Abstract
A new coherence imaging spectroscopy (CIS) system has been
characterized and validated for measurements of impurity ion
velocity in the Compact Toroidal Hybrid (CTH) experiment. CIS is an
...interferometric technique providing very high spatial resolution of
line-integrated ion flows; however, these measurements are highly
sensitive to environmental factors such as temperature fluctuations.
A compact interferometer design housed in a thermally regulated
environment yields CIS measurement variations due to thermal
fluctuations of 0.25 km/s. CIS measurements of He
+
flows in
the outer regions of CTH are benchmarked using two optical grating
spectrometers. The deviation between the measurements is typically
less than 2 km/s for multiple lines of sight which is well within
the uncertainties of the diagnostics. Additional experiments
demonstrate a moderate robustness of ion flows in the outer region
of CTH to changing the vacuum transform, direction of the magnetic
field, and plasma current. In contrast, regions of complete flow
reversal are observed when a bias probe is inserted into the plasma
edge.
Long-lived metastable states in neutral tungsten are shown to potentially impact measurements of tungsten erosion from plasma facing components. Time-dependent collisional radiative modeling of ...neutral tungsten is used to analyze the role of these states in tungsten emission and ionization. The large number of non-quasistatic atomic states in neutral tungsten can take on the order of milliseconds to reach equilibrium, depending on plasma conditions, causing erosion measurements to be affected by the metastable populations. Previous measurements using the 400.88 nm tungsten emission line could be affected by these non-quasistatic metastable effects. Therefore, a scheme for measuring the relative metastable fractions is proposed through simultaneous observation of multiple ultraviolet spectral lines of neutral W. The accuracy of gross erosion measurements could potentially be increased by inclusion of these previously unconsidered metastable effects.
The recent detection of a neutron star merger by the LIGO collaboration has renewed interest in laboratory studies of r-process elements. Accurate modeling and interpretation of the electromagnetic ...transients following the mergers requires computationally expensive calculations of both the structure and opacity of all trans-iron elements. To date, the necessary atomic data to benchmark structure codes are incomplete or, in some cases, absent entirely. Within the available laboratory studies, the literature on Au i and Au ii provides incomplete reports of the emission lines and level structures. We present a new study of Au i and Au ii lines and levels by exposing a solid gold target to plasma in the Compact Toroidal Hybrid (CTH) experiment at Auburn University. A wavelength range from 187 to 800 nm was studied. In Au i, 86 lines are observed, 43 of which are unreported in the literature, and the energies of 18 levels and 16 of the 18 known levels are corroborated by a least-squares level energy optimization. In Au ii, 76 emission lines are observed, and 51 of the lines are unreported in the literature. For both Au i and Au ii, the new lines predominantly originate from the most energetic of the known levels, and over half of the new Au ii lines have wavelengths longer than 300 nm. For the estimated electron parameters of CTH plasmas at the gold target (ne ∼ 1012 cm−3, Te ∼ 10 eV), two-electron transitions are similar in intensity to LS-allowed one-electron transitions.
Abstract
Fundamental mechanisms governing the erosion and prompt re-deposition of tungsten impurities in tokamak divertors are identified and analyzed to inform the lifetime of tungsten plasma-facing ...components in ITER and other future devices. Various experiments conducted at DIII-D to benchmark predictive models are presented, leveraging the DiMES removable sample exposure probe capability and the Metal Rings Campaign, in which toroidally symmetric rows of tungsten-coated tiles were installed in the DIII-D divertor. In tokamak divertors, the width of the electric sheath is of the order of the main ion Larmor radius, and a vast majority of sputtered tungsten impurities are typically ionized within the sheath. Therefore, W prompt redeposition is mainly governed by the ratio of the characteristic ionization mean-free path of neutral tungsten to the width of the sheath. In-situ monitoring of the prompt redeposition of tungsten impurities in divertors is demonstrated via the use of WII/WI line ratios and the ionizations/photon (S/XB) method in L-mode discharges. Even with this relatively limited set of emission measurements, net erosion measurements were found to be a consistent upper bound to an analytic scaling based on the ratio of the W ionization length,
λ
iz
,
and the width of the magnetic sheath rather than the ratio of
λ
iz
and the W
+
gyro-radius. In the far-scrape-off layer (SOL) of the ITER divertor, however, it is calculated that the measurement of photon emissions associated with the ionization of tungsten impurities up to
W
5
+
may be required. Finally, W deposition patterns on DiMES collector probes, interpreted via DIVIMP-WallDYN modelling, reveal the key roles of progressive W erosion/re-deposition staps and E × B drifts in regulating long-range high-Z material migration.
Sintered bottom ash (SBA) and vitrified ash (VA) derived from the incineration of municipal solid waste (MSW) at 1200 °C were used in this study as replacements for Type 2 Portland cement (CEM-II) ...based mortars. This approach negates the need to send them to landfill, benefits the circular economy and contributes towards the decarbonisation of cementitious construction materials in response to international net zero carbon emission agendas. The material (physico-chemical) characteristics of VA and SBA were analysed before being used as partial replacements for CEM-II in mortars, whereby compressive strength (CS) was the primary criterion for assessing engineering performance. VA and SBA replaced CEM-II at dosages of 10%, 25% and 50% based on their high inorganic and pozzolanic contents; whereby the 10% and 25% replacements did not compromise mortar strength. The alkalinity and pozzolanic properties of SBA collectively indicated it has greater potential as a cementitious material over VA, which possessed a neutral pH. The 28-day CS recorded for mixtures containing 25% VA and 10% SBA were 13.74 MPa and 11.77 MPa, respectively compared with 17.06 MPa for CEM-II control samples. The use of 2% additional water in 25% SBA mortar designs improved strength further, indicating that SBA’s water retention properties permitted further hydration and strength development with curing. Microstructural, mineralogical and infrared spectroscopy analyses indicated that these strengths were owed to the formation of silicate-based hydration products. The outcomes from this study highlight that SBA has potential for replacing CEM-II and VA as a filler in cementitious mortar.
Graphical Abstract
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Abstract
Drifts affect particle, momentum, and energy transport in the scrape-off layer (SOL) of tokamaks and stellarators, altering plasma flows and creating asymmetries between divertors. To ...understand how drifts affect SOL transport in the W7-X island divertor, an experiment was performed to compare plasmas with matched core parameters but opposite magnetic field directions, and therefore opposite drift transport directions. Parallel flow measurements made with coherence imaging spectroscopy are interpreted with the aid of a diagnostic forward model and a 1D simple SOL model that includes the
E
×
B
drift. In low-density plasmas (
n
‾
e
<
2
×
10
19
m
−3
), the poloidal
E
×
B
drift induces a large poloidal density asymmetry within the island SOL, as measured by divertor Langmuir probes. This in turn causes the parallel flow stagnation point to shift from the position halfway between targets to the X-point in the drift direction, leading to near-unidirectional flow throughout the SOL. As density increases, the effects of the poloidal
E
×
B
drift decrease substantially, resulting in a smaller density asymmetry and the development of a counter-streaming flow pattern. For the entire density range probed in this experiment (
n
‾
e
=
1.5
−
6
×
10
19
m
−3
), the experimental observations are more consistent with the effects of the poloidal
E
×
B
drift than the radial
E
×
B
drift.
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