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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. - PowerPoint PPT Presentation
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NSTX
NSTX
Controlling density rise through helium conditioning.
C H Skinner, H Kugel, R Maingi, D Mueller,...
• Surface physics
• TFTR, DIII-D, NSTX results
• XP: Controlling density rise through limiting divertor
temp. rise and through He conditioning.
PPPL Jan 7th, 2003
NSTX
Surface Physics: Complex non-linearly coupled plasma - wall system.
TFTR
tile
KC-22
200 µm
Not a simple homogeneous system on any scale: - processes on wall include:
Chiu et al., codeposit original tile
convoluted, highly porous structure,codeposit poorly thermally connected
Microscopic-scale perspective
NSTX
≈10 mm
D release
Chemical
Sputtering
Temp: 1841 °C left, 1181 °C right
Same heat flux (from laser spot)
Microhotspots - surface temperature not single value (varies x2)
Temperature effects:
Doyle et al., Roth & Moller
Vietzke &
Haasz.
Skinner et al.,
Radiation
Enhanced
Sublimation
(RES) as
temp. rises
NSTX
0
250
500
750
0 20 40 60 80 100
Edge temperature (eV)
Sheath potential (eV)
Plasma ions approaching the material surfaces areaccelerated 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+
Doyle et al.,
Interaction Depth:
z = 2
z = 1
High performance shots access depths into wall untouched by He glow GDC.
Wampler et al.,
NSTX
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].
NSTX
HELIUM DISCHARGES USEFUL FOR REDUCING RECYCLING AND IMPURITIES
• Deuterium reference discharges(12 Helium discharges between)
• D reduced
• Carbon reduced
• li slightly reduced
• Stored energy unchanged102300
102317
Ip [MA]
D [au]
CIII emission
li
WMHD [kJ]
R Maingi, P Efthimion et al., DPP APS 2000 “Wall conditioning and impurity control in NSTX”
NSTX
Density Rise: DIII-D
Rensink et al., modeling showed H-mode density rise due to longer confinement time and thinner scrape off layer more transparent to incoming particles.
Ip [MA]
PNBI/10 [MW]
ne [1019 m-3]
D [au]
WMHD*10 [MJ]
H98pby2
Maingi et al., 5 yr forum
Density Rise: NSTX
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…”
NSTX
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.
NSTX
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...
NSTX
≈10 mm
D release
Chemical
Sputtering
Temp: 1841 °C left, 1181 °C right
Same heat flux (from laser spot)
Microhotspots - surface temperature not single value (varies x2)
Temperature effects:
Doyle et al., Roth & Moller
Vietzke &
Haasz.
Skinner et al.,
Radiation
Enhanced
Sublimation
(RES) as
temp. rises
NSTX
Overview of run day:
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)
•
NSTX
H-mode from 267 - 418 ms
effect on density rise ?
Jog shot 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
NSTX
Strike point jog
L-mode
109946109947
Indication of density rollover after strike point jog, before L-mode, but...
outer strike point position
D-alpha
Line average density (1e13)
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...
MPTS comparison next VG
NSTX
... but motion away from CS causes major part of density reduction.
NSTX
NSTX
Strike point jog
L-mode
109950109952
Indication of density rollover after strike point jog, before L-mode, but...
outer strike point position
D-alpha
Line average density (1e13)
109952 had PF2L increase from -7 to -8.5 from 380 to 420 ms,
MPTS comparison next VG
NSTX
... but motion away from CS causes major part of density reduction.
NSTX
Strike point jog
L-mode
109955no time for no jog shot
Indication of density rollover after strike point jog, before L-mode, but...
outer strike point position
D-alpha
Line average density (1e13)
109955 had PF2L increase from from 320 ms,
MPTS comparison next VG
NSTX
NSTX
NSTXSummary:• 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.
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