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San Diego, CA, United States

Wang H.,Graduate University for Advanced Studies | Todo Y.,Graduate University for Advanced Studies | Todo Y.,Japan National Institute for Fusion Science | Kim C.C.,FAR Technology Inc.
Physical Review Letters | Year: 2013

Nonlinear frequency chirping of the energetic-particle-driven geodesic acoustic mode (EGAM) is investigated using a hybrid simulation code for energetic particles interacting with a magnetohydrodynamic fluid. It is demonstrated in the simulation result that both frequency chirping up and chirping down take place in the nonlinear evolution of the EGAM. It is found that two hole-clump pairs are formed in the energetic particle distribution function in two-dimensional velocity space of pitch angle variable and energy. One pair is formed in the phase space region that destabilizes the instability, while the other is formed in the stabilizing region. The transit frequency of the hole (clump) in the destabilizing region chirps up (down), while in the stabilizing region the hole (clump) chirps down (up). The transit frequencies of particles in the holes and clumps are in good agreement with the chirping EGAM frequency indicating that the particles are kept resonant with the EGAM during the nonlinear frequency chirping. Continuous energy transfer takes place from the destabilizing phase space region to the stabilizing region during the spontaneous frequency chirping of the wave. © 2013 American Physical Society. Source

We formulate a finite-size particle numerical model of strongly magnetized plasmas in the drift-kinetic approximation. We use the phase space action as an alternative to previous variational formulations based on Low's Lagrangian or on a Hamiltonian with a non-canonical Poisson bracket. The useful property of this variational principle is that it allows independent transformations of particle coordinates and velocities, i.e., transformations in particle phase space. With such transformations, a finite degree-of-freedom drift-kinetic action is obtained through time-averaging of the finite degree-of-freedom fully-kinetic action. Variation of the drift-kinetic Lagrangian density leads to a self-consistent, macro-particles and fields numerical model. Since the computational particles utilize only guiding center coordinates and velocities, there is a large computational advantage in the time integration part of the algorithm. Numerical comparison between the time-averaged fully-kinetic and drift-kinetic charge and current, deposited on a computational grid, offers insight into the range of validity of the model. Being based on a variational principle, the algorithm respects the energy conserving property of the underlying continuous system. The development in this paper serves to further emphasize the advantages of using variational approaches in plasma particle simulations. © 2014 Elsevier B.V. All rights reserved. Source

Agency: Department of Energy | Branch: | Program: SBIR | Phase: Phase I | Award Amount: 150.00K | Year: 2014

High-velocity high-density/mass plasma jets have important applications in magnetic fusion research for disruption mitigation, fueling, and driving plasma rotation. The essential potential of C60/C plasma jet, as probe for runaway electrons (REs) interaction with plasma has been envisioned, but no suitable device has been developed and tested in a poof-of-principle experiment. Such a diagnostic probe will be of great aid for a reliable, real-time technique for REs suppression/dissipation, a critical need for fusion reactors like the International Thermonuclear Nuclear Experimental Reactor (ITER). FAR-TECH, Inc. proposes to provide a diagnostic probe for runaway electron beam-plasma interaction using a novel prototype system producing a high-velocity and high-density/mass C60/C plasma jet, accelerated in a plasma gun. The overall objective is to perform a proof-of-principle experiment on a large tokamak such as DIII-D. During Phase I we will investigate the feasibility, from the view point of all of the key physics and engineering issues involved, of a proof-of-principle experiment on DIII-D tokamak, aimed to demonstrate the C60/C nanoparticle plasma jet as a spectroscopy-based active-passive diagnostic probe for RE beam- plasma interaction. We will use semi-analytical physical models and computer simulations. We will set firm grounds for a practical device supporting the development of the disruption mitigation system for ITER. Commercial Applications and Other Benefits: Plasma jets have many applications in the following areas of fusion plasmas: mitigation of plasma disruptions, core fueling for burning plasma, liner-compressed magnetized target fusion, and driving plasma rotation for improved stability. Thus our tool will have direct impact to the fusion community. The technology and tool developed for diagnosing of runaway electrons and disruption mitigation can be useful to space science and technology, biomedicine, defense and in commercial sectors where application of nanoparticle plasma jets is pursued.

Agency: Department of Energy | Branch: | Program: SBIR | Phase: Phase II | Award Amount: 1.00M | Year: 2015

Development of an economically and environmentally attractive fusion energy source is the goal of the Fusion Energy Sciences program. One main approach for plasma heating and current drive in fusion devices is to use radio frequency (RF) waves. RF waves are used for heating and/or current drive in most magnetic plasma confinement devices, such as Tokamaks, Reversed Field Pinches, Stellarators and Mirror Machines, and are also used in industrial plasma sources. Numerical modeling of RF fields in both fusion and industrial plasma devices is a very important part of analysis of performance of such devices. FAR-TECH, Inc. will develop a new parallelized full wave radio frequency code to accurately model 3-D radio frequency fields in fusion and industrial plasma devices. Feasibility study of the proposed approach of solving wave equations was performed in Phase I. Feasibility was demonstrated for numerical calculation of the plasma conductivity kernel in 3-D configuration space. Feasibility was demonstrated for solving linear equations, obtained by discretization of the wave equations using the meshless formulation, by the Krylov subspace iterative methods or by efficient direct solvers. The goal in Phase II is to develop a new parallel full wave linear RF code, which will utilize the localized nature of plasma dielectric response to the RF field, use adaptive grid to better resolve resonances in plasma and antenna structures, and solve the formulated linear equations by iterative methods or efficient direct solvers. The commercial product will be a user friendly numerical tool with a graphical user interface, comprehensive post processing, and a user manual. The code will be used: in the design, operation and performance assessment of radio frequency systems in existing and planned fusion devices, industrial radio frequency plasma devices, and electron cyclotron ion sources; in basic research on plasma waves.

Agency: Department of Energy | Branch: | Program: SBIR | Phase: Phase I | Award Amount: 150.00K | Year: 2015

Arguably the most important issue facing the further development of magnetic fusion via advanced tokamaks is to predict, avoid, or mitigate disruptions. This problem recently became one of the most challenging and hot topics in fusion research due to several potentially damaging effects, all of which can impact the ITER device. The Disruption Prediction And Simulation Suite DPASS) of codes will address all important disruption related topics: MHD dynamics, plasma edge physics, plasma-wall interaction physics and generation, and losses of runaway electrons. The numerical algorithm will allow extension in physics models and interface with other relevant codes. The DPASS will have a modular structure. Different aspects of disruption physics will be included in modules, which will be linked to a core. The core of the DPASS will be the already developed DSC-3D code, which solves the resistive one fluid non-linear time-dependent 3D MHD equations in the real geometry of the conducting tokamak vessel, utilizing the adaptive meshless technique. The DPASS will be validated against the JET disruption data and will be capable of predicting the disruption effects in ITER, it will be parallelized too. DPASS will contribute to the development of the disruption mitigation schemes and suppression of the runaway generation. Theoretical models relevant to disruptions and corresponding numerical algorithms will be carefully selected. Two numerical modules to simulate disruption mitigation schemes with massive gas and plasma jet injections will be developed, tested and incorporated into the DPASS. Initial simulations will be carried out. The DPASS will make a unique and timely contribution to the US and International tokamak fusion programs. With the projects completion, the DPASS will result in a powerful simulation tool, available and deliverable to the fusion energy science community. Being experimentally verified, the DPASS fits well the objectives of the FSP Fusion Simulation Project). Adaptive meshless method employed in the DPASS is an explicit contribution to the computational science.

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