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 PO4: Research in Support of ITER |
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Chair: Gary Taylor, Princeton Plasma Physics Laboratory Room: Plaza D |
Wednesday, November 13, 2013 2:00PM - 2:12PM |
PO4.00001: The ITER Integrated Modelling Programme Simon Pinches A major element of the ITER Physics Research Programme is the establishment of an integrated modelling programme, including benchmarking and validation activities. The overall aims of this programme are to meet the initial needs of the ITER project for more accurate predictions of ITER fusion performance and for efficient control of ITER plasmas, to support the preparation for ITER operation and, in the longer term, to provide the modelling and control tools required for the ITER exploitation phase. The Integrated Modelling {\&} Analysis Suite (IMAS) is expected to evolve toward a more self-consistent description as the ITER Research Programme progresses. This will require the coupling of diverse spatial and temporal scales, and the dynamic coupling of physics models relevant in each domain. An initial application for prototyping the IM infrastructure and developing the tools required for pulse preparation is the capability to undertake co-simulations involving a Plasma Simulator and the Plasma Control System Simulation Platform. The present status of the IM infrastructure will be presented together with the plans for future development. \textit{The views and opinions expressed herein do not necessarily reflect those of the ITER Organization}. [Preview Abstract] |
Wednesday, November 13, 2013 2:12PM - 2:24PM |
PO4.00002: DIII-D Support for ITER DMS Selection and Design J.C. Wesley DIII-D provides unique capabilities for experiments and model validation activities needed for the ITER Disruption Mitigation System (DMS). Research focuses on three key physics issues: 1) benign thermal energy (TE) disposition followed by current quench (CQ) control, 2) runaway electron (RE) avalanche avoidance, and 3) control and benign dissipation of established RE beams. DIII-D possesses numerous injector technologies, allowing comparison of the suitability of massive gas injection (MGI) and shattered pellet injection (SPI) (primary ITER DMS options), as well as shell pellet injection, for accomplishing the above physics objectives. DIII-D results have already shown the separate feasibility of TE mitigation and CQ control. Measurements of RE dissipation indicate significant anomalous loss mechanisms, providing a possible path for RE suppression. The evolution of controlled RE plateaus indicates the beam/wall interaction is benign until a critical minor radius is reached. Integrated ITER TE/CQ and radiation-symmetry requirements are being studied with toroidally and poloidally separated MGI valves. RE avalanche avoidance by SPI will be investigated. RE dissipation studies will be extended to elongated plasmas to assess RE control and dissipation in ITER. [Preview Abstract] |
Wednesday, November 13, 2013 2:24PM - 2:36PM |
PO4.00003: Radiation asymmetry and MHD activity in gas jet rapid shutdowns on Alcator C-Mod Geoffrey Olynyk, Robert Granetz, Dennis Whyte Radiative rapid shutdown via massive noble gas injection (MGI) is an integral part of the ITER disruption mitigation system (DMS). However, observations have shown that the radiation during MGI rapid shutdowns may be spatially asymmetric, particularly during the initial phase when the plasma's thermal energy is converted to radiation. ITER requires the radiation peaking factor (PF) to be less than approximately 2.0 to 2.5 in this thermal quench (TQ) phase in order to prevent melting of the beryllium wall even in the case of a successful MGI rapid shutdown. We report on observations of rotating MHD modes in single- and multiple-gas-jet rapid shutdowns on Alcator C-Mod, and discuss the role of mode rotation during the TQ in setting the radiation peaking factor. The implications for the ITER DMS are discussed. [Preview Abstract] |
Wednesday, November 13, 2013 2:36PM - 2:48PM |
