Determination of the Noninductive Current Profile in Tokamak Plasmas

Forest, C.B.; Küpfer, K.; Luce, T. C.; Politzer, Peter; Lao, L. L.; Wade, M. R.; Whyte, D.G.; Wróblewski, D.

doi:10.1103/physrevlett.73.2444

Cited by 131 publications

(135 citation statements)

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“…At this time, the plasma current is supplied by bootstrap (59%), NBCD (31%), and ECCD (8%) [7]. The measured [14] noninductive current fraction f NI = 99.5% is in reasonable agreement with that calculated by summing the individual contributions. The relatively small contribution from ECCD is very important, as both calculation and previous experience [1] shows that without it, the inductive current would gradually peak near the mid-radius.…”

Section: % Noninductive Operation With Weak Negative Shearsupporting

confidence: 71%

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Progress towards high-performance steady-state operation on DIII-D

Greenfield¹,

Murakami²,

Garofalo³

et al. 2006

Fusion Engineering and Design

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Advanced Tokamak research in DIII-D seeks to develop a scientific basis for steady-state high-performance tokamak operation. Fully noninductive (f NI ≈ 100%) in-principle steady-state discharges have been maintained for several confinement times. These * Corresponding author. Greenfield et al. / Fusion Engineering and Design 81 (2006) [2807][2808][2809][2810][2811][2812][2813][2814][2815] plasmas have weak negative central shear with q min ≈ 1.5-2, β N ≈ 3.5, and large, well-aligned bootstrap current. The loop voltage is near zero across the entire profile. The remaining current is provided by neutral beam current drive (NBCD) and electron cyclotron current drive (ECCD). Similar plasmas are stationary with f NI ≈ 90-95% and duration up to 2 s, limited only by hardware. In other experiments, β N ≈ 4 is maintained for 2 s with internal transport barriers, exceeding previously achieved performance under similar conditions. This is allowed by broadened profiles and active magnetohydrodynamic instability control. Modifications now underway on DIII-D are expected to allow extension of these results to higher performance and longer duration. A new pumped divertor will allow density control in high triangularity double-null divertor configurations, facilitating access to similar in-principle steady-state regimes with β N > 4. Additional current drive capabilities, both off-axis ECCD and on-axis fast wave current drive (FWCD), will increase the magnitude, duration, and flexibility of externally driven current.

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Section: % Noninductive Operation With Weak Negative Shearsupporting

confidence: 71%

“…The noninductive current is directly calculated from the equilibrium using the method described in Ref. [14].…”

Section: % Noninductive Operation With Weak Negative Shearmentioning

confidence: 99%

Progress towards high-performance steady-state operation on DIII-D

Greenfield¹,

Murakami²,

Garofalo³

et al. 2006

Fusion Engineering and Design

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“…The loop voltage was reduced to near zero and the net noninductive fraction of 100% was achieved. However, internal loop voltage ͑VLOOP͒ analysis 17 indicated that local inductive current was not zero near the plasma center. The negative inductive current there is a reaction to excessive NBCD near the axis which led to neutral beam overdrive near the axis and an increase in the central current density.…”

Section: Characteristics Of 100% Noninductive High ␤ Dischargesmentioning

confidence: 99%

“…2͑a͒.The inductive current is the product of the neoclassical conductivity and parallel electric field. 17 The latter is calculated from the time derivative of the poloidal flux based on a series of equilibrium reconstructions using the equilibrium fitting code, EFIT, 18 and is rather insensitive to the parameterization used in EFIT. The total current density profile is sensitive to this parameterization since it is calculated from the spatial derivatives of the poloidal flux.…”

