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Divertor Characteristics from Probe Measurements during NBI

Research Supported by. Divertor Characteristics from Probe Measurements during NBI. C.E. Bush a , R. Kaita b , P. Roney b , R. Maingi a , E.. Fredrickson b , S. Sabbagh c , V. Soukhanovskii d , J.G. Watkins e a Oak Ridge National Laboratory, Oak Ridge, TN USA

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Divertor Characteristics from Probe Measurements during NBI

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  1. Research Supported by Divertor Characteristics from Probe Measurements during NBI C.E. Busha, R. Kaitab, P. Roneyb, R. Maingia, E.. Fredricksonb, S. Sabbaghc, V. Soukhanovskiid, J.G. Watkinse aOak Ridge National Laboratory, Oak Ridge, TN USA bPrinceton Plasma Physics Laboratory, Princeton, NJ USA cColumbia University, NY USA dLawrence Livermore National Laboratory, Livermore, CA USA eSandia National Laboratories, Albuquerque, New Mexico, USA NSTX Results Review 26-28 July 2006PPPL Princeton, NJ

  2. Outline • Initial NSTX Langmuir Probe System is a coarse array • Sample IV Characteristic data • Langmuir Probe data obtained for vast majority of shots • Especially the last 3 campaigns • Data for many configurations • Data for many conditions • Report Emphasizes a Beam Power Scan • Also a series of Gas Puff experiments • Isat, Te reported for a limited set of experiments • Summary Page 2

  3. The EFIT equilibrium shows the location of the inner and outer strike-points on the divertor plates of NSTX . In general the strike-points and measured probe positions are in good agreement. Backup Slides END Lower Single-null Divertor Outer Strike-point Inner Strike-point

  4. Divertor Langmuir Probes 1 R(probe 1) = 1.02 m 2 R(probe 2) = 0.91 m 3 R(probe 3) = 0.80 m 4 R(probe 4) = 0.49 m 1 2 4 3 Page 4

  5. ~Isat Fit to IV Characteristic for Flush Probe 14 0.12 Sweep voltage ± 50 volts Only points V < VLimit included in fit. Here VLimit = +15 V The relatively flat upper part of curve due to 10 volt limit on digitizer not to electron current saturation. * Te fit corrected for nonsaturation of ion current. Te = 6.72 eV (12 eV uncorrected). Fit to IV data IV Characteristic 0.08 I Solid lines, data for 2 different sweeps I (A) V 0.04 Probe sweep voltage 0 Isat(ion) -0.04 40 0 -40 V (Volts) Page 5

  6. Outer Divertor Probe Te vs Time, Pb = 4 MW Shot 112498 Pb = 4 MW Rprobe = 0.91 m Page 6

  7. Heat flux profile becomes more peaked with increasing NBI power 50 • Peak in Isat occurs near peak heat flux • In general peak Isat is independent of Pb, heating power 0.306 sec 40 • Isat Probe 3 30 Isat (mA) 20 IsatProbe 2 10 IsatProbe 1 0 R. Maingi Page 7

  8. Isat Does not Depend Strongly on NBI Power 0.10 Shots112508112498112499 Isat(A) 0.05 Probe 1 0 Isat(A) 0.05 Probe 2 0 Isat(A) 0.05 Probe 3 0 6 Pb(MW) 3 0 0.2 0.4 0.6 0.8 0 Time (s) Page 8

  9. Isat for Probes - PDD with LDGIS GAS Puff 700 Torr 0.0 0.1 0.2 0.3 0.4 0.5 Time (s) 2711 116486 2812 60 2913 Current (mA) 40 20 0 1307 1408 80 1509 Current (mA) 60 40 20 0 1.0 Strike point radius (m) 0.8 0.6 0.4 Page 9

  10. Summary • NSTX has a coarse probe array • Radial variation of Isat Outer Divertor similar to that of the heat flux • Te along divertor surface in range 4 to 20 eV over the beam power scan • Response to Gas Puff Experiments • Probes in SOL show correlation with Dα measured at divertor plate (possible ~10 ms lag) • Signals large in SOL, smaller in private flux region • Other features Page 10

  11. END Page 11

  12. Corrected Fit Normal IV Characteristic Fit for 3 parameters Isat, Vf, Te I = Is*[1-exp(e(V-Vf)/kTe)] For nonsaturation of I(V) we need a 4th I=[Is+ I(Vf-V)][1-exp(e(V-Vf)/kTe)] Page 12

  13. Isat Does not Depend on NBI Power 0.10 Isat(A) Probe 3 0.05 0 4 D(arb) 2 0 6 Pb(MW) 3 0 0.2 0.4 0.6 0.3 0 Time (s) Page 13

  14. Isat for Probes - Neon GAS Puff 190 Torr, 4Tls 2711 116489 15 2812 2913 Current (mA) 10 Isat 5 0 1307 25 1408 1509 Current (mA) 20 Isat 15 10 0 5 1.0 Strike point radius (m) 0.8 0.6 0.4 0.0 0.1 0.2 0.3 0.4 Time (s) Page 14

  15. Histograms of Isat for Outer Divertor Probes 0.08 Isat(13) (A) 0.04 0 0.04 Isat(14) (A) 0 0.02 Isat(15) (A) 0.01 0 4 Dα(arb.) 0 400 Ip(kA) 0 0.9 R(m) 0.7 0.0 0.2 0.4 Time (s) Page 15

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