Manifestations of the geodesic acoustic mode driven by energetic ions in tokamaks

Kolesnichenko, Ya. I.; Lutsenko, V. V.; Yakovenko, Yu. V.; Lepiavko, B.; Grierson, B. A.; Heidbrink, W. W.; Nazikian, R.

doi:10.1088/0741-3335/58/4/045024

Cited by 7 publications

(8 citation statements)

References 26 publications

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“…The density perturbations of the EGAM are nearly up-down anti-symmetric, while the EGAM breaks the antisymmetry owned by the conventional GAM, and its poloidal magnetic field fluctuations can be expressed as δB θ ∝ sin 2(θ − θ 0 ) + εf (θ, θ 0 ), where θ 0 is a function of pitch angle and energy of energetic ions, and the new asymmetric structure is easily formed when |θ 0 | > π/8. We find that the EGAM instability a quite sensitive to the pitch angle of energetic ions [38]. The toroidal rotation velocity v φ is partially suppressed by EGAM excitation, indicating that part of the flow kinetic energy is consumed to drive this type of modes, a mechanism that is different from the wave-particle resonance, while the islands of LFM instabilities can lead to the formation of the 'hollow' structure of v φ .…”

Section: Discussionmentioning

confidence: 82%

Observation of electromagnetic GAMs excited by NBI in EAST

Zhang

Zhou

et al. 2018

Nucl. Fusion

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Energetic ions induced electromagnetic geodesic acoustic modes (EGAMs) instabilities during the modulated injection of neutral beams of NBI 1L and NBI 1R have been observed in EAST. The EGAMs coexist with the lower frequency modes (LFMs) instabilities: the frequencies are constant in the radial direction for EGAMs in the range of 0.5 < ρ 0.8, while LFMs are located in the range 0.1 < ρ 0.3. The density perturbation for EGAM is nearly up-down anti-symmetric, while the magnetic perturbation for EGAM that is standing wave with a principal m = 2 lobe, and an m = 4 side-lobe is commonly observed for κ > 1. EGAMs have strong correlations with the injections of energetic ions, and the toroidal rotation velocity v φ is partially suppressed by the mode excitations, while the magnetic islands of LFM instabilities can form the configuration of 'hollow' structure for v φ . The most pronounced feature of the EGAMs is that the magnetic fluctuations are not antisymmetric in the poloidal angle θ, and they can be expressed as δB θ ∝ sin 2(θ − θ 0 ) + εf (θ, θ 0 ), and the θ 0 is a function of the pitch angle and energy of energetic ion. The new structure of asymmetry for EGAM has been observed when |θ 0 | > π/8, where the radial structure extends outward in bottom section, and also exhibits non-uniformity in the toroidal direction, and one possible explanation for the asymmetry is that EGAM are modulated by LSW instabilities with frequency 0 < f x < 4 kHz.

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Section: Discussionmentioning

confidence: 82%

Observation of electromagnetic GAMs excited by NBI in EAST

Zhang

Zhou

et al. 2018

Nucl. Fusion

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“…This was later corroborated in [8] by comparing a DIII-D discharge, where fast-ion loss detector (FILD) [23] data were available, and the numerical results from a full orbit simulation with the code SPIRAL [24]. Also, a recent work provides an analytical calculation of the effect of the EGAM on well-passing particles that are trapped in the EGAM island, as well as the subsequent impact on the neutron emission [25]. However, further systematic analysis of particle transport in phase space for all classes of particles in the presence of EGAMs has so far not been conducted, nor has the fundamental physics for the trapping of particles been analysed in detail.…”

Section: Introductionmentioning

confidence: 85%

Particle transport due to energetic-particle-driven geodesic acoustic modes

Zarzoso¹,

del‐Castillo‐Negrete²,

Escande³

et al. 2018

Nucl. Fusion

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The transport of particles in the presence of energetic geodesic acoustic modes (EGAMs) is analysed by means of full-f global gyro-kinetic simulations using the multispecies version of the Gysela code and a test-particle tracking post-treatment that solves the equations of motion of passive gyro-centres embedded in the self-consistent EGAM potential obtained from Gysela simulations. It is found that EGAMs induce transport of particles that eventually results in counter-passing particle losses modulated at the EGAM frequency. A detailed analysis of the trajectories of test gyro-centres is performed and evidences of the interaction between the EGAM island and the region of magnetically trapped particles (trapping cone) is observed. In particular, we report for the first time on the complex interaction between the stochastic separatrix of the EGAM island and the X-point of the trapping cone, creating a channel for the transport of particles from v < 0 to v > 0 regions. Therefore, for the cases analysed in this work, co-injection of energetic particles might lead to a significant reduction of EGAM-induced losses. This result opens up new perspectives for further studies of the selection of energetic particle injection in order to minimize the losses due to EGAMs.

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“…In the past decade, energetic particle driven GAM (EGAM) has been observed in JET, DIII-D, the Large Helical Device (LHD), HL-2A, and ASDEX-Upgrade [7][8][9][10][11][12][13]. Many publications have been devoted to various aspects of EGAMs including the fundamental properties [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31], the continuum damping [15,[32][33][34], the high frequency and low frequency branches [15,[35][36][37][38], and the half-frequency subcritical instabilities [39][40][41]. In the DIII-D experiment, the drops in neutron emission during the EGAM activities suggest beam ion losses [9].…”

Section: Introductionmentioning

confidence: 99%

Simulation of energetic particle driven geodesic acoustic modes and the energy channeling in the Large Helical Device plasmas

et al. 2019

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Energetic particle driven geodesic acoustic modes (EGAMs) in the Large Helical Device (LHD) plasmas are investigated using MEGA code. MEGA is a hybrid simulation code for energetic particles interacting with a magnetohydrodynamic (MHD) fluid and in the present work, both the energetic particles and bulk ions are described by the kinetic equations. The low frequency EGAMs are reproduced. Also, the energy transfer is analyzed and the bulk ion heating during the EGAM activity is observed. The ions obtain energy when the energetic particles lose energy, and this indicates that an energy channel is established by EGAM. The EGAM channeling is reproduced by simulation with realistic parameters for the first time. The heating power to bulk ions is 3.4 kW/m 3 . It is found that the sideband resonance is dominant during the energy transfer from EGAM to the bulk ions, and the transit frequencies of resonant bulk ions are one-half of the EGAM frequency.

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Manifestations of the geodesic acoustic mode driven by energetic ions in tokamaks

Cited by 7 publications

References 26 publications

Observation of electromagnetic GAMs excited by NBI in EAST

Observation of electromagnetic GAMs excited by NBI in EAST

Particle transport due to energetic-particle-driven geodesic acoustic modes

Simulation of energetic particle driven geodesic acoustic modes and the energy channeling in the Large Helical Device plasmas

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