Bulletin of the American Physical Society
55th Annual Meeting of the APS Division of Plasma Physics
Volume 58, Number 16
Monday–Friday, November 11–15, 2013; Denver, Colorado
Session GO4: DIII-D Tokamak |
Hide Abstracts |
Chair: Martin Greenwald, Massachusetts Institute of Technology Room: Plaza D |
Tuesday, November 12, 2013 9:30AM - 9:42AM |
GO4.00001: Overview of Recent DIII-D Experimental Results M.E. Fenstermacher Recent DIII-D experiments have added to the ITER physics basis and to physics understanding for extrapolation to future devices. Experiments using RMP ELM suppressed, QH-, I- and VH-mode plasmas contribute to the physics basis for an ELM control solution in ITER. The effect of pellet ELM pacing on core plasma evolution and impurity accumulation at ITER scaled frequencies was also examined. New swing probe data validate models of inner divertor SOL plasma conditions and their role in divertor detachment. A strong anomalous RE loss mechanism is observed, and multiple massive gas injectors show dependence of disruption mitigation radiation asymmetries on injector number and location. Prompt loss of energetic beam ions has been observed with the application of 3D fields. Coupling of electron heating dominated ITER baseline and advanced tokamak (AT) plasmas with a radiative divertor for target heat flux control was examined. Experiments determined the effect of helium plasma on L-H transition power and bulk ion rotation in support of ITER non-nuclear scenarios. Increased understanding of the physics mechanisms controlling the energy transport in $q_{min}>2$ AT plasmas to extend these regimes to higher $\beta_N$ and fusion performance $G=\beta_NH_{89}/q_{95}^2$ will be presented. [Preview Abstract] |
Tuesday, November 12, 2013 9:42AM - 9:54AM |
GO4.00002: Overview of DIII-D Disruption Mitigation Experimental Results N.W. Eidietis Recent DIII-D experiments on disruption mitigation have focused upon providing a physics basis for the design of the ITER disruption mitigation system. Progress in understanding several key issues for that system will be presented: toroidal AND poloidal radiation asymmetries during thermal quench mitigation, the anomalous dissipation of runaway electron current, and the effect of mitigation timing on wall thermal loads during vertical displacement events. This research utilized several new capabilities, including: dual massive gas injection valves to test the affect of toroidal and poloidal separation between injector locations upon radiation asymmetries, a new argon pellet injector for creating runaway electron beams, full-vessel IR imaging, and upgraded hard x-ray diagnostics for runaway electron diagnosis. Plans will also be presented for near-term hardware upgrades and experiments supporting the ITER disruption mitigation system design. [Preview Abstract] |
Tuesday, November 12, 2013 9:54AM - 10:06AM |
GO4.00003: 3D Magnetic Measurements of Kink and Locked Modes in DIII-D J.D. King, E.J. Strait, J.M. Hanson, C. Paz-Soldan, N.C. Logan, M.J. Lanctot, D. Shiraki The DIII-D magnetics diagnostic has been greatly expanded to fully characterize non-axisymmetric ``3D" fields. Five poloidal locations now recover $n\leq 3$, while new HFS arrays provide poloidal spectral resolution of 7.4~cm. Initial measurements suggest externally driven kink structures deviate from MARS-F and IPEC models. These variations extend to the ideal regime, where toroidal agreement is observed. The plasma response to an $n=3$ RMP increases monotonically as beta increases and $q_{95}$ decreases, contrary to predictions of a screening to kink valley [1]. Finally, the temporal evolution of the 3D eigenstructure of a slowly rotating (5~Hz) quasi-static, born locked, tearing mode provides the first evidence of an appreciable $n=2$ error field, and an estimate of the phase for future correction. This new 3D capability will be used to understand and optimize control of RWMs, NTV torque, ELMs, and error field correction to extend stable tokamak operation.\par \vskip6pt \noindent [1] M.J.\ Lanctot, et al., Phys.\ Plasmas {\bf 18}, 056121 (2011). [Preview Abstract] |
