Effect of edge plasma rotation on pedestal and ELMs ~ preparation for DIII-D/JT-60U exp. ~

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Effect of edge plasma rotation on pedestal and
ELMs preparation for DIII-D/JT-60U exp.
14th meeting of the ITPA-TG on PedestalEdge
Physics Group, General Atomics, April 29-May 2,
2008
N. Oyama, H. Urano, Y. Sakamoto and the JT-60
Team JAEA Naka
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Background for PEP-17/18

• Pedestal pressure and type I ELM characteristics
  vary with edge plasma rotation. These rotation
  effects can be separated from effects of TF
  ripple.
• (Urano IAEA 2006, NF 47(2007)706)
• Grassy ELM frequency varies with edge plasma
  rotation.
• (Oyama, PPCF 49(2007)249)
• Small plasma rotation in ITER is expected. To
  obtain better prediction of ITER pedestal
  parameters (especially ELM size), it is important
  to understand the physical mechanism of rotation
  effects.
• gt Inter-machine experiments between DIII-D and
  JT-60U (PEP-17/18) will provide new information,
  making use of good capability of toroidal torque
  input in both devices.

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Configurations for rotation effects
for grassy ELM
for type I ELM 1 ripple
Ferritic Steel Tile
for type I ELM 0.5 ripple
for QH-mode
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Rotation effect on type I ELMs

• At fixed Pnet, pped gradually decreases with
  increasing ctr-VT
• At fixed Psep (Pnet1.5xPLH), fELM increases with
  increasing ctr-VT

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Rotation effect on type I ELMs

• At fixed Pnet, pped gradually decreases with
  increasing ctr-VT
• At fixed Psep (Pnet1.5xPLH), fELM increases with
  increasing ctr-VT
• Degradation of pped in ctr-rotating plasma is
  smaller than reduction of DWELM at higher fELM gt
  smaller DWELM/Wped
• These results are obtained at 1 ripple case in
  large VP config.

Fixed Psep
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Moderate TF ripple case (0.5)

• pped can increase with heating power (bp)
• At fixed Pnet, pped decreases with increasing
  ctr-rotation
• DWELM/Wped decreases with increasing ctr-rotation
• Similar changes in 1 ripple case were observed.

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Rotation effect on grassy ELMs

• Grassy ELMs can be obtained at zero rotation
  rotation shear
• Not only high q95 (gt6), rotation effect can be
  observed in moderate q95 (5)
• Sign of rotation seems to be important, similar
  to type I ELM

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Rotation effect on grassy ELMs

• Grassy ELMs can be obtained at zero rotation
  rotation shear
• Not only high q95 (gt6), rotation effect can be
  observed in moderate q95 (5)
• Sign of rotation seems to be important, similar
  to type I ELM
• In high d configuration, no degradation of pped
  was observed

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Difference between grassy ELMQH

• Grassy ELM Localized collapse near pedestal top
• QH-mode No collapse. EHO seen in Te, ne, Is

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Proposal for DIII-D as PEP-17/18

• For the comparison of pedestal H-mode
  performance,
• and ELM characteristics,
• Rotation/beta scan at different plasma
  configuration
• (low d, high d, DN)
• (Similar q95 and ne regime to JT-60U database)
• Discussions
• Possibility to get similar plasma shape for each
  target
• example type I ELM d0.35, k1.4
• grassy ELM d0.6, k1.4
• Possibility for reversed Ip/Bt for larger CTR
  torque
• If yes, may be suitable to perform QH-mode
  comparison experiments in DIII-D (PEP-14)