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The Experts below are selected from a list of 309 Experts worldwide ranked by ideXlab platform
K Itoh – 1st expert on this subject based on the ideXlab platform
quantification of turbulent driving forces for the geodesic Acoustic Mode in the jft 2m tokamakPhysical Review Letters, 2018Co-Authors: T Kobayashi, Yoshihiko Nagashima, Makoto Sasaki, K Itoh, A Fujisawa, K Kamiya, Y Miura, S Inagaki, S I ItohAbstract:
: We investigate spatial structures of turbulence and turbulent transport modulated by the geodesic Acoustic Mode (GAM), from which the excitation mechanism of the GAM is discussed. The GAM is found to be predominantly excited through a localized Reynolds stress force, rather than the dynamic shearing force. The evaluated growth rate is larger than the linear damping coefficients and is on the same order of magnitude as the effective growth rate evaluated from time evolution in the GAM kinetic energy.
multiple eigenModes of geodesic Acoustic Mode in collisionless plasmasPhysics of Plasmas, 2006Co-Authors: K Itoh, H Sanuki, J.q. DongAbstract:
We report a series of eigenModes of the geodesic Acoustic Mode (GAM), which includes the standard GAM, a branch of low-frequency Mode, and a series of ion sound wave-like Modes. The case of Ti≫Te is investigated, and eigenfrequencies of these Modes are obtained analytically from a linear gyrokinetic Model in collisionless plasmas with a rigid constant electrostatic potential around a magnetic surface.
geodesic Acoustic Mode in jft 2m tokamak plasmasPlasma Physics and Controlled Fusion, 2006Co-Authors: Y Miura, K Itoh, Y Hamada, A Fujisawa, K Kamiya, S I Itoh, K Hoshino, A Nishizawa, H Ogawa, Y KusamaAbstract:
The characteristics of geodesic–Acoustic–Mode (GAM) are investigated through direct and simultaneous measurement of electrostatic and density fluctuations with a heavy ion beam probe.The amplitude of the GAM changes in relation to the radial position; it is small near the separatrix, reaches a local maximum at 3 cm inside the separatrix and then decreases again to 5 cm inside the separatrix. The frequency is constant in the range, though the predicted GAM frequency varies according to the temperature gradient. The correlation length is about 6 cm and comparable to the structure of the amplitude of the GAM. The results indicate the GAM has a radial structure which reflects the local condition at about 3 m inside the separatrix.The phase relation between the GAM oscillation indicates that the GAM is a radial propagating wave.The interaction between the GAM and the ambient density fluctuation is shown by the high coherence between the GAM oscillation and the temporal behaviour of the ambient density fluctuation. Moreover, the phase relation between the electric field fluctuation of the GAM ( ) and the amplitude of the density fluctuation indicates that the modulation of the ambient density fluctuation delays the . The causality between the GAM and the modulation of the density fluctuation is revealed.
Ashwin Arunkumar Seshia – 2nd expert on this subject based on the ideXlab platform
Acoustic Mode confinement using coupled cavity structures in UHF unreleased MEMS resonatorsMicrosystem Technologies, 2019Co-Authors: Andreja Erbes, Wentao Wang, Dana Weinstein, Ashwin Arunkumar SeshiaAbstract:
This papers investigates device approaches towards the confinement of Acoustic Modes in unreleased UHF MEMS resonators. Acoustic Mode confinement is achieved using specially designed mechanically coupled Acoustic cavities known as Acoustic Bragg Grating Coupler structures to spatially localize the vibration energy within the resonators and thereby improve the motional impedance ($$R_x$$Rx) and mechanical quality factor (Q). This enhancement in the mechanical response is demonstrated with numerical simulations using distinct unreleased resonator technologies involving dielectric transduction mechanisms. These initial investigations show improvements in the Q as well as enhanced vibrational amplitudes within the resonator domains (i.e. translating to improved $$R_x$$Rx values) in the case of coupled cavities as opposed to single cavity designs. An initial approach to fabricate the devices in a CMOS compatible dual-trench technology are presented.
