Bulletin of the American Physical Society
50th Annual Meeting of the Division of Plasma Physics
Volume 53, Number 14
Monday–Friday, November 17–21, 2008; Dallas, Texas
Session PO3: DIII-D I |
Hide Abstracts |
Chair: Chris Hegna, University of Wisconsin Room: Reunion A |
Wednesday, November 19, 2008 2:00PM - 2:12PM |
PO3.00001: Overview of Recent DIII-D Results in Support of ITER C.M. Greenfield Recent DIII-D experiments continue to add to a physics basis for ITER design decisions. RMP ELM control, usually done using two rows of internal coils, has been demonstrated using a single row at similar perturbation levels. Rotation and stability in the interior are sensitive to nonresonant fields driven by these coils. Confirming theory-based predictions, these fields accelerate the plasma toward an offset velocity in the direction opposite the current. Discharges duplicating most of the characteristics of each ITER operational scenario have been created, including some starting from the ITER startup scenario, transitioning into a hybrid, and ramping down without disruption. Lower internal inductance than indicated in the ITER design has been observed in all demonstration scenarios, motivating modifications to ITER's poloidal field coil system. In preparation for the initial phase of ITER, the \mbox{H-mode} transition, pedestal, and local transport have been studied in hydrogen plasmas. Consistent with past results in deuterium, the L-H threshold in hydrogen is reduced significantly as rotation is decreased. [Preview Abstract] |
Wednesday, November 19, 2008 2:12PM - 2:24PM |
PO3.00002: Particle Transport in RMP H-modes R.A. Moyer, V.A. Izzo, S. Mordijck, J.A. Boedo, D.L. Rudakov, T.E. Evans, N.H. Brooks, P. Gohil, E.A. Unterberg, M.E. Fenstermacher, H. Frerichs, O. Schmitz, B. Unterberg, M.W. Jakubowski, J.G. Watkins, G.R. McKee, T.L. Rhodes, L. Schmitz, L. Zeng, C.S. Chang, G. Park Increased transport in resonant magnetic perturbations (RMP) H-modes reduces the pedestal pressure gradient below the Type I ELM stability limit. The RMP induces more particle transport and less electron thermal transport than expected from simple stochastic transport models. This increased transport starts during the RMP rise-time, and displays a broader resonance in q95 than ELM suppression. Evidence suggests that the transport is at first caused by a combination of neoclassical transport in the 3D equilibrium, $E\times B$ convection in the weakly stochastic layer, and fluctuation-driven transport. After the ELMs are suppressed, fluctuations increase due to Er shear changes. Optimizing these transport changes will improve the viability of RMP ELM-control for ITER. [Preview Abstract] |
Wednesday, November 19, 2008 2:24PM - 2:36PM |
PO3.00003: Influence of Rotation and Error Field on Tearing Stability in Low Torque ITER-like Plasmas in DIII-D R.J. Buttery, J.S. deGrassie, G.L. Jackson, R.J. La Haye, E.J. Strait, M. Maraschek, H. Reimerdes 2/1 tearing mode beta limits are known to fall in ITER baseline-like plasmas as the usual co-injected neutral beam torque is reduced. New DIII-D studies have explored the physics and sensitivities of this process in two ways. Beta limits were found to fall further as counter torque and rotation (relative to plasma current direction) was increased, reaching a minimum at modest net counter torque/rotation, before partially recovering to higher beta with strong counter torque. This suggests that rotation is not ``simply stabilizing'' to tearing modes but more subtle physics is at play. Further, resonant magnetic field probing of such plasmas shows error field sensitivity increasing substantially in the normalised beta range $\sim$1-2, both with beta, as the beta limit for intrinsic tearing is approached, or as co-torque and rotation are reduced. This leaves ITER baseline-like plasmas in DIII-D just stable, provided error fields are minimised. [Preview Abstract] |
Wednesday, November 19, 2008 2:36PM - 2:48PM |
PO3.00004: Boundary Intrinsic Velocity in DIII-D H-modes J.S. deGrassie, R.J. Groebner, K.H. Burrell, R.E. Waltz, W.M. Solomon The toroidal velocity, $V_\phi$, in the pedestal region of DIII-D H-mode discharges with negligible neutral beam injected (NBI) torque is nonzero, in the direction of the plasma current, co-$I_p$. This velocity is found to scale approximately linearly with the local ion temperature, $T_i$. Such a scaling can result simply because of thermal ion loss from the pedestal region; counter-$I_p$ thermal ions are predominantly lost leaving a net co-$I_p$ local average velocity. However, we also measure $V_\phi \sim T_i$ well inside of the pedestal region, where classical thermal ion orbit loss would not be effective. This could be explained by a toroidal momentum pinch with pinch velocity proportional to the gradient of $T_i$. There are theories that predict such a pinch driven by turbulence. We have used the GYRO code to investigate the scaling of the turbulent pinch effect in conditions typical of the edge region of these intrinsic H-mode discharges. [Preview Abstract] |
