The Experts below are selected from a list of 1518 Experts worldwide ranked by ideXlab platform
R Kaita - One of the best experts on this subject based on the ideXlab platform.
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Plasma Facing Component characterization and correlation with Plasma conditions in lithium tokamak experiment β
IEEE Transactions on Plasma Science, 2020Co-Authors: A. Maan, D P Boyle, R Majeski, R Kaita, E. T. Ostrowski, David Donovan, P E Hughes, E Merino, T Kozub, Bruce E. KoelAbstract:Lithium coatings in the Lithium Tokamak eXperiment (LTX) led to flat temperature profiles. The flat temperature profiles were observed along with a hot, low density edge, implying a broad, collisionless scrape-off layer (SOL). Additionally, in vacuo X-ray photoelectron spectroscopy (XPS) measurements established that lithium coatings evaporatively deposited onto high-Z Plasma Facing Components (PFCs) became oxidized while retaining the ability to achieve good Plasma performance long after lithium was applied to the PFCs. Longstanding theory predicted flat temperature profiles with low recycling walls, which was presumed to be due to hydrogen binding with elemental lithium to form lithium hydride. The presence of oxidized lithium, however, raised questions regarding the exact mechanism of hydrogen retention in LTX. To investigate these questions, the upgraded facility LTX- $\beta $ includes a new sample exposure probe (SEP) for more detailed in vacuo analysis of PFC samples. The SEP is equipped with a vacuum suitcase capable of transporting samples representative of the LTX- $\beta $ outer midplane PFCs to a stand-alone XPS system while maintaining pressures lower than the LTX- $\beta $ base vacuum to limit the contamination between sample exposure and analysis. The low-energy resolution XPS system used in past experiments could only enable the determination of elemental percentages on the PFC sample surfaces. Because the new XPS system has higher energy resolution, it is more direct to assign chemical compounds to the measured binding energies. This capability has been confirmed by comparing XPS data from PFC test samples with measurements using a commercial high-resolution XPS system. Quartz crystal microbalances (QCMs) were used to quantify the thickness of the deposited lithium on the LTX- $\beta $ PFCs. This article describes the application of the SEP to characterize the PFC surfaces using XPS and their relationship to Plasma conditions.
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A simple vacuum suitcase for enabling Plasma Facing Component characterization in fusion devices.
The Review of scientific instruments, 2020Co-Authors: A. Maan, Robert Ellis, R Majeski, R Kaita, E. T. Ostrowski, Dennis Boyle, David Donovan, Bruce E. Koel, T. M. BiewerAbstract:We have demonstrated a vacuum suitcase to transport samples in vacuo to a surface analysis station for characterization of tokamak Plasma Facing Components (PFCs). This technique enables surface analysis at powerful, dedicated stations that are not encumbered by design constraints imposed on them by a tokamak. The vacuum suitcase is an alternative solution to characterizing PFCs using diagnostics that are designed and built around a tokamak. The vacuum suitcase, called the Sample Exposure Probe (SEP), features mobile ultra-high vacuum pumping. Active pumping under high vacuum enables sample transfer between the Lithium Tokamak eXperiment-β (LTX-β) and a high resolution X-ray Photoelectron Spectroscopy (XPS) system that is situated close by. A thermocouple inserted in the back of the sample head measures heat flux from the Plasma during exposure, and together with a button heater, allows the sample to match the LTX-β PFCs in high temperature operations. As vacuum conditions are better during transfer and analysis than in the tokamak, less contamination is introduced to the samples. XPS scans on a dedicated analysis station enable peak identification due to higher resolution and signal to noise ratio. A similar probe could be implemented for other fusion devices. The SEP is the first vacuum suitcase implementation for fusion applications that incorporates active pumping.
