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Controlling density rise through helium conditioning.

Surface physics TFTR, DIII-D, NSTX results XP: Controlling density rise through limiting divertor temp. rise and through He conditioning. Controlling density rise through helium conditioning. C H Skinner, H Kugel, R Maingi, D Mueller,. PPPL Jan 7th, 2003.

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Controlling density rise through helium conditioning.

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  1. Surface physics TFTR, DIII-D, NSTX results XP: Controlling density rise through limiting divertor temp. rise and through He conditioning. Controlling density rise through helium conditioning. C H Skinner, H Kugel, R Maingi, D Mueller,... PPPL Jan 7th, 2003

  2. Surface Physics: Complex non-linearly coupled plasma - wall system. Microscopic-scale perspective Not a simple homogeneous system on any scale: - processes on wall include: TFTR tile KC-22 200 µm Chiu et al., codeposit original tile convoluted, highly porous structure, codeposit poorly thermally connected

  3. Temperature effects: Radiation Enhanced Sublimation (RES) as temp. rises D release Roth & Moller Doyle et al., Chemical Sputtering ≈10 mm Skinner et al., Temp: 1841 °C left, 1181 °C right Same heat flux (from laser spot) Microhotspots - surface temperature not single value (varies x2) Vietzke & Haasz.

  4. High performance shots access depths into wall untouched by He glow GDC. Interaction Depth: z = 2 z = 1 Doyle et al., Plasma ions approaching the material surfaces are accelerated by the sheath potential to an energy of E≈2T +3ZT, where T is the plasma temperature adjacent to the material and Z is the ion charge. He++ impacts at higher energy than D+ Wampler et al.,

  5. TFTR He conditioning: Strachan et al., Mansfield et al., Strachan concluded that on TFTR both L & Supershot plasma transport increased with D influx through deeper heated layer in PFCs at increased beam power and increased plasma wetted area. [NF 39 (1999) 1093].

  6. R Maingi, P Efthimion et al., DPP APS 2000 “Wall conditioning and impurity control in NSTX” HELIUM DISCHARGES USEFUL FOR REDUCING RECYCLING AND IMPURITIES • Deuterium reference • discharges(12 Helium • discharges between) • Da reduced • Carbon reduced • li slightly reduced • Stored energy • unchanged Ip [MA] Da [au] CIII emission li WMHD [kJ] 102300 102317

  7. Density Rise: DIII-D Density Rise: NSTX Ip [MA] PNBI/10 [MW] ne [1019 m-3] Da [au] #108728 WMHD*10 [MJ] H98pby2 Maingi et al., 5 yr forum The IPPA 5 year goal (for end FY 2005) includes “Determine the ability for managing intense energy and particle fluxes in the edge geometry and for increasing pulse durations…” Rensink et al., modeling showed H-mode density rise due to longer confinement time and thinner scrape off layer more transparent to incoming particles.

  8. Outline of XP: Prequisite: well boronized, NBI available D fiducial e.g. 108741 Change triangularity to jog strikepoint to reduce divertor temperature rise Compare density rise and divertor temperature. Repeat D fiducial Run He NBI discharges to deplete D in divertor. Repeat D fiducial Compare USL discharges if time permits.

  9. NSTX EXPERIMENTAL PROPOSAL XP 304 • Controlling density rise through helium conditioning • C. H. Skinner, D Mueller, H Kugel, R Maingi….. • 1. Overview of planned experiment • One run day: • Goal 1: Assess role of divertor temperature in density rise and impurity generation by strike point jog. • Goal 2: Reduce density rise by depleting D in divertor with He conditioning with NBI. • Goal 3: (time permitting) Compare conditioned LSN fiducial to same discharge but USN run on un He-conditioned upper divertor. • run Wednesday January 29th...

  10. Temperature effects: Radiation Enhanced Sublimation (RES) as temp. rises D release Roth & Moller Doyle et al., Chemical Sputtering ≈10 mm Skinner et al., Temp: 1841 °C left, 1181 °C right Same heat flux (from laser spot) Microhotspots - surface temperature not single value (varies x2) Vietzke & Haasz.

  11. Problems: machine control software (2.25 h) CA to fix Mirnov (0.75 hr) Software loads wrong TF - CA to check rectifier (2.25 hr) TF trip gives 26% Beta toroidal (#109941) XP time (3.75 hr) insufficient time for He conditioning, focus on strike point jog develop discharge with 220ms long, reasonably quiescent H-mode by adjusting CS gas feed jog strike point with PF2 (PF1 ineffective) 2.5 jog/no jog comparisons show roll over in density before loss of H-mode (caveat emptor) Overview of run day:

  12. Jog shot 109947: H-mode from 267 - 418 ms effect on density rise ? 109947 had PF2L increase from -7 to -8.5 from 380 to 415 ms, hold until 530 ms then ramp back down to -7

  13. Indication of density rollover after strike point jog, before L-mode, but... Strike point jog outer strike point position 109946 109947 109947 had PF2L increase from -7 to -8.5 from 380 to 415 ms, hold until 530 ms then ramp back down to -7 ...H-mode... L-mode D-alpha Line average density (1e13) MPTS comparison next VG

  14. ... but motion away from CS causes major part of density reduction.

  15. Indication of density rollover after strike point jog, before L-mode, but... Strike point jog outer strike point position 109950 109952 109952 had PF2L increase from -7 to -8.5 from 380 to 420 ms, L-mode D-alpha Line average density (1e13) MPTS comparison next VG

  16. ... but motion away from CS causes major part of density reduction.

  17. Indication of density rollover after strike point jog, before L-mode, but... Strike point jog 109955 no time for no jog shot outer strike point position 109955 had PF2L increase from from 320 ms, L-mode D-alpha Line average density (1e13) MPTS comparison next VG

  18. Density rollover observed after strike point jog, but causality complicated due to change in plasma shape. - jog duration before loss of H-mode too short for IR camera (33 ms frame time)- H-alpha camera data .... ? Some data gained on high Beta and H-mode behavior vs plasma shape Need more discharge development time to stay in H-mode longer and control inner gap ( RTEFIT ?) for definitive experiment on effect of jog on density rise. Still need to run helium conditioning part of XP to address access to discharges > 1 s without exceeding density limit. Summary:

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