Visualization of Fast Ion Phase-Space Flow Driven by Alfvén Instabilities

Du, Xiaodi; Zeeland, M. A. Van; Heidbrink, W. W.; Gonzalez-Martin, J.; Särkimäki, Konsta; Snicker, A.; Lin, Daniel; Collins, C.; Austin, M. E.; McKee, G. R.; Yan, Z.; Todo, Y.; Wu, Wen

doi:10.1103/physrevlett.127.235002

Cited by 7 publications

(16 citation statements)

References 25 publications

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“…where ω p is the toroidal precession frequency, ω b is the poloidal bounce frequency, ω AE is the angular frequency of the instability and L is an integer. The dominant resonance for the INPA interrogated pitch angle is identified as (n, L) = (2, 5), and is the same dominant resonance found using NOVA-K and ASCOT5 reported in [20], providing confidence that this resonance is responsible for the observed fast-ion transport. By tracking the time evolution of single markers, one can confirm that the fast-ions move along constant E = nE + ω AE P φ lines (figure 8(a)), where the toroidal canonical angular momentum is defined as P φ = eψ + m D Rv φ , e being the elementary charge, R the major radius of the ion, m D the deuterium mass and v φ the toroidal projection of the particle velocity.…”

Section: Hybrid Kinetic-mhd Modelling: Megasupporting

confidence: 70%

“…The pitch angle range interrogated by the INPA will determine the fraction of the diagnosed streamline. This observable streamline can be projected on top of the measured transport [20] and it is clear that these streamlines connect the observed inflow and outflow areas at higher and lower energies than the injection energy, crossing the q min radius. One could conclude that the fast ion population will be flattened along the streamlines producing the features (I) and (II) of the observed transport.…”

Section: Hybrid Kinetic-mhd Modelling: Megamentioning

confidence: 68%

“…Both surfaces of constant E and constant μ will intersect in lines that will define the particle migration path. In reference [20] these lines are labelled as 'streamlines'. The INPA diagnostic does not observe the entire phase-space, only a fraction of the constant E and μ surfaces, and thus only a finite length of the streamline.…”

Section: Hybrid Kinetic-mhd Modelling: Megamentioning

confidence: 99%

“…The INPA was employed to obtain unprecedented phase-space visualization of the fastion flow driven by AEs. Reference [20] explains how a beammodulation technique was used to infer the transport by comparing INPA signals in two identical discharges during the current rump up from I p = 0.5 MA to I p = 1.7 MA, with on-axis magnetic field of B 0 = 2.1 T, line integrated electron density n el = 8 × 10 −19 m −2 and on-axis electron temperature of T e = 3 keV. In one plasma pulse, the fast-ion pressure is below the AE stability threshold, where the fast-ion transport is classical, producing an INPA image of I LP (t).…”

Section: Introductionmentioning

confidence: 99%

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Modelling the Alfvén eigenmode induced fast-ion flow measured by an imaging neutral particle analyzer

Gonzalez-Martin

Du²,

Heidbrink³

et al. 2022

Nucl. Fusion

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An imaging neutral particle analyzer (INPA) provides energy and radially resolved measurements of the confined fast-ion population ranging from the high-field side to the edge on the midplane of the DIII-D tokamak. In recent experiments, it was used to diagnose fast-ion flow in the INPA-interrogated phase-space driven by multiple, marginally unstable Alfvén eigenmodes (AEs). The key features of this measured fast-ion flow are: (I) a fast-ion flow from q min and the injection energy (81 keV) towards lower energies and plasma periphery.(II) A flow from the same location towards higher energies and the plasma core, (III) a phase-space ‘hole’ at the injected energy and plasma core and (IV) a pile-up at the plasma core at lower energies (∼60 keV). Ad hoc energetic particle diffusivity modelling of TRANSP significantly deviates from the observation. Comparably, a reduced modelling, i.e. a combination of NOVA-K and ASCOT5 code with the measured mode structure and amplitude, generally reproduce some key features of the observed phase-space flow, but largely failed to interpret fast ion depletion near the plasma axis. At last, self-consistent, first-principle multi-phase hybrid simulations that include realistic neutral beam injection and collisions are able to reproduce most features of the time-resolved phase-space flow. During consecutive hybrid phases, an RSAE consistent with the experiment grows and saturates, redistributing the injected fast ions. The resulting synthetic INPA images are in good agreement with the measurement near the injection energy. The simulations track the fast-ion redistribution within the INPA range, confirming that the measured fast-ion flow follows streamlines defined by the intersection of phase-space surfaces of constant magnetic moment μ and constant E′ = nE + ωP ϕ , where n and ω are the instability toroidal mode number and frequency, and E and P ϕ the ion energy and toroidal canonical momentum. Nonperturbative effects are required to reproduce the depletion of fast ions near the magnetic axis at the injection energy.