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Effect of boronization on Plasma-Facing graphite surfaces and its correlation with the Plasma behavior in NSTX-U
Elsevier, 2018Co-Authors: F. Bedoya, R Kaita, J.p. Allain, F. Scotti, B. Labombard, P.s. KrsticAbstract:Boronization is a Plasma Facing Component (PFC) conditioning technique widely used in tokamak machines. The National Spherical Torus Experiment-Upgrade (NSTX-U) applied this conditioning, using a Plasma glow with a deuterated Trimethyl-boron (d-TMB) and He mixture. The use of boronization during the campaign improved the Plasma performance, allowing longer Plasma discharges and H-mode access. The chemical state of an ATJ graphite sample, used as a proxy for the NSTX-U PFCs, was monitored in-situ using the Materials Analysis Particle Probe (MAPP) diagnostic and X-ray Photoelectron Spectroscopy (XPS). The XPS data showed a progressive rise (from
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initial studies of Plasma Facing Component surface conditioning in the national spherical tokamak experiment upgrade with the materials analysis particle probe
Nuclear materials and energy, 2017Co-Authors: F. Bedoya, R Kaita, Bruce E. Koel, Jean Paul Allain, C H Skinner, F. ScottiAbstract:Abstract An innovative PFC diagnostic, the Materials Analysis Particle Probe (MAPP) was used to study the chemistry of Plasma Facing Components (PFCs) in the National Spherical Tokamak Experiment Upgrade (NSTX-U). NSTX-U used boronization as conditioning strategy during the 2015–2016 experimental campaign. Deposition with ∼9.1 g of deuterated tri-methyl boron (d-TMB) in a helium glow discharge resulted in coatings with an equivalent thickness of 7.0 nm at the lower outer divertor region. MAPP was used to capture for the first time the in-vacuo evolution of the chemical state of ATJ graphite PFCs after boronization and Plasma exposure via X-ray Photoelectron Spectroscopy (XPS) on a day-to-day basis. The XPS data shows the formation of B 4 C on the PFCs surface during boronization. We observed the gradual increase of the B 2 O 3 fraction in the coatings with Plasma exposures. In contrast, we measured the formation of non-stoichiometric oxides when the samples were only exposed to residual gases and an argon vent. MAPP data revealed erosion and oxidation of deposited boron coatings over the course of tens of shots (a time resolution improved several orders-of-magnitude compared to post-campaign PFC characterization) that is correlated with the transitory nature of Plasma performance enhancement with boron conditioning.
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observation of flat electron temperature profiles in the lithium tokamak experiment
Physical Review Letters, 2017Co-Authors: D P Boyle, R Majeski, J C Schmitt, C J Hansen, R Kaita, S Kubota, M Lucia, T D RognlienAbstract:It has been predicted for over a decade that low-recycling Plasma-Facing Components in fusion devices would allow high edge temperatures and flat or nearly flat temperature profiles. In recent experiments with lithium wall coatings in the Lithium Tokamak Experiment (LTX), a hot edge (>200 eV) and flat electron temperature profiles have been measured following the termination of external fueling. Reduced recycling was demonstrated by retention of ∼60% of the injected hydrogen in the walls following the discharge. Electron energy confinement followed typical Ohmic confinement scaling during fueling, but did not decrease with density after fueling terminated, ultimately exceeding the scaling by ∼200%. Achievement of the low-recycling, hot edge regime has been an important goal of LTX and lithium Plasma-Facing Component research in general, as it has potentially significant implications for the operation, design, and cost of fusion devices.
R Majeski - One of the best experts on this subject based on the ideXlab platform.
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Plasma Facing Component characterization and correlation with Plasma conditions in lithium tokamak experiment β
IEEE Transactions on Plasma Science, 2020Co-Authors: A. Maan, D P Boyle, R Majeski, R Kaita, E. T. Ostrowski, David Donovan, P E Hughes, E Merino, T Kozub, Bruce E. KoelAbstract:Lithium coatings in the Lithium Tokamak eXperiment (LTX) led to flat temperature profiles. The flat temperature profiles were observed along with a hot, low density edge, implying a broad, collisionless scrape-off layer (SOL). Additionally, in vacuo X-ray photoelectron spectroscopy (XPS) measurements established that lithium coatings evaporatively deposited onto high-Z Plasma Facing Components (PFCs) became oxidized while retaining the ability to achieve good Plasma performance long after lithium was applied to the PFCs. Longstanding theory predicted flat temperature profiles with low recycling walls, which was presumed to be due to hydrogen binding with elemental lithium to form lithium hydride. The presence of oxidized lithium, however, raised questions regarding the exact mechanism of hydrogen retention in LTX. To investigate these questions, the upgraded facility LTX- $\beta $ includes a new sample exposure probe (SEP) for more detailed in vacuo analysis of PFC samples. The SEP is equipped with a vacuum suitcase capable of transporting samples representative of the LTX- $\beta $ outer midplane PFCs to a stand-alone XPS system while maintaining pressures lower than the LTX- $\beta $ base vacuum to limit the contamination between sample exposure and analysis. The low-energy resolution XPS system used in past experiments could only enable the determination of elemental percentages on the PFC sample surfaces. Because the new XPS system has higher energy resolution, it is more direct to assign chemical compounds to the measured binding energies. This capability has been confirmed by comparing XPS data from PFC test samples with measurements using a commercial high-resolution XPS system. Quartz crystal microbalances (QCMs) were used to quantify the thickness of the deposited lithium on the LTX- $\beta $ PFCs. This article describes the application of the SEP to characterize the PFC surfaces using XPS and their relationship to Plasma conditions.
