Bulletin of the American Physical Society
2005 47th Annual Meeting of the Division of Plasma Physics
Monday–Friday, October 24–28, 2005; Denver, Colorado
Session BO3: DIII-D Tokamak |
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Chair: Stanley Kaye, Princeton Plasma Physics Lab Room: Adam's Mark Hotel Governor's Square 15 |
Monday, October 24, 2005 9:30AM - 9:42AM |
BO3.00001: Overview of Recent DIII-D Experimental Results M.R. Wade The mission of the DIII-D program is establish the scientific basis for the optimization of the tokamak approach to fusion energy production. DIII-D’s near-term goals are: 1)~to ensure ITER success by providing scientific solutions to key issues; 2)~to enhance the ITER physics program through development and characterization of advanced operating modes; and 3)~to develop the scientific basis for high $\beta$, steady-state operation. Experiments have demonstrated ELM suppression at ITER-relevant collisionalities using an n=3 resonant magnetic perturbation, avoidance of NTMs via localized ECCD in plasmas operating at the no-wall stability limit, and re-deposition of carbon near the inner divertor leg. DIII-D continues to lead the world effort in characterizing hybrid and advanced inductive operating scenarios for ITER through studies that have expanded the operating space and assessing details of energy and current transport. Advanced Tokamak experiments have demonstrated fully non-inductive operation with an aligned current profile, sustained operation with $\beta\,$50\% above the no-wall stability limit, and real-time current profile control. [Preview Abstract] |
Monday, October 24, 2005 9:42AM - 9:54AM |
BO3.00002: Advanced Tokamak Development in DIII-D C.M. Greenfield Advanced Tokamak research in DIII-D seeks to develop a scientific basis for steady-state high performance tokamak operation. We discuss recent work in several areas. Experiments in weak negative central shear plasmas with $q_{min}\approx\,$2 have demonstrated conditions with no inductively driven current anywhere ($f_{NI}\approx\,$100\%), maintained for several confinement times with $\beta_N\approx\,$3.5. Similar plasmas are stationary with $f_{NI}\approx\,$90\% and duration limited only by hardware. In other experiments, $\beta_N\approx\,$4 is maintained for 2~s with strongly negative magnetic shear and internal transport barriers, exceeding previous performance in similar conditions. This is allowed by broadened profiles and active MHD instabilities control. These studies are supported by recent experiments to develop active current profile control using neutral beam and electron cyclotron current drive as actuators and real-time equilibrium calculations, including MSE measurements. These results motivate future research incorporating improved current profile, rotation and particle control capabilities now being added to DIII-D. [Preview Abstract] |
Monday, October 24, 2005 9:54AM - 10:06AM |
BO3.00003: Feedback Control of the Safety Factor Profile Evolution in DIII-D Advanced Tokamak Discharges J.R. Ferron, P. Gohil, C.M. Greenfield, J. Lohr, T.C. Luce, C.C. Petty, M.R. Wade, T.A. Casper, R.J. Jayakumar, M.A. Makowski, M. Murakami, D. Mazon In an advanced tokamak discharge in DIII-D, the $q$ profile is
established during
the plasma current ramp-up and early flattop phases and sustained
during the
subsequent high beta phase. Initial feedback control experiments
have focused on
ensuring that the desired $q$ profile at the start of the high
beta phase,
$1.5 |
Monday, October 24, 2005 10:06AM - 10:18AM |
BO3.00004: Improved Performance in DIII-D Hybrid Discharges With a Dominant 4/3 Tearing Mode C.C. Petty, P.A. Politzer, T.C. Luce, M.R. Wade, R.J. Jayakumar, M.A. Makowski Hybrid discharges on DIII-D usually have a dominant (but relatively small) 3/2 tearing mode that maintains the safety factor above unity when $q_{95}>4$. Recent \hbox{DIII-D} experiments have shown that small changes in the plasma conditions can result in the development of a dominant 4/3 tearing mode instead, resulting in up to 30\% improvement in the energy confinement time at the same beta. Explanations for the improved confinement include increased toroidal rotation in the plasma core and less flattening of the measured pressure profile near the island location. Direct analysis of the MSE signals confirm that pressure driven currents increase near the q=1.5 surface for the 4/3 mode case compared to the 3/2 mode case. Hybrid discharges with $\beta_N=2.8$ and $q_{95}=4.7$ achieve performance close to the ITER baseline when the 4/3 mode is dominant. Even more spectacular are dominant 4/3 mode discharges with $q_{95}=3.1$, where $\beta_N H_{89}/q_{95}^2\geq 0.7$ can be maintained for several current relaxation times, exceeding the ITER baseline by 75\%. [Preview Abstract] |
