Spatial distribution of atomic and ion hydrogen flux and its effect on hydrogen recycling in long duration confined and non-confined plasmas

Kuzmin, A.; Zushi, H.; Takagi, Ikuji; Sharma, Shubham; Kobayashi, M.; Hirooka, Y.; Onchi, Takumi; Hanada, K.; Yoshida, N.; Nakamura, K.; Fujisawa, A.; Idei, H.; Nagashima, Yoshihiko; Hasegawa, Makoto; Mutoh, T.; Mishra, K.; Ohwada, Hiroki

doi:10.1016/j.nme.2017.03.027

Cited by 7 publications

(3 citation statements)

References 16 publications

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“…Although the deposition layers have a significant impact on HI dynamics in PFW [16,17], the mechanisms are still not well understood. Recently, the effect of the deposition layer was noted in the dischargetime-dependent reduction of the plasma-driven permeation (PDP) flux [18,19], which clearly indicates the importance of considering the effect of the deposition layer. PFWs in fusion experimental devices are very complex and hence, it is challenging to elucidate their effect on the plasma.…”

Section: Introductionmentioning

confidence: 99%

Particle balance investigation with the combination of the hydrogen barrier model and rate equations of hydrogen state in long duration discharges on an all-metal plasma facing wall in QUEST

et al. 2019

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The fuel particle balance during long duration discharges in the Q-shu University Experiment with steady state spherical tokamak (QUEST) was investigated. QUEST has all-metal plasma facing walls (PFWs) that were temperature controlled during the experiments. The presence of a transport barrier for hydrogen (H) at the interface between a plasma-induced deposition layer and metallic substrate was confirmed by nuclear reaction analysis with exposing deuterium plasma. An effective method to evaluate global hydrogen flux to PFWs is proposed, taking advantage of the nature of wall saturation. The outgoing flux of fuel particles from the PFWs just after the plasma termination was proportional to the square of wall-stored H, which indicates that enhanced recombination of solved hydrogen played an essential role in dynamic retention and was in agreement with predictions from the H-barrier model. A simple calculation based on the combination of wall modelling and rate equations of the H states denoted a significant impact of wall modelling on the time response of the plasma density. Hence, a proper wall model including the effects of the deposition layer creating the H barrier is required to be developed, even for all-metal PFW devices.

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Section: Introductionmentioning

confidence: 99%

Particle balance investigation with the combination of the hydrogen barrier model and rate equations of hydrogen state in long duration discharges on an all-metal plasma facing wall in QUEST

et al. 2019

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“…1 (a)) and ion flux (Γ ion ) measured by a reciprocate Langmuir probe (indicated as RLP in Fig. 1 (a)) [6]. The PdCu membrane is selected for the probe calibration system from favorable viewpoints including the faster response time, wider permeation regime, and higher sensitivity independent of the incident hydrogen flux [6].…”

mentioning

confidence: 99%

“…1 (a)) [6]. The PdCu membrane is selected for the probe calibration system from favorable viewpoints including the faster response time, wider permeation regime, and higher sensitivity independent of the incident hydrogen flux [6]. The characteristics of the PdCu permeation probe have already been experimentally investigated by Onaka et al [7].…”

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confidence: 99%

Hydrogen Permeation through Sputter-Deposited Tungsten Coated F82H in QUEST

Xu¹,

Kuzmin²,

Hirooka

et al. 2017

Plasma and Fusion Research

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Hydrogen plasma-driven permeation (PDP) experiments have been performed using a sputter-deposited tungsten (SP-W) coated F82H membrane in the spherical tokamak QUEST. It has been found that SP-W coatings tend to enhance hydrogen PDP compared with that of bare F82H membrane. Surface recombination is a key process determining the PDP flux, suggesting that surface effects on hydrogen PDP should be further investigated. In magnetic fusion devices, confinement loss particles via cross-field diffusion will bombard the first wall to induce plasma-driven permeation (PDP) (atomic hydrogen permeation included). Hydrogen isotopes (deuterium and tritium) transported into the breeding blankets by PDP will hinder the recovery efficiency of tritium and necessitate isotopes separation. Tritium permeation through the first wall may raise reactor safety issues as well. In addition, particle recycling from the plasma-facing wall would directly affect the core plasma performance [1]. Thus, it is crucial to measure the particle flux to the first wall. In our previous work [2], a permeation probe made of a reduced activation ferritic steel (RAFS) F82H was used to measure the hydrogen permeation flux in QUEST at Kyushu University. Those measurements were conducted during wall conditioning steady-state discharges. For a DEMO reactor, surface coatings made of refractory metals such as tungsten (W) are necessary to protect the plasma-facing wall made of RAFS such as F82H [3]. The characterization of hydrogen transport through W coated F82H under plasma exposure is of crucial importance to evaluate major reactor design issues including tritium retention, breeding feasibility and first wall particle recycling. In this work, a sputterdeposited tungsten (SP-W) coated F82H permeation probe has been installed in QUEST. The data have been compared with experimental results obtained by a bare F82H permeation probe [2] and the effects of SP-W coatings on hydrogen PDP are discussed.Experiments are performed in the medium sized spherical tokamak QUEST [4] with the major and minor radii of 0.68 m and 0.4 m, respectively. Schematic view of the tokamak cross-section is shown in Fig. 1 (a) ing gas is hydrogen, supplied from a nozzle on the central stack. Gas puff is done in a pulse mode, the opening time of which varies in the range of 5 -100 ms with the fueling rate of 2.0 × 10 21 H s −1 . The interval between puffs is in the range from 1 s to 50 s. The fueling gas pressure in the vessel is set in the range of 1 -10 × 10 −3 Pa. Plasma is produced by electron cyclotron resonance (ECR) alone at 2.45 GHz (<10 kW). The annular slab plasma is used in

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High voltage electrical system of 8.56 GHz CW klystron for electron cyclotron heating on QUEST spherical tokamak

Onchi

Idei

Nakamura

et al. 2019

Fusion Engineering and Design

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Spatial distribution of atomic and ion hydrogen flux and its effect on hydrogen recycling in long duration confined and non-confined plasmas

Cited by 7 publications

References 16 publications

Particle balance investigation with the combination of the hydrogen barrier model and rate equations of hydrogen state in long duration discharges on an all-metal plasma facing wall in QUEST

Particle balance investigation with the combination of the hydrogen barrier model and rate equations of hydrogen state in long duration discharges on an all-metal plasma facing wall in QUEST

Hydrogen Permeation through Sputter-Deposited Tungsten Coated F82H in QUEST

High voltage electrical system of 8.56 GHz CW klystron for electron cyclotron heating on QUEST spherical tokamak

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