Tuesday, November 12, 2013 10:06AM - 10:18AM |
GO4.00004: Pedestal Response to Resonant Magnetic Perturbations in DIII-D H-mode Plasmas R. Nazikian, P.B. Snyder, T.E. Evans, T.H. Osborne A detailed analysis of resonant magnetic perturbations (RMPs) applied to low collisionality DIII-D H-mode plasmas with ITER Similar Shape (ISS) and for a broad range of edge magnetic safety factor ($q_{95}$) reveals a systematic reduction in the pedestal pressure relative to the pre-RMP level in ELM suppressed and ELM mitigated discharges. The reduction in the pedestal pressure for ELM mitigated discharges coincides with the reduction in the pedestal density induced by the pumpout effect of the RMP. This is consistent with theoretical predictions for the onset of ELMs based on the kink-peeling mode as the limiting instability in these plasmas. At lower density, the collisionality (bootstrap current) decreases (increases) at fixed pressure, increasing the drive for the kink-peeling mode, thereby reducing the pressure for ELM onset. The pedestal pressure further decreases in plasmas with ELM suppression, indicating that the pedestal is below the limit for the mode onset. These results suggest that pedestal optimization in RMP H-mode plasmas will benefit from the development of methods that mitigate the density pumpout effect of RMPs in ISS plasmas. [Preview Abstract] |
Tuesday, November 12, 2013 10:18AM - 10:30AM |
GO4.00005: A Possible Connection of Plasma Response to RMP ELM Suppression in DIII-D A. Wingen, M.W. Shafer, E.A. Unterberg, D.L. Hillis, N.M. Ferraro, T.E. Evans, P.B. Snyder A hypothesis of a possible relation between the so-called kink-response, a flux surface oscillation which is driven by amplification of non-resonant components of the resonant magnetic perturbation (RMP) spectrum, and the re-appearance of edge localized modes (ELMs) in the presence of RMPs is presented. Several DIII-D discharges with different responses show that those with stronger kink-response are closer to the peeling-ballooning stability limit and eventually cross into the unstable region, causing ELMs to re-appear. Simulations of the magnetic topology for all cases are compared. The topology consists of a kinetic equilibrium reconstruction, the RMP fields and a linear plasma response, calculated by resistive, 2-fluid MHD. It is found that the kink response is correlated to the edge current density while screening/amplification of resonant field components is related to flows. A transition from a tearing dominated edge to a kink dominated edge is demonstrated. A kink dominated discharge with intermittent ELMs is found to be marginally unstable in an ELITE simulation while ELM suppressed, tearing dominated discharges are inside the stability limit. [Preview Abstract] |
Tuesday, November 12, 2013 10:30AM - 10:42AM |
GO4.00006: Advancing the Physics Basis of Quiescent H-mode as an Operating Scenario for ITER W.M. Solomon, B.A. Grierson, K.H. Burrell, A.M. Garofalo, P.B. Snyder, M.E. Fenstermacher Counter rotating QH-mode is an attractive ELM stable scenario for ITER because it maintains excellent confinement at low levels of neutral beam torque. Recent experiments have investigated the density requirements for QH-mode access and find no correlation with Greenwald fraction, suggesting this is not the relevant physics parameter. Indeed, with high shaping, Greenwald fractions exceeding 80\% have now been achieved. Impurity transport in QH-mode with an edge harmonic oscillation is found to exceed the level seen in comparable ELMing discharges. Access to counter-rotating QH-mode without first spinning the plasma with neutral beam torque remains a challenge because the co-intrinsic drive appears to develop faster than the counter torque driven by non-axisymmetric fields. Simultaneous achievement of high beta, high confinement and low $q_{95}$ needed for ITER $Q=10$ performance has been demonstrated, but work remains to extend this to lower torque and sustained operation. [Preview Abstract] |
