Central ion cyclotron emission in the DIII-D tokamak

Abstract

Collective ion cyclotron emission (ICE) at the ion cyclotron frequency and its harmonics is a potential passive diagnostic of the fast-ion distribution in fusion reactors. ICE is observed in most plasmas in the DIII-D tokamak and is most strongly excited by the fast ions from neutral beam injection. The conventional outboard-edge ICE is detected in H-mode plasmas. However, weaker centrally-localized ICE is measured in L-mode plasmas, including those with negative triangularity shapes. Similar ICE spectra are found with both ICE diagnostics systems, the dedicated magnetic probes and the instrumented antenna straps. Many differences in the behavior of this central ICE are generated by varying the deuterium beam injection angle into deuterium plasmas. The co-current ‘near-perpendicular’ beam excites the most central ICE from the co-current beams, with this emission detected from the fundamental to the fifth ICE harmonic. However, the counter-current ‘near-tangential’ beam destabilizes the highest amounts of centrally-localized ICE. This emission is spectrally broader than that driven by the co-current beams and is observed up to its seventh ICE harmonic. The central ICE excited by this co-current beam correlated strongly on the local electron density and related parameters (plasma current and neutron rate) and increased with deeper fast-ion loss boundaries towards the magnetic axis. This was also the case with second harmonic ICE driven by the counter-current beam but not with its stronger third harmonic emission. The central ICE harmonics destabilized by both beams are observed to have different temporal dynamics. The central ICE amplitude responds rapidly to transient MHD events; it dropped and recovered in less than a millisecond at each sawtooth event. ICE frequency splitting is triggered by both the co-current and counter-current ‘near-tangential’ beams. The data presented in this paper provide opportunities to test and validate models of excitation of ICE by energetic ions.

Density dependence of ion cyclotron emission from deuterium plasmas in the large helical device

“…In the observations from DIII-D (Ref. [10]) and ASDEX-Upgrade (Refs. [11,12,13]) the NBI ions are also sub-Alfvénic, but the observational focus is on core ICE.…”

Development of the ion cyclotron emission diagnostic for the W7-X stellarator

“…[3][4][5][6] The applicability of the diagnostic to ITER has been studied. 7 The diagnostic is shown to be sensitive to fusion products in JET and TFTR, 8 DIII-D, 9 JT-60U, 10 KSTAR, 11 ASDEX Upgrade, 12 and many others. The emission is often interpreted as magnetoacoustic cyclotron instability [13][14][15][16][17][18] and compressional Alfvén eigenmodes.…”

Origin of ion cyclotron emission at the proton cyclotron frequency from the core of deuterium plasmas in the ASDEX-Upgrade tokamak

“…Strongly suprathermal radiation known as ion cyclotron emisison (ICE) is widely observed in magnetic confinement fusion (MCF) plasmas [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23]. Its intensity is typically orders of magnitude greater than that of black-body radiation from thermal ions, and its spectral peak frequencies correspond to multiple cyclotron harmonics of one or more energetic ion species at a specific radial location.…”

“…Most of the early ICE observations were localised to the outer midplane edge region of the MCF plasmas [1,2,3,4,5,6,7,11,19,20], but recently ICE has also been detected from the core plasmas of ASDEX-Upgrade [8,9,10] and DIII-D [12,13,14]. Figure 5a of Ref.…”