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Title: Reduced model for direct induction startup scenario development on MAST-U and NSTX-U

Abstract

A reduced semi-empirical model using time-dependent axisymmetric vacuum field calculations is used to develop the prefill and feed-forward coil current targets required for reliable direct induction (DI) startup on the new MA-class spherical tokamaks, MAST-U and NSTX-U. The calculations are constrained by operational limits unique to each device, such as the geometry of the conductive elements and active coils, power supply specifications and coil heating and stress limits. The calculations are also constrained by semi-empirical models for sufficient breakdown, current drive, equilibrium and stability of the plasma developed from a shared database. A large database of DI startup on NSTX and NSTX-U is leveraged to quantify the requirements for achieving a reliable breakdown (I p ~ 20 kA). It is observed that without pre-ionization, STs access the large E/P regime at modest loop voltage (V loop) where the electrons in the weakly ionized plasma are continually accelerating along the open field lines. This ensures a rapid (order millisecond) breakdown of the neutral gas, even without pre-ionization or high-quality field nulls. The timescale of the initial increase in I p on NSTX is reproduced in the reduced model provided a mechanism for impeding the applied electric field is included. Most dischargesmore » that fail in the startup phase are due to an inconsistency in the evolution of the plasma current (I p) and equilibrium field or loss of vertical stability during the burn-through phase. Here, the requirements for the self-consistent evolution of the fields in the weakly and fully-ionized plasma states are derived from demonstrated DI startup on NSTX, NSTX-U and MAST. The predictive calculations completed for MAST-U and NSTX-U illustrate that the maximum I p ramp rate (dI p/dt) in the early startup phase is limited by the voltage limits on the poloidal field coils on MAST-U and passive vertical stability on NSTX-U.« less

Authors:
ORCiD logo [1];  [2];  [1];  [2];  [2]; ORCiD logo [1]
  1. Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
  2. Culham Centre for Fusion Energy, Oxon (United Kingdom)
Publication Date:
Research Org.:
Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1579354
Grant/Contract Number:  
EP/P012450/1; AC02-09CH11466
Resource Type:
Accepted Manuscript
Journal Name:
Nuclear Fusion
Additional Journal Information:
Journal Volume: 59; 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; spherical tokamak; inductive startup; NSTX; MAST

Citation Formats

Battaglia, D. J., Thornton, A. J., Gerhardt, S. P., Kirk, A., Kogan, L., and Menard, J. E. Reduced model for direct induction startup scenario development on MAST-U and NSTX-U. United States: N. p., 2019. Web. doi:10.1088/1741-4326/ab3bd5.
Battaglia, D. J., Thornton, A. J., Gerhardt, S. P., Kirk, A., Kogan, L., & Menard, J. E. Reduced model for direct induction startup scenario development on MAST-U and NSTX-U. United States. doi:10.1088/1741-4326/ab3bd5.
Battaglia, D. J., Thornton, A. J., Gerhardt, S. P., Kirk, A., Kogan, L., and Menard, J. E. Thu . "Reduced model for direct induction startup scenario development on MAST-U and NSTX-U". United States. doi:10.1088/1741-4326/ab3bd5.
@article{osti_1579354,
title = {Reduced model for direct induction startup scenario development on MAST-U and NSTX-U},
author = {Battaglia, D. J. and Thornton, A. J. and Gerhardt, S. P. and Kirk, A. and Kogan, L. and Menard, J. E.},
abstractNote = {A reduced semi-empirical model using time-dependent axisymmetric vacuum field calculations is used to develop the prefill and feed-forward coil current targets required for reliable direct induction (DI) startup on the new MA-class spherical tokamaks, MAST-U and NSTX-U. The calculations are constrained by operational limits unique to each device, such as the geometry of the conductive elements and active coils, power supply specifications and coil heating and stress limits. The calculations are also constrained by semi-empirical models for sufficient breakdown, current drive, equilibrium and stability of the plasma developed from a shared database. A large database of DI startup on NSTX and NSTX-U is leveraged to quantify the requirements for achieving a reliable breakdown (Ip ~ 20 kA). It is observed that without pre-ionization, STs access the large E/P regime at modest loop voltage (Vloop) where the electrons in the weakly ionized plasma are continually accelerating along the open field lines. This ensures a rapid (order millisecond) breakdown of the neutral gas, even without pre-ionization or high-quality field nulls. The timescale of the initial increase in Ip on NSTX is reproduced in the reduced model provided a mechanism for impeding the applied electric field is included. Most discharges that fail in the startup phase are due to an inconsistency in the evolution of the plasma current (Ip) and equilibrium field or loss of vertical stability during the burn-through phase. Here, the requirements for the self-consistent evolution of the fields in the weakly and fully-ionized plasma states are derived from demonstrated DI startup on NSTX, NSTX-U and MAST. The predictive calculations completed for MAST-U and NSTX-U illustrate that the maximum Ip ramp rate (dIp/dt) in the early startup phase is limited by the voltage limits on the poloidal field coils on MAST-U and passive vertical stability on NSTX-U.},
doi = {10.1088/1741-4326/ab3bd5},
journal = {Nuclear Fusion},
number = 12,
volume = 59,
place = {United States},
year = {2019},
month = {10}
}

