PFC / JA - 87 - 32 Stabilization of Sawteeth By Lower Hybrid Waves in the Alcator
نویسنده
چکیده
Sawteeth have been suppressed by lower hybrid current drive in high density Alcator C plasmas. At a density of 1.1 x 101 4 cm-3 and q(a) = 4.7 the sawteeth were eliminated by application of P,.f = 600 kW at 4.6 GHz, which represents an estimated 30% of the rf power required to fully sustain the discharge in the absence of ohmic power. Strong electron heating is observed with both current drive and anti-current drive phasings of the waveguide arrays but sawtooth stabilization occurs only in the former case. For the current drive phasing, the sawtooth period increases with rf power until the sawteeth are stabilized, while the period remains unchanged for rf injection with anti-current drive phasing. The internal inductance of the plasma increases during current drive relative to the anti-current drive case. The disappearance of sawteeth and the increase in internal inductance suggests that the rf current is driven near the q = 1 surface. At high power (Pf, > 850 kW), the sawteeth return 40 60 ms into the rf pulse, indicating that an optimal power range, or rf deposition profile, exists for successful sawtooth suppression.
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