Fluctuating zonal flows in the I-mode regime in Alcator C-Mod

• DOI: 10.1063/1.4803914
• Publication Date: 2013-05-08T22:43:34Z
• Authors: I. Cziegler; P. H. Diamond; N. Fedorczak; P. Manz; G. R. Tynan; M. Xu; R. M. Churchill; A. E. Hubbard; B. Lipschultz; J. M. Sierchio; J. L. Terry; C. Theiler
• Keywords: Alcator C-Mod; Zonal flow (plasma); Mode (computer interface); Thermal velocity

Velocity fields and density fluctuations of edge turbulence are studied in I-mode [F. Ryter et al., Plasma Phys. Controlled Fusion 40, 725 (1998)] plasmas the Alcator C-Mod [I. H. Hutchinson Plasmas 1, 1511 (1994)] tokamak, which characterized by a strong thermal transport barrier while providing little or no to both bulk impurity particles. Although previous work showed clear geodesic-acoustic modes (GAM) on C-Mod, using newly implemented, gas-puff-imaging based time-delay-estimate velocity inference algorithm, GAM now shown be ubiquitous all discharges examined date, with time histories specific [D. Whyte Nucl. 50, 105005 (2010)] Weakly Coherent Mode (WCM, f = 100–300 kHz, Δf/f≈0.5, kθ≈1.3 cm−1) closely following each other through entire duration regime. Thus, presents an example plasma state zero frequency zonal flows continuously coexist. Using two-field (density-velocity radial-poloidal velocity) bispectral methods, coupled WCM responsible for its broad structure. The effective nonlinear growth rate is estimated, comparison collisional damping seems suggest new view threshold physics.