Monday, October 24, 2005 10:18AM - 10:30AM |
BO3.00005: Comparison of Broad Spectrum Turbulence Measurements and Gyrokinetic Code Predictions on the DIII-D Tokamak T.L. Rhodes, W.A. Peebles, X. Nguyen, E.J. Doyle, L. Zeng, G. Wang, M.A. VanZeeland, G.R. McKee, J.C. DeBoo, J.S. deGrassie, C.M. Greenfield, C.C. Petty, P. Gohil Density fluctuation measurements over a broad wavenumber range (1-35 cm$^{-1}$) have been performed on DIII-D which provide a new, more complete picture of tokamak turbulence behavior. This range corresponds to $k_\perp\rho_s\approx 0.2\rightarrow 10$ and is relevant to ITG, TEM and ETG type instabilities. GKS linear stability calculations indicate the plasma unstable to ITG, TEM, and ETG consistent with the observed turbulent activity. Plasma perturbations utilizing neutral beams and electron cyclotron heating were used to modify the temperature, density, and density fluctuation behavior. The measured and calculated responses varied with wavenumber, supporting the need for broad wavenumber measurements. Additionally, the measurement and simulation show both similarities and differences. These differences could be due to complex interactions not contained in the linear code and are under investigation. [Preview Abstract] |
Monday, October 24, 2005 10:30AM - 10:42AM |
BO3.00006: Carbon Co-Deposition Studies in DIII-D L- and H-Mode Plasmas and Implications to the ITER Tritium Inventory A.G. McLean, J.W. Davis, P.C. Stangeby, A.A. Haasz, S.L. Allen, R. Ellis, M.E. Fenstermacher, M. Groth, W.R. Wampler, D.G. Whyte, N.H. Brooks, R.L. Lee, W.P. West, C.P.C. Wong, A. Nagy, D.L. Rudakov, V. Phillips, G.F. Matthews A carbon-13 tracer injection experiment into ITER-like lower single-null partially detached ELMy H-mode plasma was carried out on DIII-D. 2.2x10$^{22}$ $^{13}$C atoms were injected as $^{13}$CH$_4$ in a toroidally symmetric way in 17 identical 5s shots. Residual gas analysis of effluent during He glow indicated that $\sim$1\% of $^{13}$C atoms escaped as $^{13}$CD$_4$. 64 tiles were removed from the vessel for NRA analysis at Sandia Labs and the Univ. of Wisc. Simulation of the experiment with OEDGE and UEDGE is underway to interpret the tracer deposition pattern and better understand where tritiated hydrocarbons will collect in ITER. The Univ. of Toronto will perform oxygen baking to judge its use as a tritium removal technique. [Preview Abstract] |
Monday, October 24, 2005 10:42AM - 10:54AM |
BO3.00007: Effect of the Surface Temperature on Net Carbon Deposition and Deuterium Co-deposition in DIII-D Divertor D.L. Rudakov, J.A. Boedo, R.A. Moyer, R. Bastasz, W.R. Wampler, J.G. Watkins, J. Brooks, N.H. Brooks, W.P. West, C.P.C. Wong, W. Jacob, K. Krieger, A. Litnovsky, V. Philipps, A.G. McLean, P.C. Stangeby We report a strong effect of a moderately elevated surface temperature on net C deposition and D co-deposition in DIII-D divertor under detached conditions. A DiMES sample with a gap 2~mm wide and 15~mm deep was exposed to L-mode plasmas first at room temperature then at 200$^{\circ}$C. At the elevated temperature deuterium co-deposition in the gap was reduced an order of magnitude and net carbon erosion at a rate of 3~nm/s was measured at the plasma-facing surface of the sample. In another experiment visible deposits were produced on molybdenum mirrors recessed 2~cm under the divertor floor and exposed to ELMing H-mode plasmas for 25~seconds at room temperature. In contrast, virtually no deposits were observed on mirrors exposed to similar plasmas for 70~seconds at elevated temperatures, between 140$^{\circ}$ and 80$^{\circ}$C. [Preview Abstract] |
Monday, October 24, 2005 10:54AM - 11:06AM |
BO3.00008: ELM Control With n=3 Magnetic Perturbations R.A. Moyer, J.A. Boedo, I. Joseph, D.L. Rudakov, T.E. Evans, K.H. Burrell, T.H. Osborne, M.J. Schaffer, P.B. Snyder, N.H. Brooks, R.J. Groebner, G.L. Jackson, R.J. La Haye, A.W. Leonard, D.M. Thomas, W.P. West, P. Thomas, M. Becoulet, E.J. Doyle, T.L. Rhodes, L. Zeng, J.G. Watkins, M.E. Fenstermacher, C.J. Lasnier, K.H. Finken ELMs are eliminated with magnetic perturbation in ITER-relevant edge collisionality ($\nu_e^*\approx\,$0.1) \hbox{H-modes}. This extension of previous ELM suppression at $\nu_e^*\approx\,$1 was obtained by optimizing the poloidal mode spectrum of the perturbation and pumping to reach low $\nu_e^*$. ELITE calculations suggest that ELMs are eliminated by moving the edge gradients into an ELM stable region. The perturbation lowers the gradients by increasing particle transport while leaving the electron thermal transport nearly unchanged. This contradicts expectations for transport in stochastic fields, and demonstrates the need for improved models of plasma response to stochastic fields. [Preview Abstract] |
