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Magnetosonic Eigenmodes Near the Magnetic Field Well in a Spherical Torus

Description: The structure and spectrum of magnetosonic Alfven eigenmodes in spherical torus in the presence of magnetic field well are studied. Analytical solution for eigenmodes localized in the well is obtained and compared with the numerical one. The possibility of using the eigenmode spectrum measurements for reconstructing the magnetic field well, and, thus, central magnetic safety factor profile is discussed.
Date: July 10, 1998
Creator: Gorelenkova, M. V. & Gorelenkov, N. N.
Partner: UNT Libraries Government Documents Department

A threshold for excitation of neoclassical tearing modes

Description: Stability criterion is obtained for neoclassical tearing modes. A finite amplitude of magnetic island is required for their excitation. In both collisional and collisionless regimes the threshold is determined by the ratio of the transversal and the parallel transport near the island, when the flattening of the pressure profile eliminates the bootstrap current. A number of TFTR supershots are compared with the theory. Both the stability condition and the critical island width are consistent with experimental data.
Date: January 1, 1996
Creator: Gorelenkov, N.N.; Zakharov, L.E. & Gorelenkova, M.V.
Partner: UNT Libraries Government Documents Department

Kinetic theory of plasma adiabatic major radius compression in tokamaks

Description: A kinetic approach is developed to understand the individual charged particle behavior as well as plasma macro parameters (temperature, density, etc.) during the adiabatic R-compression in a tokamak. The perpendicular electric field from Ohm`s law at zero resistivity E = {minus}v{sub E} x B/c is made use of to obtain the equation for particle velocity evolution in order to describe the particle motion during the R-compression. Expressions for both passing and trapped particle energy and pitch angle change are obtained for a plasma with high aspect ratio and circular magnetic surfaces. The particle behavior near the trapped passing boundary during the compression is also studied to understand the shift induced loss of alpha particles produced by D-T fusion reactions in Tokamak Fusion Test Reactor experiments. Qualitative agreement is obtained with the experiments. Solving the drift kinetic equation in the collisional case, i.e., when the collisional frequency {nu}{sub coll} of given species exceeds the inverse compression time {tau}{sub compr}{sup {minus}1}, the authors obtain that the temperature and the density evolution is reduced to the MHD results T {approximately} R{sup {minus}4/3} and n {approximately} R{sup {minus}2}, respectively. In the opposite case, {nu}{sub coll} {much_lt} {tau}{sub compr}{sup {minus}1}, the longitudinal component of the temperature evolve like R(superscript)-2(end superscript) and perpendicular components of the temperature evolve like T{sub {parallel}} {approximately} R{sup {minus}2} and T{sub {perpendicular}} {approximately} R{sup {minus}1}. The effect of toroidicity is negligible in both cases.
Date: October 1, 1997
Creator: Gorelenkova, M.V.; Gorelenkov, N.N.; Azizov, E.A.; Romannikov, A.N. & Herrmann, H.W.
Partner: UNT Libraries Government Documents Department

Kinetic Theory of Plasma Adiabatic Major Radius Compression in Tokamaks

Description: A kinetic approach is developed to understand the individual charged particle behavior as well as plasma macro parameters (temperature, density, etc.) during the adiabatic R-compression in a tokamak. The perpendicular electric field from Ohm's law at zero resistivity E = -v{sub E}{times}B/c is made use of to obtain the equation for particle velocity evolution in order to describe the particle motion during the R-compression. Expressions for both passing and trapped particle energy and pitch angle change are obtained for a plasma with high aspect ratio and circular magnetic surfaces. The particle behavior near the trapped passing boundary during the compression is also studied to understand the shift induced loss of alpha particles produced by D-T fusion reactions in Tokamak Fusion Test Reactor experiments. Qualitative agreement is obtained with the experiments. Solving the drift kinetic equation in the collisional case, i.e., when the collisional frequency of given species exceeds the inverse compression time, we obtain that the temperature and the density evolution is reduced to the MHD results T {approximately} R{super -4/3} and n {approximately} R{super -2}, respectively. In the opposite case, the collisional frequency of given species is smaller than the inverse compression time, the longitudinal component of the temperature evolve like R{super -2} and perpendicular component of the temperature is R{super -1}. The effect of toroidicity is negligible in both cases.
Date: October 1, 1997
Creator: Romannikov, A.N.; Azizov, E.A.; Herrmann, H.W.; Gorelenkova, M.V. & Gorelenkov, N.N.
Partner: UNT Libraries Government Documents Department

Fast Particle Destabilization of Toroidicity Induced Alfven Eigenmodes in National Spherical Torus Experiment

Description: Toroidicity induced Alfven Eigenmode (TAE) stability in National Spherical Torus Experiment (NSTX) is analyzed using the improved NOVA-K code, which includes finite orbit width and Larmor radius effects and is able to predicts the saturation amplitude for the mode using the quasilinear theory. Broad spectrum of unstable global TAEs with different toroidal mode numbers is predicted. Due to the strong poloidal field and the presence of the magnetic well in NSTX better particle confinement in the presence of TAEs in comparison with tokamaks is illustrated making use of the ORBIT code.
Date: December 10, 1999
Creator: Cheng, C.Z.; Fu, G.Y.; Gorelenkova, M.V.; Gorelenkov, N.N.; White, R. & Kaye, S.
Partner: UNT Libraries Government Documents Department

Fast Particle Excitation of TAEs in NSTX

Description: A broad spectrum of TAEs may be unstable in NSTX. TAEs are found having global radial structure. Alfven continuum gap exist even at high beta plasma, when TAE modes are present. TAEs may have strong drive {gamma}/{omega} > 30%, which requires developing of nonperturbative codes for more robust calculations. Single and two mode calculations predict highest beam ion losses totaling in high beta high-q{sub 0} plasmas {approximately} 30% of the NBI ion population with FLR effects included, where most of the losses are prompt losses (24%). Improved confinement (vs typical tokamak plasmas) is observed in high beta plasmas because of the presence of the magnetic field well and strong poloidal field at the edge. The results from START experiments need to be analyzed to provide the understanding of TAEs drive and damping in ST.
Date: June 1, 1999
Creator: Cheng, C.Z.; Fu, G.Y.; Gorelenkova, M.V.; Gorelenkov, N.N. & others], S. Kaye
Partner: UNT Libraries Government Documents Department

Linear and Nonlinear Study of Fast Particle Excitation of Alfvén Eigemodes

Description: Recent new results concerning toroidicity-induced Alfvén eigenmode (TAE) linear stability and nonlinear amplitude saturation and associated fast ion transport are presented for tokamaks, such as the National Spherical Torus Experiment (NSTX) and the International Thermonuclear Experimental Reactor (ITER), using the numerical codes HINST, NOVA-K, and ORBIT.
Date: November 1, 1998
Creator: Berk, H.L.; Chen, Y.; Cheng, C.Z.; Fu, G.Y.; Gorelenkov, N.N; Gorelenkova, M.V. et al.
Partner: UNT Libraries Government Documents Department