Wednesday, November 19, 2008 2:48PM - 3:00PM |
PO3.00005: Ratio of Electron Temperature and Density Fluctuation Amplitudes During ECH in DIII-D Ohmic and L-mode Discharges A.E. White, L. Schmitz, W.A. Peebles, T.A. Carter, T.L. Rhodes, G. Wang, E.J. Doyle, J.C. Hillesheim, L. Zeng, G.R. McKee, M.W. Shafer, J.C. DeBoo, G.M. Staebler An increase in the ratio of the amplitudes of two fluctuating fields, $(\tilde T_e/T_e)/(\tilde n/n)$, is observed in DIII-D beam-heated ($\sim$2.5~MW, co-injected) L-mode plasmas during ECH ($\sim$2.5~MW deposited at $\rho \approx 0.17$). The amplitude of long wavelength temperature fluctuations, $\tilde T_e/T_e$, measured with a correlation ECE diagnostic (CECE), increases significantly during ECH. In contrast, the amplitude of long wavelength density fluctuations, $\tilde n/n$, measured simultaneously with a BES diagnostic, does not change. Linear stability analysis with the TGLF code shows that during ECH the ratio of the TEM and ITG growth rates increases at long wavelengths in the range relevant for the CECE and BES diagnostics. These TGLF results are found to be more sensitive to changes in the TEM drive term $a/L_{n_e}$ compared with changes in $a/L_{T_e}$ or $a/L_{T_i}$. Sensitivity scans with TGLF and comparisons with experimental results for the ratio $(\tilde T_e/T_e)/(\tilde n/n)$ measured in Ohmic plasmas with ECH will be presented. [Preview Abstract] |
Wednesday, November 19, 2008 3:00PM - 3:12PM |
PO3.00006: Local Turbulence Suppression and Shear Flow Dynamics During $q_{min}$-Triggered Internal Transport Barriers on DIII-D M.W. Shafer, G.R. McKee, D.J. Schlossberg, M.E. Austin, K.H. Burrell Long-wavelength turbulence ($k_\perp \rho_i < 1$) is locally suppressed simultaneously with a rapid but transient increase in local poloidal flow shear at the appearance of low-order rational $q_{min}$ surfaces in negative central shear discharges. At these events, reductions in energy transport are observed and Internal Transport Barriers (ITBs) may form. Application of off-axis ECH slows the $q$-profile evolution and increases $\rho_{qmin}$, both of which enhance turbulence measurements using a new high-sensitivity large-area (8$\times\,$8) 2D BES array. The measured transient turbulence suppression is localized to the low-order rational surface ($q_{min} = 2$, 5/2, 3, etc.). Measured poloidal flow shear transiently exceeds the turbulence decorrelation rate, which is consistent with shear suppression. The localized suppression zone propagates radially outward, nearly coincident with the low-order surface. [Preview Abstract] |
Wednesday, November 19, 2008 3:12PM - 3:24PM |
PO3.00007: Modulation of TEM Turbulence in DIII-D L-mode Discharges J.C. DeBoo, G.M. Staebler, T.L. Rhodes, L. Schmitz, A.E. White, E.J. Doyle, W.A. Peebles, C. Holland Results of an experiment to modulate trapped electron mode (TEM) drift wave activity by varying the local temperature gradient scale length ($a/L_{Te}$) using ECH will be discussed. When ECH deposition was repetitively switched from heating just inside to just outside the plasma mid-radius, TEM activity at wavenumbers $k_\theta =\,$5-6~cm$^{-1}$, measured with a Doppler backscattering system (DBS), was modulated at the mid-radius. The viewing location was scanned, showing that the amplitude modulation was spatially localized and peaked between the two ECH deposition regions. Modulation of a TEM drive term, $a/L_{Te}$, between 2 and 3 resulted in measured turbulent amplitude modulation of about 20\% and also produced a modulation in the frequency of the DBS measurements. The sign of the turbulent frequency variation was consistent with changes produced in the electron diamagnetic drift velocity associated with changes in the local pressure gradient. A comparison of results with gyrokinetic stability code calculations will be shown. [Preview Abstract] |
Wednesday, November 19, 2008 3:24PM - 3:36PM |
