Bulletin of the American Physical Society
62nd Annual Meeting of the APS Division of Plasma Physics
Volume 65, Number 11
Monday–Friday, November 9–13, 2020; Remote; Time Zone: Central Standard Time, USA
Session WI02: Invited: Magnetic Fusion: DivertorLive
|
Hide Abstracts |
Chair: Auna Moser, GA |
Thursday, November 12, 2020 3:00PM - 3:30PM Live |
WI02.00001: The role of the target electron temperature as a key detachment parameter in different JET-ILW divertor configurations Invited Speaker: Bartosz Lomanowski Recent JET-ILW experimental results have allowed previously reported but unexplained divertor configuration differences in global confinement (H$_{\mathrm{98}}$,W$_{\mathrm{dia}})$ and pedestal performance to be condensed into a single trend correlated with the outer target temperature, T$_{\mathrm{e,ot}}$. By utilizing an innovative spectroscopic approach to access T$_{\mathrm{e,ot}}$ in the range 0.6-20 eV, the critical role of T$_{\mathrm{e,ot}}$ as the main detachment controlling parameter was confirmed using L-mode and H-mode plasmas in varied divertor configurations and D$_{\mathrm{2}}$ puff rates. The robustness of T$_{\mathrm{e,ot}}$ as an ordering parameter extends to the upstream separatrix and pedestal densities and temperature, and outer SOL density shoulder formation in unseeded low-$\delta $ H-mode discharges at B$_{\mathrm{t}}=$2.3 T, I$_{\mathrm{p}}=$2 MA. Strong T$_{\mathrm{e,ot}}$ correlations with neutral atomic density, momentum loss and recycling cooling loss factors, volume recombination fraction and Lyman series opacity were observed experimentally on JET and shown to be in quantitative agreement with EDGE2D-EIRENE simulations. In line with experimental findings, these simulations also confirm the modest impact of available divertor configurations on upstream density. These results provide a much improved picture of the dominant detachment processes on JET-ILW with recycling cooling loss onset at T$_{\mathrm{e,ot}}=$10 eV, pressure loss onset at T$_{\mathrm{e,ot}}=$2-3 eV and the onset of volume recombination detachment at T$_{\mathrm{e,ot}}=$1 eV. The findings are of critical importance for informing pedestal studies by connecting the role of T$_{\mathrm{e,ot}}$ dependencies to neutral penetration into the confined plasma, thought to be the main mechanism for density pedestal formation; they also advance the foundational understanding of pure deuterium divertor plasma physics enabling an assessment of the relative role of neutral loss channels and seeded impurity radiative losses on target heat flux mitigation. [Preview Abstract] |
Thursday, November 12, 2020 3:30PM - 4:00PM Live |
WI02.00002: Experimental verification of X-point potential well formation in unfavorable magnetic field direction Invited Speaker: Mirko Wensing Recent TCV measurements confirm, for the first time, the predicted formation of an electric potential well below the X-point in the unfavorable $B_t$ direction, substantially reshaping the divertor $E \times B$ flow pattern \footnote{M. Wensing, \textbf{Nucl. Fusion} 60, 2020}. Such a potential well may strongly influence the divertor performance for reactor operation with unfavorable H-mode access (e.g. reverse triangularity, I-modeā¦). The local charge balance in the private flux region (PFR) of diverted tokamak plasmas is argued (JET \footnote{M. Schaffer, \textbf{J. Nucl. Mater.} 290-293, 2001}, DIII-D \footnote{A. Jaervinen, \textbf{Phys. Rev. Lett.} 121, 075001, 2018}, AUG \footnote{V. Rozhansky, \textbf{Contr. Plasma Phys.} 58, 266-269, 2018}) to be established by parallel currents and $\nabla B$ currents. This hypothesis is verified herein for TCV configurations using SOLPS-ITER simulations accounting for drifts and currents. Simulated parallel currents reproduce the characteristic features of TCV target currents measured by wall-mounted Langmuir probes whereas simulations without drifts fail. For low temperature (detached divertor) conditions, the parallel electric field is dictated by these parallel currents. This work demonstrates, for the first time, that the electric potential in the PFR becomes negative with respect to both target plates for detached operation for unfavorable H-mode access (ion $\nabla B$ away from the PFR). This implies: a reversal of the