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Section: Hybrid Kinetic-mhd Modelling: Megasupporting

confidence: 70%

Section: Hybrid Kinetic-mhd Modelling: Megamentioning

confidence: 68%

Section: Hybrid Kinetic-mhd Modelling: Megamentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Modelling the Alfvén eigenmode induced fast-ion flow measured by an imaging neutral particle analyzer

Gonzalez-Martin

Du²,

Heidbrink³

et al. 2022

Nucl. Fusion

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“…a clump and hole formation theory [99], as observed in TAE discharge [41]. The visualization of phase-space flow by Alfvén eigenmode reported in DIII-D tokamaks [100], represent the possibility of inward shift of the steep gradient region. Shift of the steep gradient region seems to be occurred due to this Alfvénic instability in this discharge.…”

Section: Observation Of Alfvénic Instabilitymentioning

confidence: 83%

Studies of energetic particle transport induced by multiple Alfvén eigenmodes using neutron and escaping energetic particle diagnostics in Large Helical Device deuterium plasmas

et al. 2022

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Studies of energetic particle transport due to energetic-particle-driven Alfvénic instability have progressed using neutron and energetic particle diagnostics in Large Helical Device deuterium plasmas. Alfvénic instability excited by injecting an intensive neutral beam was observed by a magnetic probe and a far-infrared laser interferometer. The interferometer showed Alfvénic instability composed of three modes that existed from the core to the edge of the plasma. A comparison between the observed frequency and shear Alfvén spectra suggested that the mode activity was most likely classified as an Alfvénic avalanche. A neutron fluctuation detector and a fast ion loss detector indicated that Alfvénic instability induced transport and loss of co-going transit energetic ions. The dependence of the drop rate of the neutron signal on the Alfvénic instability amplitude showed that significant transport occurred. Significant transport might be induced by the large amplitude and radially extended multiple modes, as well as a large deviation of the energetic ion orbit from the flux surface.

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Effect of the neutral beam injector operational regime on the Alfven eigenmode saturation phase in DIII-D plasma

Varela,

Spong,

Garcia

et al. 2023

Plasma Phys. Control. Fusion

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The aim of this study is to analyze the effect of the neutral beaminjector (NBI) operation regime on the saturation phase of the Alfven Eigenmodes(AE) in DIII-D plasma. The analysis is done using the linear and nonlinearversions of the gyro-fluid code FAR3d. A set of parametric analyses are performedmodifying the nonlinear simulation EP β (NBI injection power), EP energy (NBIvoltage) and the radial location of the EP density profile gradient (NBI radialdeposition). The analysis indicates a transition from the soft (local plasmarelaxation) to the hard MHD (global plasma relaxation) limit if the simulation EPβ ≥ 0.02, leading to bursting MHD activity caused by radial AEs overlapping.MHD bursts cause an enhancement of the EP transport showing ballistic-likefeatures as avalanche-like events. Simulations in the soft MHD limit show anincrement of the EP density gradient as the EP β increases. On the otherhand, there is a gradient upper limit in the hard MHD limit, consistent withthe critical-gradient behavior. AEs induce shear flows and zonal current leadingto the deformation of the flux surfaces and the safety factor profile, respectively,particularly strong for the simulation in the hard MHD limit. Simulations in thehard MHD regime show a decrease of the AE frequency in the saturation phase;this is caused by the destabilization of a transitional mode between a 9/3 − 10/3TAE and a 9/3 RSAE that may explain the AE frequency down-sweeping observedin some DIII-D discharges. Reducing the EP energy in the nonlinear simulationsleads to a weakening of the plasma perturbation. On the other hand, increasingthe EP energy causes the opposite effect. Nonlinear simulations of off-axis NBIprofiles indicate a lower plasma perturbation as the EP density gradient is locatedfurther away from the magnetic axis.

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Visualization of Fast Ion Phase-Space Flow Driven by Alfvén Instabilities

Cited by 7 publications

References 25 publications

Modelling the Alfvén eigenmode induced fast-ion flow measured by an imaging neutral particle analyzer

Modelling the Alfvén eigenmode induced fast-ion flow measured by an imaging neutral particle analyzer

Studies of energetic particle transport induced by multiple Alfvén eigenmodes using neutron and escaping energetic particle diagnostics in Large Helical Device deuterium plasmas

Effect of the neutral beam injector operational regime on the Alfven eigenmode saturation phase in DIII-D plasma

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