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Profile Comparisons from the MAST/NSTX Power Threshold Identity Experiment

Research Supported by. Profile Comparisons from the MAST/NSTX Power Threshold Identity Experiment. Rajesh Maingi Oak Ridge National Laboratory Hendrik Meyer UKAEA Fusion And the NSTX and MAST Teams NSTX Physics Meeting March 8, 2004 Princeton, NJ.

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Profile Comparisons from the MAST/NSTX Power Threshold Identity Experiment

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  1. Research Supported by Profile Comparisons from the MAST/NSTX Power Threshold Identity Experiment Rajesh Maingi Oak Ridge National Laboratory Hendrik Meyer UKAEA Fusion And the NSTX and MAST Teams NSTX Physics Meeting March 8, 2004 Princeton, NJ Page 1

  2. NSTX and MAST save similar plasma size but MAST vacuum vessel larger and outer walls further away Vpl/VVV ~ 35-40% NSTX Vpl/VVV ~ 6-10% MAST Passive stabilizing plates Page 2

  3. First Detailed MAST/NSTX Identity Experiment Has Been (Nearly) Completed! Goals: • compare L-H power threshold in same CDND (double-null with drsep < 3mm) shape with same Ip, Bt, density, inner-wall midplane fueling location, etc. • determine if PLH lowest with drsep=0 (go to +/- 10 mm) Results: • CDND NBI power very similar near LH transition (~300-350 kW); need to compute PLOSS • LDND (DN with drsep ~ 10 mm, downward) had higher PLH > 1.7 MW • NSTX shape was a little bigger, and was developed with rtEFIT control (needs only a little more development) Page 3

  4. Dithery H-mode in CDND near PLH in MAST 0.5 0.0 1.0 0.0 0.4 0.0 0.0 Ip [MA] ---- 8842 ---- 8851 ---- 8848 ---- 8852 PNBI [MW] PLH ne [1019 m-3] Type III ELMs Da[au] dithers 0.0 0.1 Time[s] 0.2 0.3 Page 4

  5. NSTX dithers not as ‘periodic’ as MAST (CDND near PLH) “firm” L-H “dithers” Page 5

  6. NSTX #111378 277msec (NBI 700 kW) MAST #8851 200msec (NBI 580 kW) NSTX #111378 343msec MAST #8851 300msec Z (m) Z (m) R (m) R (m) CDND Shapes were reasonably well matched, although NSTX shape (under rtEFIT) was a little larger Double-null Drsep<1mm (“CDND”) NSTX vac. ves. Double-null Drsep<1mm (“CDND”) NSTX vac. ves. Page 6

  7. NSTX ne profile more peaked and Te profile broader early R [m] R [m] R [m] yN yN yN Page 7

  8. NSTX ne (Te) lower(higher) later in H-mode phase R [m] R [m] R [m] yN yN yN Page 8

  9. Clear H-mode Transition in LDND near PLH in MAST 0.4 0.0 2.0 0.0 0.6 0.0 0.0 ne [1019 m-3] PLH PNBI [MW] Ip [MA] ---- 8856 ---- 8857 ---- 8859 Da[au] L-H (ELM-free) L-H (ELMy) 0.0 0.1 Time[s] 0.2 0.3 0.4 Page 9

  10. No transition observed in LDND in NSTX (too low density or MHD at NBI turn-on?) (Reconstructed) (no H-mode) Sawteeth Page 10

  11. NSTX #111383 391msec (NBI 1.1 MW) MAST #8859 280 msec (NBI 1.4 MW) NSTX #111381 301msec NSTX #111380 301msec Z(m) Z(m) R(m) R(m) NSTX LDND shape a little larger than MASTMagnetic balance (drsep) scan possible with rtEFIT Single-null Drsep~10mm (“LDND”) NSTX vac. ves. Single-null Drsep~+/- 3mm (“LDND”,”UDND”) NSTX vac. ves. Page 11

  12. NSTX never achieved H-mode in LDND, but maybe needed a little more power or higher density? R [m] R [m] R [m] yN yN yN Page 12

  13. Summary and Future Work • First joint NSTX/MAST experiment was a good first step toward the proposed 3-way NSTX/MAST/DIII-D collaboration on the effect of aspect ratio on pedestal • CDND power threshold was remarkably similar in terms of NBI power -> wall proximity does not play a big role in these conditions?! • Higher power CDND discharge had type IIII ELMs in MAST but largely ELM-free in NSTX • Need more LDND data from NSTX (w/edge rotation data…) • Need to work out issues related to mapping of profiles inside and outside of magnetic axis • Need better comparison shots well in H-mode, at higher Ip… Page 13

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