Research Areas / Fusion energy / PSFC & D-IIID Collaboration
1) MIT is contributing a major hardware enhancement to DIII-D which will drive off-axis current using a High Field Side (HFS) launched Lower Hybrid Current Drive (LHCD) System. Completion and first operation of the HFS-LHCD on DIII-D will occur in the first year of this proposal. Subsequent experiments using HFS-LHCD will allow us to assess the expected benefits of HFS launch on power coupling, validate our understanding of LH edge interactions, and evaluate current drive efficiency and profile control in a range
of discharges. MIT also collaborates on a project to study plasma boundary effects on radio frequency (RF) heating and current drive, centered on WEST.
2) We build on our leadership in disruption research to focus on several highlight topics. (1) Multi-machine disruption prediction, aided by Machine Learning (ML) methodologies, ultimately probes the existence of a universal disruption predictor capable of working on a new device based on existing tokamak data. (2) Pre-disruptive instabilities may be used to produce real-time estimates of metrics for proximity to a number of unstable operating scenarios, with special emphasis on tearing mode onset. (3) Efforts to quantify the
impact of high-Z plasma facing components on disruption likelihood and dynamics may be extended as metal plasma facing components (PFCs) are introduced into DIII-D. (4) Alternative disruption mitigation strategies require exploration for future devices, partly due to the potential formation of runaway electron beams, motivating MIT to collaborate on the science and technology enabling a passive runaway electron mitigation coil and on the exploration of massive gas detachment.
3) MIT has a long history of leadership in developing high confinement regimes with intrinsic suppression of edge localized modes (ELMs). Our team will explore the physics of I-mode by conducting further experiments on DIII-D, AUG and WEST, continuing to explore the turbulent edge transport in the regime, as well as the access window as determined by factors such as global operational parameters, edge radial electric field, application of 3D magnetic fields, and fueling. Detailed study of both core and pedestal turbulent transport will be undertaken in ELM-suppressed regimes. We will support this experimentally using MIT’s turbulence diagnostics at AUG, and through leading simulation and machine learning techniques. Domestically, we will lead in the FY22 US Joint Research Target activity on ELM-suppressed regimes, and in developing quiescent H-mode and Wide Pedestal Quiescent H-mode (QH, WPQH) regimes on DIII-D. We plan to conduct new experiments which will be supported by advanced analysis and simulations, including gyrokinetic simulations of both pedestal and core turbulence, continuing our leading validation efforts comparing to fluctuation measurements using advanced synthetic diagnostics. Also on DIII-D there are exciting prospects of probing the transport physics of negative triangularity discharges, which exhibit high global confinement without an H-mode edge.
4) MIT will advance the integration of core, pedestal and SOL transport models and accelerate experimental development of favorable burning plasma relevant scenarios, using the capabilities of the DIII-D facility. Existing DIII-D data and new experiments will be used to gather validation quality measurements of impurities from the core, pedestal, and the scrape off layer, utilizing unique capabilities such as MIT’s Laser Blow Off (LBO) system. We will use these data to validate an array of impurity transport models in the core/pedestal and edge/divertor regions, leading to a framework for wall-to-axis impurity density and radiation. MIT will continue innovation in measuring the fueling neutral species on DIII-D, to improve the characterization of neutral density and ionization profiles at multiple poloidal locations. This will move us further toward a comprehensive picture of edge particle transport, which will inform predictive capability of the density pedestal in high confinement regimes. Our diagnostic work will support scenario development for burning plasmas aimed at compatibility of a high-performance pedestal with desirable divertor heat flux management.
5) High fidelity core transport and profile prediction relies on computationally expensive gyrokinetic simulations. By applying optimization techniques, more efficient simulation of DIII-D target discharges will be obtained, which will in turn enable the use of advanced machine learning techniques to develop a profile prediction workflow that is accessible to the community and enables relatively tractable evaluation of steady-state plasma profiles based on nonlinear gyrokinetic simulation. In parallel, gyrokinetic model validation will be extended from the inner core plasma toward the top of the H-mode pedestal. Additional tools developed in house can contribute to scenario optimization and experimental planning on multiple devices, and to the understanding of multi-channel interactions in core turbulence and their effect on validation metrics (e.g. measurements of incremental thermal diffusivity) with integrated modeling and perturbative analysis. Prediction of full rotation velocity profiles is an important consideration, and a variety of models will be evaluated, from ongoing exercises in non-dimensional multi-machine scalings for intrinsic torque to full measurement and simulation of radial momentum transport coefficients. Innovative turbulence diagnostics such as soft x-ray imaging for large wavenumber electron temperature fluctuations will be explored.
6) Depth marker implantation has been utilized as a technique for studying erosion and redeposition of materials in tokamaks, and we propose to pursue the technique on DIII-D, studying materials such as SiC-based ceramics and tungsten coatings. Preparatory work to establish the net erosion diagnostic techniques on yet-to-be tested materials can begin at the DIONISIS facility at MIT, prior to deployment of marked materials on DIII-D. Exposures of materials on DIII-D will be complemented by installation of the Wall Interaction Tile Station (WITS) platform, and MIT collaboration on this hardware component is under discussion. Our PMI team also proposes to assess a novel in-situ, space- and time-resolved surface mapping diagnostic technique based on deploying an electron beam steerable to first wall PFCs in DIII-D and energy dispersive x-ray analysis to survey surface composition. This would introduce a powerful measurement capability for plasma-facing component (PFC) surfaces in magnetic confinement devices that will substantially advance the science of PMI, one of the key remaining technical challenges for magnetic fusion
energy.
The MIT PSFC engages in the DIII-D program on multiple levels. Major facility upgrades like design and installation of an advanced current drive system and novel diagnostics are ongoing. Experimental science coupled with modeling and simulation are a central focus with scientists and students stationed onsite at DIII-D and on campus at MIT leading physics groups, conducting experiments, and contributing to the analysis ecosystem. Graduate students, postdoctoral researchers, and staff scientists participate at varying levels in research areas spanning advanced current drive techniques, disruption science and machine learning, pedestal and core-edge integration physics, plasma transport, and diagnostic development.
The MIT PSFC engages in the DIII-D program on multiple levels. Major facility upgrades like design and installation of an advanced current drive system and novel diagnostics are ongoing. Experimental science coupled with modeling and simulation are a central focus with scientists and students stationed onsite at DIII-D and on campus at MIT leading physics groups, conducting experiments, and contributing to the analysis ecosystem. Graduate students, postdoctoral researchers, and staff scientists participate at varying levels in research areas spanning advanced current drive techniques, disruption science and machine learning, pedestal and core-edge integration physics, plasma transport, and diagnostic development.