Bulletin of the American Physical Society
60th Annual Meeting of the APS Division of Plasma Physics
Volume 63, Number 11
Monday–Friday, November 5–9, 2018; Portland, Oregon
Session UO5: Research in Support of ITER |
Hide Abstracts |
Chair: Francesca Turco, Columbia University Room: OCC B113-114 |
Thursday, November 8, 2018 2:00PM - 2:12PM |
UO5.00001: The new stable ITER Baseline Scenario with zero torque Tim Luce, Francesca Turco The ITER Baseline Scenario has been made passively stable at zero injected torque, obtaining robust operation at q95=3, betaN<=2.1, with and without ECH power. The new results show that a passively stable stationary state exists, and have determined a way to get there, that is non-DIII-D specific. The new recipe is based on the previous study showing that the current profile evolution in the first tauR is crucial for the stability of the disruptive 2/1 modes. The early J evolution was deterministically changed by manipulating the Ip ramp rate, Hmode transition timing, Lmode density. Although ELMs are not the trigger for the 2/1 modes, the pedestal stability is correlated with the core MHD stability, and was optimised by tuning the gas injection. Scans of the interplay between the recipe ingredients show the trade-offs and parameter space that can be achieved. Scans in the EC power injection location show that the early EC deposition location is crucial for maintaining stability, while moving the EC power from the core to the edge leads to significant confinement degradation. |
Thursday, November 8, 2018 2:12PM - 2:24PM |
UO5.00002: Advances in EAST long pulse H-mode experiment and contributions to steady state operation of ITER Xianzu Gong, Juan Huang, Jinping Qian, Erzhong Li, Guosheng Xu, Bingjia Xiao, Baonian Wan, baonian wan, Jiangang Li, Andrea MV Garofalo, Christopher T Holcomb The demonstration of 100 seconds time scale long-pulse steady-state scenario with good plasma performance (H98y2 ~ 1.1) and good control of impurity and heat exhaust with ITER-like tungsten divertor has been successfully achieved on EAST using RF power heating and current drive. This steady-state scenario was characterized by fully non-inductive current drive and high-frequency edge localized modes (ELMs). The operational window has been extended towards a high βPregime with integrated small-ELM (ISE) regime, which is a promising operational regime for future ITER long-pulse operation. Utilizing ECRH yields two significant advantages: a decrease of up to 40% in tungsten concentration in the core plasma, and an increase in the electrons which can resonate with the LH waves, resulting in enhanced current drive when combining ECCD and LHCD. In addition, the reduction of the peak heat flux on the divertor was successfully demonstrated either in a quasi snow-flake (QSF) configuration or exploiting the active radiation feedback control. The experience in and understanding of high-performance long-pulse operation on EAST will be extremely valuable for ITER. |
Thursday, November 8, 2018 2:24PM - 2:36PM |
UO5.00003: Modeling of an "inside out" thermal quench by core deposition of impurities Valerie Izzo MHD simulations support several promising features of shell pellet injection, which aims to deliver a radiating payload directly to the core while minimally perturbing the edge plasma. In practice, the shell pellet method, recently demonstrated on DIII-D, encloses the payload in a low-Z shell that slowly ablates then breaks open in the center of the plasma. Disruption mitigation for ITER must simultaneously meet several criteria for thermal and mechanical loads and runaway electron avoidance, some of which are in tension with one another. For instance, prevention of a runaway electron avalanche may be possible if complete flux surface destruction during the thermal quench de-confines the primary runaway electron population before the secondary avalanche can ensue. But the same flux surface destruction that allows runaway electrons to follow open field lines to the wall may just as easily conduct electron heat to the wall. In the simulations, the high-Z payload is assumed to be delivered directly to the core. The strong core cooling produces an “inside-out” thermal quench that propagates toward the edge, and results in an annular current profile and an increase in total current due to dropping inductance during the thermal quench. Importantly, the flux surfaces also break up from the inside out, with the outermost surfaces remaining intact until the end of the thermal quench, resulting in a very high radiated energy fraction. Nonetheless, once the last closed flux surface is broken, a very rapid loss of test particle runaway electrons is observed. |
