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Columbia UComp-X

General AtomicsINEL

Johns Hopkins ULANLLLNL

LodestarMIT

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UC DavisUC Irvine

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U WisconsinCulham Sci Ctr

Hiroshima UHIST

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TRINITIKBSI

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E.J. SynakowskiPPPL

Alcator C-Mod Ideas ForumDecember 2-3, 2004

Perturbative momentum transport studies through configuration modification

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• You have found (LaBombard ‘04): small changes in configuration have a profound effect in the edge, and large changes in core V

• Tease apart influence of power and SOL flows on core V: L-H transition induces a change in SOL and core rotation, but other core profiles change, too

• Minimize changes in other core profiles: Can a rapid (but small ~ 5 - 10 mm) change in X-point balance be used to induce a V pulse from the edge into the core without changing confinement regime?

Simple idea: change configuration rapidly within a discharge and induce a sudden change in the core

flow

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Challenge: make a small change in the balance, keep the confinement regime the same, and meaure

the V propagation time to the core• In H mode: aim to keep the ELM type the same (or stay in

EDA). Change separatrix balance as rapidly as possible.

• Use as high a power as required to get into desired regime in the most difficult configuration (USN). Then transit to LSN and balanced configs in separate plasmas

• Measure change in edge flows

• Measure V(r,t) deep in the core. Take multiple reproducible shots to make for averagable data to improve time resolution

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Perform systematic scans in ohmic, EDA, and/or benign ELM regimes

• Ohmic: choose a few density & Ip points: USN to LSN highest priority

• With ICRF, perform a power scan– In addition to EDA or ELMy H

mode, L mode would also be of value

• Also basic confinement knobs like Ip

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(B): isotope swap would provide an additional knob

• Change edge Mach flow by using hydrogen, induce edge flow perturbations with configuration changes

• If edge flows increase with H, is there a corresponding increase in core flow velocity?

• For a given confinement time, how do core and edge rotation speeds differ?

• Start-of-run, or end-of-run use of H will minimize impact on RF

• Even a comparison of ohmic current and density scans along the lines of those just described would be of value

• Other fans of an isotope swap? Turbulence studies, including imaging?