Bulletin of the American Physical Society
57th Annual Meeting of the APS Division of Plasma Physics
Volume 60, Number 19
Monday–Friday, November 16–20, 2015; Savannah, Georgia
Session TO6: Research in Support of ITER |
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Chair: Amanda Hubbard, Massachusetts Institute of Technology Room: 201/202 |
Thursday, November 19, 2015 9:30AM - 9:42AM |
TO6.00001: ITER Plasma Control System Development Joseph Snipes The development of the ITER Plasma Control System (PCS) continues with the preliminary design phase for 1$^{\mathrm{st}}$ plasma and early plasma operation in H/He up to I$_{\mathrm{p}}=$15 MA in L-mode. The design is being developed through a contract between the ITER Organization and a consortium of plasma control experts from EU and US fusion laboratories, which is expected to be completed in time for a design review at the end of 2016. This design phase concentrates on breakdown including early ECH power and magnetic control of the poloidal field null, plasma current, shape, and position. Basic kinetic control of the heating (ECH, ICH, NBI) and fueling systems is also included. Disruption prediction, mitigation, and maintaining stable operation are also included because of the high magnetic and kinetic stored energy present already for early plasma operation. Support functions for error field topology and equilibrium reconstruction are also required. All of the control functions also must be integrated into an architecture that will be capable of the required complexity of all ITER scenarios. A database is also being developed to collect and manage PCS functional requirements from operational scenarios that were defined in the Conceptual Design with links to proposed event handling strategies and control algorithms for initial basic control functions. A brief status of the PCS development will be presented together with a proposed schedule for design phases up to DT operation. [Preview Abstract] |
Thursday, November 19, 2015 9:42AM - 9:54AM |
TO6.00002: Nonlinear Control and Online Optimization of the Burn Condition in ITER Eugenio Schuster, Mark D. Boyer, Andres Pajares-Martinez Regulation of the fusion power through modulation of fueling, external heating sources and non-axisymmetric magnetic fields, referred to as burn control, is one of the fundamental problems in burning plasma research. Active control will be essential for achieving and maintaining desired operating points, responding to changing power demands, and ensuring stable operation in ITER. A volume-averaged nonlinear model for the evolutions of the density of energy, deuterium and tritium fuel ions, alpha-particles, and impurity ions has been used to synthesize a multi-variable nonlinear burn control strategy that can reject large perturbations and move between operating points. The control approach makes use of the different possible actuators for altering the fusion power, including auxiliary heating sources, isotopic fueling, in-vessel coils, and impurity injection. Adaptive control techniques are used to account for uncertainty in model parameters, including particle confinement times and recycling rates. Furthermore, a model-based constrained optimization scheme is proposed to drive the system as close as possible to desired fusion power and temperature references. [Preview Abstract] |
Thursday, November 19, 2015 9:54AM - 10:06AM |
TO6.00003: Sawtooth period control by power modulation Menno Lauret, Eugenio Schuster, Marco de Baar, Federico Felici, Maurice Heemels, Alexander Gomes, Tim Goodman, Doohyun Kim, Olivier Sauter, Gerd Vandersteen, Gert Witvoet, Morten Lennholm It is foreseen that long sawtooth oscillations will occur during ITER H-mode scenarios leading to confinement loss and even disruptions. Sawtooth period control is therefore crucial. Most sawtooth period control approaches depend on changing the deposition location of electron-cyclotron current drive (ECCD) near r(q$=$1). In contrast to this, several TCV and AUG experiments with fixed ECCD deposition location show that ECCD power modulation, either periodic or feedback controlled, can lead to fast and reliable period control. To understand this nonlinear phenomenon, a reduced and `hybrid' reset model has been derived that models the nonlinear dynamics. Analysis reveals that the sawtooth period can be controlled by power modulation, even in the case of significant model uncertainties or when there is a significant lengthening effect of the fast particles on the sawtooth period, as there will be in ITER. The model can also be used to design period control using ICRH influencing this fast particle effect. [Preview Abstract] |
Thursday, November 19, 2015 10:06AM - 10:18AM |
