Observation of Flat Electron Temperature Profiles in the Lithium Tokamak Experiment

Boyle, Dennis; Majeski, R.; Schmitt, J. C.; Hansen, Chris; Kaita, R.; Kubota, S.; Lucia, M.; Rognlien, T. D.

doi:10.1103/physrevlett.119.015001

Cited by 50 publications

(37 citation statements)

References 48 publications

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“…As the lightest metal, Li has a low Z (Z = 3) and its content can be highly tolerated in fusion core plasma. Owing to its high affinity with hydrogen isotopes (HI), the use of Li as a PFM can lower HI recycling rate and significantly improve plasma performance, which has been demonstrated in TFTR [19,20], CDX-U [21], LTX [22], EAST [17,23,24] and NSTX [15,25], amongst other devices [26]. However, due to safety issues arising from the radioactivity of tritium (T) and the fact that tritium is a scarce fusion fuel which must be generated in the reactor itself, it is required that tritium inventory in PFMs should be as low as possible.…”

Section: Introductionmentioning

confidence: 99%

Deuterium retention and removal in liquid lithium determined by in situ NRA in Magnum-PSI

Ou¹,

Arnoldbik²,

Li³

et al. 2022

Nucl. Fusion

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In this work, Li-filled 3D-printed porous tungsten samples were exposed to deuterium (D) plasma in Magnum-PSI with a wide ion flux from 4 × 1022 to 1.5 × 1024 m−2 s−1 and with a corresponding wide temperature range from below Li melting point (180.5 °C) to above Li deuteride (LiD) melting point (∼690 °C). The formation, decomposition and melting of LiD have been directly observed in the experiment via infra-red thermometry and visually post-mortem while still in vacuo, and correlated to the D retained content. The LiD formation was characterized by a solid precipitate layer formed on the surface with high emissivity (0.6–0.9) characterized by a blue or dark blue color after exposure. The melting of Li–LiD layer was found to occur close to the temperature predicted by Li–LiD phase diagram. In situ nuclear reaction analysis (NRA) was applied to perform the measurement of D retained in Li samples immediately after exposure without breaking the vacuum. D depth profiles were determined by NRA, in which the highest D concentration (15–45 at.%) was found in the top several micrometers and decreases with depth to low levels (<5%) within 5–30 μm. No pure LiD layer was found on the sample surfaces, however a D concentration close to 50 at.% was observed on a Li-D co-deposited layer on the clamping ring in some cases. The experiments also indicate that the D retained increases with increasing temperature until ∼500 °C. At temperatures beyond ∼500 °C the dissociation of LiD starts to dominate and the deuterium retention started to decrease. Overall, D retained fraction for all cases was found to be below ∼2%, which is significantly different from literatures where full uptake has been suggested. A 1D reaction–diffusion (RD) model based on D diffusion and chemical reactions with Li has been built. D depth profiles from the RD modelling can roughly match that from NRA measurement and a low D retained fraction below ∼2% was also indicated by the model. The model can also help explain the relationship between D retained and the surface temperature and fluence. After D plasma exposure, either helium or H plasma was utilized to remove the retained D in Li and both were proved to be effective and the removal efficiency can be as high as 96% above 420 °C.

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Section: Introductionmentioning

confidence: 99%

Deuterium retention and removal in liquid lithium determined by in situ NRA in Magnum-PSI

Ou¹,

Arnoldbik²,

Li³

et al. 2022

Nucl. Fusion

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“…Conventional treatments of emission [4,10] maintain that Tet, the plasma electron temperature near the target (surface), can far exceed the sub-eV temperature of thermionic electrons Temit. This seems reasonable since laboratory plasma sources tend to have electron temperatures ranging from a few eV [6] to hundreds of eV [11] or more. But in this Letter, we show that strong emission causes a sharp reduction of Tet to Temit.…”

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confidence: 99%

Thermionic Cooling of the Target Plasma to a Sub-eV Temperature

Campanell

Johnson

2019

Phys. Rev. Lett.

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Contemporary models of bounded plasmas assume that the target plasma electron temperature far exceeds the temperature of the cold electrons emitted from the target, Temit. We show that when the sheath facing a collisional plasma becomes inverted, the target plasma electron temperature has to equal Temit even if the upstream plasma is hotter by orders of magnitude. This extreme cooling effect can alter the plasma properties and the heat transmission to thermionically emitting surfaces in many applications. It also opens a possibility of using thermionic divertor plates to induce detachment in tokamaks.

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“…Lithium has long been known to be an attractive first wall candidate, leading to low-recycling boundaries that lead to improved plasma performance [2]. Flat temperature profiles were recently observed in LTX [3]. This temperature-gradient free regime was accessible with a low-recycling boundary of lithium coated PFCs [4,5].…”

Section: Introductionmentioning

confidence: 99%

Neutral beam prompt loss in LTX- β

Capecchi¹,

Anderson²,

Boyle³

et al. 2021

Nucl. Fusion

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Prompt loss of beam injected fast ions approaches 100% in lithium tokamak experiment-beta (LTX-β) discharges, though significantly improved confinement is expected for the higher current plasmas made available by a recent upgrade to the Ohmic heating power supply. Modeling of fast ions using TRANSP/NUBEAM finds a maximum coupled beam fraction of 76% at the near-term limits of the LTX-β operating space. The full ion orbit code POET is employed to validate NUBEAM results against possible non-adiabatic effects on fast ion orbits, but corrections to the prompt loss fraction due to collisionless transport are found to be small. The graphical method code CONBEAM is used to investigate the topology of fast ion phase space as it relates to neutral beam deposition, and counter-injected NBI is considered as a way to access a region of high field side beam deposition. A metric is developed within the CONBEAM using a beam filament model to estimate the prompt loss fraction and shown to agree well with both POET and NUBEAM, enabling near real-time analysis and potential feedback to operators between plasma discharges.

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Observation of Flat Electron Temperature Profiles in the Lithium Tokamak Experiment

Cited by 50 publications

References 48 publications

Deuterium retention and removal in liquid lithium determined by in situ NRA in Magnum-PSI

Deuterium retention and removal in liquid lithium determined by in situ NRA in Magnum-PSI

Thermionic Cooling of the Target Plasma to a Sub-eV Temperature

Neutral beam prompt loss in LTX- β

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