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E. Edlund , PPPL, and M. Porkolab, R . Parker, S. Shiraiwa , N. Tsujii , S . Wukitch , MIT

Alfven Cascades in Reversed Shear RF Driven C-Mod Plasmas . E. Edlund , PPPL, and M. Porkolab, R . Parker, S. Shiraiwa , N. Tsujii , S . Wukitch , MIT .

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E. Edlund , PPPL, and M. Porkolab, R . Parker, S. Shiraiwa , N. Tsujii , S . Wukitch , MIT

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  1. Alfven Cascades in Reversed Shear RF Driven C-Mod Plasmas E. Edlund, PPPL, and M. Porkolab, R. Parker, S. Shiraiwa, N. Tsujii, S. Wukitch, MIT • Reversed Shear Alfven Eigenmodes (RSAE) have been studied previously in ohmically driven C-Mod plasmas with ICRF injected during current ramp and in-between sawtooth crashes (E. Edlund, PhD Thesis, MIT, 2009; E.M. Edlund et al, PRL, 102,165003 (2009)) • In 2005 we proposed (M. Porkolab, et al, 2005 Ideas Forum) to characterize reversed shear (RS) plasmas, with ICRF and LHCD added, in the steady state or with LHCD ramped, with PCI measuring the RSAE spectrum • Modeling of these results with the NOVA and NOVA-K code indicated great sensitivity of the RSE spectrum and its radial structure to the q(r) profile • Only recently was it shown (S. Shiraiwa, C-Mod physics meeting, 2010, December ) that RS plasmas could be created with LHCD and ICRF, as determined by MSE measurements; however, the q-profiles were ambiguous due to the uncertainty of • EFIT reconstruction techniques • Here we propose to use ICRF driven RSAE spectrum and its radial structure as measured by PCI, to further constrain the q profiles as a function of LHCD power, the launched N// spectrum and plasma parameters in LHCD reversed shear plasmas .

  2. Results of NOVA modeling, q profiles, plasma parameters, etc

  3. Summary and Conclusions • Modeling with NOVA –K shows that the MSE determined Reversed shear q profiles can be further refined with the measured RSAE spectrum as determined by the PCI diagnostic • By such techniques it may be possible to develop better AT target plasmas for future high power experiments, as well as compare LH RF codes with the measured q-profiles • Such experiments can be started with the presently available LHCD power (0.8 MW) at relatively low densities (ne < 1020 m-3) (Phase I) • In the future, when two LHCD launchers become available, (Phase II) the density can be further increased toward relevant AT regimes where increased bootstrap current can be obtained as proposed originally • Phase II success will depend to some extent on devising ways to increase the density limit in diverted plasmas • Phase II at low densities would allow the study of deeply reversed shear plasmas and their impact on the RSAE spectrum and fast ion tail confinement • Compound LH spectra in Phase II will add further refinement to the q profiles

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