Compatibility of the Radiating Divertor with High Performance Plasmas in DIII-D

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Excessive thermal power loading on the divertor structures presents a design difficulty for future-generation, high powered tokamaks. This difficulty may be mitigated by ''seeding'' the divertor with impurities which radiate a significant fraction of the power upstream of the divertor targets. For this ''radiating divertor'' concept to be practical, however, the confinement and stability of the plasma cannot be compromised by excessive leakage of the seeded impurities into the core plasma. One proposed way of reducing impurity influx is to enhance the directed scrape-off layer (SOL) flow of deuterium ions toward the divertor [1-5]. We report here on the successful ... continued below

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6 p. (0.2 MB)

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Petrie, T; Wade, M; Allen, S; Brooks, N; Fenstermacher, M; Ferron, J et al. June 24, 2005.

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Excessive thermal power loading on the divertor structures presents a design difficulty for future-generation, high powered tokamaks. This difficulty may be mitigated by ''seeding'' the divertor with impurities which radiate a significant fraction of the power upstream of the divertor targets. For this ''radiating divertor'' concept to be practical, however, the confinement and stability of the plasma cannot be compromised by excessive leakage of the seeded impurities into the core plasma. One proposed way of reducing impurity influx is to enhance the directed scrape-off layer (SOL) flow of deuterium ions toward the divertor [1-5]. We report here on the successful application of the radiating divertor scenario to high performance plasma operation in a DIII-D ''hybrid'' H-mode regime. The ''hybrid'' regime [6,7] has many features in common with conventional ELMing H-mode regimes, such as high confinement, e.g., H{sub ITER89P} > 2, where H{sub ITER89P} is the energy confinement normalized to the 1989 ITER L-mode scaling [8]. The main difference is the absence of sawtooth activity in the hybrid. Argon was selected as the seeded impurity for this experiment because argon radiates effectively at both the divertor and pedestal temperatures found in DIII-D hybrid H-mode operation and has a relatively short ionization mean free path. Carbon is also present as the dominant intrinsic impurity in DIII-D discharges. The geometry of this experiment is shown in Fig. 1. A double-null cross-sectional shape was biased upward (dRsep = +1.0 cm). To increase the deuterium ion flow toward the divertor at the top of the vessel, deuterium gas was introduced near the bottom. Argon was injected directly into the private flux region (PFR) of the upper divertor. In-vessel pumping of deuterium and argon was done by cryopumps located in the two upper divertor plenums, shown in cross-hatching [9]. The upper divertor, which we hereafter will simply refer to as the ''divertor'', is the region lying above the dashed line in Fig. 1, and is relatively ''closed''.

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6 p. (0.2 MB)

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  • Presented at: 32nd EPS Plasma Physics Conference, Tarragona, Spain, Jun 27 - Jul 01, 2005

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  • Report No.: UCRL-CONF-213295
  • Grant Number: W-7405-ENG-48
  • Office of Scientific & Technical Information Report Number: 877746
  • Archival Resource Key: ark:/67531/metadc877217

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  • June 24, 2005

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  • Sept. 21, 2016, 2:29 a.m.

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  • April 17, 2017, 12:11 p.m.

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Petrie, T; Wade, M; Allen, S; Brooks, N; Fenstermacher, M; Ferron, J et al. Compatibility of the Radiating Divertor with High Performance Plasmas in DIII-D, article, June 24, 2005; Livermore, California. (digital.library.unt.edu/ark:/67531/metadc877217/: accessed April 21, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.