Beam-driven Alfvén eigenmodes (AEs) have been studied in the TJ-II low-magnetic-shear flexible heliac (B 0 = 0.95 T, R = 1.5 m, a = 0.22 m), in L-mode hydrogen plasmas with hydrogen NBI and ECR heating (P NBI 1.0 MW, E NBI = 32 keV, P ECRH 0.6 MW). In low-density plasmas in the range = (0.3-1.5) ×1019 m-3, a large variety of AEs have been observed in the plasma core with the heavy ion beam probe diagnostic and Mirnov coils, in the frequency range 50 kHz < f AE < 380 kHz. In experiments in which the vacuum rotational transform is varied during the shot (dynamic configuration scan), some AEs exhibit changes in their nonlinear evolution from bursting-amplitude AEs with chirping frequency to steady-frequency AEs, and back. The range of intervals within which the AEs studied are chirping or steady-state is determined.
All Science Journal Classification (ASJC) codes