Energetic Ion Experiments in DIII-D

Heidbrink, W. W.

doi:10.13182/fst05-a1050

Cited by 8 publications

(4 citation statements)

References 75 publications

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“…Strong NBI heating leads to the destabilization of AE as TAE [64], EAE [65], NAE [66], BAE [67], RSAE [68] and GAE [69]. DIII-D experiments measured a larger transport and enhanced energetic particle losses linked to unstable AE [70,71,72].…”

Section: Introductionmentioning

confidence: 99%

Subdominant modes and optimization trends of DIII-D reverse magnetic shear configurations

et al. 2019

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Alfvén Eigenmodes (AE) and magneto-hydrodynamic (MHD) modes are destabilized in DIII-D reverse magnetic shear configurations and may limit the performance of the device. We use the reduced MHD equations in a full 3D system, coupled with equations of density and parallel velocity moments for the energetic particles (with gyro-fluid closures) as well as the geodesic acoustic wave dynamics, to study the properties of instabilities observed in DIII-D reverse magnetic shear discharges. The aim of the study consists in finding ways to avoid or minimize MHD and AE activity for different magnetic field configurations and neutral beam injection (NBI) operational regimes. The simulations show at the beginning of the discharge, before the reverse shear region is formed, a plasma that is AE unstable and marginally MHD stable. As soon as the reverse shear region appears, ideal MHD modes are destabilized with a larger growth rate than the AEs. Both MHD modes and AEs coexist during the discharge, although the MHD modes are more unstable as the reverse shear region deepens. The simulations indicate the destabilization of Beta induced AE (BAE), Toroidal AE (TAE), Elliptical AE (EAE) and Reverse Shear AE (RSAE) at different phases of the discharges, showing a reasonable agreement between the frequency range of the dominant modes in the simulations and the diagnostic measurements. A further analysis of the NBI operational regime indicates that the AE stability can arXiv:1904.01193v1 [physics.plasm-ph] 2 Apr 2019Optimization of DIII-D reverse shear configurations 2 be improved if the NBI injection is off axis, because on-axis injection leads to AEs with larger growth rate and frequency. In addition, decreasing the beam energy or increasing the NBI relative density (the ratio between the energetic particle and thermal plasma density) leads to AEs with larger growth rate and frequency, so an NBI operation in the weakly resonant regime requires higher beam energies than in the experiment (V th,f /V A0 > 0.3). The MHD linear stability can be also improved if the reverse shear region and the q profile near the magnetic axis are in between the rational surfaces q = 2 and q = 1, particularly if there is a region in the core with negative shear, avoiding a flat q profile near the magnetic axis. The simulations also show a smooth transition between MHD modes and low frequency AE, no critical β f , pointing out an overlap between MHD and AE activity for modes with frequencies lower than 30 kHz. This is in the range of Beta Acoustic Alfven Eigenmodes (BAAE) and BAE.

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Section: Introductionmentioning

confidence: 99%

Subdominant modes and optimization trends of DIII-D reverse magnetic shear configurations

et al. 2019

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“…The destabilization of AE linked to strong NBI heating was measured before in DIII-D, triggering a large variety of AE instabilities as GAE 50 , TAE 51 , RSAE 52 , BAE 53 , EAE 54 and NAE 55 . The AE instabilities reduce the device performance, increasing the transport and enhancing energetic particle losses [56][57][58] .…”