Tuesday, November 12, 2013 10:42AM - 10:54AM |
GO4.00007: Overview of Recent Steady-State Scenario Experiments on DIII-D C.T. Holcomb, J.R. Ferron, A.M. Garofalo, D.C. Pace, T.W. Petrie, T.C. Luce, C.C. Petty, J.M. Park, W.W. Heidbrink, G.R. McKee, T.L. Rhodes, C. Holland, F. Turco, W.M. Solomon On DIII-D, on- and off-axis neutral beams and electron cyclotron heating have expanded access to a wide range of $q$-profiles. Plasmas with $q_{min}=1-3$ have been evaluated for high $\beta$ steady-state operation. With $q_{min}>2$ and no internal transport barrier, ideal-wall kink mode $\beta_N$ limits $>$4 are calculated but the global energy confinement is low compared to lower $q_{min}$ plasmas. The thermal and fast ion transport dependence on $q_{min}$ will be discussed, as well as the dependence of stability and confinement on $\rho_{qmin}$ and $q_0-q_{min}$, and the characteristics of plasmas dominated by bootstrap current at high $\beta_p$. At intermediate $q_{min}\geq 1.5$, high noninductive current fraction is possible with performance that projects to $Q\sim 5$ in ITER, both in double null and ITER-like shape. Divertor heat flux is reduced using increased radiation from impurity gas injection. At $q_{min}\sim 1$, ``high-$\ell_i$'' plasmas transiently reach $\beta_N>5$ with excellent confinement, but MHD avoidance and profile control are needed to achieve stationary high performance. [Preview Abstract] |
Tuesday, November 12, 2013 10:54AM - 11:06AM |
GO4.00008: Advanced Divertor Developments at DIII-D E. Kolemen, S.L. Allen, M.A. Makowski, V.A. Soukhanovskii, B.D. Bray, D. Eldon, D.A. Humphreys, R. Johnson, A.W. Leonard, C. Liu, B.G. Penaflor, T.W. Petrie, A.G. McLean, E.A. Unterberg Novel divertor configurations and control schemes have been implemented at DIII-D to test and optimize heat and particle handling capabilities for advanced tokamaks. The snowflake configuration is stabilized by first calculating the position of the two null-points using real-time equilibrium reconstruction and then regulating the shaping coil currents. Experiments in which the snowflake divertor is stabilized for many confinement times show that it is compatible with high-performance operation and results in greatly reduced divertor heat flux. An advanced divertor control system regulates the gas injection to achieve partial or full detachment by using the divertor temperature measurements from real-time Thomson diagnostics and a line ratio measurement, and adjusts the core and divertor radiation via measurement of the real-time bolometer diagnostics. Prospects of achieving acceptable divertor target heat fluxes for future fusion reactors are analyzed and challenges are presented. [Preview Abstract] |
Tuesday, November 12, 2013 11:06AM - 11:18AM |
GO4.00009: Measurements of Temperature, Density, and Flows on the Inboard Side Scrape-off Layer of DIII-D Plasmas Using the Swing-Probes C.K. Tsui, J.D. Elder, P.C. Stangeby, S.L. Allen, J.A. Boedo, A.W. Leonard, A.G. McLean, J.G. Watkin Measurements of temperature, density, and parallel flow velocity have been made in the inboard, high-field side scrape-off layer (SOL) from the wall to the separatrix using new swing-probes, one at the entrance of each divertor. Prior to their installation, the inboard SOL could only be measured using passive spectroscopic techniques in most plasma shapes. Edge codes can now be fully constrained across the whole SOL. Swing-probe data taken over a density scan of L-mode and H mode plasmas are presented and compared with those from other diagnostics. In L-mode plasmas, the Langmuir characteristic curves are quite quiescent suggesting that turbulence is largely absent from the inboard SOL. $n_e$ increases linearly with $\bar{n}_e$ at first, then saturates and rolls over. This is the standard feature of detachment observed by probes installed in divertor targets, indicating the spatial extent of the region of momentum loss and/or volume recombination. [Preview Abstract] |