parallel electric field in the PFR, a significant enhancement of the radial electric field close to the separatrix and a substantially altered $E\times B$ drift pattern with much stronger poloidal flows. The reported experimental validation follows the installation of a reciprocating divertor probe array on TCV providing unprecedented insights into 2D plasma profiles in the divertor \footnote{H. de Oliveira, 46th EPS Conference on Plasma Physics, P2.1028, 2019}. A simple analytical model, based on electron momentum balance and the leading order terms in the current continuity equation, highlights the underlying physics and generates a scaling of the potential well depth with divertor conditions and machine size. [Preview Abstract] |
Thursday, November 12, 2020 4:00PM - 4:30PM Live |
WI02.00003: High-$\beta$, Weakly Magnetized and Hall Dominated Plasma Couette Flow Invited Speaker: K. Flanagan A novel plasma equilibrium in the high-$\beta$, Hall regime that produces centrally-peaked, high Mach number Couette flow is described. Flow is driven using a weak, uniform magnetic field (0-10 G) and large, cross field currents (100-300 A). Large magnetic field amplification (factor 20) due to the Hall effect is observed when electrons are flowing radially inward, and near perfect field expulsion is observed when the current is reversed. In the reversed direction, flow is weak and driven from the outer edge, creating a solid-body profile. However, a high-$\beta$ extension of the gradient drift instability is observed, driven by large toroidal Hall currents. High-resolution spectroscopy shows evidence of Landau damping of this electromagnetic wave and heating of cold ions ($T_{i}\sim0.5$~eV heated to $T_{i}\sim1.5$~eV). Co-authors: J. Milhone, J. Egedal, D. Endrizzi, J. Olson, University of Wisconsin-Madison, E.E. Peterson, Massachusetts of Institute of Technology, R. Sassella, C.B. Forest, University of Wisconsin-Madison [Preview Abstract] |
Thursday, November 12, 2020 4:30PM - 5:00PM Live |
WI02.00004: First Observation of A Fully Detached Divertor with Natural Compatibility with A High Confinement Plasma State for Steady-state Operation Invited Speaker: Huiqian Wang Excellent compatibility of actively controlled full divertor detachment with a high-performance ($\beta_{\mathrm{N\thinspace }}$\textasciitilde 3, $\beta_{\mathrm{p\thinspace }}$\textgreater 2, H$_{\mathrm{98\thinspace }}$\textasciitilde 1.5) core plasma has been achieved, for the first time, in DIII-D high-$\beta_{\mathrm{p}}$ (poloidal beta) plasmas associated with a sustained core internal transport barrier (ITB) and an H-mode edge transport barrier (ETB). Compared to standard H-mode plasmas, the high-$\beta_{\mathrm{p}}$ plasmas exhibit a much wider window of detachment compatible with a high confinement core. With a newly developed detachment control system, coupled with optimized nitrogen impurity seeding, fully detached divertor plasmas were achieved with low plasma temperature (Te\textless 5eV), low particle flux and low heat flux across the entire divertor target plate. It is found that this high-p high confinement plasma scenario enables full divertor detachment at lower density due to long connection length associated with the high edge safety factor, needed for steady-state, and reduced loss power from core to boundary plasma associated with the high confinement. Furthermore, the divertor detachment facilitates the access to an even stronger ITB at large radius with a weakened ETB through self-organized synergy between ITB and ETB, leading to improved high confinement, in contrast to confinement degradation with divertor detachment in standard H-mode. The presence of a large-radius ITB compensates the degradation of ETB by the divertor detachment, while a weak ETB is more prone to an edge regime with natural small edge localized modes. In particular, with neon injection, a long-period no-ELM H-mode phase has been achieved simultaneously with high-performance core and partially detached divertor plasmas. These results demonstrate the possibility of integrating excellent core plasma performance with an efficient divertor solution, an essential step towards steady-state operation of reactor-grade plasmas. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700