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A simple vacuum suitcase for enabling Plasma Facing Component characterization in fusion devices.
The Review of scientific instruments, 2020Co-Authors: A. Maan, Robert Ellis, R Majeski, R Kaita, E. T. Ostrowski, Dennis Boyle, David Donovan, Bruce E. Koel, T. M. BiewerAbstract:We have demonstrated a vacuum suitcase to transport samples in vacuo to a surface analysis station for characterization of tokamak Plasma Facing Components (PFCs). This technique enables surface analysis at powerful, dedicated stations that are not encumbered by design constraints imposed on them by a tokamak. The vacuum suitcase is an alternative solution to characterizing PFCs using diagnostics that are designed and built around a tokamak. The vacuum suitcase, called the Sample Exposure Probe (SEP), features mobile ultra-high vacuum pumping. Active pumping under high vacuum enables sample transfer between the Lithium Tokamak eXperiment-β (LTX-β) and a high resolution X-ray Photoelectron Spectroscopy (XPS) system that is situated close by. A thermocouple inserted in the back of the sample head measures heat flux from the Plasma during exposure, and together with a button heater, allows the sample to match the LTX-β PFCs in high temperature operations. As vacuum conditions are better during transfer and analysis than in the tokamak, less contamination is introduced to the samples. XPS scans on a dedicated analysis station enable peak identification due to higher resolution and signal to noise ratio. A similar probe could be implemented for other fusion devices. The SEP is the first vacuum suitcase implementation for fusion applications that incorporates active pumping.
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observation of flat electron temperature profiles in the lithium tokamak experiment
Physical Review Letters, 2017Co-Authors: D P Boyle, R Majeski, J C Schmitt, C J Hansen, R Kaita, S Kubota, M Lucia, T D RognlienAbstract:It has been predicted for over a decade that low-recycling Plasma-Facing Components in fusion devices would allow high edge temperatures and flat or nearly flat temperature profiles. In recent experiments with lithium wall coatings in the Lithium Tokamak Experiment (LTX), a hot edge (>200 eV) and flat electron temperature profiles have been measured following the termination of external fueling. Reduced recycling was demonstrated by retention of ∼60% of the injected hydrogen in the walls following the discharge. Electron energy confinement followed typical Ohmic confinement scaling during fueling, but did not decrease with density after fueling terminated, ultimately exceeding the scaling by ∼200%. Achievement of the low-recycling, hot edge regime has been an important goal of LTX and lithium Plasma-Facing Component research in general, as it has potentially significant implications for the operation, design, and cost of fusion devices.
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observation of flat electron temperature profiles in the lithium tokamak experiment
Physical Review Letters, 2017Co-Authors: D P Boyle, R Majeski, J C Schmitt, C J Hansen, R Kaita, S Kubota, M Lucia, T D RognlienAbstract:It has been predicted for over a decade that low-recycling Plasma-Facing Components in fusion devices would allow high edge temperatures and flat or nearly flat temperature profiles. In recent experiments with lithium wall coatings in the Lithium Tokamak Experiment (LTX), a hot edge ($g200\text{ }\text{ }\mathrm{eV}$) and flat electron temperature profiles have been measured following the termination of external fueling. Reduced recycling was demonstrated by retention of $\ensuremath{\sim}60%$ of the injected hydrogen in the walls following the discharge. Electron energy confinement followed typical Ohmic confinement scaling during fueling, but did not decrease with density after fueling terminated, ultimately exceeding the scaling by $\ensuremath{\sim}200%$. Achievement of the low-recycling, hot edge regime has been an important goal of LTX and lithium Plasma-Facing Component research in general, as it has potentially significant implications for the operation, design, and cost of fusion devices.
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lithium as a Plasma Facing Component to optimize the edge Plasma
IEEE Symposium on Fusion Engineering, 2015Co-Authors: R Maingi, R Majeski, M A Jaworski, J E Menard, R KaitaAbstract:The use of lithium to coat Plasma-Facing Components (PFCs) or serve directly as liquid PFCs has resulted in energy confinement improvement in several devices. Coupled with the demonstrated ability of liquid Li to exhaust high power fluxes, the use of Li could resolve the two leading problems of high-Z PFCs. The effect of Li in NSTX, EAST, and DIII-D is compared, and common features are identified. A compact spherical tokamak-based Fusion Nuclear Science Facility design could deliver an attractive neutral wall loading for materials testing, with Li PFCs enabling access to the required high confinement scenarios.
