Excitation of elliptical and toroidal AE modes by 3He-ions of the MeV energy range in hydrogen-rich JET plasmas

Excitation of elliptical and toroidal AE modes by 3He-ions of the MeV energy range in hydrogen-rich JET plasmas

Excitation of elliptical and toroidal AE modes by 3He-ions of the MeV energy range in hydrogen-rich JET plasmas 150 150 UKAEA Opendata
UKAEA-CCFE-CP(20)69

Excitation of elliptical and toroidal AE modes by 3He-ions of the MeV energy range in hydrogen-rich JET plasmas

Elliptical AE (EAE) and TAE mode instabilities have been observed in hydrogen-rich (nH/(nH+nD)~70-90% JET discharges of so-called “three-ion scenario”, i.e. D-(3He)-H three ion ICRH scenario [1], which is characterized by strong absorption of radio frequency waves at very low concentrations of the resonant 3He-ions. In the experiments, the core localized TAEs with a frequency fTAE ≈ 280 kHz were observed. Following the phase with TAE excitation, EAE modes at higher frequencies fEAE ≈ 550-580 kHz with mode numbers n=±1, ±3, ±5 were seen. These high frequency modes indicate that a MeV range population of trapped energetic ions was present in the plasma interacting with the modes via ω=nωDh+pωbh resonance (here ω, n are the frequency and toroidal mode number of AE, ωDh and ωbh are toroidal precession drift and bounce frequencies of the hot ions, and p is integer). The experimental evidence of the existence of the MeV-energy 3He-ions able to excite the AEs is provided by neutron and gamma-ray diagnostics as well as fast ion loss (FILD) measurements. It was found that the anomalous DD neutron rate in the ICRF-only heated plasma is provided by a population of energetic deuterons formed via elastic head-on scattering of the MeV 3He-ions on deuterium (knock-on effect): D(3He,3He)Dknock-on => D(Dknock-on,n)3He. Gamma-ray diagnostics [2] shows that some neutrons are also generated in the nuclear reaction 9Be(3He,n)11C, which takes place with 3He-ions in the MeV-range. The fast ion loss detector [3] indicates the MeV 3He-ion losses related to the core localized TAEs ended with a spike of monster sawtooth loss and then losses correlated to the EAE modes were observed. The analysis of FILD data indicates, the lost 3He-ion energies exceeding 2 MeV. The back-in-time orbit analysis of FILD data shows that the TAE-related 3He-ion losses are localised in the plasma centre (R≈3.0 m), however, the 3He-ions related to EAEs lost from R≈3.2-3.4 m. The MHD analysis confirms the experimental data showing that the MeV 3He ions are resonant interacting with TAE and EAE modes.   a See author list of [4].   [1] Ye.O. Kazakov, D. Van Eester, R. Dumont and J. Ongena, Nucl. Fusion 55 (2015) 032001 [2] V.G. Kiptily, F.E. Cecil and S.S. Medley, Plasma Phys. Control. Fusion 48 (2006) R59–R82 [3] D. Darrow et al. Rev. Sci. Instrum. 77 (2006) 10E701 [4] X. Litaudon et al., Nucl. Fusion 57, 102001 (2017).

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16th IAEA Technical Meeting on Energetic Particles in Magnetic Confinement Systems, Shizuoka City, Japan, 3-6 September 2019
Published date:
25/08/2020