Emission in the ion cyclotron range of frequencies (ICE) on NSTX and NSTX-U
Autor: | R.E. Bell, N. N. Gorelenkov, Ahmed Diallo, B.P. LeBlanc, Nstx Team, Mario Podesta, E.D. Fredrickson |
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Rok vydání: | 2019 |
Předmět: |
Physics
Tokamak Astrophysics::High Energy Astrophysical Phenomena Cyclotron Plasma Condensed Matter Physics 01 natural sciences 010305 fluids & plasmas Ion law.invention Computational physics Magnetic field Alfvén wave Amplitude Physics::Plasma Physics law Harmonics Physics::Space Physics 0103 physical sciences 010306 general physics |
Zdroj: | Physics of Plasmas. 26:032111 |
ISSN: | 1089-7674 1070-664X |
Popis: | We report here on observations of magnetic fluctuations in the ion-cyclotron frequency range on NSTX and NSTX-U. In many respects, the fluctuations appear similar to the ion cyclotron emission (ICE) seen in conventional tokamaks. However, a significant difference between previous observations of ICE and the ICE on NSTX is that the frequency of ICE in conventional tokamaks is typically near the ion cyclotron frequency of the energetic fast ions at the plasma edge. In NSTX and NSTX-U, the magnetic fluctuation frequency corresponds to the ion cyclotron frequency deeper in the plasma, near the location of an internal transport barrier. As on conventional tokamaks, higher harmonics of the deuterium cyclotron frequency, as high as the seventh, are seen with the strongest signal sometimes from higher harmonics. The emission usually appears as an irregular sequence of short bursts typically ≤100 μs in duration although nearly continuous emission for several ms has also been seen under some conditions. Measurements of the emission with a toroidal array of fast probes show that the emission is a long wavelength, spatially coherent mode. The emission frequency does not follow an Alfvenic scaling with density, as seen for compressional Alfven eigenmodes, but does show a linear scaling with local magnetic field strength. The measured emission shows a compressional polarization consistent with a compressional Alfven wave. No correlation between the neutron rate and the ICE amplitude is seen. Three-wave coupling between the instability responsible for the ICE and lower frequency modes has also been observed. |
Databáze: | OpenAIRE |
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