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Works referenced in this record:

Plasma formation in START and MAST spherical tokamaks
journal, July 2006


Application of Townsend avalanche theory to tokamak startup by coaxial helicity injection
journal, November 2017


The genesis of toroidal discharges
journal, February 1976


Low voltage Ohmic and electron cyclotron heating assisted startup in DIII-D
journal, November 1991


Characterisation of plasma breakdown at JET with a carbon and ITER-like wall
journal, April 2013


Progress towards steady state on NSTX
journal, January 2006


Observation of Instability-Induced Current Redistribution in a Spherical-Torus Plasma
journal, August 2006


Tokamak Start-Up Modeling and Design for EAST First Plasma Campaign
journal, January 2010

  • Leuer, J. A.; Xiao, B. J.; Humphreys, D. A.
  • Fusion Science and Technology, Vol. 57, Issue 1
  • DOI: 10.13182/FST10-A9268

Evidence of a turbulent ExB mixing avalanche mechanism of gas breakdown in strongly magnetized systems
journal, August 2018


The physics of tokamak start-up
journal, May 2013


Ohmic flux consumption during initial operation of the NSTX spherical torus
journal, September 2001


On the breakdown modes and parameter space of ohmic tokamak start-up
journal, October 2018


Progress in preparing scenarios for operation of the International Thermonuclear Experimental Reactor
journal, February 2015

  • Sips, A. C. C.; Giruzzi, G.; Ide, S.
  • Physics of Plasmas, Vol. 22, Issue 2
  • DOI: 10.1063/1.4904015

ITER breakdown and plasma initiation revisited
journal, August 2019


Control of the vertical instability in tokamaks
journal, January 1990


MAST Upgrade Divertor Facility: A Test Bed for Novel Divertor Solutions
journal, May 2018

  • Morris, William; Harrison, J. R.; Kirk, A.
  • IEEE Transactions on Plasma Science, Vol. 46, Issue 5
  • DOI: 10.1109/TPS.2018.2815283

Vessel eddy current measurement for the National Spherical Torus Experiment
journal, December 2004

  • Gates, D. A.; Menard, J. E.; Marsala, R. J.
  • Review of Scientific Instruments, Vol. 75, Issue 12
  • DOI: 10.1063/1.1813091

Plasma equilibrium reconstructions in the lithium tokamak experiment
journal, May 2012


Overview of the physics and engineering design of NSTX upgrade
journal, July 2012


Microwave preionization of the tokamak discharge at the electron cyclotron resonance
journal, June 1980


Scenario development during commissioning operations on the National Spherical Torus Experiment Upgrade
journal, February 2018