PO3.00008: Impact of Divertor Magnetic Balance and Particle Drifts on Radiating Divertor Behavior in DIII-D T.W. Petrie, N.H. Brooks, J.R. Ferron, A.W. Hyatt, A.W. Leonard, T.C. Luce, M.R. Wade, W.P. West, M.E. Fenstermacher, M. Groth, C.J. Lasnier, G.D. Porter, J.G. Watkins Recent DIII-D experiments show that both magnetic balance between upper and lower divertors and the particle drifts in the SOL and divertors are important to understanding how argon impurities accumulate in double-null plasmas in a ``puff and pump" radiating divertor scenario. The best results to-date in terms of coupling a radiating divertor approach to an H-mode plasma with minimal degradation in $\tau_E$ have been produced in a double-null shape biased opposite to the ion ${\bf B}\times\nabla B$ drift direction. Edge transport modeling with UEDGE [1] shows that the maintenance of low core impurity levels in this configuration can be largely ascribed to the central role of particle drifts. Additionally, it is found that ion ${\bf B}\times\nabla B$ drift direction plays a much more important role than divertor closure in controlling plasma density.\par \vskip6pt \noindent [1]~T.D.\ Rognlien, et al., Phys.\ Plasmas {\bf 34}, 362 (1994). [Preview Abstract] |
Wednesday, November 19, 2008 3:36PM - 3:48PM |
PO3.00009: Direct Measurements of Chemical Sputtering Yield and Photon Efficiencies in the DIII-D Divertor A.G. McLean, P.C. Stangeby, Y. Mu, J.W. Davis, A.A. Haasz, S.L. Allen, M.E. Fenstermacher, M. Groth, C.J. Lasnier, B.D. Bray, N.H. Brooks, T.H. Osborne, T.W. Petrie, W.P. West, C.P.C. Wong, D.G. Whyte, J.A. Boedo, D.L. Rudakov, R.E. Isler, J.G. Watkins, S. Brezinsek, M. Jakubowski Intrinsic chemical erosion yield near the outer strike point has been measured in-situ in DIII-D to be $\sim$2.6\% in attached divertor plasma and $\sim$1.7\% in semi-detached divertor plasma. These values are close to theoretical predictions and lab experiments. In fully detached conditions, as will occur at the ITER targets, near total extinction of the CH band occurred which is not predicted or included in current ITER modeling. Measurements were made with an artificial methane injection rate nearly equal to the expected intrinsic chemical erosion rate. Photon efficiencies for CH, CII and C$_2$ dimer from the breakup of injected CH$_4$ yielded significantly lower values than previous results at higher puff rates, underscoring the importance of minimizing perturbation to the local plasma. [Preview Abstract] |
Wednesday, November 19, 2008 3:48PM - 4:00PM |
PO3.00010: Studies in DIII-D of High Beta Discharge Scenarios Appropriate for Steady-state Tokamak Operation With Burning Plasmas J.R. Ferron, J.C. DeBoo, T.C. Luce, T.W. Petrie, C.C. Petty, P.A. Politzer, H. Reimerdes, M. Schneider, T.A. Casper, C.T. Holcomb, J.M. Park, M. Murakami, Y. Ou, E. Schuster, E.J. Doyle In the DIII-D steady-state scenario with $q_{min} =\,$1.5-2.0, the duration with the noninductive current fraction ($f_{NI}$) near 1 has been extended to 70\% of the resistive time. To extend duration, ECCD is deposited with a broad profile in order to avoid the 2/1 tearing mode, enabling reliable operation at $\beta_N =\,$3.6-3.7. These discharges have double-null shape biased in the direction opposite the $\nabla B$ drift, in order to simultaneously optimize confinement and divertor pumping, and ECCD power up to 3~MW. An alternate scenario with internal inductance increased to 1.1-1.4 is under study, motivated by the possibility of steady-state operation at $\beta_N=\,$4-5 without wall stabilization. Thus far, $\beta_N=\,$4.6, just below the calculated $n=1$ and $n =\infty$ stability limits, has been achieved transiently with $f_{NI} = 0.85$. [Preview Abstract] |
Wednesday, November 19, 2008 4:00PM - 4:12PM |
PO3.00011: Wall-stabilization and Its Limits in High Beta DIII-D Plasmas H. Reimerdes, J.W. Berkery, M.J. Lanctot, M.S. Chu, A.M. Garofalo, G.L. Jackson, R.J. La Haye, E.J. Strait, A.S. Welander, Y. In, Y.Q. Liu, M. Okabayashi, W.M. Solomon The resistive wall mode (RWM) in high beta DIII-D discharges remains stable over a wide range of plasma rotation profiles. Suppressing the $m/n=2/1$ neoclassical tearing mode with localized electron cyclotron current drive near the $q=2$ surface can extend the stable operating regime even below the previously reported rotation thresholds. The observed operating regime is consistent with improved calculations of kinetic effects on the linear RWM stability. Instability is, however, observed when the plasma is perturbed by externally applied $n=1$ fields or plasma generated MHD activity such as ELMs or fishbones. In the cases of a static $n=1$ error field, where the limit manifests itself by a loss of torque balance and a subsequent rotation collapse, the stability can be improved by increasing the applied torque or reducing the resonant component of the error field. In the case of plasma generated perturbations, fast magnetic feedback has been successfully used to improve stability. [Preview Abstract] |
Wednesday, November 19, 2008 4:12PM - 4:24PM |
