Abstract
Combined neutral beam injection and fast wave heating at the fourth and fifth cyclotron harmonics accelerate fast ions in the DIII-D tokamak. Measurements with a nine-channel fast-ion D-alpha (FIDA) diagnostic indicate the formation of a fast-ion tail above the injection energy. Tail formation correlates with enhancement of the d–d neutron rate above the value that is expected in the absence of fast-wave acceleration. FIDA spatial profiles and fast-ion pressure profiles inferred from the equilibrium both indicate that the acceleration is near the magnetic axis for a centrally located resonance layer. The enhancement is largest 8–10 cm beyond the radius where the wave frequency equals the cyclotron harmonic, probably due to a combination of Doppler-shift and orbital effects. The fast-ion distribution function calculated by the CQL3D Fokker–Planck code is fairly consistent with the data.
Highlights
Cyclotron damping of fast waves in the ion cyclotron range of frequencies is a standard heating scheme in magnetic fusion devices
Injected beam ions have been accelerated by ion cyclotron heating (ICH) at cyclotron harmonics in many tokamaks [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17]
Balmer-alpha spectroscopy is a powerful technique for the diagnosis of ion cyclotron acceleration of hydrogenic fast ions
Summary
Cyclotron damping of fast waves in the ion cyclotron range of frequencies is a standard heating scheme in magnetic fusion devices. Injected beam ions have been accelerated by ion cyclotron heating (ICH) at cyclotron harmonics in many tokamaks [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17]. A new fast-ion diagnostic technique was demonstrated at DIII-D during neutral beam injection [28]. Fast ions that charge exchange with an injected neutral beam can emit Doppler-shifted Balmer-alpha light.
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