Tuesday, November 12, 2013 11:18AM - 11:30AM |
GO4.00010: Toroidal Asymmetry of Heat Deposition During Transient Events in DIII-D C.J. Lasnier, W.H. Meyer, S.L. Allen, M.E. Fenstermacher We show measurements of toroidal and poloidal distribution of heat from ELMs, disruptions, and magnetic perturbations; and outer-wall steady-state heating during diverted discharges, using a new wide-angle tangential viewing system for IR (and visible) emission. The IR data cover 3-5~$\mu$m, with 110 degrees of toroidal angle and full poloidal coverage of the wall, and complement the existing vertically viewing IR camera. Radial, poloidal, and toroidal profiles are extracted from images using a 3D model rendering that is warped to fit the real image. Wire-frame features are extracted from this rendering and aligned to the data image to determine the physical location viewed by each pixel. The IR data show that heat flux during ELMs forms multiple spiral stripes in the divertor, not inconsistent with expectations for an intermediate-n peeling/ballooning instability. Somewhat surprisingly, we observe volumetric emission from the inner wall during MARFEs, and also from the X-point area during disruptions. While not anticipated at 3-5~$\mu$m, these new data raise the prospect of imaging the dynamics of portions of the radiated power profiles during rapid transients. [Preview Abstract] |
Tuesday, November 12, 2013 11:30AM - 11:42AM |
GO4.00011: Alfv\'en Eigenmode Induced Fast Ion Transport in \mbox{DIII-D} Resulting From Finite Larmor Radius Effects G.J. Kramer, G.Y. Fu, R. Nazikian, M.A. Van Zeeland, R.K. Fisher, D.C. Pace, L. Chen, X. Chen, W.W. Heidbrink Alfv\'en Eigenmode (AE) induced fast-ion redistribution and loss are commonly observed in DIII-D. In those experiments the perpendicular wave vector times the fast-ion Larmor radius is of order unity ($k_\perp\rho_i\sim 1$), which allows fast ion orbits to traverse the AE mode structures asymmetrically causing a significant change in magnetic moment. Full-orbit simulations of the expected transport in DIII-D plasmas show that this effect can lead to fast-ion radial diffusion constants of 5~m$^2$/s at the measured mode amplitudes. This level of diffusion is not captured with a guiding center approximation and is in agreement with that deduced in DIII-D experiments when AE activity was present. [Preview Abstract] |
Tuesday, November 12, 2013 11:42AM - 11:54AM |
GO4.00012: Analysis and Modeling of DIII-D Experiments With OMFIT and Neural Networks O. Meneghini, C. Luna, S.P. Smith, L.L. Lao The OMFIT integrated modeling framework is designed to facilitate experimental data analysis and enable integrated simulations. This talk introduces this framework and presents a selection of its applications to the DIII-D experiment. Examples include kinetic equilibrium reconstruction analysis; evaluation of MHD stability in the core and in the edge; and self-consistent predictive steady-state transport modeling. The OMFIT framework also provides the platform for an innovative approach based on neural networks to predict electron and ion energy fluxes. In our study a multi-layer feed-forward back-propagation neural network is built and trained over a database of DIII-D data. It is found that given the same parameters that the highest fidelity models use, the neural network model is able to predict to a large degree the heat transport profiles observed in the DIII-D experiments. Once the network is built, the numerical cost of evaluating the transport coefficients is virtually nonexistent, thus making the neural network model particularly well suited for plasma control and quick exploration of operational scenarios. The implementation of the neural network model and benchmark with experimental results and gyro-kinetic models will be discussed. [Preview Abstract] |