Particulate mass sensing with piezoelectric bulk Acoustic Mode resonators2016 IEEE International Frequency Control Symposium (IFCS), 2016Co-Authors: Arthur T. Zielinski, Markus Kalberer, Roderic L. Jones, Abhinav Prasad, Ashwin Arunkumar SeshiaAbstract:
Current portable particle detection instruments typically rely on optical methods which are limited to 100 nm diameter particles. Microfabricated bulk Acoustic resonators, when used as mass balances, could take particle detection below this limit. This study examines the collection of particles onto piezoelectric bulk Acoustic Mode resonators from gaseous flow using classical impaction. Collection of both polystyrene latex particles and α-pinene secondary organic aerosol particles was examined in terms of frequency shift and collection efficiency. A new experimental setup was introduced which allows for adjusting major impactor, resonator, and aerosol properties. Preliminary results show the setup works for both particles while the saturation limit was not reached within an hour despite highly elevated particle concentrations.
a bulk Acoustic Mode single crystal silicon microresonator with a high quality factorJournal of Micromechanics and Microengineering, 2008Co-Authors: Ashwin Arunkumar SeshiaAbstract:
This paper details a bulk Acoustic Mode resonator fabricated in single-crystal silicon with a quality factor of 15 000 in air, and over a million below 10 mTorr at a resonant frequency of 2.18 MHz. The resonator is a square plate that is excited in the square-extensional Mode and has been fabricated in a commercial foundry silicon-on-insulator (SOI) MEMS process through MEMSCAP. This paper also presents a simple method of extracting resonator parameters from raw measurements heavily buried in electrical feedthrough. Its accuracy has been demonstrated through a comparison between extracted motional resistance values measured at different voltage biases and those predicted from an analytical Model. Finally, a method of substantially cancelling electrical feedthrough through system-level electronic implementation is also introduced.
J.q. Dong – 3rd expert on this subject based on the ideXlab platform
Radial properties of the geodesic Acoustic ModePhysics of Plasmas, 2017Co-Authors: Zhenqian Li, J.q. Dong, Zheng-mao Sheng, M. Y. Yu, W. X. WangAbstract:
In magnetized toroidal plasmas, neoclassical effects and turbulent drift waves can induce the geodesic Acoustic Mode (GAM). We simulate the GAM using the gyro-kinetic code GTS for typical tokamak parameters and investigate its properties, especially its frequency continuum, evolution of its radial wave number, and propagation characteristics. The simulation results are compared with those of the relevant theory and experiment. It is found that the radial phase velocity of the GAM is roughly proportional to the ion thermal speed.
Excitation of geodesic Acoustic Mode continuum by drift wave turbulenceJournal of Plasma Physics, 2012Co-Authors: Jun Yu, J.q. Dong, X. X. Li, D. Du, X. Y. GongAbstract:
AbstractExcitation of the geodesic Acoustic Mode continuum by drift wave turbulence is studied using the wave kinetic approach. For a Model profile of weak non-uniform ion temperature, the forms of growth rate and radial structure of geodesic Acoustic Modes are obtained analytically. The growth rate is analyzed for several conditions for present-day tokamaks and compared with that for uniform ion temperature, as well as that given by the coherent Mode approach for non-uniform ion temperature.
spectral features of the geodesic Acoustic Mode and its interaction with turbulence in a tokamak plasmaPhysics of Plasmas, 2008Co-Authors: C X Yu, J.q. Dong, K J Zhao, W Y Hong, J Cheng, D L Yu, J P Qian, Q W YangAbstract:
The three-dimensional wavenumber and frequency spectrum for the geodesic Acoustic Mode (GAM) has been measured in the HuanLiuqi-2A tokamak for the first time. The spectrum provides definite evidence for the GAM, which is characterized by kθ=kϕ=0 and krρi≈0.04−0.09 with the full width at half-maximum Δkrρi≈0.03−0.07. The localized GAM packet is observed to propagate outward in the radial direction with nearly the same phase and group velocity. The envelopes of the radial electric field and density fluctuations are observed to be modulated by the GAM. By comparing the experimental result with that of the envelope analysis using Model signals, the mechanism of the envelope modulation has been identified. The results strongly suggest that the envelope modulation of the Er fluctuations is dominantly caused by the direct regulation of the GAM during the GAM generation in the energy-conserving triad interaction, and the envelope modulation of the density fluctuations is induced by the GAM shearing effect, which…