Thursday, November 8, 2018 2:36PM - 2:48PM |
UO5.00004: Synchrotron spectra, images, and polarization measurements from runaway electrons in Alcator C-Mod Roy Alexander Tinguely, Robert S Granetz, Mathias Hoppe, Ola Embreus, Tunde Fulop, Steve Scott, Robert T Mumgaard In Alcator C-Mod, runaway electrons (REs) generated during flattop plasma discharges emit synchrotron radiation (SR) in the visible wavelength range. Spectrometers, cameras, and the Motional Stark Effect diagnostic measure absolutely-calibrated spectra, distortion-corrected images, and polarization information of SR, respectively. Due to the complex interplay of the RE phase-space distribution, magnetic topology, and detector geometry, the synthetic diagnostic SOFT [M. Hoppe, et al., Nucl. Fusion 58 (2018)] is used to simulate all three measurements. As inputs, RE distributions are calculated using a test-particle model [J.R. Martin-Solis, et al., Phys. Plasmas 5 (1998)] and kinetic solver CODE [M. Landreman, et al., Comput. Phys. Commun. 185 (2014)]. Synchrotron spectra measured at three magnetic fields (B0 = 2.7, 5.4, and 7.8 T) indicate a decrease in RE energy as higher B enhances synchrotron power loss [R.A. Tinguely, et al., Nucl. Fusion 58 (2018)]. MHD activity appears to increase RE transport and decrease the RE beam size as observed in synchrotron images. Profiles of linearly-polarized SR and polarization angle are explored as a novel RE diagnostic. |
Thursday, November 8, 2018 2:48PM - 3:00PM |
UO5.00005: First demonstration of disruption mitigation using shell pellets for core impurity deposition on DIII-D Nicholas W Eidietis, Eric M Hollmann, Paul B Parks, Richard A Moyer, Jeffrey L Herfindal, Andrey Lvovskiy, Daisuke Shiraki Experiments injecting boron-filled diamond shell pellets into the DIII-D tokamak provide the first demonstration of disruption mitigation through core impurity deposition. Core impurity injection shows promise to provide “inside-out” radiative cooling of the plasma, as well as high impurity assimilation and global stochastization of the plasma field lines to suppress runaway electron seed formation [1]. The shell pellet technique utilizes a thin, minimally perturbative shell to transport the enclosed radiating impurity (boron dust) to the plasma core before dispersal, delaying the onset of global MHD that is typically initiated by conventional edge-cooling techniques (e.g. massive gas injection). Visible imaging shows the shell ablating gradually until the boron is released near the magnetic axis. 0-D mitigation metrics generally improve with injection velocity, indicative of the importance of deep deposition. Density measurements account for a large fraction of electrons provided by the pellets, indicating high impurity assimilation fraction. Future work and the design of ITER-relevant shells are discussed. [1] V. A. Izzo and P. B. Parks, Phys. Plasmas 24, 060705 (2017) |
Thursday, November 8, 2018 3:00PM - 3:12PM |
UO5.00006: Effect of radial magnetic perturbations on turbulence-flow dynamics at the L-H transition on DIII-D David Matthew Kriete, George R McKee, Lothar W Schmitz, Raymond John Fonck, David R Smith, Zheng Yan Low-k density fluctuation amplitudes measured with beam emission spectroscopy (BES) leading up to the L-H transition are altered in a toroidally dependent manner when RMPs are applied, potentially contributing to the resulting increase of the L-H power threshold. In the 50 ms period leading up to L-H transitions in ITER-shaped low-torque plasmas with applied n=3 magnetic perturbations, two turbulence instabilities coexist in the ρ=0.95–1 region: a low-frequency (~5 kHz) mode peaking at the separatrix and a high-frequency (~30 kHz) mode peaking at ρ≈0.95. RMPs raise the low-frequency mode amplitude at different toroidal phases, but only raise the high-frequency mode amplitude at one toroidal phase, implying the turbulence is toroidally-modulated by the RMPs. RMPs also destabilize a high-frequency (~80 kHz), counter-propagating mode. In contrast, non-resonant fields, which do not raise PLH, do not significantly affect turbulence. Zonal flow structures in the turbulence poloidal flow spectrum are somewhat surprisingly found to have higher amplitude when RMPs are applied, since RMPs have been predicted to damp zonal flows. |
