H-mode access in the low density regime on JET

Y. Andrew, R. Sartori, E. Righi, E. De la Luna, S. Hacquin, D.F. Howell, N.C. Hawkes, L.D. Horton, A. Huber, A. Korotkov, M.G. O'Mullane, JET EFDA Contributors

Research output: Contribution to journalArticle

37 Citations (Scopus)

Abstract

1 H-mode access studies under conditions of very low plasma density provide valuable information on the, physics of the edge transport barrier formation and are an important part of the operational scenario development for the next step fusion device, ITER. JET operation with a very low edge electron density, (n) over bar (e) = 0.8-1.4 x 10(19) m(-3), with the MkII gas box septum divertor was found to have a significant effect on the power threshold for the L-H transition, P-th. A sharp `turning point' below which P-th increases with decreasing (n) over bar (e) is found for I-p/B-t values of 2.5 MA/2.7 T, 2.5 MA/2.6T 2.5 MA/2.4T and 2.2 MA/2.4T. The pedestal electron temperature demonstrates a very similar dependence on the edge (n) over tilde (e) as P-th. The role of Z(eff) in the variation of the H-mode power threshold with density is also considered. Shots with the divertor septum present are compared with an identical (n) over bar (e) scan, run with the MkII GB septum replacement plate divertor at 2.5 MA/2.7 T and 2.5 MA/2.6 T. The results from this investigation indicate that removal of the septum may have lowered the (n) over tilde (e) `turning point' for P-th.
Original languageEnglish
Pages (from-to)479-488
Number of pages10
JournalPlasma Physics and Controlled Fusion
Volume48
Issue number4
DOIs
Publication statusPublished - 1 Apr 2006

    Fingerprint

Keywords

  • spherical tokamaks
  • boundary layer effects
  • plasma-material interactions
  • plasma devices

Cite this

Andrew, Y., Sartori, R., Righi, E., De la Luna, E., Hacquin, S., Howell, D. F., ... Contributors, JET. EFDA. (2006). H-mode access in the low density regime on JET. Plasma Physics and Controlled Fusion, 48(4), 479-488. https://doi.org/10.1088/0741-3335/48/4/001