Section: Characteristics Of 100% Noninductive High ␤ Dischargesmentioning

confidence: 99%

Progress toward fully noninductive, high beta conditions in DIII-D

et al. 2006

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The DIII-D Advanced Tokamak ͑AT͒ program in the DIII-D tokamak ͓J. L. Luxon, Plasma Physics and Controlled Fusion Research, 1986, Vol. I ͑International Atomic Energy Agency, Vienna, 1987͒, p. 159͔ is aimed at developing a scientific basis for steady-state, high-performance operation in future devices. This requires simultaneously achieving 100% noninductive operation with high self-driven bootstrap current fraction and toroidal beta. Recent progress in this area includes demonstration of 100% noninductive conditions with toroidal beta, ␤ T = 3.6%, normalized beta, ␤ N = 3.5, and confinement factor, H 89 = 2.4 with the plasma current driven completely by bootstrap, neutral beam current drive, and electron cyclotron current drive ͑ECCD͒. The equilibrium reconstructions indicate that the noninductive current profile is well aligned, with little inductively driven current remaining anywhere in the plasma. The current balance calculation improved with beam ion redistribution that was supported by recent fast ion diagnostic measurements. The duration of this state is limited by pressure profile evolution, leading to magnetohydrodynamic ͑MHD͒ instabilities after about 1 s or half of a current relaxation time ͑ CR ͒. Stationary conditions are maintained in similar discharges ͑ϳ90% noninductive͒, limited only by the 2 s duration ͑1 CR ͒ of the present ECCD systems. By discussing parametric scans in a global parameter and profile databases, the need for low density and high beta are identified to achieve full noninductive operation and good current drive alignment. These experiments achieve the necessary fusion performance and bootstrap fraction to extrapolate to the fusion gain, Q = 5 steady-state scenario in the International Thermonuclear Experimental Reactor ͑ITER͒ ͓R. Aymar et al., Fusion Energy Conference on Controlled Fusion and Plasma Physics, Sorrento, Italy ͑International Atomic Energy Agency, Vienna, 1987͒, paper IAEA-CN-77/OV-1͔. The modeling tools that have been successfully employed to both plan and interpret the experiment are used to plan future DIII-D experiments with higher power and longer pulse ECCD and fast wave and co-and counterneutral beam injection in a pumped double-null configuration. The models predict our ability to control the current and pressure profiles to reach full noninductivity with increased beta, bootstrap fraction, and duration. The same modeling tools are applied to ITER, predicting favorable prospects for the success of the ITER steady-state scenario.

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“…[16][17][18][19][20] The neoclassical bootstrap current arises from the particle orbit excursion across radial pressure gradient. It has been known that source of the current is mostly the trapped particles, but the current is carried mostly by the passing particles via collisional coupling between trapped and passing particles.…”

Section: Introductionmentioning

confidence: 99%

Bootstrap current for the edge pedestal plasma in a diverted tokamak geometry

Koh

Chang

et al. 2012

Physics of Plasmas

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The edge bootstrap current plays a critical role in the equilibrium and stability of the steep edge pedestal plasma. The pedestal plasma has an unconventional and difficult neoclassical property, as compared with the core plasma. It has a narrow passing particle region in velocity space that can be easily modified or destroyed by Coulomb collisions. At the same time, the edge pedestal plasma has steep pressure and electrostatic potential gradients whose scale-lengths are comparable with the ion banana width, and includes a magnetic separatrix surface, across which the topological properties of the magnetic field and particle orbits change abruptly. A driftkinetic particle code XGC0, equipped with a mass-momentum-energy conserving collision operator, is used to study the edge bootstrap current in a realistic diverted magnetic field geometry with a self-consistent radial electric field. When the edge electrons are in the weakly collisional banana regime, surprisingly, the present kinetic simulation confirms that the existing analytic expressions [represented by O. Sauter et al., Phys. Plasmas 6, 2834] are still valid in this unconventional region, except in a thin radial layer in contact with the magnetic separatrix. The agreement arises from the dominance of the electron contribution to the bootstrap current compared with ion contribution and from a reasonable separation of the trapped-passing dynamics without a strong collisional mixing. However, when the pedestal electrons are in plateau-collisional regime, there is significant deviation of numerical results from the existing analytic formulas, mainly due to large effective collisionality of the passing and the boundary layer trapped particles in edge region. In a conventional aspect ratio tokamak, the edge bootstrap current from kinetic simulation can be significantly less than that from the Sauter formula if the electron collisionality is high. On the other hand, when the aspect ratio is close to unity, the collisional edge bootstrap current can be significantly greater than that from the Sauter formula. Rapid toroidal rotation of the magnetic field lines at the high field side of a tight aspect-ratio tokamak is believed to be the cause of the different behavior. A new analytic fitting formula, as a simple modification to the Sauter formula, is obtained to bring the analytic expression to a better agreement with the edge kinetic simulation results. V C 2012 American Institute of Physics.

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Determination of the Noninductive Current Profile in Tokamak Plasmas

Cited by 131 publications

References 10 publications

Progress towards high-performance steady-state operation on DIII-D

Progress towards high-performance steady-state operation on DIII-D

Progress toward fully noninductive, high beta conditions in DIII-D

Bootstrap current for the edge pedestal plasma in a diverted tokamak geometry

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