Physics and performance of the I-mode regime over an expanded operating space on Alcator C-Mod

Hubbard, A. E.; Baek, S. -G.; Brunner, Daniel; Creely, A. J.; Cziegler, I.; Edlund, E.; Hughes, J. W.; LaBombard, B.; Lin, Y.; Liu, Z.; Marmar, E. S.; Reinke, Matthew L.; Rice, J. E.; Sorbom, B.; Sung, C.; Terry, James; Theiler, Christian; Tolman, E. A.; Walk, J. R.; White, A. E.; Whyte, D.; Wolfe, S. M.; Wukitch, S.; Xu, X. Q.

doi:10.1088/1741-4326/aa8570

Title: Physics and performance of the I-mode regime over an expanded operating space on Alcator C-Mod

Abstract

New results on the I-mode regime of operation on the Alcator C-Mod tokamak are reported. This ELM-free regime features high energy confinement and a steep temperature pedestal, while particle confinement remains at L-mode levels, giving stationary density and avoiding impurity accumulation. I-mode has now been obtained over nearly all of the magnetic fields and currents possible in this high field tokamak (I_p 0.55–1.7 MA, B_T 2.8–8 T) using a configuration with B × ∇B drift away from the X-point. Results at 8 T confirm that the L–I power threshold varies only weakly with B_T, and that the power range for I-mode increases with B_T; no 8 T discharges transitioned to H-mode. Parameter dependences of energy confinement are investigated. Core transport simulations are giving insight into the observed turbulence reduction, profile stiffness and confinement improvement. Pedestal models explain the observed stability to ELMs, and can simulate the observed weakly coherent mode. Conditions for I–H transitions have complex dependences on density as well as power. I-modes have now been maintained in near-DN configurations, leading to improved divertor power flux sharing. Overall, prospects for I-mode on future fusion devices such as ITER and ARC are encouraging. Further experiments on other tokamaks are neededmore »« less

Authors:

Hubbard, A. E. ^[1]; Baek, S. -G. ^[1];

^[1]; Creely, A. J. ^[1]; Cziegler, I. ^[2]; Edlund, E. ^[1]; Hughes, J. W. ^[1];

^[1]; Lin, Y. ^[1]; Liu, Z. ^[3]; Marmar, E. S. ^[1];

^[4]; Rice, J. E. ^[1]; Sorbom, B. ^[1]; Sung, C. ^[5];

^[1];

^[6]; Tolman, E. A. ^[1]; Walk, J. R. ^[1]; White, A. E. ^[1] more »

Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)
Univ. of York (United Kingdom)
Chinese Academy of Sciences (CAS), Hefei (China); Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Univ. of California, Los Angeles, CA (United States)
Ecole Polytechnique Federale Lausanne (EPFL) (Switzerland)
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)

Publication Date:: Wed Oct 04 00:00:00 EDT 2017

Research Org.:: Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)

Sponsoring Org.:: USDOE National Nuclear Security Administration (NNSA); USDOE Office of Science (SC), Fusion Energy Sciences (FES); National Natural Science Foundation of China (NSFC)

Contributing Org.:: Alcator C-Mod team

OSTI Identifier:: 1873641

Report Number(s):: LLNL-JRNL-789241
Journal ID: ISSN 0029-5515; 987424; TRN: US2307060

Grant/Contract Number:: AC52-07NA27344; FC02-99ER54512; 11405217

Resource Type:: Accepted Manuscript

Journal Name:: Nuclear Fusion

Additional Journal Information:: Journal Volume: 57; Journal Issue: 12; Journal ID: ISSN 0029-5515

Publisher:: IOP Science

Country of Publication:: United States

Language:: English

Subject:: 70 PLASMA PHYSICS AND FUSION TECHNOLOGY; FEC 2016; tokamak; I-mode; pedestal; transport

Citation Formats


                    Hubbard, A. E., Baek, S. -G., Brunner, Daniel, Creely, A. J., Cziegler, I., Edlund, E., Hughes, J. W., LaBombard, B., Lin, Y., Liu, Z., Marmar, E. S., Reinke, Matthew L., Rice, J. E., Sorbom, B., Sung, C., Terry, James, Theiler, Christian, Tolman, E. A., Walk, J. R., White, A. E., Whyte, D., Wolfe, S. M., Wukitch, S., and Xu, X. Q. Physics and performance of the I-mode regime over an expanded operating space on Alcator C-Mod.  United States: N. p., 2017. 
Web.  doi:10.1088/1741-4326/aa8570.