PO4.00004: Status of US ITER Diagnostics B. Stratton, L. Delgado-Aparicio, K. Hill, D. Johnson, N. Pablant, R. Barnsley, G. Bertschinger, M.F.M. De Bock, R. Reichle, V.S. Udintsev, C. Watts, M. Austin, P. Phillips, P. Beiersdorfer, T.M. Biewer, G. Hanson, C.C. Klepper, T. Carlstrom, M.A. Van Zeeland, D. Brower, E. Doyle, A. Peebles, R. Ellis, F. Levinton, H. Yuh The US is providing 7 diagnostics to ITER: the Upper Visible/IR cameras, the Low Field Side Reflectometer, the Motional Stark Effect diagnostic, the Electron Cyclotron Emission diagnostic, the Toroidal Interferometer/Polarimeter, the Core Imaging X-Ray Spectrometer, and the Diagnostic Residual Gas Analyzer. The front-end components of these systems must operate with high reliability in conditions of long pulse operation, high neutron and gamma fluxes, very high neutron fluence, significant neutron heating (up to 7 MW/m$^{3})$, large radiant and charge exchange heat flux (0.35MW/m$^{2})$, and high electromagnetic loads. Opportunities for repair and maintenance of these components will be limited. These conditions lead to significant challenges for the design of the diagnostics. Space constraints, provision of adequate radiation shielding, and development of repair and maintenance strategies are challenges for diagnostic integration into the port plugs that also affect diagnostic design. The current status of design of the US ITER diagnostics is presented and R{\&}D needs are identified. [Preview Abstract] |
Wednesday, November 13, 2013 2:48PM - 3:00PM |
PO4.00005: ICRF Compatibility with Metallic PFCs: Implications for ITER S.J. Wukitch, D. Brunner, M.L. Garrett, A. Hubbard, B. Labombard, Y. Lin, B. Lipschultz, D. Miller, R. Ochoukov, M.L. Reinke, J.L. Terry Application of ion cyclotron range of frequency (ICRF) heating remains a major challenge in devices with metallic plasma facing components (PFCs) due to impurity contamination and enhanced heat loads. For standard ICRF antennas, where the antenna straps are aligned to the toroidal magnetic field, core impurity contamination in devices with all high Z metal PFCs [C-Mod, AUG] and devices with a mixture of low and high Z PFCs has been observed.[JET] The Impurity contamination, both sources and transport, and enhanced heat loads are thought to linked to RF electric fields parallel to the magnetic field, E\textbar \textbar . One means to minimize E\textbar \textbar is through geometry: field align the ICRF antenna where the antenna straps and antenna box are perpendicular to the total magnetic field. Initial results confirm that the field aligned antenna has reduced impurity source at the antenna, reduced impurity contamination, reduced RF enhanced heat flux to the antenna, and is more load tolerant than a standard ICRF antenna. Another approach to mitigate impurity contamination utilizes low Z impurity seeding, ie. nitrogen or neon. The core high Z impurity contamination and the RF enhanced plasma potential are reduced with seeding. Finally, an emerging explanation for the presence of far field sheaths, fast wave field converting to slow wave field at conducting surfaces where the magnetic field is at an oblique angle, will be presented and its implication for ITER discussed. [Preview Abstract] |
Wednesday, November 13, 2013 3:00PM - 3:12PM |
PO4.00006: Development of the Q$=$10 Scenario for ITER on ASDEX Upgrade Josef Schweinzer, Arne Kallenbach, Peter Lang, Joerg Stober, Wolfgang Suttrop, Hartmut Zohm The development of the baseline H-mode scenario foreseen for ITER on the ASDEX Upgrade tokamak, i.e. discharges at q$_{95}=$3, relatively low $\beta_{\mathrm{N}}$, high normalized density n/n$_{\mathrm{GW}}$ and high triangularity $\delta =$0.4, has been focused on the integration of elements foreseen for ITER and readily available on ASDEX Upgrade, such as ELM suppression with RMPs and pellets in combination with a metallic wall. Values for density and energy confinement came simultaneously close to the requirements of the ITER baseline scenario as long as $\beta _{\mathrm{N}}$ stayed above 2. However, it has been found that stationary discharges are not easily achieved under these conditions due to the low natural ELM frequency occurring at the low q$_{95}$ / high $\delta $ operational point. ELM parameters are not always controllable with the tools developed in other scenarios. We will point out the challenges and a possible route for a reliable Q$=$10 scenario on ITER as well as studies on alternative operational points at higher $\beta_{\mathrm{N}}$ and q$_{95}$, relying on the ``improved H-mode'' scenario and increased n/n$_{\mathrm{GW}}$. [Preview Abstract] |
