Aspect ratio scaling of toroidal plasma equilibria and the tokamak bootstrap effect

Weening, R. H.

doi:10.1063/1.872410

Cited by 4 publications

(2 citation statements)

References 14 publications

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“…3. Soloviev-type configuration [24,26,27] To simulate a tokamak pedestal region, we use the simple Soloviev-type equilibrium of up-down symmetry, and assume the following type solution of the Grad-Shafranov equation:…”

Section: Growth Rate Of the Peeling Modementioning

confidence: 99%

Toroidicity and shape dependence of peeling mode growth rates in axisymmetric toroidal plasmas

Shi¹

2014

Chinese Phys. B

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The growth rate of the peeling mode instability with large toroidal mode number is calculated for general axisymmetric toroidal plasmas, including tokamaks and the spherical torus (ST) equilibia by using formalism presented by Connor et al. Analytic equilibia with non-zero edge current density and quasi-uniform current profiles are assumed. It is found that in sharp D-shape tokamak plasma, the derivative of the safety factor with respect to the poloidal flux becomes very large, making the perturbed poloidal motion very large, in turn making a significant reduction of the growth rate of the peeling mode, similar to the X-point effect in diverted plasma. The large aspect ratio effect is also studied, which reduces the growth rate further.

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Section: Growth Rate Of the Peeling Modementioning

confidence: 99%

Toroidicity and shape dependence of peeling mode growth rates in axisymmetric toroidal plasmas

Shi¹

2014

Chinese Phys. B

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“…Studies carried out for DIII-D [26] and ASDEX [27] plasmas also find pedestal KBMs that play an important role in ELM onset. Low aspect ratio can stabilize KBMs [28].…”

Section: Introductionmentioning

confidence: 99%

Low n electromagnetic modes in spherical tokamaks

Chowdhury

McMillan

2021

Plasma Phys. Control. Fusion

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The performance of spherical tokamak reactors depends on plasma β, and an upper limit is set by long-wavelength kinetic ballooning modes (KBMs). We examine how these modes become unstable in spherical-tokamak reactor relevant plasmas, which may contain significant fast-ion pressure. In a series of numerically generated equilibria of increasing β, the KBM becomes unstable at sufficiently high plasma β, and for such cases, it is also significantly unstable even in the long-wavelength limit. The β threshold for the KBMs is similar to the ideal Magnetohydrodynamics (MHD) threshold, and in cases without fast ions, their frequencies are as predicted by diamagnetic-drift stabilised MHD. To isolate and explore the KBMs, simulations are performed where the pressure gradient is entirely due to the density profile, or entirely due to the temperature profile; the resulting KBMs have similar properties in the long-wavelength regime. The introduction of energetic ions restricts the KBMs to longer wavelengths, and reduces the β threshold somewhat; for parameter regimes of current-day devices, this is such long wavelength that a global analysis would become necessary. Mode frequencies in plasmas with a significant fast particle population are seen to be controlled by fast particle precession frequencies.

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Analytic spherical torus plasma equilibrium model

Weening

2000

Physics of Plasmas

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An analytic spherical torus plasma equilibrium model is developed from a general solution to the Grad–Shafranov equation. The analytic model allows the calculation of axisymmetric plasma equilibria with arbitrary aspect ratio, elongation, triangularity, and diamagnetism. Using a numerical method, examples of optimized analytic equilibria are presented with plasma profiles similar to those of bootstrapped spherical tokamaks. Numerical results obtained from analytic equilibrium solutions for plasmas with aspect ratios A=1.4, elongations κ=3.0, and Troyon factors g=6.7 suggest that spherical tori can achieve toroidal beta values as large as βt≈35% at poloidal beta values βp≈1.53, with stable magnetic wells, W⩾0.

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Aspect ratio scaling of toroidal plasma equilibria and the tokamak bootstrap effect

Cited by 4 publications

References 14 publications

Toroidicity and shape dependence of peeling mode growth rates in axisymmetric toroidal plasmas

Toroidicity and shape dependence of peeling mode growth rates in axisymmetric toroidal plasmas

Low n electromagnetic modes in spherical tokamaks

Analytic spherical torus plasma equilibrium model

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