ORCID Profile
0000-0002-7345-8149
Current Organisations
Princeton University
,
Princeton Plasma Physics Laboratory
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Publisher: IOP Publishing
Date: 05-06-2019
Publisher: AIP Publishing
Date: 05-2006
DOI: 10.1063/1.2186049
Abstract: Reversed shear Alfvén eigenmodes (RSAE) that were observed in the Joint European Torus (JET) [P. H. Rebut and B. E. Keen, Fusion Technol.11, 13 (1987)] and DIII-D [J. L. Luxon, Nucl. Fusion42, 614 (2002)] are studied with the ideal magnetohydrodynamic code NOVA-K [C. Z. Cheng, Phys. Rep.211, 1 (1992)]. It was found that the frequency behavior of the RSAEs can be described accurately by the NOVA-K code when plasma compressibility effects and toroidal plasma rotation are taken into account. For the mode activity on JET, the calculated drive exceeds the mode d ing rate, consistent with experimental observations, while on DIII-D the growth rate from neutral beam ions for modes with high toroidal mode numbers is insufficient to account for the excitation of the modes and a major part of the drive comes from the background plasma.
Publisher: AIP Publishing
Date: 27-02-2008
DOI: 10.1063/1.2839286
Abstract: Core localized Alfvén eigenmodes in DIII-D [J. L. Luxon, Nucl. Fusion 42, 614 (2002)] and Joint European Torus (JET) [P. H. Rebut and B. E. Keen, Fusion Technol. 11, 13 (1987)] plasmas are driven by deuterium neutral beam ions traveling well below the Alfvén speed. Modes are observed in reverse magnetic shear discharges with deuterium ion velocities as low as 0.23 and 0.16 of the Alfvén speed parallel to the magnetic field in DIII-D and JET plasmas, respectively. Ellipticity-induced Alfvén eigenmodes in DIII-D and toroidicity-induced Alfvén eigenmodes in JET are excited by deuterium ions traveling well below the fundamental passing ion resonance condition, indicating the role of high-order resonances in driving these modes. NOVA-K analysis reveals many high-order resonances as contributing to the mode drive at high central safety factor due to the correspondingly large poloidal orbit width and the decrease in the perpendicular scale length of the modes.
Publisher: AIP Publishing
Date: 05-2014
DOI: 10.1063/1.4879802
Abstract: Continuum resonance d ing is an important factor in determining the stability of certain global modes in fusion plasmas. A number of analytic and numerical approaches have been developed to compute this d ing, particularly, in the case of the toroidicity-induced shear Alfvén eigenmode. This paper compares results obtained using an analytical perturbative approach with those found using resistive and complex contour numerical approaches. It is found that the perturbative method does not provide accurate agreement with reliable numerical methods for the range of parameters examined. This discrepancy exists even in the limit where d ing approaches zero. When the perturbative technique is implemented using a standard finite element method, the d ing estimate fails to converge with radial grid resolution. The finite elements used cannot accurately represent the eigenmode in the region of the continuum resonance, regardless of the number of radial grid points used.
Publisher: American Physical Society (APS)
Date: 30-10-2008
Publisher: IOP Publishing
Date: 27-03-2015
Publisher: IOP Publishing
Date: 30-04-2009
DOI: 10.1088/0029-5515/49/6/065003
Abstract: Neutral beam injection into reversed magnetic shear DIII-D plasmas produces a variety of Alfvénic activity including toroidicity and ellipticity induced Alfvén eigenmodes (TAE/EAE, respectively) and reversed shear Alfvén eigenmodes (RSAE) as well as their spatial coupling. These modes are studied during the discharge current r phase when incomplete current penetration results in a high central safety factor and strong drive due to multiple higher order resonances. It is found that ideal MHD modelling of eigenmode spectral evolution, coupling and structure are in excellent agreement with experimental measurements. It is also found that higher radial envelope harmonic RSAEs are clearly observed and agree with modelling. Some discrepancies with modelling such as that due to up/down eigenmode asymmetries are also pointed out. Concomitant with the Alfvénic activity, fast ion (FIDA) spectroscopy shows large reductions in the central fast ion profile, the degree of which depends on the Alfvén eigenmode litude. Interestingly, localized electron cyclotron heating (ECH) near the mode location stabilizes RSAE activity and results in significantly improved fast ion confinement relative to discharges with ECH deposition on axis. In these discharges, RSAE activity is suppressed when ECH is deposited near the radius of the shear reversal point and enhanced with deposition near the axis. The sensitivity of this effect to deposition power and current drive phasing as well as ECH modulation are presented.
Publisher: IOP Publishing
Date: 07-02-2008
Publisher: IOP Publishing
Date: 26-06-2008
DOI: 10.1088/0029-5515/48/8/084001
Abstract: Neutral beam injection into a plasma with negative central shear produces a rich spectrum of toroidicity-induced and reversed-shear Alfvén eigenmodes in the DIII-D tokamak. The application of fast-ion D α (FIDA) spectroscopy shows that the central fast-ion profile is flattened in the inner half of the discharge. Neutron and equilibrium measurements corroborate the FIDA data. The temporal evolution of the current profile is also strongly modified. Studies in similar discharges show that flattening of the profile correlates with the mode litude and that both types of Alfvén modes correlate with fast-ion transport. Calculations by the ORBIT code do not explain the observed fast-ion transport for the measured mode litudes, however. Possible explanations for the discrepancy are considered.
Publisher: American Physical Society (APS)
Date: 15-03-2006
Location: United States of America
No related grants have been discovered for Nikolai Gorelenkov.