Interpretation of core localized Alfvén eigenmodes in DIII-D and Joint European Torus reversed magnetic shear plasmas

Kramer, G. J.; Nazikian, R.; Alper, B.; Baar, M. de; Berk, H. L.; Fu, G. Y.; Gorelenkov, N. N.; McKee, G. R.; Pinches, S. D.; Rhodes, T.L.; Sharapov, S. E.; Solomon, W. M.; Zeeland, M. A. Van; Contributors, Jet

doi:10.1063/1.2186049

Cited by 35 publications

(46 citation statements)

References 36 publications

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“…Recent work has suggested these modes may interact with thermal ions. 21 In the discharges discussed here, a drop in core ion temperature is observed, just before the temperature rises associated with q = 3 and q = 2 as seen in Fig. 1 at 700 and 1100 ms, respectively.…”

Section: Timing and Behavior Of Transport Changes Near Q Min =2mentioning

confidence: 92%

Core barrier formation near integer q surfaces in DIII-D

Austin¹,

Burrell

Waltz

et al. 2006

Physics of Plasmas

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Recent DIII-D experiments have significantly improved the understanding of internal transport barriers (ITBs) that are triggered close to the time when an integer value of the minimum in q is crossed. While this phenomenon has been observed on many tokamaks, the extensive transport and fluctuation diagnostics on DIII-D have permitted a detailed study of the generation mechanisms of q-triggered ITBs as pertaining to turbulence suppression dynamics, shear flows, and energetic particle modes. In these discharges, the evolution of the q profile is measured using motional Stark effect polarimetry and the integer qmin crossings are further pinpointed in time by the observation of Alfvén cascades. High time resolution measurements of the ion and electron temperatures and the toroidal rotation show that the start of improved confinement is simultaneous in all three channels, and that this event precedes the traversal of integer qmin by 5–20ms. There is no significant low-frequency magnetohydrodynamic activity prior to or just after the crossing of the integer qmin and hence magnetic reconnection is determined not to be the precipitant of the confinement change. Instead, results from the GYRO code point to the effects of zonal flows near low order rational q values as playing a role in ITB triggering. A reduction in local turbulent fluctuations is observed at the start of the temperature rise and, concurrently, an increase in turbulence poloidal flow velocity and flow shear is measured with the beam emission spectroscopy diagnostic. For the case of a transition to an enduring internal barrier the fluctuation level remains at a reduced amplitude. The timing and nature of the temperature, rotation, and fluctuation changes leading to internal barriers suggests transport improvement due to increased shear flow arising from the zonal flow structures.

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Section: Timing and Behavior Of Transport Changes Near Q Min =2mentioning

confidence: 92%

Core barrier formation near integer q surfaces in DIII-D

Austin¹,

Burrell

Waltz

et al. 2006

Physics of Plasmas

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“…The process begins with equilibrium reconstruction and TRANSP [56] runs to validate the kinetic data and simulate beam deposition. The TAE are characterized with Mirnov coil arrays which measure the toroidal mode numbers and with a reflectometer array which provides an absolute, internal measurement of the mode amplitude evolution , as well as some information on the radial structure of the modes [57] and the NOVA-k code [58,59] is used to predict the linear growth and damping rates. In this paper we focus primarily on the ORBIT simulations.…”

Section: Introductionmentioning

confidence: 99%

Fast-ion energy loss during TAE avalanches in the National Spherical Torus Experiment

et al. 2012

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Strong TAE avalanches on NSTX, the National Spherical Torus Experiment [M. Ono, et al., Nucl. Fusion 40 (2000) 557] are typically correlated with drops in the neutron rate in the range of 5% -15%. In previous studies of avalanches in L-mode plasmas, these neutron drops were found to be consistent with modeled losses of fast ions. Here we expand the study to TAE avalanches in NSTX H-mode plasmas with improved analysis techniques. At the measured TAE mode amplitudes, simulations with the ORBIT code predict that fast ion losses are negligible. However, the simulations predict that the TAE scatter the fast ions in energy, resulting in a small (≈ 6%) drop in fast ion β. The net decrease in energy of the fast ions is sufficient to account for the bulk of the drop in neutron rate, even in the absence of fast ion losses. This loss of energy from the fast ion population is comparable to the estimated energy lost by damping from the Alfvén wave during the burst. The previously studied TAE avalanches in L-mode are re-evaluated using an improved calculation of the potential fluctuations in the ORBIT code.

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“…It should be noted that the frequency downsweeps observed in JET 8,22,23 are of much longer duration than the fishhook downsweeps observed in DIII-D. Thus, it is possible that the JET modes are different.…”

Section: Discussionmentioning

confidence: 91%

“…Very rarely, 8,22,23 a mode will sweep downward to the minimum frequency, then sweep upward in the normal fashion. In a Joint European Torus (JET) database, this phenomenon was observed "in only 26 discharges as opposed to more than 5000 discharges where upward sweeping" RSAEs were observed.…”

Section: Introductionmentioning

confidence: 99%

Measurements of the eigenfunction of reversed shear Alfvén eigenmodes that sweep downward in frequency

et al. 2013

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Reversed shear Alfven eigenmodes (RSAEs) usually sweep upward in frequency when the minimum value of the safety factor q min decreases in time. On rare occasions, RSAEs sweep downward prior to the upward sweep. Electron cyclotron emission measurements show that the radial eigenfunction during the downsweeping phase is similar to the eigenfunction of normal, upsweeping RSAEs. V C 2013 AIP Publishing LLC. [http://dx

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Interpretation of core localized Alfvén eigenmodes in DIII-D and Joint European Torus reversed magnetic shear plasmas

Cited by 35 publications

References 36 publications

Core barrier formation near integer q surfaces in DIII-D

Core barrier formation near integer q surfaces in DIII-D

Fast-ion energy loss during TAE avalanches in the National Spherical Torus Experiment

Measurements of the eigenfunction of reversed shear Alfvén eigenmodes that sweep downward in frequency

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