Abstract
Direct observation of ICRF (∼80 MHz) waves (k⊥≃0.5 cm−1−10 cm−1) is now possible in Alcator C-Mod using an optical heterodyne technique on the Phase Contrast Imaging (PCI) system, which uses a CO2 laser to observe electron density fluctuations. The PCI observations are vertical chord averages, so the full-wave ICRF code TORIC [1] has been used to simulate the wave fields in these plasmas to aid in interpretation. Mode-converted ion Bernstein waves (IBW) in plasmas composed of H, D and 3He at 6 T have been observed at both high (1 MA) and low (400 kA) current. The fast magnetosonic wave launched from the low-field side has been observed in high density (∼5×1020 m−3) D(H) plasmas with off-axis ICRH at 4.5 T. Comparison between PCI measurements and code results are presented. The measured wave numbers are in good agreement with the local dispersion relations for both types of waves.
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