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Status of NSTX/DIII-D/MAST aspect ratio core confinement comparison studies

Status of NSTX/DIII-D/MAST aspect ratio core confinement comparison studies. M. Peng, for E.J. Synakowski For the ITPA Transport Physics Working Group Kyota, Japan April 18 - 21, 2005.

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Status of NSTX/DIII-D/MAST aspect ratio core confinement comparison studies

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  1. Status of NSTX/DIII-D/MAST aspect ratio core confinement comparison studies M. Peng, for E.J. Synakowski For the ITPA Transport Physics Working Group Kyota, Japan April 18 - 21, 2005

  2. Primary participants: E. Synakowski (PPPL), C. Petty (GA), M. Valovic (MAST). Ran a DIII-D leg of an NSTX/DIII-D/MAST core confinement similarity experiment • Starting point: an NSTX LSN H mode with  ~ 15 - 20%, good confinement, high JBS and long pulse. Well-documented w.r.t. transport (excellent ions, lossy electrons). Shape accessible on DIII-D. Focus on two times in the plasma with differing stored energies. • A challenge in developing the proposal: what do we match when we run on DIII-D? Single time slice of NSTX target discharge

  3. The NSTX target discharge had fairly constant Te and Ti, and time-evolving ne Ip = 0.8 MA BT = 0.5 T PNBI = 6 MW ENBI= 80-100 keV bT = 18% W = 0.25 MJ Density profile broadens during H-mode

  4. The plan on the DIII-D run day was as follows: • Initially, followed a similar (scaled) path in beam timing & Ip ramp. • Hope for H mode with small/no ELMs, as in NSTX case. Obtained strong ELMs on DIII-D. Their impact to be determined. Density ramp came for free. • Matched shape very nicely with = 2.0,  = 0.4, but slightly smaller minor radius than on NSTX (“shelf” inside DIII-D vessel is an obstruction).

  5. 3 plasma conditions are being pursued • Match *pol and p, and a simplifed * definition • Ip, ne, Te, Ti similar to NSTX values, but with increased BT (1.2 T) to get similar average q. Ip ~ 820 kA • Result of first DIII-D day: did well in bracketing NSTX cases of interest. • Fix *pol and p, and match usual * definition • D’less scaling arguments ==>> BT near 2 T, Ip ~ 1.3 MA. • Together with first condition, yields a matched pair with * varied by the ratio of the aspect ratios • Result for first DIII-D day:got the lower stored energy case matched • Fix *tor and p, usual *: of highest interest to MAST • D’less scaling arguments ==>> BT near 0.6 T, Ip ~ 0.4 MA. • With first condition, yields a matched pair with * varied by the ratio of the aspect ratios • Result:Not obtained on first day, got a better match on a recent DIII-D 2 hour run. Preferred case to match by MAST team.

  6. NSTX shape was very well matched • DIII-D minor radius slightly smaller than NSTX Scaled NSTX (reduced ~ 5%), actual DIII-D

  7. Next step on NSTX is an iteration from the DIII-D run • A surprise: between NSTX and DIII-D, where density and stored energy (properly scaled) were matched, temperatures did not match • Zeff and fast ion confinement possible players. NSTX next-step may include intentially dirtier plasmas, lowered beam energy to reduce fast ion stored energy • Archeology of TRANSPed DIII-D plasmas may reveal decent matches with existing data at some time points • As we went to the NSTX shape, we got different edge stability properties I.e. small ELMs on NSTX, more vigorous ELMs on DIII-D. To be addressed is how to treat these differences.

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