Tuesday, November 12, 2013 11:54AM - 12:06PM |
GO4.00013: Ion Loss as Intrinsic Momentum Source in Tokamaks J.A. Boedo Measurements of D$^+$ parallel velocity at the DIII-D edge are consistent with the kinetic loss of thermal ions as the mechanism for edge momentum generation. Edge velocity profiles exhibit a co-$I_p$ peak velocity of 40-60~km/s in OH, L- and H-mode. The flow layer acts as a robust boundary value not affected by NBI injection. D$^+$ velocity measurements are compared to a first-principles, collisionless, kinetic model predicting the existence of a loss-cone distribution in velocity space resulting in a co-$I_p$ directed velocity. A fine $E_r$ structure, found by probes, has 10-20~kV/m peaks in the scrape-off layer (SOL) and LCFS and when incorporated in the kinetic model, results in: 1) $\sim$30\%-50\% increase in the peak parallel velocity over the zero field case and, 2) broadened rotation profile into the SOL. The model-data agreement shows this mechanism is important, competing with pre-sheath acceleration and Pfirsch-Schluter drives. Computations with XGC0, a full-f particle-in-cell drift-kinetic solver with collisional kinetic ions and electrons, and NEO, a drift kinetic code with multiple species and linearized F-P collisions confirms the relevance of the ion orbit loss the impact of kinetic effects on $E_r$ and the measured C$^{6+}$ and D$^+$ velocities inside the LCFS. [Preview Abstract] |
Tuesday, November 12, 2013 12:06PM - 12:18PM |
GO4.00014: Multi-field Characteristics and Eigenmode Spatial Structure of Geodesic Acoustic Modes (GAMs) in DIII-D G. Wang, W.A. Peebles, T.L. Rhodes, E.J. Doyle, L. Schmitz, L. Zeng, J.C. Hillesheim, M.E. Austin, Z. Yan, G.R. McKee, R.J. La Haye, K.H. Burrell, M.J. Lanctot, C.C. Petty, S.P. Smith, E.J. Strait, M.A. Van Zeeland, R. Nazikian Understanding GAMs is important since they are thought to regulate turbulence and transport levels in the outer regions of fusion plasmas. For the first time, two simultaneous, radially-overlapping eigenmode GAMs (constant frequency vs radius) have been observed in the poloidal $E\times B$ flow in L-mode \mbox{DIII-D} plasmas. Intermediate-k density fluctuations ($k_\theta^\ast \rho_s \sim 1$) are modified by these GAMs. Multi-field oscillations at the GAM frequency are also clearly observed in $n_e$, $T_e$, and $B_\theta$. Magnetic GAM activity is much stronger on the high-field side of the tokamak. This unique information provides a new perspective on GAM activity. Direct comparison with global gyrokinetic simulations (GYRO) will be presented to improve understanding. [Preview Abstract] |
Tuesday, November 12, 2013 12:18PM - 12:30PM |
GO4.00015: Changes in Particle Transport as a Function of Collisionality and Rotation S. Mordijck, X. Wang, E.J. Doyle, L. Zeng, L. Schmitz, T.L. Rhodes The performance of future tokamaks depends strongly on enhanced density peaking at low collisionality, which has been attributed to changes in turbulence regime from the ion temperature gradient (ITG) to trapped electron mode (TEM) regime and related changes in toroidal rotation [1]. In DIII-D the measured density peaking in H-mode discharges remained fixed during a collisionality scan, and no difference in the density peaking was observed by changing the turbulence regime from ITG to TEM-dominated (as inferred from TGLF linear gyrofluid stability calculations). Moreover, we could not discern any effect on density peaking from changes in the toroidal rotation. We will present the characteristics of low and intermediate-k fluctuations in both regimes, as well as the dependence of the transport coefficients D and $v_r$ (extracted from perturbative particle transport measurements) on collisionality, turbulence regime/instability growth rates, and $E\times B$ shear.\par \vskip6pt \noindent [1] C.~Angioni, et al., Nucl.\ Fusion {\bf 52}, 114003 (2012). [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