A megawatt-level 28 GHz heating system for the National Spherical Torus Experiment Upgrade

Taylor, G.; Ellis, R.; Fredd, E.; Gerhardt, S. P.; Greenough, N.; Harvey, R. W.; Hosea, J.; Parker, R.; Poli, F. M.; Raman, R.; Shiraiwa, S.; Смирнов, А. П.; Terry, D.R.; Wallace, Grant; Wukitch, S.

doi:10.1051/epjconf/20158702013

Cited by 6 publications

(2 citation statements)

References 8 publications

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“…An additional 500 kW, for example, would raise the maximum density to 1.1 × 10 19 m −3 . However, depending on which heating method(s) are implemented, the planned NSTX-U 28 GHz system [29] may be limited to the cutoff density of n co = 9.7 × 10 18 m −3 . All three of these limits are at least a factor of two above the typical densities for NSTX CHI plasmas.…”

Section: Radiation-limiting Pressurementioning

confidence: 99%

Application of Townsend avalanche theory to tokamak startup by coaxial helicity injection

2017

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Townsend avalanche theory is employed to model and interpret plasma initiation in NSTX by Ohmic heating and coaxial helicity injection (CHI). The model is informed by spatially resolved vacuum calculations of electric field and magnetic field line connection length in the poloidal cross-section. The model is shown to explain observations of Ohmic startup including the duration and location of breakdown. Adapting the model to discharges initiated by CHI offers insight into the causes of upper divertor (absorber) arcs in cases where the discharge fails to initiate in the lower divertor gap. Finally, upper and lower limits are established for vessel gas fill based on requirements for breakdown and radiation. It is predicted that CHI experiments on NSTX-U should be able to use as much as four times the amount of prefill gas employed in CHI experiments in NSTX. This should provide greater flexibility for plasma start-up, as the injector flux is projected to be increased in NSTX-U.

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Section: Radiation-limiting Pressurementioning

confidence: 99%

Application of Townsend avalanche theory to tokamak startup by coaxial helicity injection

2017

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“…The effects of dissipation and finite aperture width are also discussed. Due to their general nature, the results presented here will have applications beyond laser fusion experiments; for example, they may be useful for magnetic fusion researchers attempting to heat overdense plasmas via mode-conversion methods [16][17][18][19] , or attempting to measure turbulent fluctuations via Doppler backscattering 20,21 .…”

Section: Introductionmentioning

confidence: 99%

On the intensity of focused waves near turning points

Lopez¹,

Kur²,

Strozzi³

2023

Preprint

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Development of fully non-inductive plasmas heated by medium and high-harmonic fast waves in the national spherical torus experiment upgrade

Taylor

Poli

Bertelli

et al. 2015

AIP Conference Proceedings

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Abstract.A major challenge for spherical tokamak development is to start-up and ramp-up the plasma current (I p ) without using a central solenoid. Experiments in the National Spherical Torus eXperiment (NSTX) demonstrated that 1.4 MW of 30 MHz high-harmonic fast wave (HHFW) power could generate an I p = 300 kA H-mode discharge with a non-inductive I p fraction, f NI ~ 0.7. The discharge had an axial toroidal magnetic field (B T (0)) of 0.55 T, the maximum B T (0) available on NSTX. NSTX has undergone a major upgrade (NSTX-U), that will eventually allow the generation of B T (0) ≤ 1 T and I p ≤ 2 MA plasmas. Full wave simulations of 30 MHz HHFW and medium harmonic fast wave (MHFW) heating in NSTX-U predict significantly reduced FW power loss in the plasma edge at the higher B T (0) achievable in NSTX-U. HHFW experiments will aim to generate stable, f NI ~ 1, I p = 300 kA H-mode plasmas and to ramp I p from 250 to 400 kA with FW power. Time-dependent TRANSP simulations are used to develop non-inductive I p ramp-up and sustainment using 30 MHz FW power. This paper presents results from these RF simulations and plans for developing non-inductive plasmas heated by FW power.

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A megawatt-level 28 GHz heating system for the National Spherical Torus Experiment Upgrade

Cited by 6 publications

References 8 publications

Application of Townsend avalanche theory to tokamak startup by coaxial helicity injection

Application of Townsend avalanche theory to tokamak startup by coaxial helicity injection

On the intensity of focused waves near turning points

Development of fully non-inductive plasmas heated by medium and high-harmonic fast waves in the national spherical torus experiment upgrade

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