CO2 and H2 Gas Mixture Inclusion Effect on Shrinkage of Ar Induction Thermal Plasmas

Plasma Chem Plasma Process

2009

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Here the authors developed a two-dimensional two-temperature chemical nonequilibrium (2T-NCE) model of Ar-CO 2 -H 2 inductively coupled thermal plasmas (ICTP) around atmospheric pressure (760 torr). Assuming 22 different particles in this model and by solving mass conservation equations for each particle, considering diffusion, convection and net production terms resulting from 198 chemical reactions, chemical non-equilibrium effects were taken into account. Species density of each particle or simply particle composition was also derived from the mass conservation equation of each one taking the non chemical equilibrium effect into account. Transport and thermodynamic properties of Ar-CO 2 -H 2 thermal plasmas were self-consistently calculated using the first order approximation of the Chapman-Enskog method at each iteration point implementing the local particle composition and temperature. Calculations at reduced pressure (500 and 300 torr) were also done to investigate the effect of pressure on non-equilibrium condition. Results obtained by the present model were compared with results from one temperature chemical equilibrium (1T-CE) model, one-temperature chemically non equilibrium (1T-NCE) model and finally with 2T-NCE model of Ar-N 2 -H 2 plasmas. Investigation shows that consideration of non-chemical equilibrium causes the plasma volume radially wider than CE model due to particle diffusion. At low pressure with same input power, presence of diffusion is relatively stronger than at high pressure. Comparison of present reactive model with non-reactive Ar-N 2 -H 2 plasmas shows that maximum temperature reaches higher in reactive C-H-O molecular system than non-reactive plasmas due to extra contribution of reaction heat.

Section: Comparison With Non-reactive Ictpmentioning

confidence: 99%

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confidence: 99%

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confidence: 99%

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Two-Temperature Two-Dimensional Non Chemical Equilibrium Modeling of Ar–CO2–H2 Induction Thermal Plasmas at Atmospheric Pressure

Al-Mamun

Tanaka

Plasma Chem Plasma Process

2009

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“…Probe measurements of Ar/H 2 mixture plasmas in these experiments show that the electron temperature and electron densities near the target position 1, and ion fluxes onto the target 1 are in the range 0.5-1.5 eV, 10 16 -10 17 m -3 and 10 19 -10 20 m -2 s -1 respectively. On other hand, atomic hydrogen density and hydrogen ion density have been estimated using electromagnetic fluid simulation under local thermodynamic equilibrium [3]. Figure 2 shows the estimated atomic hydrogen and hydrogen ion densities as a function of the H 2 gas flow rate.…”

Section: Plasma Parameter Of Icpmentioning

confidence: 99%

Study of carbon dust formation and their structure using inductively coupled plasmas under high atomic hydrogen irradiation

Takeguchi

Kyo

Journal of Nuclear Materials

et al. 2009

Experiments on erosion and dust formation on graphite materials have been performed using high power induction plasmas containing high atomic hydrogen flux (~10 24 m -2 s -1 ). Chemical sputtering by atomic hydrogen irradiation with incident energy below 1 eV eroded the graphite targets significantly, and the sputtering yield was roughly estimated to be 0.002-0.005, which is as high as that obtained by ion beam and fusion plasma experiments. The transport of the released hydrocarbon along the gas flow, interacting with low temperature plasmas, results in carbon dust formation on the eroded graphite target and also on the silicon and graphite samples located at the remote position. The dust size and density observed on the samples decreases with distance from the graphite target. The dust shape strongly depends on the target surface temperature, and the graphite dust turns into polyhedral particle like diamond when the surface temperature rises to 1100 K.

“…Figure 1 shows the weight loss of the BDD and the graphite targets as a function of atomic hydrogen fluence. Here, atomic hydrogen fluence is estimated using the results of an electromagnetic fluid simulation under local thermodynamic equilibrium conditions [5]. The erosion of both the graphite and the BDD target increases linearly with increasing hydrogen fluence.…”

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confidence: 99%

Chemical Erosion of Diamond-Coated Graphite under Low-Energy Hydrogen Atom Irradiation

Takeguchi

Kyo

Plasma and Fusion Research

et al. 2010

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We experimentally investigate chemical erosion of polycrystalline graphite targets coated with boron-doped diamond (BDD) using an induction plasma containing low-energy, high-atomic-hydrogen flux. Chemical erosion is drastically suppressed by diamond coating the graphite target. The chemical sputtering yield for the BDD layer is about two orders of magnitude lower than that for the graphite target. After exposure in low-temperature hydrogen plasmas, however, the surface morphology of the BDD target is significantly modified. The polycrystalline diamond is eroded near the grain boundary, and many pits with diamond-like shapes are observed on the crystal surface. X-ray photoelectron spectroscopy and Raman spectroscopy reveal that the hydrogen atoms penetrate into the BDD target to a depth of at least ∼20 nm. In using graphite materials as plasma-facing components (PFCs) in fusion devices such as divertor tiles, it is recognized that the high chemical erosion rate due to the presence of hydrogen fuel and the related carbon dust formation will cause severe performance degradation in future fusion reactors. Diamond, which is a typical carbon crystal and has an sp 3 electronic structure, offers several features including an extremely high thermal conductivity, a low chemical reactivity, [1] and an increase of electrical conductivity that is possible through boron doping, making it superior for use as a PFC in fusion reactors. To date, several experimental efforts have focused on diamond erosion by energetic-ion irradiation [2, 3], but little effort has been devoted to low-energy atomic hydrogen. In the present research, boron-doped diamond (BDD) is tested for erosion by low-temperature (∼1 eV), high-flux hydrogen neutrals to check its suitability for divertor tiles used in a detached divertor.The experiments were performed in an Ar/H 2 mixture plasma generated by an inductively coupled plasma (ICP), which has the characteristic features of high neutral particle flux Γ H ∼ 10 23 -10 24 m −2 · s −1 , low ion flux Γ i ∼ 10 19 -10 20 m −2 · s −1 , and low electron temperature T e ∼ 1 eV [4]. The working gas pressure is ∼4 kPa. An approximately 30-nm thick polycrystalline BDD layer covers an isotropic graphite, where the boron doping rate is ∼0.5%. We deposit a BDD coating on an isotropic graphite target using hot-filament chemical vapor deposition (CVD). We vary irradiation time from 60 to 1200 minutes to examine the author's e-mail: 1027take@ee.t.kanazawa-u.ac.jp effect of target erosion due to hydrogen fluence into the target. The surface temperature is measured thorough a quartz window using a radiation thermometer. Figure 1 shows the weight loss of the BDD and the graphite targets as a function of atomic hydrogen fluence. Here, atomic hydrogen fluence is estimated using the results of an electromagnetic fluid simulation under local thermodynamic equilibrium conditions [5]. The erosion of both the graphite and the BDD target increases linearly with increasing hydrogen fluence. The chemical sputtering yield (Y) is estim...