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XP 505: The dependence of power threshold on dr sep and X-point height

Research Supported by. XP 505: The dependence of power threshold on dr sep and X-point height. Hendrik Meyer EURATOM/UKAEA Fusion, UK Rajesh Maingi Oak Ridge National Laboratory, USA Ted Biewer Massachusetts Institute of Technology, USA. Improved H-mode access in DN. Motivation:

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XP 505: The dependence of power threshold on dr sep and X-point height

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  1. Research Supported by XP 505: The dependence of power threshold on drsep and X-point height Hendrik Meyer EURATOM/UKAEA Fusion, UK Rajesh Maingi Oak Ridge National Laboratory, USA Ted Biewer Massachusetts Institute of Technology, USA NSTX Research Forum, 12 - 16 Dec. 2005, PPPL

  2. Improved H-mode access in DN Motivation: • Pthr reduced by factor 2 in C-DN on MAST (NSTX similarity shape). • 20 % of Pthr reduction in C-DN on AUG. • Results on NSTX in 2004 suggested similar effect. [1] Meyer et.al., PPCF 47 p843 (2005) [2] Meyer et.al., NF to be publ. In Dec. 2005 NSTX Research Forum, 12 - 16 Dec. 2005, PPPL

  3. from toroidal He+ velocity MAST from Doppler reflectometry Er more negative in C-DN (L-mode) • SOL flow pattern sets-up Er in during L-mode. • B2SOLPS5.0 simulations [IAEA TM H-mode]. • Changes on HFS more pronounced than on LFS. • Agreement with MAST and AUG data. NSTX Research Forum, 12 - 16 Dec. 2005, PPPL

  4. Goals of XP • Measure Pthr in DN, L-SN, and U-SN with NBI heating. • Compare Pthr with RF and NBI heating • Effect of momentum input. • Measure edge rotation and edge profiles before and after the L/H transition. • Measure Pthr with different heights of X-point inL-SN. NSTX Research Forum, 12 - 16 Dec. 2005, PPPL

  5. Lowest Pthr in DN ― highest in U-SN NBI heated:Ip= 0.6 MA, Bt = 0.45 T RF heated:Ip = 0.6 MA, Bt = 0.45 T Ohmic:Ip = 0.9 MA, Bt = 0.45 T, -24 mm < drsep < 0 (117754, 117756) NSTX Research Forum, 12 - 16 Dec. 2005, PPPL

  6. Sharp transition in L-SN and U-SN (NBI) #117752 #117747 #117750 #117752@0.24 #117747@0.24 #117750@0.24 NSTX Research Forum, 12 - 16 Dec. 2005, PPPL

  7. #117776 #117777 #117782 #117776@0.3 #117777@0.3 #117782@0.3 Pthr increases with drsep (RF) NSTX Research Forum, 12 - 16 Dec. 2005, PPPL

  8. Results Summary • Local minimum of Pthr in C-DN. • Pthr 4 times higher in U-SN than in L-SN. • Similar to conventional tokamaks. • First H-mode in U-SN in an ST. • Similar behaviour with RF heating. • Pthr seems to increase with RF shot history (impurities?) • Pthr increases with drsep in L-SN. NSTX Research Forum, 12 - 16 Dec. 2005, PPPL

  9. Steps towards publication • Compare net power rather then injected power. • Compare edge Te, ne and Ti evolution through the L/H transition. • Comparison with L/H threshold theories. • Compare E£B shearing rate with linear growth rate of fluctuations. NSTX Research Forum, 12 - 16 Dec. 2005, PPPL

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