XP-815: Investigation of SOL widths

1
XP-815 Investigation of SOL widths in NSTX
H-mode plasmas
J-W. Ahn1, R.Maingi2, J.A.Boedo1, V.Soukhanovskii3
Acknowledgement B. LeBlanc and R. Kaita for TS
data
1University of California San Diego 2Oak Ridge
National Laboratory 3Lawrence Livermore National
Laboratory
2
Introduction

• Primary Objectives of XP-815
• 1. To find dependence of near SOL widths on
  plasma parameters
• ? comparison with existing scaling laws
• ? develop empirical scaling laws for NSTX H-mode
  plasmas
• 2. To compare upstream SOL widths and target heat
  flux width to investigate parallel (and/or
  perpendicular) SOL transport
• 3. To find relation of SOL widths with edge
  turbulence characteristics
• Diagnostics
• Reciprocating mid-plane fast probe 0.5ms
  temporal, 1mm spatial resolution for Te and ne
  measurement
• Divertor target IR camera (33ms temporal, 6mm
  spatial resolution) target heat flux profile
  measurement
• Thomson Scattering 60Hz temporal, 1-2cm spatial
  resolution in the SOL
• Edge turbulence measurement Probe Isat tip, GPI,
  reflectometry, USXR, mid-plane Dß camera, etc

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Edge density profile is fixed during the
H-mode density ramping period
1. Te,sep estimated from 2 point model ? TS
profiles as a function of R-Rsep 2. ne,sep
appears to be fixed irrespective of nebar 3. This
enables us to ensemble TS profiles at different
time slices for identical H-mode shots to
construct a profile with higher spatial resolution
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Density scan ?Te, ?ne, and ?q
t648ms
t382ms
1. nebar continuously rises during the H-mode, by
a factor of 2, with ne,sep fixed 2. ?q stays at
4-5mm over the whole density ramping period 3.
?Te and ?ne also stay constant
5
Ip scan1 ?jsat and ?q
1. Ip ? ? ?jsat ? and ?q ? 2. R-Rsep for fast
probe Jsat data is from equilibrium
reconstruction ? The apparent radial shift
of Jsat profiles with respect to each other is
thought to be due to the uncertainty in LCFS
position determined by equilibrium reconstruction
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Ip scan 2 ?Te and ?ne
Ip ? ? ?Te decreases and ?ne stays constant
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Power scan ?Te and ?ne
1. PNBI ? ? ?Te decreases and ?ne stays
constant 2. ?q decreases from 0.7cm to 0.5cm
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Comparison with H-mode SOL width scaling laws
from conventional tokamaks
from AUG1
from AUG1
from JET2
1. ?Te , ?ne , and ?q dependence on Ip and power
consistent with scaling laws 2. ?q dependence on
density consistent with scaling law 3. ?Te and
?ne dependence on density different trend from
scaling laws
1K. McCormick, JNM 266-269 (1999)
99 2W.Fundamenski, NF 44 (2004) 20
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Relation between ?q and ?Te in Near SOL
(conduction-limited regime)
Dominant electron conduction with ?Te
(2) Assume offset exponential
profiles
(1) Assume simple exponential
profiles
Additional factor introduced
Conventional relation
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?Te/?q ratio for ELM-free and Type-V ELM H-modes

• ?Te/?q
• is expected if e-conduction is dominant,
  considering flat Te and ne profiles in the far
  SOL
• (ie, ?Te/?q2-2.5)
• 2. Experimental results
• ELM-free H-mode
• ?Te/?q 2
• Type-V ELM H-mode
• ?Te/?q 1

ELMs playing a role in reducing ?Te/?q ratio???,
eg multiple stripes at the divertor target,
therefore broadening the measured (time averaged)
?q??? Detailed physical mechanisms to be
investigated using the fast IR camera
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Summary and conclusions

• Confirmed dependence of ?q, ?Te, ?jsat, and ?ne
  on Ip, power, and nebar
• in H-mode plasmas
• ? negative dependence on Ip and power
• ? no dependence on nebar
• ? ?q change appears to be driven primarily by
  ?Te change
• 2. ?ne remains unchanged by any parameter scan
• 3. Comparison with H-mode scaling laws from
  conventional tokamaks
• ? ?Te , ?ne , and ?q dependences on Ip and power
  consistent with
• scaling laws
• ? ?q dependence on density consistent with the
  scaling law
• ? ?Te and ?ne dependence on density shows
  different trend from
• scaling laws
• 4. NSTX near SOL plasma appears e-conduction
  dominated without ELMs
• 5. ELMs reduce ?Te/ ?q ratio? Physical mechanisms
  to be investigated (eg, due to target ?q
  broadening, etc)

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Future Work
1. More data point and confidence ? SOL width
scaling laws ? Comparison with theoretical
models eg, SOLPS results and analytic
models (J.Canik, R.Maingi) ? Extrapolation to
future machines 2. Detailed investigation of SOL
transport ? roles of heat conduction and
convection associated with ELMs ?
perpendicular particle transport (eg, Deff from
edge Dß profile) 3. Investigate relation of SOL
widths with edge turbulence characteristics
(collaboration with J.Boedo)
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Backup Ensembled TS profiles, reliable???
Ip1MA, PNBI1MW Type-V ELM H-mode 45 TS profiles
Te,sep35eV (from 2pt model)
Te,sep70eV
1. ?2 stays low up to Te,sep45eV 2. For Te,sep
gt 45eV, ensembled profile becomes more scattered
? Te,sep35eV is in the ball park?? 3.
However, some ensembled profiles show monotonic
?2 increase from lower Te,sep
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Backup Ip scan, ?Te and ?ne
1. Te and ne profiles from the fast probe 2.
Large R-Rsep values for the profiles the
respective profile shift ? due to
uncertainty in LCFS position determined by
LRDFIT??? ? Te,sep is expected to be 30eV
from power balance consideration