Physics studies in W7-AS

Hartfuß, H. J.; Endler, M.; Erckmann, V.; Gasparino, U.; Giannone, L.; Grigull, P.; Herre, G.; Kick, M.; Kühner, G.; Niedermeyer, H.; Ringler, H.; Sardei, F.; Stroth, U.; Sattler, Sebastian; Wagner, F.; Weller, A.

doi:10.1088/0741-3335/36/12b/002

Cited by 36 publications

(53 citation statements)

References 22 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The ratio χ HP /χ PB is called the "stiffness parameter", since such a nonlinear dependence of χ can cause the stiffness. As for the stellarators, on the other hand, studies in Wendelstein 7-AS [18][19][20][21] have shown that no systematic discrepancy between χ HP and χ PB is found [19,21] and therefore strong temperature gradient dependence can be ruled out. The transient transport analysis has been also applied to LHD plasmas with an electron internal transport barrier (e-ITB) [22][23][24].…”

Section: Iss95mentioning

confidence: 99%

Electron Pressure Profiles in High-Density Neutral Beam Heated Plasmas in the Large Helical Device

Miyazawa

Yamada

Peterson

et al. 2005

J. Plasma Fusion Res.

View full text Add to dashboard Cite

In the Large Helical Device (LHD), electron pressure profiles in gas-fueled high-density discharges tend to have a similar shape, as if these were frozen. This frozen profile is insensitive to variations in the magnetic field strength and moderate changes in the neutral beam heat deposition profile. At the same time, however, the absolute value of the electron pressure itself increases with the heating power, the electron density, and the magnetic field strength. In this study, a reference model for the electron pressure is proposed which consists of the frozen profile and parametric dependences derived from experimental observations. It is possible to define an operational regime where this typical profile appears by comparing the electron pressure profiles with this model. In the standard configuration, at which the maximum plasma stored energy in LHD has been obtained, the frozen profile appears in the plateau to the PfirshSchlüter regimes. As the collisionality decreases to the collisionless regime, the electron pressure becomes smaller than the prediction of the model and the deterioration is significant in the plasma core region. This tendency is enhanced in the configuration with the outward-shifted magnetic axis. The global energy confinement time, τ E , in the high-collisionality regime has a weaker density dependence together with the mitigated power degradation, scaling as τ E ∝ ne 0.28 P -0.43 (ne and P are the line-averaged density and the heating power, respectively), compared with the International Stellarator Scaling 95, where τ E ∝ ne 0.51 P -0.59 .

show abstract

Section: Iss95mentioning

confidence: 99%

Electron Pressure Profiles in High-Density Neutral Beam Heated Plasmas in the Large Helical Device

Miyazawa

Yamada

Peterson

et al. 2005

J. Plasma Fusion Res.

View full text Add to dashboard Cite

show abstract

“…However, as the profiles are not available to us, we base our discussions to the responses generated in [2] instead of our own estimates of χ e .…”

Section: Resultsmentioning

confidence: 99%

“…Consider the model as given in equation (1) in which P (t) is given by (2). Furthermore, we assume that just before t + and just before t + + ∆t the temperature is at equilibrium, i.e., T (t + ) = α and T (t + + ∆t) = β, see also Fig.…”

Section: Appendix: Preservation Of Time Constant Under Applied Transfmentioning

confidence: 99%

See 1 more Smart Citation

Technical note on the linearity and power dependence of the diffusion coefficient in W7-AS

Berkel

Zwart

Hogeweij

et al. 2017

Plasma Phys. Control. Fusion

View full text Add to dashboard Cite

Abstract. Transient electron temperature measurements of a step power experiment at W7-AS are reassessed by direct comparison of the up-and downward responses of the electron temperature. The analysis shows that the response at some distance to the center behaves linear and that the model predicted responses based on a power dependent diffusion coefficient are at variance with the measured step responses.

show abstract

“…These and other non-linear transport properties have been analyzed using perturbations (often via the heat pulse diffusivity χ HP ) at different operating points and comparing them to each other and to steadystate results (power balance diffusivity χ P B ) [34,2]. Alternatively, model codes based on the physics are used to fit parameters of the non-linear models, e.g., [20,35]. The problem with such an approach is that they generally prove the existence of a non-linearity, but their interpretations depend on the used transport model.…”

Section: Introductionmentioning

confidence: 99%

New evidence and impact of electron transport non-linearities based on new perturbative inter-modulation analysis

et al. 2017

View full text Add to dashboard Cite

Abstract.A new methodology to analyze non-linear components in perturbative transport experiments is introduced. The methodology has been experimentally validated in the Large Helical Device (LHD) for the electron heat transport channel. Electron cyclotron resonance heating (ECRH) with different modulation frequencies by two gyrotrons have been used to directly quantify the amplitude the non-linear component at the inter-modulation frequencies. The measurements show significant quadratic non-linear contributions, but also the absence of cubic and higher order components. The non-linear component is analyzed using Volterra series, which is the non-linear generalization of transfer functions. This allows to study the radial distribution of the non-linearity of the plasma and to reconstruct linear profiles in the case the measurements were not distorted by non-linearities. The reconstructed linear profiles are significantly different from the measured profiles showing the significant impact the non-linearity can have.

show abstract

Physics studies in W7-AS

Cited by 36 publications

References 22 publications

Electron Pressure Profiles in High-Density Neutral Beam Heated Plasmas in the Large Helical Device

Electron Pressure Profiles in High-Density Neutral Beam Heated Plasmas in the Large Helical Device

Technical note on the linearity and power dependence of the diffusion coefficient in W7-AS

New evidence and impact of electron transport non-linearities based on new perturbative inter-modulation analysis

Contact Info

Product

Resources

About