Spherical tokamaks: Present status and role in the development of fusion power

Morris, A.W.; Akers, R.; Counsell, G.; Hender, T. C.; Lloyd, B.; Sykes, A.; Voss, G.M.; Wilson, H. R.

doi:10.1016/j.fusengdes.2005.08.025

Cited by 18 publications

(17 citation statements)

References 23 publications

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“…This interaction between the toroidal rotation and the presence of MHD instabilities is discussed in [65] and will be the focus of future nonlinear stability analysis. In future spherical tokamaks, such as the Component Test Facility (ST-CTF) [66][67][68] where the toroidal rotation may be significantly larger, the stability to the LLM in these advanced tokamak regimes may be improved. That said, a compromise between stability and realizable current profiles must be reached since current drive efficiency degrades at strong rotation [69].…”

Section: Figure 15mentioning

confidence: 99%

Saturated ideal modes in advanced tokamak regimes in MAST

et al. 2010

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The sensitivity of the stability of the ideal n = 1 internal kink mode is analysed both analytically and numerically in rotating tokamak plasmas. These stability analyses have been carried out including the centrifugal effects of toroidal plasma rotation upon the equilibrium, and also inconsistently when the equilibrium is treated as static. The plasma stability is partially (consistent equilibrium) or wholly (inconsistent treatment) determined by the radial profiles of the plasma density and rotation velocity. It is found that the internal kink mode stability is strongly influenced by small variations in these plasma profiles. Indeed, modest perturbations to the profiles inside the q = 1 surface of only a few percent can result in a stabilising effect upon the kink mode with respect to the static mode growth rate becoming a destabilising effect at the same rotation amplitude, or vice versa. The implications of this extreme sensitivity are discussed, with particular reference to experimental data from MAST.

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Section: Figure 15mentioning

confidence: 99%

Saturated ideal modes in advanced tokamak regimes in MAST

et al. 2010

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“…12 In a series of simulations, the assumed number of toroidal field coils was varied from N ¼ 7 to N ¼ 20, the maximum ripple amplitude within the plasma varying from 0.8% to 0.0001%. Despite this large variation the computed loss rates for N ranging from 9 to 20 were found to be statistically indistinguishable (and well above the prompt rate), suggesting that the losses were being enhanced by finite Larmor radius effects, arising from either the ripple resonance given by Eq.…”

Section: Toroidal Ripple In Mastmentioning

confidence: 99%

Toroidal ripple transport of beam ions in the mega-ampère spherical tokamak

McClements¹,

Hole²

2012

Physics of Plasmas

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The transport of injected beam ions due to toroidal magnetic field ripple in the mega-ampère spherical tokamak (MAST) is quantified using a full orbit particle tracking code, with collisional slowing-down and pitch-angle scattering by electrons and bulk ions taken into account. It is shown that the level of ripple losses is generally rather low, although it depends sensitively on the major radius of the outer midplane plasma edge; for typical values of this parameter in MAST plasmas, the reduction in beam heating power due specifically to ripple transport is less than 1%, and the ripple contribution to beam ion diffusivity is of the order of 0.1 m 2 s -1 or less. It is concluded that ripple effects make only a small contribution to anomalous transport rates that have been invoked to account for measured neutron rates and plasma stored energies in some MAST discharges. Delayed (non-prompt) losses are shown to occur close to the outer midplane, suggesting that banana-drift diffusion is the most likely cause of the ripple-induced losses. [http://dx.

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“…The relevant parameters for this device are given in Table 1 Velocity ratio, Table 1. Typical parameters for the Mega Ampere Spherical Tokamak (MAST) and a conceptual spherical tokamak Component Test Facility (CTF) device [3,4]. CTF (2) refers to the parameters at the normalised minor radius at which the NBI current drive is maximum, as determined by TRANSP simulations [5,6].…”

Section: Introductionmentioning

confidence: 99%

Effect of plasma rotation on the beam-driven current

Cottrell¹,

Kemp²

2009

Nucl. Fusion

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In a rotating plasma, with co-neutral beam injection (NBI), the Doppler shift of the NBI particles, as viewed in the frame of the plasma, can result in a significant reduction in the beam-driven (Ohkawa) current when the rotation is strong (i.e. with rotational Mach numbers, M ≥ 0.5). The correction applies to the toroidal fast-ion current calculated for a non-rotating plasma and is independent of the normal Z eff and electron trapping terms. A simple analytical model is presented to estimate the magnitude of the effect for plasmas with arbitrary toroidal rotation and the conditions where this is important have been identified. This model has been compared to the results from existing Monte Carlo neutral beam codes and found to reproduce their results. The important parameters in this problem are the ratio, ρ Lab = v Lab f 0 vcrit , of the NBI injection particle velocity (in the laboratory frame) to the critical velocity of the plasma, and the ratio ρ φ = v φ vcrit which is related to the rotational Mach number. A phase plot in dimensionless (ρ Lab , ρ φ) space is presented which enables the fast ion current drive efficiencies to be compared for different tokamaks. For strongly rotating plasmas, the degradation in fast ion current efficiency is significant for ρ Lab ≤ 1. However, when ρ Lab is larger than this, the degradation in fast ion current drive is less severe. Approaches to improve the fast ion current drive efficiency are briefly discussed.

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Spherical tokamaks: Present status and role in the development of fusion power

Cited by 18 publications

References 23 publications

Saturated ideal modes in advanced tokamak regimes in MAST

Saturated ideal modes in advanced tokamak regimes in MAST

Toroidal ripple transport of beam ions in the mega-ampère spherical tokamak

Effect of plasma rotation on the beam-driven current

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