Wednesday, November 13, 2013 3:12PM - 3:24PM |
PO4.00007: Impact of the Radiating Divertor Approach on Future Tokamaks T.W. Petrie, A.W. Leonard, T.C. Luce, F. Turco, S.L. Allen, M.E. Fenstermacher, C.T. Holcomb, C.J. Lasnier, R.A. Moyer, J.G. Watkins We report on recent results that apply the deuterium/neon-based radiating divertor approach to three future tokamak concepts: (1) ITER Baseline plasmas, (2) AT high performance plasmas, and (3) H-mode plasmas that are isolated from their divertor targets (Super X-like). Analysis of H-mode plasmas in the ITER Baseline shape, characterized by $q_{95}=3.15$, $I/aB=1.4$, $\beta_N=2$ in the ITER shape, indicates significant a heat flux reduction ($\sim$2.5x) during both ELMing and between ELM periods and a factor of two increase in radiated power, almost all of which occurs in the divertor/SOL regions. Radiating divertor applied to AT plasmas (e.g., $\beta_N=3$ and $H_{89p}=2.4$) is shown to reduce heat flux at least 30\%, while at the same time maintaining high performance characteristics. We present our most recent results of studies designed to assess the value of increasing parallel connection length ($L_{||}$) of the outer divertor leg in a radiating divertor environment. Previous experiments have suggested that significant heat flux reduction at the OSP can be possible by increasing $L_{||}$. [Preview Abstract] |
Wednesday, November 13, 2013 3:24PM - 3:36PM |
PO4.00008: 3D modeling of toroidal asymmetry due to localized divertor nitrogen puffing on Alcator C-Mod J.D. Lore, M.L. Reinke, B. LaBombard, B. Lipschultz, R. Pitts For inductive operation at Q$=$10, ITER will need to run with partially detached divertor plasmas in order to maximize target lifetime and remain below engineering heat-flux limits. The radiated power fraction will be controlled via a divertor gas injection system that consists of six valves. To investigate the effect of potential toroidal asymmetry introduced by a finite number of gas valves, or the failure of one or more valves, experiments were performed on Alcator C-Mod. Nitrogen was injected through each of five toroidally spaced divertor gas valves into Ohmic L-mode plasmas with a high recycling divertor. Clear, reproducible toroidal variation in divertor radiated power and impurity line radiation was measured. The 3D scrape-off-layer transport code EMC3-EIRENE [1] is being used to model and interpret these experiments. Initial results indicate that trends in the radiated power and nitrogen emission asymmetry are reproduced. Both experimental and modeling results will be presented. \\[4pt] [1] Y. Feng, et al, J. Nucl. Mater. 266, 812 (1999). [Preview Abstract] |
Wednesday, November 13, 2013 3:36PM - 3:48PM |
PO4.00009: KSTAR contributions to ITER long-pulse operations Jinseok Ko The achievements made by the Korea Superconducting Tokamak Advanced Research (KSTAR) for the last couple of years are noticeable with respect to the ITER-relevant studies. Some include the long-pulse H-mode (15 sec), ELM suppression by RMP (with either n $=$ 1 or n $=$ 2), high normalized beta (2.9) with low li (0.7) exceeding the n $=$ 1 no-wall limit, and the advanced scenarios with early diverted, sawtooth-free internal transport barriers. Along the path of exploring ITER urgent issues, progresses in longer-pulse (more than 20 sec) H-mode operations, disruption detection and mitigation techniques, utilization of the non-axisymmetric magnetic perturbation for the rotation control as well as physics understanding of ELM responses are underway. KSTAR also embraces several ITER prototype techniques such as 170 GHz ECH, Thomson laser, and plasma control by density feedback. [Preview Abstract] |
