Preliminary Design of ITER Divertor Langmuir Probe System

Zhao, Weiduo; Wang, Yali; Jin, Yuzhong; Zhao, Li; Zhou, H.Y.; Nie, Lin; Zhong, Guangwu; Liu, Chunjia; Watts, Christopher; Gunn, J.

doi:10.1080/15361055.2019.1674123

Cited by 7 publications

(1 citation statement)

References 17 publications

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“…One can thus estimate I sat by performing a fit on the negative saturation branch of the I -V curve, and extrapolating to V b = 0. In (tokamak divertor) conditions of shallow incidence, the Child-Langmuir sheath expansion is frequently used [27,28]. In the current setup under perpendicular incidence, this principle is not applicable, and in this work, a simple linear fit was performed in the domain -50 < V b < -25 V. The uncertainty in I sat is given by the standard deviation over the five sections, and propagated into Γ LP .…”

Section: Flush-mounted Langmuir Probementioning

confidence: 99%

Thermalized collisional pre-sheath detected in dense plasma with coherent and incoherent Thomson scattering

et al. 2021

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In the direct vicinity of plasma-facing surfaces, the incident plasma particles interact with surface-recombined neutrals. Remarkably high near-surface plasma pressure losses were observed in the high-flux linear plasma generator Magnum-PSI. Combining the incoherent and coherent Thomson scattering diagnostics, we directly measured particle, momentum and energy fluxes down to 3 mm from the plasma target surface. At the surface, the particle and total heat flux were also measured, using respectively an in-target Langmuir probe and thermographic methods. The near-surface momentum and energy losses scale with density, and amount to at least 50 % and 20 %, respectively, at ne = 8•10 20 m −3 . These losses are attributed to the efficient exchange of charge, momentum and energy between incident plasma and surface-recombined neutrals. In low-temperature plasmas with sufficient density, incident particles go through several cycles of interaction and surface deposition before leaving the plasma, thereby providing an effective alternative dissipation channel to the incident plasma. Parallel plasma parameter profiles exhibit a transition with increasing plasma density. In lowdensity conditions, the plasma temperature is constant and near-surface ion acceleration is observed, attributed to the ambipolar electric field. Conversely, deceleration and plasma cooling are observed in dense conditions. These results are explained by the combined effect of ionneutral friction and electron-ion thermal equilibration in the so-called thermalized collisional pre-sheath. The energy available for ambipolar acceleration is thus reduced, as well as the upstream flow velocity. In the ITER divertor, enhanced near-surface p-n interaction is expected as well, given the overlap in plasma conditions. Including these effects in finite-element scrape-off layer models requires a near-surface resolution smaller than the neutral mean free path. This amounts to 1 mm in Magnum-PSI, and possibly an order of magnitude smaller in ITER.

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Section: Flush-mounted Langmuir Probementioning

confidence: 99%