mTorr) are shown in Fig.…”

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Thomson Scattering Measurement of Two Electron Temperature Components in Transition to Detached Plasmas

Ohshima

Kajita

Tanaka

et al. 2018

Plasma and Fusion Research

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We have performed laser Thomson scattering (LTS) measurements during the transition between attached and detached helium plasmas in the linear divertor simulator NAGDIS-II. In the detached plasma, the LTS spectrum shows a discrepancy with a single Gaussian function. The discrepancy is resolved by the spectrum fitting with a sum of two Gaussian functions, indicating that the electron energy distribution contains two different temperature components.Detached plasma plays an essential role for magnetically confined fusion devices to prevent divertor plates from being seriously damaged. In the detached plasmas, volume plasma recombination is one of the most important processes, strongly depending on electron temperature T e and density n e . In order to design DEMO and future devices, reliable plasma simulations should be established to predict the particle and heat loads on the divertor plate. A recent SOLPS modeling of DIII-D detached plasmas indicated that atomic and molecular processes and kinetic effects were important for reliable modeling particularly in low-temperature recombining plasmas [1]. Therefore, the precise measurements of T e and n e in the detached plasmas are an essential issue.Laser Thomson scattering (LTS) is known as a reliable technique for the measurements of T e and n e . LTS measurements of detached plasmas have been conducted in linear devices. In the MAP-II device, T e below 0.1 eV was acquired and compared with T e measured with Boltzmann plot and collisional-radiative (CR) model [2]. In the Magnum-PSI device, single-laser-pulse LTS measurements were performed with low observational errors [3]. LTS techniques for measurements of detached plasmas have also been used in the DIII-D device. A 2D divertor characterization was performed using the divertor Thomson scattering system through the transition from attached to detached plasmas [4].In this study, we applied LTS techniques to helium (He) plasma in the linear plasma device NAGIDIS-II (NAGoya DIvertor Simulator) and measured T e and n e in between attached and detached plasma states. In this LTS system, the second harmonics (wavelength 532 nm) of an Nd:YAG laser (Continuum: Surelite II-10: pulse width 5 -6 ns, pulse energy −0.3 J, repetition rate 10 Hz) was used. The collected light is transferred through the optical fiber (23 channels for observation) to the spectrometer, in which a volume phase holographic grating (2600 l/mm) was used. The signals were measured with the Gen-III ICCD camera (Andor: iStar) and accumulated for 300 s (3000 laser pulses). In order to reduce the stray light, baffles are equipped on the laser path, and a viewing dump is placed at the end of the field of view (detailed setup was described in Ref. [5]). Detachment was induced by controlling the neutral gas pressure, P, via the amount of injected gas near the end target.A typical LTS spectrum and fitting curve in attached He plasma (P = 5 mTorr) are shown in Fig. 1. The spec- Fig. 1 Typical LTS spectrum and fitting curve in attached plasma (P = 5.1 mTorr).

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Thomson Scattering Measurement of Two Electron Temperature Components in Transition to Detached Plasmas

Ohshima

Kajita

Tanaka

et al. 2018

Plasma and Fusion Research

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“…In period II, it is seen that spiral structure was clearly detached from the plasma column. Recently, laser Thomson scattering in NAGDIS-II revealed that a cold (∼0.1 eV) high density plasma existed in the peripheral region in detached plasmas [14]. It is likely that the plasma blowoffs shown in Fig.…”

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Mode Structure Analysis of Detached Plasmas with 2D Images

Kajita

Tanaka

Ohno

et al. 2018

Plasma and Fusion Research

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In linear plasma devices, blob-like cross-field transport is enhanced especially in detached plasmas. Formation of blob-like plasmas in the linear plasma device NAGDIS-II was observed using a fast framing camera, and the mode analysis was conducted using the emission from the plasma column. From the Fourier analysis, it was seen that plasma instability was enhanced before the ejection of blob-like plasmas from the plasma column. It was found that blob-like plasmas are generated at the peripheral region of the plasma column associated with low mode number (m = 0 -2) plasma instability inside the plasma column.

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“…An LTS measurement system, installed on the downstream side of the NAGDIS‐II, is able to measure T e below 1 eV. Measured T e by using the LTS was compared with T ed measured with the double probe at the same position.…”

Section: Methodsmentioning

confidence: 99%

Double‐probe measurement in recombining plasma using NAGDIS‐II

Hayashi

Nishikata

Ohno

et al. 2019

Contributions to Plasma Physics

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We have studied the validity of the double-probe method in recombining plasmas. Electron temperature (T e ) measured with a double probe was quantitatively evaluated by taking into account the influences of plasma potential fluctuation, plasma resistivity, and electron density fluctuation on the current-voltage characteristics. Differential potential fluctuation and plasma resistivity between two electrodes have a minor effect on T e especially when the inter-distance is small (typically 1 mm). Scattering of measured T e due to the density fluctuation was sufficiently suppressed by making the data acquisition time long (typically 4 s) and taking the average. There is a good agreement between T e measured with the optimized double-probe method and that with laser Thomson scattering diagnostics. KEYWORDSdouble probe, electron temperature, recombining plasma 1

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Behavior of 23S metastable state He atoms in low-temperature recombining plasmas

Cited by 22 publications

References 29 publications

Thomson Scattering Measurement of Two Electron Temperature Components in Transition to Detached Plasmas

Thomson Scattering Measurement of Two Electron Temperature Components in Transition to Detached Plasmas

Mode Structure Analysis of Detached Plasmas with 2D Images

Double‐probe measurement in recombining plasma using NAGDIS‐II

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