Thursday, November 8, 2018 3:12PM - 3:24PM |
UO5.00007: Advancement of Wide Pedestal Quiescent H-mode Scenario at Zero Torque to ITER-like Shape Theresa M Wilks, Carlos Alberto Paz-Soldan, Jerry W Hughes, Kshitish Kumar Barada, Keith Burrell, Xi Chen, Andrea MV Garofalo, Darin R Ernst, Philip B Snyder Recent experiments on DIII-D have advanced the operational limits of wide pedestal QH-mode plasmas towards increased ITER relevance by demonstrating well-matched plasma shape and net zero injected torque simultaneously. Quiescent H-modes (QH-modes) are a candidate regime for ITER and future reactors because they maintain a stationary pedestal without ELMs via additional edge transport generated by either an edge harmonic oscillation (EHO), broadband turbulence, a limit cycle oscillation (LCO), or some combination thereof. Comparing to the traditional double null shape, the ITER-like shape is shown to have 1) a narrower pedestal width, 2) lower frequency LCOs, yet larger density fluctuations, and 3) larger ExB shear in the inner Er well pedestal region. In the peeling-ballooning stability space, the ITER-like shape operates far from the kink/peeling boundary, suggesting much higher power and possibly wider pedestal operation can be achieved in future experiments. The H98y2 confinement factor was shown to increase with pedestal width, suggesting a favorable scaling for ITER in this regime. |
Thursday, November 8, 2018 3:24PM - 3:36PM |
UO5.00008: JINTRAC Coupled Core/SOL/Divertor Transport Simulations in Support of ITER Elina Militello Asp, Yuriy Baranov, Francis Casson, Gerard Corrigan, Daniela Farina, Lorenzo Figini, Luca Garzotti, Derek Harting, Peter Knight, Florian Koechl, Alberto Loarte, Hans Nordman, Vassili Parail, Simon D Pinches, Alexei Polevoi, Roberta Sartori, Pär Strand The inductive goal of ITER is to produce 500s long burning plasmas with Q=Pfus/Paux>=10. This requires the development of operationally robust scenarios that span the whole plasma discharge from start-up to termination. We show the value of integrated modelling to the challenge of developing scenarios that are relevant to ITER, and take a holistic approach using the core/pedestal/SOL/divertor/wall integrated modelling code JINTRAC. |
Thursday, November 8, 2018 3:36PM - 3:48PM |
UO5.00009: Unified scaling of divertor heat flux widths across confinement regimes to reactor-relevant magnetic fields in the Alcator C-Mod tokamak Dan Brunner, Brian LaBombard, Adam Q Kuang, James Layton Terry New data from Alcator C-Mod have extended the range of heat flux measurements and scalings to poloidal magnetic fields above ITER-level (1.2 T). An international database indicated that λq scaled inversely with the poloidal magnetic field (Bp) up to 0.8 T and had no other significant dependencies. Alcator C-Mod has been the only diverted tokamak capable of operating at reactor-level Bp. A major focus of the final campaign on Alcator C-Mod was to characterize λq over a wide range of conditions, utilizing a unique array of heat flux sensors with unprecedented spatial resolution and heat flux dynamic range. The heat flux width scaling is found to extend up to Bp~1.3 T in H-mode. Looking across confinement regimes (L-, I-, and H-modes) we find the remarkable result that λq exhibits a unified dependence on core volume-averaged core plasma pressure. Within a standard deviation of ~20%, the heat flux width in any of the C-Mod plasmas studied is proportional to the inverse square root of core volume-averaged core plasma pressure. These results stand in stark contrast to recent simulations, indicating ~10 times wider heat flux width for ITER. |
Thursday, November 8, 2018 3:48PM - 4:00PM |
