Particle exhaust studies in ASDEX Upgrade

Bosch, H.‐S.; Coster, D.; Dux, R.; Haas, G.; Kallenbach, A.; Kaufmann, Michael; Lackner, K.; Neuhäuser, J.; Hempel, S. De Pena; Poschenrieder, W.; Schneider, R.; ASDEX-Upgrade-Team,; NI-Team,; ICRH-Team,; ECRH-Team,

doi:10.1088/0741-3335/39/11/002

Cited by 32 publications

(34 citation statements)

References 44 publications

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“…Additional puffing of deuterium reduced the Ar content in the plasma strongly, and this effect was attributed to the streaming of Ar with the D 2 into the divertor chamber. Similar experiments on ASDEX Upgrade have also shown a strong increase of the exhaust rate for Ne and Ar [8] and for He [9] with external D 2 gas puffing.…”

Section: Invariance Of Divertor Retention On External Particle Flow Isupporting

confidence: 55%

“…ASDEX Upgrade is equipped with 14 turbomolecular pumps with a pumping speed (measured in the divertor chamber) of larger than 13 m 3 ͞s for D 2 or He, increasing with the divertor neutral gas pressure [9]. For the experiments reported here, the full pumping speed (with all 14 pumps active) was actually 17 m 3 ͞s, because at such neutral gas flux densities the collisions between the D 2 molecules already become important.…”

Section: Invariance Of Divertor Retention On External Particle Flow Imentioning

confidence: 99%

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Invariance of Divertor Retention on External Particle Flow in Detached ASDEX Upgrade Discharges

et al. 1996

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Divertor plasmas with strong external gas puffing in ASDEX Upgrade have shown very efficient impurity retention, increasing with the divertor neutral gas density. The experiments presented here use feedback-controlled gas puffs in discharges with different pumping speed to keep the divertor neutral gas flux density the same. This allows for the first time a decoupling of the divertor neutral gas flux density and the external gas flow. The resulting plasmas are almost identical and show identical impurity retention, clearly demonstrating the importance of the divertor neutral gas density over the externally induced flow. PACS numbers: 52.55.Fa, 52.40.Hf Strong external gas puffing into the edge of a fusion plasma strongly affects its properties. Generally, in Ohmically heated and L-mode plasmas, the line averaged density is increased, eventually leading to a density limit disruption. The energy and particle confinement times decrease with external gas puffing. More directly, however, gas puffing modifies the scrape-off layer and divertor plasma in a divertor tokamak, and increasing the neutral gas density in the divertor has been proposed for a long time as a means of increasing power losses via radiation or collisions with the neutral gas [1,2]. Experiments with strong puffing of D 2 in the DIII-D tokamak [3,4] and in JET [5] resulted in a power load reduction at the divertor target plates and in a detached plasma at the outer target plate [5]. In all these cases, however, the energy confinement time was degraded by the gas puffing.Strong gas puffing has also often been proposed as a means of inducing particle flows in the scrape-off layer. Such flows should entrain impurities by friction, thereby flushing them into the divertor [6]. Recently the flow of impurities in the scrape-off layer of DIII-D was investigated using the "puff and pump" technique, where Ar was puffed either at the top of the vacuum vessel or in the private flux region [7]. Additional puffing of deuterium reduced the Ar content in the plasma strongly, and this effect was attributed to the streaming of Ar with the D 2 into the divertor chamber. Similar experiments on ASDEX Upgrade have also shown a strong increase of the exhaust rate for Ne and Ar [8] and for He [9] with external D 2 gas puffing.These ASDEX Upgrade results were interpreted, however, rather as an effect of the associated increase of the neutral gas and plasma densities in the divertor, which would tend to shift the ionization zone for the recycling noble gas atoms closer to the target plates. In this region, the strong background plasma flow towards the target plates would increasingly dominate over the thermal force trying to push impurity ions out of the divertor chamber, back towards the bulk plasma. This explanation of the observed variation of divertor retention with neutral density is supported by earlier, 1D scrape-off layer modeling calculations for ASDEX [10], but requires obvious confirmation by the 2D modeling effort currently under way.Experiments carried out at f...

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Section: Invariance Of Divertor Retention On External Particle Flow Isupporting

confidence: 55%

Section: Invariance Of Divertor Retention On External Particle Flow Imentioning

confidence: 99%

Invariance of Divertor Retention on External Particle Flow in Detached ASDEX Upgrade Discharges

et al. 1996

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“…As an estimate for the helium concentration in the main plasma an upper and lower limit are found in agreement with the CXRS measurements. [20] The comparison of Z eff determined from the bremsstrahlung with the one calculated from the helium concentration was performed for discharge #23619. This discharge with plasma parameters I P = 1.0 MA, B t = −2.3 T and n e,0 = 9.1 × 10 19 m −3 was carried out without NBI heating to avoid additional deuterium influx and, therefore, enable a high helium concentration.…”

Section: Helium Dischargesmentioning

confidence: 99%

Estimation of profiles of the effective ion charge at ASDEX Upgrade with Integrated Data Analysis

Rathgeber

Fischer

Fietz

et al. 2010

Plasma Phys. Control. Fusion

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Abstract.The knowledge of the effective ion charge Z eff which indicates the degree of plasma pollution is of high interest, since the tolerable impurity concentration to achieve successful ignition of a fusion plasma is limited. The quantification of Z eff at ASDEX Upgrade has been carried out by means of Integrated Data Analysis in the framework of Bayesian Probability Theory which allows the combined analysis of different bremsstrahlung and charge exchange diagnostics to obtain one joint Z eff profile. With this tool it is possible to assess the quality of the data acquired by the individual diagnostics and to find a reasonable selection of data for the routine Z eff analysis. The Z eff results are validated by the examination of different discharge scenarios and successfully applied to simulations of the neutron rate and the loop voltage. The investigation of Z eff for nitrogen seeded discharges reveals a correlation between the confinement improvement and the increase of Z eff .

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“…Two measures of divertor retention are impurity compression and impurity enrichment. 40,41 Impurity compression is defined as C z = n 0,z div / n z core where n 0,z div is the divertor impurity neutral density and n z core is the core impurity ion density. Maximizing compression can result in more power exhausted through radiation in the divertor if the temperature is optimal.…”

Section: B Impurity Transportmentioning

confidence: 99%

High confinement dissipative divertor operation on Alcator C-Mod

et al. 1999

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Alcator C-Mod [I. H. Hutchinson, et al., Phys. Plasmas 1 , 1511(1994] has operated a High-confinement-mode (H-mode) plasma together with a dissipative divertor and low core Z eff . The initially attached plasma is characterized by steady-state enhancement factor, H ITER89P [P. N. Yushmanov, et al., Nucl. Fusion 30, 1999(1990], of 1.9, central Z eff of 1.1, and a radiative fraction of ~50%. Feedback control of a nitrogen gas puff is used to increase radiative losses in both the core/edge and divertor plasmas in almost equal amounts. Simultaneously, the core plasma maintains H ITER89P of 1.6 and Z eff of 1.4 in this nearly 100% radiative state. The power and particle flux to the divertor plates have been reduced to very low levels while the core plasma is relatively unchanged by the dissipative nature of the divertor.

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Particle exhaust studies in ASDEX Upgrade

Cited by 32 publications

References 44 publications

Invariance of Divertor Retention on External Particle Flow in Detached ASDEX Upgrade Discharges

Invariance of Divertor Retention on External Particle Flow in Detached ASDEX Upgrade Discharges

Estimation of profiles of the effective ion charge at ASDEX Upgrade with Integrated Data Analysis

High confinement dissipative divertor operation on Alcator C-Mod

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