Section: Introductionmentioning

confidence: 99%

Study of Alfven eigenmodes stability in plasma with multiple NBI driven energetic particle species

et al. 2019

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The aim of this study is to analyze the destabilization of Alfven Eigenmodes (AE) by multiple energetic particles (EP) species in DIII-D and LHD discharges. We use the reduced MHD equations to describe the linear evolution of the poloidal flux and the toroidal component of the vorticity in a full 3D system, coupled with equations of density and parallel velocity moments for the energetic particles species, including the effect of the acoustic modes, diamagnetic currents and helical couplings. We add the Landau damping and resonant destabilization effects using a closure relation. The simulations with multiple NBI lines show three different regimes: the non damped regime where the multi beam AEs growth rate is larger compared to the growth rate of the AEs destabilized by the individual NBI lines, the interaction regime where the multi beam AEs growth rate is smaller than the single NBI AEs and the damped regime where the AEs are suppressed. Operations in the damped regime requires EP species with different density profile flatness or gradient locations. In addition, the AEs growth rate in the interaction regime is further reduced if the combined NBI lines have similar beam temperatures and the β of the NBI line with flatter EP density profile increases. Then, optimization trends are identified in DIII-D high poloidal β and LHD low density / magnetic field discharges with multiple NBI lines as well as the configuration requirements to operate in the damped and interaction regimes. DIII-D simulations show a decrease of the n = 2 to 6 AEs growth rate and n = 1 AE are stabilized in the LHD case. The helical coupling effects in LHD simulations lead to a transition from the interaction to the damped regime of the n = 2, −8, 12 helical family.

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“…The destabilization of AE linked to strong NBI heating was measured before in DIII-D, triggering a large variety of AE instabilities as GAE [42], TAE [43], RSAE [44], BAE [45], EAE [46] and NAE [47]. The AE instabilities reduce the device performance, increasing the transport and enhancing energetic particle losses [48,49,50].…”

Section: Introductionmentioning

confidence: 99%

Analysis of Alfven eigenmode destabilization in DIII-D high poloidal β discharges using a Landau closure model

Varela¹,

Spong²,

Garcia³

et al. 2018

Nucl. Fusion

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Alfvén Eigenmodes are destabilized at the DIII-D pedestal during transient beta drops in high poloidal β discharges with internal transport barriers (ITBs), driven by n = 1 external kink modes, leading to energetic particle losses. There are two different scenarios in the thermal β recovery phase: with bifurcation (two instability branches with different frequencies) or without bifurcation (single instability branch). We use the reduced MHD equations in a full 3D system, coupled with equations of density and parallel velocity moments for the energetic particles as well as the geodesic acoustic wave dynamics, to study the properties of the instabilities observed in the DIII-D high poloidal β discharges and identify the conditions to trigger the bifurcation. The simulations suggest that instabilities with lower frequency in the bifurcation case are ballooning modes driven at the plasma pedestal, while the instability branch with higher frequencies are low n (n < 4) Toroidal Alfvén Eigenmodes nearby the pedestal. The reverse shear region between the middle and plasma periphery in the non-bifurcated case avoids the excitation of ballooning modes at the pedestal, although Toroidal Alfvén Eigenmodes and Reverse Shear Alfvén Eigenmodes are unstable in the reverse shear region. The n = 1 and n = 2 Alfvén Eigenmode activity can be suppressed or minimized if the neutral beam injector (NBI) intensity is lower than the experimental value (β f < 0.03). In addition, if the beam energy or neutral beam injector voltage is lower than in the experiment (V th,f /V A0 < 0.2), the resonance between beam and thermal plasma is weaker. The n = 3, 4, 5 and 6 AE activity can't be fully suppressed, although the growth rate and frequency is smaller for an optimized neutral beam injector operation regime. In conclusion, AE activity in high poloidal β discharges can be minimized for optimized NBI operation regimes.

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Energetic Ion Experiments in DIII-D

Abstract: A summary of fast ion experiments in the DIII-D tokamak is given. Most of the experiments involve

Cited by 8 publications

References 75 publications

Subdominant modes and optimization trends of DIII-D reverse magnetic shear configurations

Subdominant modes and optimization trends of DIII-D reverse magnetic shear configurations

Study of Alfven eigenmodes stability in plasma with multiple NBI driven energetic particle species

Analysis of Alfven eigenmode destabilization in DIII-D high poloidal β discharges using a Landau closure model

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