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                    Hubbard, A. E., Baek, S. -G., Brunner, Daniel, Creely, A. J., Cziegler, I., Edlund, E., Hughes, J. W., LaBombard, B., Lin, Y., Liu, Z., Marmar, E. S., Reinke, Matthew L., Rice, J. E., Sorbom, B., Sung, C., Terry, James, Theiler, Christian, Tolman, E. A., Walk, J. R., White, A. E., Whyte, D., Wolfe, S. M., Wukitch, S., & Xu, X. Q. Physics and performance of the I-mode regime over an expanded operating space on Alcator C-Mod.  United States.  https://doi.org/10.1088/1741-4326/aa8570

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                    Hubbard, A. E., Baek, S. -G., Brunner, Daniel, Creely, A. J., Cziegler, I., Edlund, E., Hughes, J. W., LaBombard, B., Lin, Y., Liu, Z., Marmar, E. S., Reinke, Matthew L., Rice, J. E., Sorbom, B., Sung, C., Terry, James, Theiler, Christian, Tolman, E. A., Walk, J. R., White, A. E., Whyte, D., Wolfe, S. M., Wukitch, S., and Xu, X. Q. Wed .  
"Physics and performance of the I-mode regime over an expanded operating space on Alcator C-Mod".  United States.  https://doi.org/10.1088/1741-4326/aa8570.  https://www.osti.gov/servlets/purl/1873641.

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@article{osti_1873641,

  title        = {Physics and performance of the I-mode regime over an expanded operating space on Alcator C-Mod},

  author       = {Hubbard, A. E. and Baek, S. -G. and Brunner, Daniel and Creely, A. J. and Cziegler, I. and Edlund, E. and Hughes, J. W. and LaBombard, B. and Lin, Y. and Liu, Z. and Marmar, E. S. and Reinke, Matthew L. and Rice, J. E. and Sorbom, B. and Sung, C. and Terry, James and Theiler, Christian and Tolman, E. A. and Walk, J. R. and White, A. E. and Whyte, D. and Wolfe, S. M. and Wukitch, S. and Xu, X. Q.},

  abstractNote = {New results on the I-mode regime of operation on the Alcator C-Mod tokamak are reported. This ELM-free regime features high energy confinement and a steep temperature pedestal, while particle confinement remains at L-mode levels, giving stationary density and avoiding impurity accumulation. I-mode has now been obtained over nearly all of the magnetic fields and currents possible in this high field tokamak (Ip 0.55–1.7 MA, BT 2.8–8 T) using a configuration with B × ∇B drift away from the X-point. Results at 8 T confirm that the L–I power threshold varies only weakly with BT, and that the power range for I-mode increases with BT; no 8 T discharges transitioned to H-mode. Parameter dependences of energy confinement are investigated. Core transport simulations are giving insight into the observed turbulence reduction, profile stiffness and confinement improvement. Pedestal models explain the observed stability to ELMs, and can simulate the observed weakly coherent mode. Conditions for I–H transitions have complex dependences on density as well as power. I-modes have now been maintained in near-DN configurations, leading to improved divertor power flux sharing. Overall, prospects for I-mode on future fusion devices such as ITER and ARC are encouraging. Further experiments on other tokamaks are needed to improve confidence in extrapolation.},

  doi          = {10.1088/1741-4326/aa8570},

  journal      = {Nuclear Fusion},

  number       = 12,

  volume       = 57,

  place        = {United States},

  year         = {Wed Oct 04 00:00:00 EDT 2017},

  month        = {Wed Oct 04 00:00:00 EDT 2017}

}

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Title: Physics and performance of the I-mode regime over an expanded operating space on Alcator C-Mod

Abstract

Citation Formats

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Chapter 2: Plasma confinement and transport journal, December 1999

Validation of nonlinear gyrokinetic simulations of L- and I-mode plasmas on Alcator C-Mod journal, May 2017

Characterization of density fluctuations during the search for an I-mode regime on the DIII-D tokamak journal, August 2015

Edge energy transport barrier and turbulence in the I-mode regime on Alcator C-Mod journal, May 2011

Plasma confinement at JET journal, December 2015

Nonlinear gyrokinetic simulations of the I-mode high confinement regime and comparisons with experimenta) journal, May 2015

Multi-device studies of pedestal physics and confinement in the I-mode regime journal, July 2016

Geodesic oscillations and the weakly coherent mode in the I-mode of ASDEX Upgrade journal, June 2015

Turbulence Nonlinearities Shed Light on Geometric Asymmetry in Tokamak Confinement Transitions journal, March 2017

