XP 1017: RF heating at divertor/SOL regions

1. NSTX Supported by XP 1017: RF heating at divertor/SOL regions College W&M Colorado Sch Mines Columbia U Comp-X General Atomics INEL Johns Hopkins U LANL LLNL Lodestar MIT Nova Photonics New York U Old Dominion U ORNL PPPL PSI Princeton U Purdue U SNL Think Tank, Inc. UC Davis UC Irvine UCLA UCSD U Colorado U Maryland U Rochester U Washington U Wisconsin J.C. Hosea, PPPL J-W Ahn2, R. E. Bell1, E. Feibush1, E. Fredrickson1, D. L. Green2, R. W. Harvey3, E. F. Jaeger2, B. P. LeBlanc1, R. Maingi2, C. K. Phillips1, L. Roquemore1, P. M. Ryan2, G. Taylor1, K. Tritz4 , E. J. Valeo1, J. Wilgen2, J. R. Wilson1 and the NSTX Team 1Princeton Plasma Physics Laboratory, Princeton, NJ, USA 3Oak Ridge National Laboratory, Oak Ridge, TN, USA 2CompX, Del Mar, CA USA 4Johns Hopkins University, Baltimore, MD, USA Culham Sci Ctr U St. Andrews York U Chubu U Fukui U Hiroshima U Hyogo U Kyoto U Kyushu U Kyushu Tokai U NIFS Niigata U U Tokyo JAEA Hebrew U Ioffe Inst RRC Kurchatov Inst TRINITI KBSI KAIST POSTECH ASIPP ENEA, Frascati CEA, Cadarache IPP, Jülich IPP, Garching ASCR, Czech Rep U Quebec XP Review April 1, 2010

2. XP 1017: RF heating at divertor/SOL regions Goals: • Understand the characteristics of the HHFW edge heating that has been observed in “hot” zones on the outer divertor plates • Help benchmark edge heating effects in advanced RF heating codes Objectives: • Probe divertor and antenna hot zones and investigate heating characteristics and processes • Divertor hot zones • Characterize divertor hot zones with visible and IR cameras, as well as with probes • Enhance exploration of hot zone with scans in magnetic field pitch, gapout, and antenna phase • Antenna hot zones • Characterize antenna hot zones with visible and IR cameras, as well as with probes, reflectometer • Many additional diagnostics needed to investigate edge heating properties • ERD, TS, CHERS, etc. 2

3. Run Plan Overview • In order to perform this study in the presence of the new LLD system, it is necessary to perform a power scan for the “hot” zone located on the LLD plate to determine the maximum HHFW power compatible with the LLD operation. • This will be followed by a magnetic pitch scan to sweep the “hot” zone into the views of the Bay I and H IR cameras, and simultaneously, over the RF probes at Bay J. Ideally the camera at Bay J can be filtered to give IR data as well. Also, it is essential to have camera views as usual of the global plasma/center stack region and of the antenna. • A camera filtered to give IR data viewing the antenna is needed to assess the local heating on the antenna. The antenna local probes and reflectometer as well as the ERD/TS/CHERS/etc will add to the documentation of the edge heating and RF fields. • Once these steps are done, the effect on the ‘hot’ zone heating of gapout scans and of antenna phase scans will be conducted to see if the zones map with the location of the onset density for perpendicular wave propagation. 3

4. RF heated pattern on lower divertor plate follows the change in magnetic field pitch (PRF = 2.7 MW) -90° -90° Bay G IR view Bay I IR view 452 ms 455 ms RF RF 439.64 – 439.31 ms

5. IR cameras and probes are critical for documenting edge heating 135325 135333 -90° Bay H fast IR view Bay G IR view Bay I IR view Antenna probes, reflectometer Bay J IR view (filtered) 455 ms Antenna IR view (filtered) Bay J probes 452 ms B = 4.5 kG, IP = 0.8 MA • New IR views of Bay J bottom and of antenna are needed for power deposition measurements • Field pitch can be varied to pass hot zone over probe at Bay J bottom • Higher field pitch will permit view of hot zone by fast IR at Bay H 439.64 – 439.31 ms 5

6. RF “hot” zone should be in fast IR view at Bay H for IP = 1 MA at BT = 4.5 kG BT = 4.5 kG, IP = 0.8 MA case Comparison with Bay I indicates shift of peak will suffice for viewing at Bay H ELM heat deposition peaks at outer strike point and diminishes with R. Does ELM affect hot zone deposition directly?

7. Location of heat zone has apparent small dependence on phase at lower and upper divertor plates 439.64 – 439.31 ms Can this be enhanced and related to the onset density with a gap scan? Does gap size affect edge heating?

8. Experimental run plan I Edge HHFW heating vs power: • Setup conditions of shot 135337 but with PRF = 500 kW – 2 shots (1 no RF) • 4.5 kG, 0.8 MA • Alternative: 5.5 kG, 1MA if better for stability • Increase PRF in steps of 500 kW to maximum allowed by LLD operation – 6 shots • Closely for monitor molybdenum impurity and stop at acceptable level • Also, monitor effect on lithium in discharge II Scan magnetic field pitch at best PRF: • 4.5 kG, 1 MA - 2shots (1 no RF) • 4.5 kG, 0.9 MA - 2shots (1 no RF) • 4.5 kG, 0.7MA - 2shots (1 no RF) • 4.5 kG, 0.6 MA - 2shots (1 no RF) • Alternative: scan current with B = 5.5 kG starting at 1.2 MA 8

9. Experimental run plan (cont.) III Scan gapout: • With 135337 conditions with acceptable PRF, run shots with and without RF for three gaps – 6 shots • 4-6-8 cm or 4-8-12 cm gaps IV Scan phase in single shot: • 135337 case above with 4.5 kG, .8 MA • -150° to -90° during pulse – 100 ms each – 1 shot Total shots 23 9