UO5.00010: Gyrokinetic prediction of the divertor heat-load width for ITER C-S Chang, S. Ku, R M Churchill, and the XGC Team The total-f gyrokinetic code XGC has been used across the separatrix and SOL to study the fundamental multiscale physics behind the divertor heat-flux width. XGC shows that in today’s tokamaks, the ion neoclassical orbit physics tends to lead the divertor heat-flux width physics, and agree with the “Eich scaling.” Sheared ExB-flow across the magnetic separatrix surface is strong, and turbulence is “blobby." In ITER with full magnetic field, however, simulations find that the mean ExB flow shear is weak due to the small ρ* effect, that the turbulence pattern across the separatrix becomes of streamer type with long radial correlation length. As a result, the heat-flux width becomes several times greater than the Eich-predicted value. Relation between the up-stream “scrape-off layer width” and the down-stream divertor heat-flux width is not strong, which implies that the length of the divertor leg and the magnetic structure in the divertor chamber could be an important factor in setting the divertor heat-load width in ITER. The first-phase ITER plasma at B=1.8T does not show such enhancement in the divertor heat-flux width over the Eich value, supporting the rho* physics effect, and indicating a bifurcation event. |
Thursday, November 8, 2018 4:00PM - 4:12PM |
UO5.00011: Integrated, multi-physics modeling of erosion, redeposition and gas retention in the ITER divertor Ane Lasa, Sophie Blondel, Guinevere Shaw, Brian Wirth, Tim Younkin, David Edward Bernholdt, John Canik, Mark R Cianciosa, Wael Elwasif, David L Green, Philip C Roth, Davide Curreli, Jon T Drobny, Matthew Baldwin, Russ Doerner, Daisuke Nishijima We present an integrated model designed to capture the multi-physics nature of interactions between the edge plasma and surrounding wall surfaces. This workflow includes SOLPS simulations of the edge plasma in steady-state; the effect of the sheath at shallow magnetic angles, evaluated by hPIC; GITR calculations of transport and redeposition of impurities eroded from the surface; and the response of the wall modeled by coupling F-TRIDYN and Xolotl, which evaluate surface growth and erosion and sub-surface gas dynamics. We benchmark this workflow against PISCES experiments, which measured mass loss, spectroscopy and gas concentration profiles for W substrates exposed to D-He plasmas. Given the positive comparison, we apply the model to predicting impurity migration and redeposition, surface growth and erosion, and gas recycling in the ITER divertor, under conditions expected for He and burning-plasma operations. |
Thursday, November 8, 2018 4:12PM - 4:24PM |
UO5.00012: Experimental and theoretical characterisation of He plasmas confinement in view of the ITER pre-fusion power operation phase Pierre Manas, Clemente Angioni, Athina Kappatou, Francois Ryter, Philip Schneider Helium plasmas are foreseen for the non--nuclear phase of ITER operation, in particular due to L-H power thresholds significantly lower than those in H. On the other hand, they are regularly observed to have lower confinement compared to deuterium plasmas. For the first time, in the ASDEX Upgrade tokamak the confinement of helium plasmas is experimentally demonstrated to increase with increasing fraction of electron heating, reaching values comparable to those of the D plasmas. These observations have been identified to be a combination of core and edge effects. Nonlinear electromagnetic gyrokinetic simulations show that the different impact of zonal flows in regulating the core turbulence in the limit of low electron heating in D and He plasmas breaks the gyro-Bohm scaling of transport, leading to higher levels of transport in He. Additionally, the thermal coupling between electrons and ions and stronger destabilization of electron temperature gradient modes lead to reduced confinement at the edge of He plasmas. This results in that regimes with large fraction of electron heating and low collisionality, as expected in the initial ITER pre-fusion power phase of operation, are found to be beneficial in terms of He plasma confinement. |
Thursday, November 8, 2018 4:24PM - 4:36PM |