TO6.00004: Risk mitigation for ITER by a prolonged and joint international operation of JET Antonius J. Donne, Steve Cowley, Timothy Jones, Xavier Litaudon Prolonged operation of the Joint European Torus (JET) in a set-up involving all ITER partners will be beneficial for ITER. Experiments at JET with its ITER-like wall and using a D-T plasma mixture will help to mitigate risks in the ITER research plan. Training of the ITER operators, technicians and engineers at JET will save valuable time when ITER comes into operation. Moreover, the way in which the future ITER experiments will be organized can already be experienced at JET, by imposing a similar organisational structure. This paper will present arguments in favour of an extension of JET and additionally briefly discuss a number of enhancements that will make experiments on JET even more relevant for ITER. [Preview Abstract] |
Thursday, November 19, 2015 10:18AM - 10:30AM |
TO6.00005: Testing RMP ELM suppression models in low torque ITER Baseline Scenario R.A. Moyer, N.M. Ferraro, R.J. Groebner, R.J. La Haye, T.C. Luce, T.H. Osborne, C. Paz-Soldan, B.A. Grierson, R. Nazikian, W.M. Solomon, T.L. Rhodes, L. Zeng, G.R. McKee, Z. Yan, J.M. Hanson, F. Turco, S. Mordijck, M.E. Fenstermacher RMP ELM suppression experiments in low torque ($T_{inj}$) ITER Baseline Scenario provide an excellent test of our emerging model of ELM suppression when the edge plasma bifurcates to tearing response. In 2-fluid theory, this bifurcation occurs where the electron perpendicular rotation $\Omega_{\bot e}\sim0$, where $\Omega_{\bot e}$ is the sum of the $E\times B$ and electron diamagnetic rotation $\Omega_{D e}$ frequencies. To extend RMP ELM suppression to $T_{inj}\sim1$ Nm, we reduced $T_{inj}$ from 5 to 3.5 Nm, which produced lower core radial electric field and loss of ELM suppression as the $\Omega_{\bot e}\sim0$ point moved deeper into the core. We also varied $\Omega_{D e}$ at high $T_{inj}$ by reducing the edge electron density, which led to ELM suppression. These results will be compared with expectations from 2-fluid theory. [Preview Abstract] |
Thursday, November 19, 2015 10:30AM - 10:42AM |
TO6.00006: Advances in ELM control towards long-pulse H-mode plasmas on EAST Guosheng Xu Several ELM control techniques have been developed on EAST recently. ELM pacing by short pulses of LHCD has been demonstrated. The delay time between the triggered ELM and the pulse rising edge is 1-5 ms which decreases with increasing power. ELM mitigation with n$=$1 Resonant Magnetic Perturbations has been observed. The ELM frequency increases by a factor of 5 and the amplitude is reduced by the same factor. Footprint splitting is observed in both static and rotating field cases and agrees well with vacuum modeling. Small-ELM regime with enhanced Dalpha emission and strong edge coherent mode (ECM) has been achieved with different combination of heating schemes. Its parameter space was extended to lower q95$=$4 in the last campaign. Long-pulse stationary ELM-free H-mode plasmas have been achieved by using continuous real-time lithium-aerosol injection which appears to enhance the ECM. Without lithium-aerosol injection, stationary ELM-free plasmas were achieved only with 4.6GHz LHCD alone. In addition, ELM pacing by lithium granule injection up to 180Hz has been demonstrated on EAST. [Preview Abstract] |
Thursday, November 19, 2015 10:42AM - 10:54AM |
TO6.00007: ELM-induced W sputtering sources in JET S. Brezinsek, N. den Harder, C. Guillemaut JET equipped with Be wall and W divertor showed after one year of operation intact W surfaces at the target plates. Eroded W from both divertor legs contributes to the total W source and content in the plasma. Detailed analysis of the intra-ELM and inter-ELM W source in H-mode discharges has been carried out using spectroscopy of W, D and Be emission and, independently, using ECE and LP to determine respectively the ion impact energies and fluxes to the target plate. The inter-ELM W source can be eliminated in detached conditions due to impact energies below the sputtering threshold, leaving the intra-ELM source to be the dominant one (80{\%}). Comparison between inner and outer divertor showed that both sources are comparable in the intra-ELM phase. Dedicated composition analysis reveals that sputtering by Be ions can account for the residual inter-ELM source, but cannot explain the intra-ELM source due to the low Be concentration in the plasma (1{\%}). D$+$ with energies above 1keV dominate the intra-ELM W sputtering whereas in the inter-ELM phase energies of D$+$ are below the threshold. These energetic ions are transported from the pedestal region to the target plate during ELM excursion. The W source and content as function of the ELM frequency and ion impact energy has been studied for a set of plasmas showing initially a linear increase before decoupling due to ELM-flushing of W from the confined region sets in at about 40Hz. The range of ELM frequencies in JET covers the frequencies predicted for the ITER H-mode baseline scenarios with ELM pacing and detached inter-ELM phase. The W source in ITER will be determined by the intra-ELM phase. [Preview Abstract] |
Thursday, November 19, 2015 10:54AM - 11:06AM |