Wednesday, November 13, 2013 3:48PM - 4:00PM |
PO4.00010: Heating and current drive requirements towards steady state operation in ITER Francesca Poli, Charles Kessel, Paul Bonoli, Donald Batchelor, Bob Harvey Steady state scenarios envisaged for ITER aim at optimizing the bootstrap current, while maintaining sufficient confinement and stability. Non-inductive scenarios will need to operate with Internal Transport Barriers (ITBs) to reach adequate fusion gain at typical currents of 9 MA. Scenarios are established as relaxed flattop states with time-dependent transport simulations with TSC. The $E\times B$ flow shear from toroidal plasma rotation is expected to be low in ITER, with a major role in the ITB dynamics being played by magnetic geometry. Combinations of external sources that maintain weakly reversed shear profiles and $\rho(q_{min})\ge0.5$ are the focus of this work. Simulations indicate that, with a trade-off of the EC equatorial and upper launcher, the formation and sustainment of ITBs could be demonstrated with the baseline configuration. However, with proper constraints from peeling-ballooning theory on the pedestal width and height, the fusion gain and the maximum non-inductive current (6.2MA) are below the target. Upgrades of the heating and current drive system, like the use of Lower Hybrid current drive, could overcome these limitations. With 30MW of coupled LH in the flattop and operating at the Greenwald density, plasmas can sustain $\sim9$MA and achieve $Q\sim4$. [Preview Abstract] |
Wednesday, November 13, 2013 4:00PM - 4:12PM |
PO4.00011: ELM Mitigation Using Pellet Injection and Plans for ITER L.R. Baylor, N. Commaux, S.J. Meitner, D.A. Rassmussen, C.J. Lasnier, M.E. Fenstermacher, S.L. Allen, A.W. Leonard, T.H. Osborne, P.B. Parks, R.A. Moyer, A. Loarte, G. Huijsmans, S. Maruyama D$_2$ pellet injection has been used on the DIII-D tokamak to demonstrate the triggering of edge localized modes (ELMs) at a 12x higher rate with much smaller intensity than natural ELMs [1]. The triggering of small ELMs by pellet injection has been proposed as a method to prevent large ELMs that can erode the ITER plasma facing components. The demonstration was made by injecting slow ($<$200~m/s) 1.3 mm diameter deuterium pellets at up to 60 Hz from the low field side in an ITER similar plasma with 5 Hz natural ELMs resulting in total and peak divertor heat flux reduction by more than 90\%. New experiments with smaller pellets and higher rep rates are underway. Determining the minimum size perturbation and the resulting heat flux pattern in the divertor are the subject of these new experiments. The implications of these results for pellet ELM mitigation in ITER and the design of the pellet injection system for ITER will be discussed.\par \vskip6pt \noindent [1] L.R.\ Baylor et al., Phys.\ Rev.\ Lett.\ {\bf 110}, 245001 (2013). [Preview Abstract] |
Wednesday, November 13, 2013 4:12PM - 4:24PM |
PO4.00012: 3D Perturbed Equilibria and ELM Suppression in DIII-D and Implications for ITER N.M. Ferraro, T.E. Evans, R. Nazikian Non-axisymmetric perturbed equilibria are calculated for a series of DIII-D discharges in which 3D magnetic perturbations were applied, with the goal of gaining insight into the mechanism of resonant magnetic perturbation edge localized mode (ELM) suppression by identifying features of the 3D equilibria that are correlated with ELM suppressed states. Perturbed equilibria are also calculated for several 15 MA ITER scenarios in order to evaluate the extent to which these suppression-correlated features are expected to be attainable with the proposed internal coils in ITER. The equilibria are calculated with the M3D-C1 code, which implements a linear two-fluid model that includes experimentally realistic values of resistivity, rotation, and diamagnetic effects. Finally, nonlinear calculations are carried out with M3D-C1 to investigate the direct interaction between low-n applied fields and moderate-n peeling-ballooning modes. [Preview Abstract] |
Wednesday, November 13, 2013 4:24PM - 4:36PM |