UO5.00013: Prediction of the likelihood of Alfvénic mode chirping in ITER baseline scenarios Vinicius N Duarte, Nikolai Gorelenkov The confinement of fast ions is a critical issue to ensure ITER's burning plasma operation. ITER will employ two negative-ion-based neutral beam injection (NBI) sources, which will account for 33MW of injected power. Both the 3.5MeV fusion-born alpha particles and the tangentially injected 1MeV NBI ions will have supra-Alfvénic velocities, allowing them to interact with TAEs via their main resonance. Therefore, to predict and model Alfvénic mode evolution and the nature of fast ion transport due to Alfvénic instabilities in ITER, it is instructive to anticipate whether the modes will be more prone to have their frequencies locked to the background equilibrium or be subject to rapid chirps. Those two typical scenarios lead to mostly diffusive and convective losses, respectively. We present predictive studies of the probable spectral behavior of Alfvénic eigenmodes for baseline ITER cases consisting of elmy, advanced and hybrid scenarios. It has been observed that most cases are found to be in the borderline between the fixed-frequency steady and the chirping phases, with a tendency for steady response if additional stochasticity mechanisms, such as scattering due to radio frequency fields or mode overlap are present. |
Thursday, November 8, 2018 4:36PM - 4:48PM |
UO5.00014: A tokamak-agnostic control system for actuator management and integrated control with application to ITER and TCV Trang Vu, Thomas Blanken, Federico Felici, Cristian Galperti, Mengdi Kong, Bert Maljaars, Olivier Sauter Integrated real-time control and robust event handling are critical for long-pulse and complex tokamaks like ITER. The plasma control system (PCS) has to deal with multiple control tasks and actuator sharing to fulfill the physics goals. A generic PCS architecture including a tokamak-agnostic layer and an interface one is proposed. The tokamak-agnostic layer is designed with a so-called task-based approach where a supervisor and actuator manager handle control tasks using generic controllers and actuator resources. This layer is linked to the tokamak by the interface layer. The task-based approach provides an abstraction layer for the operators as they only need to specify the control tasks from the pulse schedule regardless of the details of the relevant controllers. Standardized interfaces between controllers and actuator manager allow to reduce implementation errors, improve maintenance and development capabilities. The proposed scheme was applied to an ITER simulation with highly complex actuator system and conflicting control tasks. The same tokamak-agnostic layer was utilized in TCV experiments for NTM, central heating and β control tasks with TCV's EC H&CD system, providing a first experimental demonstration of the proposed approach. |
Thursday, November 8, 2018 4:48PM - 5:00PM |
UO5.00015: The Development of First Plasma Operations on ITER Joseph Snipes, Himank Anand, Ken Blackler, Peter C de Vries, Juan Luis Fernandez-Hernando, Yuri Gribov, Mark Andrew Henderson, Jean-Yves Journeaux, Tim Luce, Ignacio Prieto-diaz, Anders Wallander, Luca Zabeo, Isabel Nunes ITER construction is well underway and first plasma operations are planned at the end of 2025. Plant system commissioning has begun and will proceed up to the closure of the cryostat in late 2024, which defines the start of integrated commissioning, including that of the Central Interlock System (CIS), the Plasma Control System (PCS), and associated diagnostics to ensure investment protection and central control functions can be carried out. An independent system will also be commissioned for superconducting magnet protection to avoid approaching force, field, and temperature limits. First plasma scenarios in hydrogen with BT = 2.65 T will first attempt Ohmic breakdown within a neutral pressure range of 0.3 mPa < p < 0.7 mPa, limited by runaways at the low end and by inability to ensure Ip ≥ 100 kA for ≥ 100 ms at the high end. If Ohmic breakdown is unsuccessful, electron cyclotron heating will be added in 0.83 MW steps for short pulses (< 300 ms), possibly up to 6.7 MW injected at 2nd harmonic. The PCS must ensure that Ip < 1 MA to stay within structural limits of the vacuum vessel supports to the temporary poloidal stainless steel limiters. A backup option to improve breakdown is to operate at full toroidal field of 5.3 T with 1st harmonic ECH after magnet commissioning. |
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