Relevance of E × B drifts for particle and heat transport in divertors
Abstract Radial electric fields up to ∼4 kV m −1 are observed in the boundary between the private flux region (PFR) and the scrape-off layer (SOL) driving E × B drifts between the inner and outer targets at speeds up to 2.8 km s −1 in the Tokamak à configuration variable divertor. The resulting E ×...
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Published in | Plasma physics and controlled fusion Vol. 64; no. 6; pp. 65008 - 65020 |
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Main Authors | , , , , , |
Format | Journal Article |
Language | English |
Published |
United States
IOP Publishing
01.06.2022
IOP Science |
Subjects | |
Online Access | Get full text |
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Summary: | Abstract
Radial electric fields up to ∼4 kV m
−1
are observed in the boundary between the private flux region (PFR) and the scrape-off layer (SOL) driving
E
×
B
drifts between the inner and outer targets at speeds up to 2.8 km s
−1
in the Tokamak à configuration variable divertor. The resulting
E
×
B
fluxes, located in a narrow region (
Δ
ρ
Ψ
<
0.012
in normalized radius or
Δ
R − R
sep
<4 mm mapped to the outer midplane) are equivalent to around 20% of the total heat and particle flux to the divertor targets (inner + outer). At the peak
E
r
, the
E
×
B
poloidal transport is equivalent to parallel flows with
M
∥
∼ 3. In the snowflake divertor with a second X-point in the outer SOL, the drifts in the PFR-SOL boundary were equivalent to around 30% of the total heat and particle flux to the divertor targets and cover a region ∼50% wider than in the single null (
Δ
ρ
Ψ
∼ 0.018,
Δ
R − R
sep
∼ 6 mm). The location of the PFR-SOL boundary drift shifts radially in the
E
∥
×
B
direction when reversing the toroidal field direction. Peaks in density and electron pressure have been identified near the primary X-point along with large gradients in density, temperature, and potential, the latter resulting in a local electric field ∼2.7 kV m
−1
which drives a drift (1.9 km s
−1
) upwards towards the closed flux surfaces. Floating potential (
V
f
) magnitudes up to 75 V (∼2 kT
e
) were measured, indicating that
V
f
and parallel currents should not be neglected when estimating plasma potential. |
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Bibliography: | PPCF-103775.R2 USDOE Office of Science (SC) SC0010529 |
ISSN: | 0741-3335 1361-6587 |
DOI: | 10.1088/1361-6587/ac6890 |