Observation of the L − H Confinement Bifurcation Triggered by a Turbulence-Driven Shear Flow in a Tokamak Plasma journal, March 2014

The physics mechanisms of the weakly coherent mode in the Alcator C-Mod Tokamak journal, December 2016

Threshold conditions for transitions to I-mode and H-mode with unfavourable ion grad B drift direction journal, October 2012

A first-principles predictive model of the pedestal height and width: development, testing and ITER optimization with the EPED model journal, August 2011

Multi-scale gyrokinetic simulations: Comparison with experiment and implications for predicting turbulence and transport journal, April 2016

Toward integrated multi-scale pedestal simulations including edge-localized-mode dynamics, evolution of edge-localized-mode cycles, and continuous fluctuations journal, May 2016

Development of the gas puff charge exchange recombination spectroscopy (GP-CXRS) technique for ion measurements in the plasma edge journal, September 2013

Edge-localized mode avoidance and pedestal structure in I-mode plasmas journal, May 2014

Edge profile stiffness and insensitivity of the density pedestal to neutral fuelling in Alcator C-Mod edge transport barriers journal, August 2007

H mode confinement in Alcator C-Mod journal, June 1997

Reduction of core turbulence in I-mode plasmas in Alcator C-Mod journal, June 2014

Power requirement for accessing the H-mode in ITER journal, July 2008

Attainment of a stable, fully detached plasma state in innovative divertor configurations journal, May 2017

I-mode studies at ASDEX Upgrade: L-I and I-H transitions, pedestal and confinement properties journal, October 2016

Gyrokinetic investigation of the ASDEX Upgrade I-mode pedestal journal, December 2019

Access and sustainment of naturally ELM-free and small-ELM regimes journal, September 2018

Access to pedestal pressure relevant to burning plasmas on the high magnetic field tokamak Alcator C-Mod journal, September 2018

I-mode investigation on the Experimental Advanced Superconducting Tokamak journal, July 2019

H-mode grade confinement in L-mode edge plasmas at negative triangularity on DIII-D journal, April 2019

High fusion performance in Super H-mode experiments on Alcator C-Mod and DIII-D journal, June 2019

Dependence of alpha-particle-driven Alfvén eigenmode linear stability on device magnetic field strength and consequences for next-generation tokamaks journal, March 2019

Scaling laws from theory-based modeling for different regimes in the DEMO fusion reactor journal, July 2019

Experimental energy confinement time scaling with dimensionless parameters in C-Mod I-mode plasmas journal, October 2019

27th IAEA Fusion Energy Conference: summary of sessions EX/C, EX/S and PPC journal, January 2020

Radiative heat exhaust in Alcator C-Mod I-mode plasmas journal, March 2019

Grassy-ELM regime with edge resonant magnetic perturbations in fully noninductive plasmas in the DIII-D tokamak journal, July 2018

The dependence of divertor power sharing on magnetic flux balance in near double-null configurations on Alcator C-Mod journal, May 2018

High-resolution heat flux width measurements at reactor-level magnetic fields and observation of a unified width scaling across confinement regimes in the Alcator C-Mod tokamak journal, July 2018

Influence of high magnetic field on access to stationary H-modes and pedestal characteristics in Alcator C-Mod journal, February 2018

Performance assessment of long-legged tightly-baffled divertor geometries in the ARC reactor concept journal, September 2019

Inboard and outboard radial electric field wells in the H- and I-mode pedestal of Alcator C-Mod and poloidal variations of impurity temperature
journal, June 2014

Perturbative thermal diffusivity from partial sawtooth crashes in Alcator C-Mod
journal, February 2016

I-mode: an H-mode energy confinement regime with L-mode particle transport in Alcator C-Mod
journal, August 2010

H-mode power threshold and transition in ASDEX Upgrade
journal, May 1998

Zonal flow production in the L–H transition in Alcator C-Mod
journal, May 2014

Fluctuating zonal flows in the I-mode regime in Alcator C-Mod
journal, May 2013

Radial localization of edge modes in Alcator C-Mod pedestals using optical diagnostics
journal, January 2017

Electron temperature fluctuations associated with the weakly coherent mode in the edge of I-mode plasmas
journal, October 2011

Edge radial electric field structure and its connections to H-mode confinement in Alcator C-Mod plasmas
journal, May 2009

ARC: A compact, high-field, fusion nuclear science facility and demonstration power plant with demountable magnets
journal, November 2015

Heat-flux footprints for I-mode and EDA H-mode plasmas on Alcator C-Mod
journal, July 2013

