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Stanley M. Kaye, PPPL C. Bush, ORNL Rajesh Maingi, ORNL Hendrik Meyer, MAST ITPA Meeting

Status of L-H Threshold Analysis and Recent Results From STs. Stanley M. Kaye, PPPL C. Bush, ORNL Rajesh Maingi, ORNL Hendrik Meyer, MAST ITPA Meeting Lisbon, Portugal 8-10 November 2004. L-H Threshold vs Probed as Part of NSTX/MAST Identity Experiment. NSTX #111378 277msec

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Stanley M. Kaye, PPPL C. Bush, ORNL Rajesh Maingi, ORNL Hendrik Meyer, MAST ITPA Meeting

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  1. Status of L-H Threshold Analysis and Recent Results From STs Stanley M. Kaye, PPPL C. Bush, ORNL Rajesh Maingi, ORNL Hendrik Meyer, MAST ITPA Meeting Lisbon, Portugal 8-10 November 2004 1

  2. L-H Threshold vs Probed as Part of NSTX/MAST Identity Experiment NSTX #111378 277msec MAST #8851 200msec Z (m) R (m) rtEFIT crucial for fine Drsep control Vary Drsep to study PLH vs configuration PLH in double-null (Drsep<1 mm)comparable 350 kW @ 0.5 MA, 0.45 T PLH significantly higher for |Drsep|>1 mm 2 (Maingi, Meyer)

  3. H-mode physics on MAST close to double null H. Meyer et.al. 5cm  8 i L/H transition physics: • Reduced L/H threshold in exact double null configuration on MAST, NSTX and ASDEX Upgrade. • Possible cause: difference of radial electric field in L-mode. ELM stability: • Edge profiles in single null are more stable to ELMs on MAST than in double null. • Not due to effect of 2nd X-point on magnetic shear. -1 kV/m Difference of Er between exact DN and lower SN in L-mode. 3

  4. Results for Ohmic H-mode Scoping Study (NSTX) • H-modes at 600 to 900 kA, 3.0 to 4.5 kG TF • Short H-mode at Ip = 600 kA, Bt = 3 kG • OH H-modes obtained for 1st time ever on NSTX during this run • Most readily obtained after hot boronization • Alternating helium conditioning shots seem to help • Obtained both double null (DN) and lower single null (LSN) divertor • Most short duration, some with ELMs and some ELM-free • Peaked ne • ELMy: Small high frequency ELMs keep ears from developing • ELM-free: have ears, but edge peak lower than central ne 4

  5. Decrease in Er in NSTX Prior 30 ms Prior to L-H Transition 5

  6. PLOSS for NBI and OH H-modes 6 (Bush)

  7. Test of L/H transition theories against MAST data H. Meyer et.al. Statistical comparison: • Four leading theories tested using fit to high resolution Thomson scattering. • MAST data support finite  drift-wave turbulence suppression by self generated flow shear [Guzdar et.al., PRL, (2001)]. • Predicted critical Te needs to be scaled by factor of ~2 for quantitative agreement. Profile comparison in L-mode just below Pthr: • Kinetic profiles not affected by change in magnetic configuration from L-SN to C-DN. • Element of physics leading to easier H-mode access in exact DN not included in tested theories. 7

  8. L-H Transition Theories Have Limited Predictive Capability For NSTX Peeling Drift Alfvén No agreement with finite-b drift wave theory 8 (Kaye)

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