T D Rognlien - One of the best experts on this subject based on the ideXlab platform.
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observation of flat electron temperature profiles in the lithium tokamak experiment
Physical Review Letters, 2017Co-Authors: D P Boyle, R Majeski, J C Schmitt, C J Hansen, R Kaita, S Kubota, M Lucia, T D RognlienAbstract:It has been predicted for over a decade that low-recycling Plasma-Facing Components in fusion devices would allow high edge temperatures and flat or nearly flat temperature profiles. In recent experiments with lithium wall coatings in the Lithium Tokamak Experiment (LTX), a hot edge (>200 eV) and flat electron temperature profiles have been measured following the termination of external fueling. Reduced recycling was demonstrated by retention of ∼60% of the injected hydrogen in the walls following the discharge. Electron energy confinement followed typical Ohmic confinement scaling during fueling, but did not decrease with density after fueling terminated, ultimately exceeding the scaling by ∼200%. Achievement of the low-recycling, hot edge regime has been an important goal of LTX and lithium Plasma-Facing Component research in general, as it has potentially significant implications for the operation, design, and cost of fusion devices.
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observation of flat electron temperature profiles in the lithium tokamak experiment
Physical Review Letters, 2017Co-Authors: D P Boyle, R Majeski, J C Schmitt, C J Hansen, R Kaita, S Kubota, M Lucia, T D RognlienAbstract:It has been predicted for over a decade that low-recycling Plasma-Facing Components in fusion devices would allow high edge temperatures and flat or nearly flat temperature profiles. In recent experiments with lithium wall coatings in the Lithium Tokamak Experiment (LTX), a hot edge ($g200\text{ }\text{ }\mathrm{eV}$) and flat electron temperature profiles have been measured following the termination of external fueling. Reduced recycling was demonstrated by retention of $\ensuremath{\sim}60%$ of the injected hydrogen in the walls following the discharge. Electron energy confinement followed typical Ohmic confinement scaling during fueling, but did not decrease with density after fueling terminated, ultimately exceeding the scaling by $\ensuremath{\sim}200%$. Achievement of the low-recycling, hot edge regime has been an important goal of LTX and lithium Plasma-Facing Component research in general, as it has potentially significant implications for the operation, design, and cost of fusion devices.
J C Schmitt - One of the best experts on this subject based on the ideXlab platform.
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observation of flat electron temperature profiles in the lithium tokamak experiment
Physical Review Letters, 2017Co-Authors: D P Boyle, R Majeski, J C Schmitt, C J Hansen, R Kaita, S Kubota, M Lucia, T D RognlienAbstract:It has been predicted for over a decade that low-recycling Plasma-Facing Components in fusion devices would allow high edge temperatures and flat or nearly flat temperature profiles. In recent experiments with lithium wall coatings in the Lithium Tokamak Experiment (LTX), a hot edge (>200 eV) and flat electron temperature profiles have been measured following the termination of external fueling. Reduced recycling was demonstrated by retention of ∼60% of the injected hydrogen in the walls following the discharge. Electron energy confinement followed typical Ohmic confinement scaling during fueling, but did not decrease with density after fueling terminated, ultimately exceeding the scaling by ∼200%. Achievement of the low-recycling, hot edge regime has been an important goal of LTX and lithium Plasma-Facing Component research in general, as it has potentially significant implications for the operation, design, and cost of fusion devices.
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observation of flat electron temperature profiles in the lithium tokamak experiment
Physical Review Letters, 2017Co-Authors: D P Boyle, R Majeski, J C Schmitt, C J Hansen, R Kaita, S Kubota, M Lucia, T D RognlienAbstract:It has been predicted for over a decade that low-recycling Plasma-Facing Components in fusion devices would allow high edge temperatures and flat or nearly flat temperature profiles. In recent experiments with lithium wall coatings in the Lithium Tokamak Experiment (LTX), a hot edge ($g200\text{ }\text{ }\mathrm{eV}$) and flat electron temperature profiles have been measured following the termination of external fueling. Reduced recycling was demonstrated by retention of $\ensuremath{\sim}60%$ of the injected hydrogen in the walls following the discharge. Electron energy confinement followed typical Ohmic confinement scaling during fueling, but did not decrease with density after fueling terminated, ultimately exceeding the scaling by $\ensuremath{\sim}200%$. Achievement of the low-recycling, hot edge regime has been an important goal of LTX and lithium Plasma-Facing Component research in general, as it has potentially significant implications for the operation, design, and cost of fusion devices.