PO3.00012: Feedback stabilization of current-driven resistive-wall-modes (RWMs) near $q_{95}\sim 4$ in DIII-D Y. In, J.S. Kim, I.N. Bogatu, G.L. Jackson, R.J. La Haye, M.J. Schaffer, E.J. Strait, A.M. Garofalo, M.J. Lanctot, H. Reimerdes, M. Okabayashi, L. Marrelli, P. Martin Complete feedback stabilization of current-driven RWM at $q_{95}\sim 4$ has been demonstrated in DIII-D. Taking advantage of the reproducible RWMs in ohmic plasmas with fast current ramps, we assessed the RWM feedback algorithm that had not been fully evaluated with pressure-driven RWMs. Using the internal control coils powered with a broadband supply, we suppressed the current-driven RWM at $q_{95}\sim 4$; successful feedback is attributable to both error field correction and direct mode feedback. The use of derivative gains expanded the stable range of proportional gains. The current-driven RWMs are frequently accompanied by magnetic island-like structures near $q=2$ surface: the evolution of such internal structures is also used to assess the efficacy of feedback stabilization. The experimental results will be used for a benchmark of RWM feedback models. [Preview Abstract] |
Wednesday, November 19, 2008 4:24PM - 4:36PM |
PO3.00013: 1-D Modeling of Massive Particle Injection (MPI) in Tokamaks W. Wu, P.B. Parks, V.A. Izzo A 1-D Fast Current Quench (FCQ) model is developed to study current evolution and runaway electron suppression under massive density increase. The model consists of coupled toroidal electric field and energy equations, and it is solved numerically for DIII-D and ITER operating conditions. Simulation results suggest that fast shutdown by D$_2$ liquid jet/pellet injection is in principle achievable for the desired plasma cooling time ($\sim$15~ms for DIII-D and $\sim$50~ms for ITER) under $\sim$150$\times$ or higher densification. The current density and pressure profile are practically unaltered during the initial phase of jet propagation when dilution cooling dominates. With subsequent radiation cooling, the densified discharge enters the strongly collisional regime where Pfirsch-Schluter thermal diffusion can inhibit current contraction on the magnetic axis. Often the 1/1 kink instability, addressed by Kadomtsev's magnetic reconnection model, can be prevented. Our results are compared with NIMROD simulations in which the plasma is suddenly densified by $\sim$100$\times$ and experiences instantaneous dilution cooling, allowing for use of actual (lower) Lundquist numbers. [Preview Abstract] |
Wednesday, November 19, 2008 4:36PM - 4:48PM |
PO3.00014: Experimental and Model Validation of ITER Operational Scenarios T.A. Casper, W.H. Meyer, D.A. Humphreys, A.W. Hyatt, G.L. Jackson, T.C. Luce Modified startup scenarios demonstrated in DIII-D contributed to new ITER startup scenarios with a full-sized plasma and X-point formation early in time. Higher internal inductance in the original experiments led to modifications of the current ramp and the development of feedback control methods. While experimental validation in DIII-D provides a necessary demonstration of ITER operational modes, evaluation of the extrapolation to ITER requires a modeling approach. Our emphasis is on validating models used in ITER simulations by comparison to DIII-D experimental data. Meaningful startup predictions require an accurate model of electron thermal transport since the electron temperature is critical to the current profile evolution that affects the response of the control system. Using results of this model validation, free-boundary predictive simulations have explored the ITER operational issues of flux consumption, stability and performance of the ITER poloidal-field coils and controller during the current rise and into the burn phase. [Preview Abstract] |
Wednesday, November 19, 2008 4:48PM - 5:00PM |
PO3.00015: Recent Advances in Alfv\'en Eigenmode Research on DIII-D R. Nazikian, N.N. Gorelenkov, G.J. Kramer, M.E. Austin, H.L. Berk, W.W. Heidbrink, G.R. McKee, M.W. Shafer, E.J. Strait, M.A. Van Zeeland Previous studies have revealed a large anomalous redistribution of fast ions in DIII-D in the presence of Alfv\'en eigenmodes (AEs). Rapid progress has been made in the last year on understanding AEs and their effects on fast ion transport in reverse magnetic shear plasmas on DIII-D. New transport simulations taking account of the compressional component of the shear Alfv\'en modes, together with the frequency sweeping of the observed instabilities, produces much high transport levels than previous estimates. Validating the mode structure used in simulation is essential. The results on the simultaneous measurement of the temperature (ECE) and density (BES) fluctuation profile of AEs will be shown and compared to theory. These measurements enable a stringent test of kinetic theory for the plasma response to shear Alfv\'en waves in fusion 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