Observation of<i>z</i>-dependent impurity accumulation in the PBX tokamak

Ida, K.; Fonck, R.J.; Šesnić, S.; Hülse, R.; LeBlanc, B.

doi:10.1103/physrevlett.58.116

Cited by 46 publications

(42 citation statements)

References 11 publications

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“…More recent experiments on ASDEX [3][4][5], TEXT [6,7], JET [8] and TFTR [9] have also demonstrated impurity peaking on axis following the injection of frozen hydrogen pellets or the transition to other improved confinement regimes. Similarly, Z-dependent impurity accumulation, in general agreement with estimates of neoclassical transport, has been measured during neutral-beam-heated H mode discharges in PBX [10,11]. Furthermore, heavy impurity peaking in improved confinement modes in ASDEX has been accurately modelled using a neoclassical model [4], and light impurity peaking in high density discharges can also be explained by neoclassical models [5].…”

Section: Introductionmentioning

confidence: 63%

Neoclassical analysis of impurity transport following transition to improved particle confinement

Wenzel

Sigmar

1990

Nucl. Fusion

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Strongly peaked impurity density profiles have been observed in Alcator C after frozen hydrogen pellet injection. More recent experiments in ASDEX, PBX, TEXT, JET, and TFTR have exhibited similar impurity accumulation during regimes of improved confinement. In this context, we present calculations of the neoclassically predicted equilibrium profiles of the intrinsic impurities in Alcator C. These theoretical calculations were performed for comparison with the experimentally determined peaked profiles observed after pellet fueling. Profiles of the main impurities in Alcator, carbon (C) and molybdenum (Mo), were measured using soft x-ray diagnostics. C exists in the plateau collisionality regime, and its transport is dominated by collisions with the hydrogen background ions and temperature gradient effects. Mo is in the Pfirsch-Schliiter regime, and it is driven mostly by collisions with C inside r/a ~ 0.25 and temperature gradients outside this radius. The rigorous multi-ion, mixed regime calculation necessary for the Mo transport is shown here. The predicted C profile is in excellent agreement with observation, and the profile predicted for Mo (which is not as close to equilibrium as C) is in fair agreement with observation.

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Section: Introductionmentioning

confidence: 63%

Neoclassical analysis of impurity transport following transition to improved particle confinement

Wenzel

Sigmar

1990

Nucl. Fusion

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“…This potentially serious problem is counteracted by an effect known as temperature screening, which reduces the inward directed drift velocity of the impurity ions. While in some experiments no such Z dependence of the impurity transport was seen (Marmar et al 1982,Giannella et al 1994,Mattioli et al 1998, others do confirm this behaviour at least qualitatively (Ida et al 1987, Rapp et al 1997, Dux et al 1999. The ambiguity of the results may be attributed to other mechanisms, which add to the neoclassical transport, such as plasma turbulence and MHD instabilities.…”

Section: Impurity Transportmentioning

confidence: 95%

Internal transport barriers in tokamak plasmas*

Wolf

2002

Plasma Phys. Control. Fusion

325

310

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Internal transport barriers in tokamak plasmas are explored in order to improve confinement and stability beyond the reference scenario, used for the ITER extrapolation, and to achieve higher bootstrap current fractions as an essential part of non-inductive current drive. Internal transport barriers are produced by modifications of the current profile using external heating and current drive effects, often combined with partial freezing of the initial skin current profile. Thus, formerly inaccessible ion temperatures and Q eq DT values have been (transiently) achieved. The present paper reviews the state of the art of these techniques and their effects on plasma transport in view of optimizing the confinement properties. Implications and limits for possible steady state operations and extrapolation to burning plasmas are discussed.

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“…Sawtooth crashes have been modelled as a complete flattening of the total impurity density within the mixing radius r mix = r inv · √ 2, where r inv is the position of the q = 1 surface [28,29]. The quality of the fit is defined by the total χ 2 considering lines of sight of camera I within the diagnostic sensitivity range.…”

Section: Benchmarking Against χ 2 -Minimization Methodsmentioning

confidence: 99%

Local effects of ECRH on argon transport in L-mode discharges at ASDEX Upgrade

Sertoli

Angioni

Dux

et al. 2011

Plasma Phys. Control. Fusion

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Abstract. The transport of argon as trace impurity has been investigated in electron cyclotron resonance heated L-mode discharges at ASDEX Upgrade to test recent theories predicting the rise of an outward impurity convection. The profiles of the argon transport coefficients for r/a < 0.65 have been determined by analysing the linear flux-gradient dependency of the total argon ion density evolution after the puff. A new methodology to experimentally obtain the total impurity ion density from the integrated use of two spectroscopic diagnostic and the 1D impurity transport code STRAHL has been developed. Results confirm the enhancement in diffusivity and the rise of the positive convection observed in previous studies, but show for the first time how these effects are strongly localized around the electron cyclotron resonance heating deposition radius. These experimental results are found in promising qualitative agreement with a set of quasi-linear gyrokinetic simulations with the code GS2.

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Observation ofz-dependent impurity accumulation in the PBX tokamak

Cited by 46 publications

References 11 publications

Neoclassical analysis of impurity transport following transition to improved particle confinement

Neoclassical analysis of impurity transport following transition to improved particle confinement

Internal transport barriers in tokamak plasmas*

Local effects of ECRH on argon transport in L-mode discharges at ASDEX Upgrade

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