Monday, October 24, 2005 11:06AM - 11:18AM |
BO3.00009: MHD Analysis of the Tokamak Edge Pedestal in the Low Collisionality Regime P.B. Snyder, K.H. Burrell, M.S. Chu, T.H. Osborne, H.R. Wilson, C. Konz The peeling-ballooning model proposes that intermediate wavelength MHD instabilities are responsible for edge localized modes (ELMs) and impose constraints on the pedestal height. In typical discharges with ELMs, the pedestal goes unstable to coupled peeling-ballooning or pure ballooning modes shortly before an ELM is observed. However, at very low collisionality, the bootstrap current in the pedestal region can be large, even very near the separatrix, and the discharge can be most unstable to current-driven kink/peeling modes, typically at relatively low mode number ($n\sim\,$1-10). Recently, interesting ELM-free regimes, including both Quiescent (QH) and Resonant Magnetic Perturbation (RMP) H-mode, have been observed to occur in this low collisionality regime. Here we systematically explore MHD stability in this regime, including the effects of a conducting wall and sheared toroidal flow. We consider the implications for both RMP and QH discharges, including possible connections between the EHO observed in QH mode and low-n kink/peeling modes. [Preview Abstract] |
Monday, October 24, 2005 11:18AM - 11:30AM |
BO3.00010: Nonlinear Evolution of Edge Localized Modes With Flow Shear D.P. Brennan, M.S. Chu, L.L. Lao, P.B. Snyder, A. Pankin, D.D. Schnack, S.E. Kruger A predictive understanding of edge localized modes (ELMs), including onset conditions and dynamic evolution, is crucial to next generation burning plasma experiments such as ITER. A new initiative was formed to study the dynamic evolution of ELMs with the 3D extended MHD code NIMROD. The first objective is to understand the physics of the nonlinear ELM evolution in single fluid extended MHD, with flow shear and anisotropic thermal energy transport. The equilibria employed are unstable only to a robust edge instability with parameters typical of DIII-D H-mode discharges. Linear results compare favorably to linear ideal codes in both mode structure and ballooning/peeling characteristics. The early nonlinear evolution of the mode shows a peak in the energy spectrum at lowest n nonlinearly driven by nearest neighbor coupling of high n modes, followed by energy cascading. The nonlinear mode structure shows filaments of high temperature flowing outward. Resistivity, thermal anisotropy and flow shear modify linear stability and strongly affect the nonlinear evolution. [Preview Abstract] |
Monday, October 24, 2005 11:30AM - 11:42AM |
BO3.00011: Robustness of RWM Feedback Performance in AT Plasmas M. Okabayashi, R. Hatcher, H. Takahashi, M.S. Chu, G.L. Jackson, R.J. La Haye, J.T. Scoville, E.J. Strait, A.M. Garofalo, G.A. Navratil, H. Reimerdes, Y. In High-speed actuators with frequency response of dc-40~kHz have been installed to upgrade the resistive wall mode (RWM) feedback capability in \hbox{DIII-D}. These actuators are configured to drive the \hbox{DIII-D} internal coil set (I-coils). The experimental observations qualitatively support that the voltage-controlled feedback does assist achieving long duration high beta plasmas. However, non-reproducibility of the RWM onset makes it harder to provide a quantitative measure of direct feedback and to separate the effects rotational stabilization. Possible causes of non-reproducibility are: (1)~coupling to ELMs, (2)~residual error field persisting even after the dynamic error field correction, (3)~possible coupling of RWM, ELMs and residual error field. The experimental observations will be discussed in light of these possibilities along with MARS-F analysis. [Preview Abstract] |
Monday, October 24, 2005 11:42AM - 11:54AM |
