People

Nathan Howard

Principal Research Scientist

617-253-4785

NW17-103

Biography

Education

Ph.D. (Nuclear Science and Engineering) Massachusetts Institute of Technology (2012)
B.S. (Physics) University of Illinois – Urbana Champaign (2005)

Professional Experience

Oct 2015 – Present : Research Scientist, MIT Plasma Science and Fusion Center
Oct 2013 – Sept 2015 : ORISE Fusion Postdoctoral Fellow
May 2013 – Sept 2013 : Postdoctoral Associate, University of California – San Diego
May 2012 – April 2013 : Postdoctoral Fellow, MIT Plasma Science and Fusion Center

Expertise

Core turbulence and transport experiment in fusion plasmas; turbulence modeling, impurity transport, and model validation utilizing high performance computing

Awards and Professional Activities

APS DPP Community Planning Process, Program Committee Co-Chair (2019–2020)
Nuclear Fusion Award (2019)
NERSC Scientific Achievement Award – Early Career (2016)
NERSC Users Group Executive Committee (NUGEX) (2016-Present)
U.S. Transport Task Force (TTF) Executive Committee (2015-Present)
IAEA Technical Meeting on Fusion Data Processing, Validation, and Analysis Executive Committee (2015-Present)
Reviewer for Journals: Physics of Plasmas, Plasma Physics and Controlled Fusion, Fusion Science and Technology

Research

My research focuses generally on turbulence and transport in fusion plasmas. After decades of research, it is generally accepted that plasma turbulence, driven by plasma pressure gradients, is primarily responsible for the loss (transport) of heat and particles observed in the core of fusion devices. With the advent of high performance computing, we have made significant progress in understanding and predicting plasma turbulence in tokamaks. It is generally thought that our leading model of plasma turbulence, gyrokinetics, contains sufficient physics to both model existing experiments and predict the performance of future experiments. Much of my research is focused on comparison of the gyrokinetic model with experiment. This process, known as model validation, lies at the intersection of experiment and computation. Using dedicated experiments (on the Alcator C-Mod and DIII-D tokamaks) that are designed to accurate measure aspects of turbulence and transport (heat fluxes, fluctuations, transport coefficients, etc.), as well as cutting-edge modeling performed on some of the world’s largest supercomputers, rigorous comparisons are made between experiment and simulation to assess the fidelity of the gyrokinetic model of plasma turbulence. The ultimate goal of this research is the development of a validated model of plasma turbulence and transport, which can be used for both interpreting existing experiments and predicting the performance of future fusion devices.

Current projects

Currently I am working on the design and construction of a laser blow-off system for installation on the DIII-D tokamak. This system is used for the introduction of trace amounts of impurities into fusion plasmas. These tracers are measured using a variety of spectroscopic techniques and information on the transport of impurities can be exacted. Results from this new system will be compared with gyrokinetic modeling to better understand the physical mechanisms dictating impurity transport and hopefully point towards methods of impurity control in fusion plasmas.

In addition to the projects related to laser blow-off and impurity transport, my current research focuses on multi-scale gyrokinetic simulation of tokamak plasmas. Unlike almost all gyrokinetic simulations to date, these simulations capture both ion-scale (long wavelength) and electron-scale (short wavelength) turbulence simultaneously. The wide range of spatial and temporal scales required for such simulations requires extreme computing resources with a single simulation requiring approximately 20,000 CPUs and 20,000,000 CPU hours to perform on some of the world’s largest supercomputers. These cutting edge simulations have provided new insights into the dynamics of plasma turbulence and likely are able to explain discrepancies between theory and experiment which have existed for half a century.

Publications

A full list of publications can be found at my google scholar page

X. Chen, J. Ruiz Ruiz, N.T. Howard et al. "Feasibility study for a high-k temperature fluctation diagnostic based on soft x-ray imaging" Review of Scientific Instruments, 92, 053537 (2021).

N.T Howard, C. Holland, A.E. White, M. Greenwald, J. Candy, and A.J. Creely Multi-scale Gyrokinetic Simulations: Comparison with Experiment and Implications for Predicting Turbulence and Transport Physics of Plasmas 23 056109 (2016)

N.T. Howard, C. Holland, A.E. White, M. Greenwald, and J. Candy Multi-scale Gyrokinetic Simulation of Tokamak Plasmas: Enhanced Heat Loss Due to Cross-Scale Coupling of Plasma Turbulence Nuclear Fusion 56 014004 (2016)

N.T Howard, A.E. White, M. Greenwald, C. Holland, and J. Candy Fidelity of Reduced and Realistic Electron Mass Ratio Multi-Scale Gyrokinetic Simulations of Tokamak Discharges Plasma Physics and Controlled Fusion 57 065009 (2015)

A.E. White, N.T. Howard, A.J. Creely, M.A. Chilenski, M. Greenwald, A.E. Hubbard, J.W. Hughes, E. Marmar, J.E. Rice, J.M. Sierchio, C. Sung, J.R. Walk, D.G. Whyte, D.R. Mikkelsen, E.M. Edlund, C. Sung, C. Holland, J. Candy, C.C. Petty, M.L. Reinke, C. Theiler Nonlinear Gyrokinetic Simulations of the I-mode High Confinement Regime and Comparisons with Experiment Physics of Plasmas 22 056109 (2015)

N.T Howard, C. Holland, A.E. White, M. Greenwald, and J. Candy Synergistic Cross-Scale Coupling of Turbulence in a Tokamak Plasma Physics of Plasmas 21 112510 (2014)

N.T Howard, A.E. White, M. Greenwald, C. Holland, J. Candy, and J.E. Rice, Impurity Transport, Turbulence Transitions, and Intrinsic Rotation in Alcator C-Mod Plasmas Plasma Physics and Controlled Fusion 56 124004 (2014) - Invited Impurity Transport Issue

N.T. Howard, C. Sung, A.E. White Measurement of Electron Temperature Fluctuations Using a Tunable Correlation Electron Cyclotron Emission System on Alcator C-Mod Review of Scientific Instruments 85 11D811 (2014)

N.T Howard, A.E. White, M. Greenwald, C. Holland, and J. Candy Multi-Scale Gyrokinetic Simulation of Tokamak Discharges Physics of Plasmas 21, 032308 (2014)

N.T Howard, A.E. White, M. Greenwald, M.L. Reinke, C. Holland, J. Candy, and J. Walk Validation of the Gyrokinetic Model in ITG and TEM Dominated L-Mode Plasmas Nuclear Fusion 53 123011 (2013)

A.E. White, N.T. Howard, M.Greenwald, M.L. Reinke, C. Sung, S. Baek, M. Barnes, J. Candy, A. Dominguez, D. Ernst, C. Gao, A. Hubbard, J.W. Hughes, Y. Lin, D. Mikkelsen, F. Parra, M. Porkolab, J.E. Rice, J. Walk, S.J. Wukitch, and Alcator C-Mod Multi-Channel Transport Experiments at Alcator C-Mod and Comparison with Gyrokinetic Simulations Physics of Plasmas 20 056106 (2013)