Beam ion losses due to energetic particle geodesic acoustic modes

Fisher, R. K.; Pace, D. C.; Kramer, G. J.; Zeeland, M. A. Van; Nazikian, R.; Heidbrink, W. W.; García-Muñoz, M.

doi:10.1088/0029-5515/52/12/123015

Cited by 18 publications

(34 citation statements)

References 18 publications

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“…, with Φ = e T and L = 0.3 m, which seems realistic (the local E r can be much higher, up to 28 keV m −1 ) [8]. Figure 1 confirms our consideration above.…”

Section: Motion and Change Of The Energy Of Resonant Ions In The Gam supporting

confidence: 85%

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

Kolesnichenko

Lutsenko

Yakovenko

et al. 2016

Plasma Phys. Control. Fusion

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Effects of the energetic-ion-driven Geodesic Acoustic modes (GAM and E-GAM) on the toroidally passing energetic ions and the concomitant change of the neutron yield of beam-plasma fusion reactions in tokamaks are considered. It is shown that due to large perturbations of the plasma density, the resonant energetic ions driving the instability can be considerably slowed down for a few tens of the particle transit periods, which is much less than the collisional slowing down time. The time of the collisionless slowing down is actually determined by the period of the particle motion within the resonance island arising because of the GAM / E-GAM. Being trapped in the island, the resonant particles can not only lose their energy but also gain it. One more effect of GAMs is the flattening on the distribution function of the resonant particles. Due to conservation of the canonical angular momentum during a GAM / E-GAM instability, the change of the particle energy is accompanied by a radial displacement of the resonant particle for a distance up to the poloidal Larmor radius of energetic ions. The particles are displaced inwards or outwards, depending on the direction of their motion along the magnetic field. Expressions describing the change of the neutron yield due to GAM modes are derived. It is found that the distortion of the velocity distribution of the resonant particles can lead to a considerable drop of the neutron emission even when effects of the particle radial displacement are small. The developed theory is applied to an E-GAM experiment on the DIII-D tokamak. Relations for the period of the motion within the resonance island of passing (both well passing and marginally passing) particles and the width of the resonance of the energetic particles with GAM modes and low-frequency Alfvén modes are derived.

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“…, with Φ = e T and L = 0.3 m, which seems realistic (the local E r can be much higher, up to 28 keV m −1 ) [8]. Figure 1 confirms our consideration above.…”

Section: Motion and Change Of The Energy Of Resonant Ions In The Gam supporting

confidence: 85%

“…These drops indicated the expulsion of the injected ions from the plasma core and, possibly, their loss (neutrons were produced mainly by the beam-plasma fusion reaction) [6]. Later DIII-D experiments have given a direct evidence of the influence of the E-GAM instability on the deterioration of the confinement of injected ions [8].…”

mentioning

confidence: 99%

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

Kolesnichenko

Lutsenko

Yakovenko

et al. 2016

Plasma Phys. Control. Fusion

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“…However, recent numerical simulations suggest that the impact of EGAMs on turbulence may not always be as positive as expected, and requires further investigation 16 . EGAMs can also be responsible for fast ion losses under certain circumstances 17 .…”

Section: -11mentioning

confidence: 99%

“…The radial extension of the EGAM is assumed to be significantly smaller than the minor radius of the tokamak. Therefore, in expression (14), only the sin θ∂ r term is retained as it is assumed to be dominant over the (17) At leading order in ρ * , the first two poloidal harmonics of equation (13) read:…”

Section: A Gyrokinetic Equation For Thermal and Kinetic Ionsmentioning

confidence: 99%

Relation between energetic and standard geodesic acoustic modes

et al. 2014

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Geodesic Acoustic Modes (GAMs) are electrostatic, axisymmetric modes which are non-linearly excited by turbulence. They can also be excited linearly by fast-particles; they are then called Energetic-particle-driven GAMs (EGAMs). Do GAMs and EGAMs belong to the same mode branch? Through a linear, analytical model, in which the fast particles are represented by a Maxwellian bump-on-tail distribution function, we find that the answer depends on several parameters. For low values of the safety factor q and for high values of the fast ion energy, the EGAM originates from the GAM. On the contrary, for high values of q and for low values of the fast ion energy, the GAM is not the mode which becomes unstable when fast particles are added: the EGAM then originates from a distinct mode, which is strongly damped in the absence of fast particles. The impact of other parameters is further explored: ratio of the ion temperature to the electron temperature, width of the fast particle distribution, mass and charge of the fast ions. The ratio between the EGAM and the GAM frequencies was found in experiments (DIII-D) and in non-linear numerical simulations (code GYSELA) to be close to 1/2: the present analytical study allows one to recover this ratio.

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“…Changes in the beam ion loss due to the energetic particle-induced geodesic acoustic mode (EGAM) [22] are also apparent. The EGAM and coherent beam ion losses are commonly observed in DIII-D during the use of counter-current beam injection [23,24]. Shot 166396 features the counter-current tangential beam beginning at its lowest energy and the EGAM-induced beam ion losses appear during this early stage and dissipate by 340 ms ( figure 4( f )).…”

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confidence: 94%

Control of power, torque, and instability drive using in-shot variable neutral beam energy in tokamaks

et al. 2016

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In-shot variation of neutral beam energy has been applied in a tokamak plasma for the first time, and this capability is now being optimized for application in a range of DIII-D experiments. A recent experiment on the DIII-D tokamak [1,2] demonstrated that it is possible to produce finely controlled evolution of neutral beam injected power and torque by adjusting the beam energy (i.e. the voltage at which the ions are accelerated prior to neutralizing and entering the device) in time. Time-dependent beam energies also led to changes in the drive of instabilities in plasmas that are similar except for the beam energy program. Neutral beams are a major auxiliary heating and current drive system for present tokamaks, and the system being built for ITER will be responsible for providing an injected power of 34 MW [3]. A sampling of the most recent worldwide effort to advance neutral beam technology and its application in magnetic confinement fusion includes: the creation of a new, detailed simulation code for the specific ITER beams

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Beam ion losses due to energetic particle geodesic acoustic modes

Cited by 18 publications

References 18 publications

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

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

Relation between energetic and standard geodesic acoustic modes

Control of power, torque, and instability drive using in-shot variable neutral beam energy in tokamaks

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