PO4.00013: Conceptual Design of the ITER Plasma Control System J.A. Snipes The conceptual design of the ITER Plasma Control System (PCS) has been approved and the preliminary design has begun for the 1$^{\mathrm{st}}$ plasma PCS. This is a collaboration of many plasma control experts from existing devices to design and test plasma control techniques applicable to ITER on existing machines. The conceptual design considered all phases of plasma operation, ranging from non-active H/He plasmas through high fusion gain inductive DT plasmas to fully non-inductive steady-state operation, to ensure that the PCS control functionality and architecture can satisfy the demands of the ITER Research Plan. The PCS will control plasma equilibrium and density, plasma heat exhaust, a range of MHD instabilities (including disruption mitigation), and the non-inductive current profile required to maintain stable steady-state scenarios. The PCS architecture requires sophisticated shared actuator management and event handling systems to prioritize control goals, algorithms, and actuators according to dynamic control needs and monitor plasma and plant system events to trigger automatic changes in the control algorithms or operational scenario, depending on real-time operating limits and conditions. [Preview Abstract] |
Wednesday, November 13, 2013 4:36PM - 4:48PM |
PO4.00014: Novel Aspects of Plasma Control in ITER D.A. Humphreys, M.L. Walker, G. Ambrosino, J. Lister, W. Treutterer, J. Snipes, A. Winter ITER will place uniquely high demands on performance and reliability of plasma control, yet with constrained actuators and limited opportunity to tune algorithms. For example, divertor and core radiation must be regulated to minimize target heat flux. Plasma burn state must be controlled to achieve the $Q=10$ mission and minimize disruptivity. Performance-limiting instabilities such as tearing modes must be robustly stabilized through regulation of current profile characteristics, control of sawteeth and error fields, or active ECCD suppression. Satisfying these and other control goals requires advances in both physics understanding and model-based control mathematics solutions. For example, control of proximity to tearing limits requires improved understanding of resistive stability physics to identify key profile control parameters and produce models for control design. Ensuring robust control performance relies on advances in model-based algorithm design. We describe selected plasma control challenges for ITER, highlighting novel aspects and needs for improved understanding in both physics and control mathematics. [Preview Abstract] |
Wednesday, November 13, 2013 4:48PM - 5:00PM |
PO4.00015: Error Field Detection and Mode Locking Avoidance by the Interaction of Applied Rotating 3D Fields With Otherwise Locked Modes D. Shiraki, K.E.J. Olofsson, F.A. Volpe, R.J. La Haye, E.J. Strait, C. Paz-Soldan, N. Logan, M. Okabayashi The resonant interaction of locked modes (LMs) with non-axisymmetric magnetic fields is used to control the toroidal phase of LMs in DIII-D, with applications to error field (EF) detection as well as to disruption avoidance. The measured toroidal dynamics of LMs in the presence of rotating $n=1$ perturbations is understood by modeling the resonant torques applied by the coils. This technique is applied to EF detection, where the island dynamics is interpreted as satisfying a torque balance between the EF and applied perturbation. The optimal correction currents are inferred to be those which best cancel the EF torque. This optimization of EF correction is completed in a single discharge, without restriction to low-density. The technique is promising for initial ITER operation, when lack of full auxiliary heating systems make existing techniques based on rotation or plasma amplification unsuitable. The ability to control the toroidal phase of magnetic islands with rotating 3D fields was also used to control and sustain the rotation of decelerating islands to prevent locking. [Preview Abstract] |
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