Effects of Toroidal Rotation Sshear on Toroidicity-induced Alfven Eigenmodes in the National Spherical Torus Experiment PDF Download
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Author: Publisher: ISBN: Category : Languages : en Pages : 203
Book Description
The effects of a sheared toroidal rotation on the dynamics of bursting Toroidicity-induced Alfven eigenmodes are investigated in neutral beam heated plasmas on the National Spherical Torus Experiment (NSTX) [M. Ono et al., Nucl. Fusion 40 557 (2000)]. The modes have a global character, extending over most of the minor radius. A toroidal rotation shear layer is measured at the location of maximum drive for the modes. Contrary to results from other devices, no clear evidence of increased damping is found. Instead, experiments with simultaneous neutral beam and radio-frequency auxiliary heating show a strong correlation between the dynamics of the modes and the instability drive. It is argued that kinetic effects involving changes in the mode drive and damping mechanisms other than rotation shear, such as continuum damping, are mostly responsible for the bursting dynamics of the modes.
Author: Publisher: ISBN: Category : Languages : en Pages : 203
Book Description
The effects of a sheared toroidal rotation on the dynamics of bursting Toroidicity-induced Alfven eigenmodes are investigated in neutral beam heated plasmas on the National Spherical Torus Experiment (NSTX) [M. Ono et al., Nucl. Fusion 40 557 (2000)]. The modes have a global character, extending over most of the minor radius. A toroidal rotation shear layer is measured at the location of maximum drive for the modes. Contrary to results from other devices, no clear evidence of increased damping is found. Instead, experiments with simultaneous neutral beam and radio-frequency auxiliary heating show a strong correlation between the dynamics of the modes and the instability drive. It is argued that kinetic effects involving changes in the mode drive and damping mechanisms other than rotation shear, such as continuum damping, are mostly responsible for the bursting dynamics of the modes.
Author: Publisher: ISBN: Category : Languages : en Pages :
Book Description
The National Spherical Torus Experiment (NSTX, [M. Ono et al., Nucl. Fusion 40, 557 (2000)]) routinely operates with neutral beam injection as the primary system for heating and current drive. The resulting fast ion population is super-Alfvenic, with velocities 1
Author: National Research Council Publisher: National Academies Press ISBN: 0309090822 Category : Science Languages : en Pages : 209
Book Description
Significant advances have been made in fusion science, and a point has been reached when we need to decide if the United States is ready to begin a burning plasma experiment. A burning plasmaâ€"in which at least 50 percent of the energy to drive the fusion reaction is generated internallyâ€"is an essential step to reach the goal of fusion power generation. The Burning Plasma Assessment Committee was formed to provide advice on this decision. The committee concluded that there is high confidence in the readiness to proceed with the burning plasma step. The International Thermonuclear Experimental Reactor (ITER), with the United States as a significant partner, was the best choice. Once a commitment to ITER is made, fulfilling it should become the highest priority of the U.S. fusion research program. A funding trajectory is required that both captures the benefits of joining ITER and retains a strong scientific focus on the long-range goals of the program. Addition of the ITER project will require that the content, scope, and level of U.S. fusion activity be defined by program balancing through a priority-setting process initiated by the Office of Fusion Energy Science.
Author: Publisher: ISBN: Category : Languages : en Pages : 28
Book Description
The high frequency, low mode number toroidicity-induced Alfven eigenmodes (TAE) are shown to be driven unstable by the circulating and/or trapped?-particles through the wave-particle resonances. Satisfying the resonance condition requires that the?-particle birth speed v{sub?} ≥ v{sub A}/2{vert bar}m-nq{vert bar}, where v{sub A} is the Alfven speed, m is the poloidal model number, and n is the toroidal mode number. To destabilize the TAE modes, the inverse Landau damping associated with the?-particle pressure gradient free energy must overcome the velocity space Landau damping due to both the?-particles and the core electrons and ions. The growth rate was studied analytically with a perturbative formula derived from the quadratic dispersion relation, and numerically with the aid of the NOVA-K code. Stability criteria in terms of the?-particle beta?{sub?},?-particle pressure gradient parameter (?{sub {asterisk}}/?{sub A}) (?{sub {asterisk}} is the?-particle diamagnetic drift frequency), and (v{sub {alpha}}/v{sub A}) parameters will be presented for TFTR, CIT, and ITER tokamaks. The volume averaged {alpha}-particle beta threshold for TAE instability also depends sensitively on the core electron and ion temperature. Typically the volume averaged {alpha}-particle beta threshold is in the order of 10−4. Typical growth rates of the n=1 TAE mode can be in the order of 10−2?{sub A}, where?{sub A}=v{sub A}/qR. Other types of global Alfven waves are stable in D-T tokamaks due to toroidal coupling effects.
Author: Publisher: ISBN: Category : Languages : en Pages : 15
Book Description
An enlarged spectrum of ideal toroidal Alfven eigenmodes is demonstrated to exist within a toroidicity-induced Alfven gap when the inverse aspect ratio is comparable to or larger than the value of the magnetic shear. This limit is appropriate for the low-shear region in most tokamaks, especially those with low aspect ratio. The new modes may be destabilized by fusion-product alpha particles more easily than the standard toroidal Alfven eigenmodes.
Author: Publisher: ISBN: Category : Languages : en Pages :
Book Description
The coupling of Alfvén Cascade (AC) modes or reversed-shear Alfvén eigenmodes (rsAE) to Geodesic Acoustic Modes (GAM) implies that the range of the AC frequency sweep is reduced as the electron? is increased. This model provides an explanation for the otherwise surprising absence of AC modes in reverse shear NSTX plasmas, given the rich spectrum of beam-driven instabilities typically seen in NSTX. In experiments done at very low? to investigate this prediction, AC modes were seen, and as the?e was increased from shot to shot, the range of the AC frequency sweep was reduced, in agreement with this theoretical prediction.
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Author: National Research Council
Author: N. N. Gorelenkov
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Author: C.Z. Cheng
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Author: G. Y. Fu