Title: Poloidal asymmetry in the narrow heat flux feature in the TCV scrape-off layer

Abstract

Heat flux profiles inferred from a reciprocating probe at the outer midplane of the TCV tokamak during inner wall limited discharges feature radial fall-off lengths that shorten near the last closed flux surface (LCFS) consistent with the so-called narrow feature. The narrow feature is significantly wider on the outboard side compared with that measured on the inner wall by infrared thermography, so it is difficult to discern from the main scrape-off layer feature. After small shifts were applied for alignment, the fraction of the power contained in the narrow feature matches between inboard and outboard measurements, and they scale together with plasma current Ip, suggesting that we are observing the same phenomenon. The outboard side fall-off length within the narrow feature is found to scale closely with the radial correlation length of the edge turbulence as expected if the narrow feature arises due to radially sheared E x B flows. This is found to hold true even for cases where the narrow feature is weak and the fall-off lengths are approaching that of the far scrape-off layer. After the small shifts for alignment, non-zero floating potential profiles were found to match between inboard and outboard sides. A simple model ofmore » polarization and diamagnetic cross-field currents is described, which is consistent with the shape of these floating potential profiles. The model predicts that the floating potential at the LCFS must be negative, which supports the argument to shift the upstream measurements. The predicted currents are also consistent with the E x B flows believed to cause the narrow feature. The model is used to predict the magnitude of the floating potential of the LCFS, and the results are found to match measurements for all values of I_p. This paper therefore demonstrates consistency between the measurements of the narrow feature on the inboard and outboard sides of the plasma, as well as consistency between the measurements, non-linear turbulence simulations, and analytical models of the narrow feature arising from sheared E x B flows.« less

Authors:

Tsui, C. K. ^[1]; Boedo, J. A.  ^[2];

• Search DOE PAGES for author "Boedo, J. A."
• Search DOE PAGES for ORCID "0000-0003-2230-4112"

Halpern, F. D. ^[3]; Loizu, J. ^[4]; Nespoli, F. ^[5]; Horacek, J.  ^[6];

• Search DOE PAGES for author "Horacek, J."
• Search DOE PAGES for ORCID "0000-0002-4276-3124"

Labit, B. ^[5]; Morales, J. ^[5]; Reimerdes, H. ^[5]; Ricci, P.  ^[5];

• Search DOE PAGES for author "Ricci, P."
• Search DOE PAGES for ORCID "0000-0003-3117-2238"

Theiler, C. ^[5]; Coda, S. ^[5]; Duval, B. P. ^[5]; Furno, I. ^[5]

---

+ Show Author Affiliations

1. Univ. of California, San Diego, CA (United States); Ecole Polytechnique Federale Lausanne (Switzlerland). Swiss Plasma Center (SPC)
2. Univ. of California, San Diego, CA (United States)
3. General Atomics, San Diego, CA (United States)
4. Max-Planck-Inst. fur Plasmaphysik, Greifswald (Germany)
5. Ecole Polytechnique Federale Lausanne (Switzlerland). Swiss Plasma Center (SPC)
6. Academy of Sciences of the Czech Republic (ASCR), Prague (Czech Republic). Inst. of Plasma Physics

Publication Date:

Wed Jun 14 00:00:00 EDT 2017

Research Org.:

Univ. of California, San Diego, CA (United States); General Atomics, San Diego, CA (United States)

Sponsoring Org.:

USDOE Office of Science (SC)

Contributing Org.:

TCV Team; EUROfusion MST1 Team

OSTI Identifier:

1474309

Alternate Identifier(s):

OSTI ID: 1363832

Grant/Contract Number:  

SC0010529; FG02-95ER54309

Resource Type:

Accepted Manuscript

Journal Name:

Physics of Plasmas

Additional Journal Information:

Journal Volume: 24; Journal Issue: 6; Journal ID: ISSN 1070-664X

Publisher:

American Institute of Physics (AIP)

Country of Publication:

United States

Language:

English

Subject:

70 PLASMA PHYSICS AND FUSION TECHNOLOGY