D P Boyle - One of the best experts on this subject based on the ideXlab platform.
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Plasma Facing Component characterization and correlation with Plasma conditions in lithium tokamak experiment β
IEEE Transactions on Plasma Science, 2020Co-Authors: A. Maan, D P Boyle, R Majeski, R Kaita, E. T. Ostrowski, David Donovan, P E Hughes, E Merino, T Kozub, Bruce E. KoelAbstract:Lithium coatings in the Lithium Tokamak eXperiment (LTX) led to flat temperature profiles. The flat temperature profiles were observed along with a hot, low density edge, implying a broad, collisionless scrape-off layer (SOL). Additionally, in vacuo X-ray photoelectron spectroscopy (XPS) measurements established that lithium coatings evaporatively deposited onto high-Z Plasma Facing Components (PFCs) became oxidized while retaining the ability to achieve good Plasma performance long after lithium was applied to the PFCs. Longstanding theory predicted flat temperature profiles with low recycling walls, which was presumed to be due to hydrogen binding with elemental lithium to form lithium hydride. The presence of oxidized lithium, however, raised questions regarding the exact mechanism of hydrogen retention in LTX. To investigate these questions, the upgraded facility LTX- $\beta $ includes a new sample exposure probe (SEP) for more detailed in vacuo analysis of PFC samples. The SEP is equipped with a vacuum suitcase capable of transporting samples representative of the LTX- $\beta $ outer midplane PFCs to a stand-alone XPS system while maintaining pressures lower than the LTX- $\beta $ base vacuum to limit the contamination between sample exposure and analysis. The low-energy resolution XPS system used in past experiments could only enable the determination of elemental percentages on the PFC sample surfaces. Because the new XPS system has higher energy resolution, it is more direct to assign chemical compounds to the measured binding energies. This capability has been confirmed by comparing XPS data from PFC test samples with measurements using a commercial high-resolution XPS system. Quartz crystal microbalances (QCMs) were used to quantify the thickness of the deposited lithium on the LTX- $\beta $ PFCs. This article describes the application of the SEP to characterize the PFC surfaces using XPS and their relationship to Plasma conditions.
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observation of flat electron temperature profiles in the lithium tokamak experiment
Physical Review Letters, 2017Co-Authors: D P Boyle, R Majeski, J C Schmitt, C J Hansen, R Kaita, S Kubota, M Lucia, T D RognlienAbstract:It has been predicted for over a decade that low-recycling Plasma-Facing Components in fusion devices would allow high edge temperatures and flat or nearly flat temperature profiles. In recent experiments with lithium wall coatings in the Lithium Tokamak Experiment (LTX), a hot edge (>200 eV) and flat electron temperature profiles have been measured following the termination of external fueling. Reduced recycling was demonstrated by retention of ∼60% of the injected hydrogen in the walls following the discharge. Electron energy confinement followed typical Ohmic confinement scaling during fueling, but did not decrease with density after fueling terminated, ultimately exceeding the scaling by ∼200%. Achievement of the low-recycling, hot edge regime has been an important goal of LTX and lithium Plasma-Facing Component research in general, as it has potentially significant implications for the operation, design, and cost of fusion devices.
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observation of flat electron temperature profiles in the lithium tokamak experiment
Physical Review Letters, 2017Co-Authors: D P Boyle, R Majeski, J C Schmitt, C J Hansen, R Kaita, S Kubota, M Lucia, T D RognlienAbstract:It has been predicted for over a decade that low-recycling Plasma-Facing Components in fusion devices would allow high edge temperatures and flat or nearly flat temperature profiles. In recent experiments with lithium wall coatings in the Lithium Tokamak Experiment (LTX), a hot edge ($g200\text{ }\text{ }\mathrm{eV}$) and flat electron temperature profiles have been measured following the termination of external fueling. Reduced recycling was demonstrated by retention of $\ensuremath{\sim}60%$ of the injected hydrogen in the walls following the discharge. Electron energy confinement followed typical Ohmic confinement scaling during fueling, but did not decrease with density after fueling terminated, ultimately exceeding the scaling by $\ensuremath{\sim}200%$. Achievement of the low-recycling, hot edge regime has been an important goal of LTX and lithium Plasma-Facing Component research in general, as it has potentially significant implications for the operation, design, and cost of fusion devices.