1 Columbia U Comp-X General Atomics INEL Johns Hopkins U LANL LLNL Lodestar MIT Nova Photonics NYU ORNL PPPL PSI SNL UC Davis UC Irvine UCLA UCSD U Maryland U New Mexico U Rochester U Washington U Wisconsin Culham Sci Ctr Hiroshima U HIST Kyushu Tokai U Niigata U Tsukuba U U Tokyo Ioffe Inst TRINITI KBSI KAIST ENEA, Frascati CEA, Cadarache IPP, Jülich IPP, Garching U Quebec E.J. Synakowski PPPL Alcator C-Mod Ideas Forum December 2-3, 2004 Perturbative momentum transport studies through configuration modification

2 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 ~ 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

3 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

4 Perform systematic scans in ohmic, EDA, and/or benign ELM regimes Ohmic: choose a few density & I p 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 I p

5 (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?