Zonal flow triggers the L-H transition in the Experimental Advanced Superconducting Tokamak
journal, July 2012

Scaling of the power exhaust channel in Alcator C-Mod
journal, May 2011

Chapter 2: Plasma confinement and transport
journal, December 1999

Validation of nonlinear gyrokinetic simulations of L- and I-mode plasmas on Alcator C-Mod
journal, May 2017

Characterization of density fluctuations during the search for an I-mode regime on the DIII-D tokamak
journal, August 2015

Edge energy transport barrier and turbulence in the I-mode regime on Alcator C-Mod
journal, May 2011

Plasma confinement at JET
journal, December 2015

Nonlinear gyrokinetic simulations of the I-mode high confinement regime and comparisons with experimenta)
journal, May 2015

Multi-device studies of pedestal physics and confinement in the I-mode regime
journal, July 2016

Geodesic oscillations and the weakly coherent mode in the I-mode of ASDEX Upgrade
journal, June 2015

Turbulence Nonlinearities Shed Light on Geometric Asymmetry in Tokamak Confinement Transitions
journal, March 2017

Observation of the $L − H$ Confinement Bifurcation Triggered by a Turbulence-Driven Shear Flow in a Tokamak Plasma
journal, March 2014

The physics mechanisms of the weakly coherent mode in the Alcator C-Mod Tokamak
journal, December 2016

Threshold conditions for transitions to I-mode and H-mode with unfavourable ion grad B drift direction
journal, October 2012

A first-principles predictive model of the pedestal height and width: development, testing and ITER optimization with the EPED model
journal, August 2011

Multi-scale gyrokinetic simulations: Comparison with experiment and implications for predicting turbulence and transport
journal, April 2016

Toward integrated multi-scale pedestal simulations including edge-localized-mode dynamics, evolution of edge-localized-mode cycles, and continuous fluctuations
journal, May 2016

Development of the gas puff charge exchange recombination spectroscopy (GP-CXRS) technique for ion measurements in the plasma edge
journal, September 2013

Edge-localized mode avoidance and pedestal structure in I-mode plasmas
journal, May 2014

Edge profile stiffness and insensitivity of the density pedestal to neutral fuelling in Alcator C-Mod edge transport barriers
journal, August 2007

H mode confinement in Alcator C-Mod
journal, June 1997

Reduction of core turbulence in I-mode plasmas in Alcator C-Mod
journal, June 2014

Power requirement for accessing the H-mode in ITER
journal, July 2008

Attainment of a stable, fully detached plasma state in innovative divertor configurations
journal, May 2017

I-mode studies at ASDEX Upgrade: L-I and I-H transitions, pedestal and confinement properties
journal, October 2016

Gyrokinetic investigation of the ASDEX Upgrade I-mode pedestal
journal, December 2019

Access and sustainment of naturally ELM-free and small-ELM regimes
journal, September 2018

Access to pedestal pressure relevant to burning plasmas on the high magnetic field tokamak Alcator C-Mod
journal, September 2018

I-mode investigation on the Experimental Advanced Superconducting Tokamak
journal, July 2019

H-mode grade confinement in L-mode edge plasmas at negative triangularity on DIII-D
journal, April 2019

High fusion performance in Super H-mode experiments on Alcator C-Mod and DIII-D
journal, June 2019

Dependence of alpha-particle-driven Alfvén eigenmode linear stability on device magnetic field strength and consequences for next-generation tokamaks
journal, March 2019

Scaling laws from theory-based modeling for different regimes in the DEMO fusion reactor
journal, July 2019

Experimental energy confinement time scaling with dimensionless parameters in C-Mod I-mode plasmas
journal, October 2019

27th IAEA Fusion Energy Conference: summary of sessions EX/C, EX/S and PPC
journal, January 2020

Radiative heat exhaust in Alcator C-Mod I-mode plasmas
journal, March 2019

Grassy-ELM regime with edge resonant magnetic perturbations in fully noninductive plasmas in the DIII-D tokamak
journal, July 2018

The dependence of divertor power sharing on magnetic flux balance in near double-null configurations on Alcator C-Mod
journal, May 2018

High-resolution heat flux width measurements at reactor-level magnetic fields and observation of a unified width scaling across confinement regimes in the Alcator C-Mod tokamak
journal, July 2018

Influence of high magnetic field on access to stationary H-modes and pedestal characteristics in Alcator C-Mod
journal, February 2018

Performance assessment of long-legged tightly-baffled divertor geometries in the ARC reactor concept
journal, September 2019