Statistical properties of ion and electron temperature fluctuations in the edge of the COMPASS tokamak

Cipciar, D.; Adámek, Jiřı́; Horáček, J.; Cavalier, J.; Hron, M.

doi:10.1088/1361-6587/ac5a0b

Cited by 1 publication

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“…In particular, due to an extremely low (µA) current, the reversed field analyzer (RFA) cannot measure quickly enough to resolve ELMs nor turbulence. Only recently, the fast-sweeping of a ball-pen probe (BPP) demonstrated that it could measure not only slow T i profiles [3] consistent with RFA measurements, but also 100 kHz turbulence [4]. For low temporal resolution, it was shown with both RFA [5] and BPP [3] that, whilst at separatrix T i ∼ T e , in the far scrape-off layer (SOL) T i ≫ T e because ions cool down much slower than electrons do [6].…”

Section: Motivation For Fast T I Elm Estimationmentioning

confidence: 90%

ELM temperature in JET and COMPASS tokamak divertors

et al. 2023

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Analysis of the divertor ELM electron temperature at a uniquely high temporal resolution (1e-5 s) was reported at the JET tokamak [C. Guillemaut et al. Nucl. Fusion 58 (2018) 066006]. By collecting divertor probe data obtained during many dozens of ELMs, the conditional-average technique (CAV) yields surprisingly low peak electron temperatures, much below the pedestal ones (a reduction by 70% up to 99%!) which we, however, question. This result was interpreted through the collisional free-streaming kinetic model of ELMs, by a transfer of most of the electron energy to ions, implying a high tungsten sputtering for unmitigated ELMs in future fusion devices like ITER. Recently, direct microsecond temperature measurements on the COMPASS tokamak, however, showed that the electron temperature peak of ELM filaments measured in the divertor is reduced by less than ⅓ with respect to the pedestal one. This was further confirmed by a dedicated 1D PIC simulation and tends to prove that the pedestal electrons can transfer only their parallel energy to ions (due to low collisionality), thus less than ⅓ as is predicted by the collision-less free-streaming model. This finding is in strong contradiction with the JET observations. We have therefore compared the CAV to the direct (microsecond) ball-pen and Langmuir probes measurements in COMPASS and found very good agreement between them. Revisiting the mentioned JET CAV analysis yields indeed that the electron temperatures are much higher than previously reported, nearly as predicted by the PIC simulation, and thus the ion energy seems not significantly increasing in the SOL.

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