795 research outputs found
A fast edge charge exchange recombination spectroscopy system at the ASDEX Upgrade tokamak
In this work, a new type of high through-put Czerny-Turner spectrometer has been developed which
allows us to acquire multiple channels simultaneously with a repetition time on the order of 10
μ
s
at different wavelengths. The spectrometer has been coupled to the edge charge exchange recom-
bination system at ASDEX Upgrade which has been recently refurbished with new lines of sight.
Construction features, calibration methods, and initial measurements obtained with the new setup will
be presented.European Commission (EUROfusion 633053
Pedestal and Er profile evolution during an edge localized mode cycle at ASDEX Upgrade
The upgrade of the edge charge exchange recombination spectroscopy diagnostic at ASDEX
Upgrade has enabled highly spatially resolved me
asurements of the impurity ion dynamics during an
edge-localized mode cycle
(
ELM
)
with unprecedented temp
oral resolution, i.e. 65
μ
s. The increase of
transport during an ELM induces a relaxation of the
ion, electron edge gradients in impurity density
and
fl
ows. Detailed characterization of the recovery
of the edge temperature gradients reveals a
difference in the ion and electron channe
l: the maximum ion temperature gradient
T
i
is
re-established on similar timescales as
n
e
, which is faster than the recovery of
T
e
.Afterthe
clamping of the maximum gradient,
T
i
and
T
e
at the pedestal top continue to rise up to the next ELM
while
n
e
stays constant which means that the temperatur
e pedestal and the resu
lting pedestal pressure
widen until the next ELM. The edge radial electric
fi
eld
E
r
at the ELM crash is found to reduce to
typical L-mode values and its ma
ximum recovers to its pre-ELM conditions on a similar time scale as
for
n
e
and
T
i
. Within the uncertainties, the measurements of
E
r
align with their neoclassical
predictions
E
r,neo
for most of the ELM cycle, thus indicating that
E
r
is dominated by collisional
processes. However, between 2 and 4 ms af
ter the ELM crash, other contributions to
E
B
́
fl
ow,
e.g. zonal
fl
ows or ion orbit effects, could not be
excluded within the uncertainties.European Commission (EUROfusion 633053
SOLPS-ITER modeling of ASDEX Upgrade L-mode detachment states
SOLPS-ITER is used to model ASDEX Upgrade L-mode detachment states including the onset of detachment, the fluctuating detachment, and the complete detachment states, considering drifts and mimicking filamentary convective transport with a radial outward velocity in the low field side. The effect of drifts, perpendicular outward convection and core boundary conditions on the numerical solution is presented. The modeling results are validated against experimental data. We find a good agreement of particle flux at the inner target between modeling results and experimental data. On the opposite, at the outer target computations underestimate measured particle flux by a factor of about 2 ∼ 3 in the onset of detachment and the fluctuating detachment states
Experimental conditions to suppress edge localised modes by magnetic perturbations in the ASDEX Upgrade tokamak
Access conditions for full suppression of Edge Localised Modes (ELMs) by
Magnetic Perturbations (MP) in low density high confinement mode (H-mode)
plasmas are studied in the ASDEX Upgrade tokamak. The main empirical
requirements for full ELM suppression in our experiments are: 1. The poloidal
spectrum of the MP must be aligned for best plasma response from weakly stable
kink-modes, which amplify the perturbation, 2. The plasma edge density must be
below a critical value, ~m. The edge collisionality
is in the range (ions) and
(electrons). However, our data does not show that the edge collisionality is
the critical parameter that governs access to ELM suppression. 3. The pedestal
pressure must be kept sufficiently low to avoid destabilisation of small ELMs.
This requirement implies a systematic reduction of pedestal pressure of
typically 30\% compared to unmitigated ELMy H-mode in otherwise similar
plasmas. 4. The edge safety factor lies within a certain window.
Within the range probed so far, , one such window,
has been identified. Within the range of plasma rotation
encountered so far, no apparent threshold of plasma rotation for ELM
suppression is found. This includes cases with large cross field electron flow
in the entire pedestal region, for which two-fluid MHD models predict that the
resistive plasma response to the applied MP is shielded
Assessment of the current density evolution during an ELM cycle using beam emission polarimetry at ASDEX Upgrade
EUROfusion Consortium 63305
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