TO6.00008: Application of Pellet Injection to Mitigate Transient Events in ITER Larry Baylor The injection of cryogenic pellets has been shown to be useful for mitigation of ELMs and disruptions, which are potentially damaging transient events that can to lead to reduced operating time in ITER. The triggering of small ELMs by pellets has been demonstrated as a method to prevent large ELMs that can erode plasma facing components [1]. D$_{2}$ pellets \textless 3mm in size are planned for ITER to trigger ELMs at higher rates than they will naturally occur. Injection of multiple large pellets \textgreater 25mm in size of neon, argon, and D$_{2}$ mixtures are planned to mitigate disruptions. Shattered pellets have been shown to successfully mitigate thermal and current quenches in DIII-D with higher assimilation than massive gas injection [2]. A flexible multi-barrel system for shattered pellet injection is now being designed for disruption mitigation in ITER. The technology and the physics of the pellet plasma interactions for these systems on ITER will be discussed. \\[4pt] [1] L.R. Baylor \textit{et al}., \textit{Phys. Rev. Lett.} 245001 (2013)\\[0pt] [2] N. Commaux \textit{et al}., submitted for publication. [Preview Abstract] |
Thursday, November 19, 2015 11:06AM - 11:18AM |
TO6.00009: Disruption Mitigation of Plasmas with Locked Modes R. Granetz, A. Tinguely, I. Faust, T. Golfinopoulos, A. Kuang, M.L. Reinke Disruption mitigation using massive gas injection (MGI) has been studied in a number of tokamaks, and has been shown to be very successful. But these studies have been done by using MGI to trigger disruptions of stable plasmas. In actuality, active disruption mitigation in ITER will be used on plasmas that are experiencing warning signs of an impending disruption, such as NTMs, locked modes, etc. ITER has requested that experiments using MGI on such plasmas be carried out to gauge its effectiveness compared to MGI on stable plasmas. On Alcator C-Mod, we use a set of external coils to apply m=2/n=1 error fields in order to controllably generate locked modes. MGI has been used on these MHD-unstable plasmas, and compared to MGI on similar plasmas without locked modes. We find no significant differences in any mitigation-relevant parameters, including fraction of energy converted to radiation, energy deposition to the divertor, extent of vertical motion, halo current, n=1 MHD activity, or degree of Prad asymmetry. We conclude that MGI works equally well on plasmas with and without locked modes. [Preview Abstract] |
Thursday, November 19, 2015 11:18AM - 11:30AM |
TO6.00010: Effect of thick blanket modules on neoclassical tearing mode locking in ITER R.J. La Haye, C. Paz-Soldan, Y. Liu m/n=2/1 tearing modes can be slowed and stop rotating (lock) by eddy currents induced in resistive walls, a particular issue in ITER with large inertia and low applied torque. Previous estimates of tolerable 2/1 island widths in ITER, based on a forecast of initial island rotation, the n=1 resistive penetration time of the $\it{inner} {vacuum} {vessel}$ wall and benchmarked to DIII-D high-torque plasmas, found that the ITER ECCD system could catch and subdue such islands before they persisted long and grew large enough to lock. However, rotating tearing modes in ITER will also induce eddy currents in the $\it{blanket}$ as the effective first wall that can shield the inner vessel. The closer fitting blanket wall has a much shorter time constant and will allow several times smaller islands to lock several times faster in ITER. Recent DIII-D ITER baseline scenario plasmas with low-applied torque allow better modeling and scaling to ITER with the blanket as the first resistive wall. This motivates using the ITER ECCD system in a CW preemptive operation of as little as a well-aligned 3 MW to avoid destabilizing the 2/1 NTM. [Preview Abstract] |
Thursday, November 19, 2015 11:30AM - 11:42AM |
TO6.00011: Predictive modelling of the impact of a radiative divertor on pedestal confinement on ASDEX Upgrade Mike Dunne, Steffen Potzel, Marco Wischmeier, Elisabeth Wolfrum, Lorenzo Frassinetti, Felix Reimold In future devices, tailoring of the edge density profile and radiation profile for power exhaust control via a deuterium gas puff and extrinsic impurity seeding will be necessary. It has been observed on present day machines that high D fuelling can reduce the plasma stored energy while adding impurity seeding can act to improve confinement by up to 40{\%}. This study presents a combination of observations and modelling completed on AUG with the aim of determining the mechanisms behind the confinement degradation with a gas puff and improvement with impurity seeding. In particular, predictive modelling, based on the EPED pedestal model, has been extensively used. Alterations of the temperature and density at the separatrix are found to have large impacts on pedestal stability. Measured changes in divertor properties are used to inform the direction and magnitude of these alterations, with experimentally relevant confinement changes being recovered via pressure profile shifts. [Preview Abstract] |
Thursday, November 19, 2015 11:42AM - 11:54AM |
