Studies of a flexible heliac configuration

C., Hender, T.; Cantrell, J. L.; Harris, J. H.; Carreras, B. A.; Lynch, V. E.; Lyon, J. F.; A., Fabregas, J.; Guasp, J.; Lopez-Fraguas, A.; Navarro, A. P.

doi:10.2172/6007697

Cited by 2 publications

(3 citation statements)

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“…not have a consistent strong trend with Z. This is observed in both QA and QH configurations, as well as the non-quasisymmetric TJ-II stellarator (Hender 1988), and the W7-X standard configuration. Note that symmetry-breaking harmonics of B are not modified in figure 9.…”

Section: Comparison To Gyro-bohm Turbulence Estimatementioning

confidence: 84%

Impurity temperature screening in stellarators close to quasisymmetry

Martin

Landreman

2020

J. Plasma Phys.

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Impurity temperature screening is a favourable neoclassical phenomenon involving an outward radial flux of impurity ions from the core of fusion devices. Quasisymmetric magnetic fields lead to intrinsically ambipolar neoclassical fluxes that give rise to temperature screening for low enough $\unicode[STIX]{x1D702}^{-1}\equiv d\ln n/d\ln T$ . In contrast, neoclassical fluxes in generic stellarators will depend on the radial electric field, which is predicted to be inward for ion-root plasmas, potentially leading to impurity accumulation. Here, we examine the impurity particle flux in a number of approximately quasisymmetric stellarator configurations and parameter regimes while varying the amount of symmetry breaking in the magnetic field. For the majority of this work, neoclassical fluxes have been obtained using the SFINCS drift-kinetic equation solver with electrostatic potential $\unicode[STIX]{x1D6F7}=\unicode[STIX]{x1D6F7}(r)$ , where $r$ is a flux-surface label. Results indicate that achieving temperature screening is possible, but unlikely, at low-collisionality reactor-relevant conditions in the core. Thus, the small departures from symmetry in nominally quasisymmetric stellarators are large enough to significantly alter the neoclassical impurity transport. A further look at the magnitude of these fluxes when compared to a gyro-Bohm turbulence estimate suggests that neoclassical fluxes are small in configurations optimized for quasisymmetry when compared to turbulent fluxes.

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Section: Comparison To Gyro-bohm Turbulence Estimatementioning

confidence: 84%

Impurity temperature screening in stellarators close to quasisymmetry

Martin

Landreman

2020

J. Plasma Phys.

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“…Varying the value of c F [14] modifies the corner ripple, e c . The values of e c for the alternate configurations are also presented in Fig.…”

Section: Description Of the Magnetic Fieldmentioning

confidence: 99%

“…This study investigates the effects of magnetic configuration details and ambipolar electric fields on the transport properties of a heliac. The flexible heliac to be built in Spain, TJ-II [12][13][14], was used as a well documented example of a heliac. Three different magnetic configurations at different values of radial electric fields are considered in this study.…”

Section: Introductionmentioning

confidence: 99%

Study of transport in the flexible heliac TJ-II

1988

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A numerical analysis of the classical loss mechanisms in the heliac TJ-II is presented. By using a guiding centre orbit code in flux co-ordinates, it is found that collisionless direct losses can be eliminated by electric drift effects for potentials of the order of the ion temperature. Neoclassical losses resulting from the interaction of collisions and complex orbits are calculated by solving the drift kinetic equation. When electric drifts are included, the resulting transport coefficients are comparable to those of a tokamak with the same aspect ratio and a rotational transform equal to the transform per field period in TJ-II. In the absence of auxiliary heating, the expected energy confinement time in TJ-II is 2.5 ms, and it decreases with increasing ion temperature.

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Studies of a flexible heliac configuration

Cited by 2 publications

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Impurity temperature screening in stellarators close to quasisymmetry

Impurity temperature screening in stellarators close to quasisymmetry

Study of transport in the flexible heliac TJ-II

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