BO3.00012: Recent Fast-ion Experiments W.W. Heidbrink, Y. Luo, K.H. Burrell, R.I. Pinsker, E.D. Fredrickson, R. Nazikian, M.A. Van Zeeland, T.L. Rhodes, G. Wang Diagnostic improvements and operational flexibility have facilitated new fast-ion studies on \hbox{DIII-D}. The Balmer$_\alpha$ light from deuterium ions that neutralize as they pass through a neutral beam yields the fast-ion energy distribution and spatial profile; neutral particle, neutron, and beam-ion loss diagnostics corroborate the D$_\alpha$ diagnostic. In plasmas with fast-wave heating at the fourth, fifth, and sixth cyclotron harmonic, fast ions are accelerated above the injection energy; the profile data show that the acceleration is greatest near the cyclotron harmonic resonance layer. Internal density and external magnetic fluctuations produced by fast-ion instabilities with MHz frequencies are now measured. Experiments with magnetic fields as low as 0.5~T indicate that compressional Alfv\'en eigenmodes are readily excited in conventional tokamaks and will probably be excited in ITER. A study of Alfv\'en cascade modes provides our first simultaneous measurements of internal fluctuations and the resulting impact on the fast-ion profile. [Preview Abstract] |
Monday, October 24, 2005 11:54AM - 12:06PM |
BO3.00013: Simulation of Fast Alfv\'en Wave Interaction with Resonant Ions in Tokamaks Using Monte Carlo Orbit Code Coupled with Full Wave Code M. Choi, V.S. Chan, R.I. Pinsker, R. Prater, P. Bonoli, J. Wright, M. Porkolab, V. Tang, R. Parker, L.A. Berry, E.F. Jaeger Recent DIII-D fast Alfv\’en FW wave current drive experiments have demonstrated much stronger beam ion acceleration at 4th harmonic than at 8th harmonic. Recent \hbox{C-Mod} fundamental heating experiments have also measured rf-induced non-Maxwellian tails. The Monte-Carlo code, ORBIT-RF provides a comprehensive physics package to investigate the interactions between non-Maxwellian ions with finite orbit and FW. ORBIT-RF coupled with TORIC4 wave fields using a single dominant toroidal and poloidal Fourier mode reproduces qualitatively experimental observations in both \hbox{C-Mod} and \hbox{DIII-D}. This suggests that ORBIT-RF may be used to predictively model the interactions of rf-induced non-Maxwellian ion distribution with FW. To study the contributions of multiple poloidal modes, we will couple the full wave code AORSA to ORBIT-RF to evaluate rf-induced changes in perpendicular energy. [Preview Abstract] |
Monday, October 24, 2005 12:06PM - 12:18PM |
BO3.00014: NTM Stabilization With Optimal ECCD Alignment in DIII-D R.J. La Haye A key focus of the DIII-D program is establishing the basis for electron cyclotron current drive stabilization of neoclassical tearing modes in ITER. In the recent campaign, important issues evaluated include: (1) the effectiveness of island suppression as a function of the width of the ECCD and alignment of the ECCD with respect to the island location, (2) real-time compensation for the effect of refraction on the ECCD absorption location, and (3) preemptive ECCD for avoiding either the $m/n=3/2$ or $m/n=2/1$ mode. With preemptive ECCD, stable operation up to the free boundary beta limit was achieved without the $m/n=2/1$ NTM becoming unstable. A key element for the success of ECCD in NTM elusion at higher beta is the use of real-time Motional Stark Effect EFIT reconstructions to accurately locate rational surfaces to keep the ECCD aligned without a mode. Plans for the upcoming campaign will also be presented. [Preview Abstract] |
Monday, October 24, 2005 12:18PM - 12:30PM |
BO3.00015: Upgrades to the DIII-D Facility during the Long Torus Opening Activities Period in FY05-06 J.F. Tooker, P.I. Petersen During FY05 and FY06 the DIII-D facility has put its normal two periods for construction, refurbishment and maintenance back to back in order to establish a sufficiently long period to make major hardware upgrades. These upgrades, which are driven by physics needs, include modifying the lower divertor, rotating one of the existing four neutral beam lines, and adding three 1 MW long pulse gyrotrons. The new lower divertor will allow pumping of high triangularity plasmas needed to study the ultimate performance of highly shaped plasmas. There are several motivations for rotating one of the neutral beam lines: the physics of plasma rotation, QDB regime with central co-rotation, RWM stability with low rotation, etc. The long pulse gyrotrons will replace the aging short pulse Russian gyrotrons. In addition to these high priority tasks, we will start upgrade of the toroidal coil return bus and upgrade and modernize the infrastructure, which includes replacing two cooling towers and installing a new high voltage transformer for the auxiliary heating systems. [Preview Abstract] |
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