TO6.00012: Time Dependent Predictive Modeling of DIII-D ITER Baseline Scenario using Predictive TRANSP B.A. Grierson, R.G. Andre, R.V. Budny, W.M. Solomon, X. Yuan, J. Candy, R.I. Pinsker, G.M. Staebler, C. Holland, T. Rafiq ITER baseline scenario discharges on DIII-D are modeled with TGLF and MMM transitioning from combined ECH (3.3MW)$+$NBI(2.8MW) heating to NBI only (3.0 MW) heating maintaining $\beta_{\mathrm{N}}=$2.0 on DIII-D predicting temperature, density and rotation for comparison to experimental measurements. These models capture the reduction of confinement associated with direct electron heating H$_{\mathrm{98y2}}=$0.89 vs. 1.0) consistent with stiff electron transport. Reasonable agreement between experimental and modeled temperature profiles is achieved for both heating methods, whereas density and momentum predictions differ significantly. Transport fluxes from TGLF indicate that on DIII-D the electron energy flux has reached a transition from low-k to high-k turbulence with more stiff high-k transport that inhibits an increase in core electron stored energy with additional electron heating. Projections to ITER also indicate high electron stiffness. [Preview Abstract] |
Thursday, November 19, 2015 11:54AM - 12:06PM |
TO6.00013: Status of the ITER plasma modeling activities in JAEA Junya Shiraishi, Mitsuru Honda, Nobuhiko Hayashi, Nobuyuki Aiba, Mitsunori Toma, Akinobu Matsuyama, Osamu Naito, Yoshiaki Miyata, Shizuo Inoue, Emi Narita, Katsuhiro Shimizu, Kiyotaka Hamamatsu, Shunsuke Ide, Masatoshi Yagi JAEA has been contributing to the ITER plasma modeling in a wide range of research areas. Among them we report recent integrated modeling activities in JAEA. The integrated modeling is indispensable for predictive simulations of autonomous ITER plasmas, which exhibit multi-physics nature. JAEA has been developing an integrated modeling code, the TOPICS suite. The TOPICS suite has been incorporating many physics factors to enhance its prediction capability and has delivered many important findings on ITER plasm. A recent achievement is the success of predictive simulation of toroidal rotation in ITER [1]. The TOPICS suite has been coupled with the 3D equilibrium code VMEC and the 3D drift-kinetic solver FORTEC-3D to compute the NTV, the radial electric field, and the resultant toroidal rotation self-consistently. Another achievement is the quantitative estimate of reduction of ELM energy loss by pellet injection in ITER [2]. The TOPICS suite has been coupled with a new pellet model and with the MHD stability code MARG2D to calculate finite-n modes for modeling the ELM-enhanced diffusivities.\\[4pt] [1] M. Honda et al., Nucl. Fusion 55, 073033 (2015).\\[0pt] [2] N. Hayashi et al., Contrib. Plasma Phys. 54, 599 (2014). [Preview Abstract] |
Thursday, November 19, 2015 12:06PM - 12:18PM |
TO6.00014: The Impact of Zonal Flows on the Performance Predictions for ITER G.M. Staebler, J. Candy Gyrokinetic turbulence simulations of the core of ITER with the GYRO code have found that the zonal fluctuations produce a significant upshift of the effective critical gradient and a reduction in the stiffness of the energy transport. These results are consistent with previous work on the Dimits shift regime.\footnote{A. M. Dimits, et al., Phys. Rev. Lett. 77 (1996) 71.} These Dimits shift effects are not included in the quasilinear transport model TGLF. Here we report on a model for the Dimits shift effects that has been developed for TGLF and calibrated with GYRO turbulence simulations. The positive impact of the Dimits shift on the TGLF predictions for ITER performance are reported. The model used in TGLF is based on the predator-prey model\footnote{P. H. Diamond, et al., 2005 Plasma Phys. Control. Fusion 47 (2005) R35} of the saturation of the turbulence. With simple assumptions about the nature of the non-linear damping of zonal fluctuations, the Dimits shift regime observed in the GYRO simulations can be modeled. [Preview Abstract] |
Thursday, November 19, 2015 12:18PM - 12:30PM |
TO6.00015: Progress in the Design and Development of the ITER Low-Field Side Reflectometer (LFSR) System E.J. Doyle, G. Wang, W.A. Peebles The US has formed a team, comprised of personnel from PPPL, ORNL, GA and UCLA, to develop the LFSR system for ITER. The LFSR system will contribute to the measurement of a number of plasma parameters on ITER, including edge plasma electron density profiles, monitor Edge Localized Modes (ELMs) and L-H transitions, and provide physics measurements relating to high frequency instabilities, plasma flows, and other density transients. An overview of the status of design activities and component testing for the system will be presented. Since the 2011 conceptual design review, the number of microwave transmission lines (TLs) and antennas has been reduced from twelve (12) to seven (7) due to space constraint in the ITER Tokamak Port Plug. This change has required a reconfiguration and recalculation of the performance of the front-end antenna design, which now includes use of monostatic transmission lines and antennas. [Preview Abstract] |
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