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  • 1
    Electronic Resource
    Electronic Resource
    Effect of low magnetic shear induced by lower hybrid current drive on high performance internal transport barriers in the Joint European Torus (JET) (2002)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 9 (2002), S. 3205-3208 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A low/negative magnetic shear profile is maintained in the Joint European Torus in a plasma target with plasma current of 2.4 MA using 2.2 MW of lower hybrid (LH) power combined with neutral beam injection and ion cyclotron radiofrequency heating. In this scenario, an internal transport barrier (ITB) with time duration up to about 4 s is produced. The fraction of LH driven current is about 25% the total plasma current. During LH power application, the layer with reversed shear q-profile can be maintained in a suitable radial position to inhibit the onset of turbulence, which might otherwise drive the ITB to collapse. LH power could be used as a tool to drive moderate amounts of noninductive off-axis current and sustain high performance ITBs at high plasma current. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1488951
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  • 2
    Electronic Resource
    Electronic Resource
    Quasilinear damping of ion Bernstein waves on the harmonic resonant layer (1998)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 5 (1998), S. 2871-2877 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The damping of an ion Bernstein wave (IBW) across a resonant layer of the minority species of the plasma is calculated within the framework of quasilinear theory. The model uses the analytical solution of the one-dimensional Fokker–Planck equation for the ion distribution function. A greater reduction of the damping has been found in this case compared with the one obtained with the linear model. This allows the wave to penetrate further towards the plasma core. In addition, a particle flux induced by the sharp spatial gradient of the distribution function across the resonant layer, due to the IBW field, has also been evaluated. This shows that modification of the distribution function generates a flux of particles from the outside which tends to increase the particle density in the vicinity of the resonance itself. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.873008
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  • 3
    Electronic Resource
    Electronic Resource
    Quasilinear analysis of absorption of ion Bernstein waves by electrons (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 1510-1520 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effects induced on plasma electrons by an externally launched ion Bernstein wave (IBW), in the presence of a lower hybrid wave (LHW) in the current drive regime, are studied by analytical integration of the IBW ray-tracing equations, along with the amplitude transport equation (Poynting theorem). The electric field amplitude parallel and perpendicular to the external magnetic field, the quasilinear diffusion coefficient, and the modified electron distribution function are analytically calculated in the case of IBW. The analytical calculation is compared to the numerical solution obtained by using a two-dimensional (2-D) Fokker–Planck code for the distribution function, without any approximation for the collision operator. The synergy between the IBW and LHW can be accounted for, and the absorption of the IBW power when the electron distribution function presents a tail generated by the LHW in the current drive regime can be calculated. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871480
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  • 4
    Electronic Resource
    Electronic Resource
    Progress in internal transport barrier plasmas with lower hybrid current drive and heating in JET (Joint European Torus) : Review,Tutorial and Invited Papers from the 43rd Annual Meeting of the APS Division of Plasma Physics (2002)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 9 (2002), S. 2156-2164 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In optimized shear plasmas in the Joint European Torus [P. H. Rebut and B. E. Keen, Fusion Technol. 11, 13 (1987)], safety factor (q) profiles with negative magnetic shear are produced by applying lower hybrid (LH) waves during the plasma current ramp-up phase. These plasmas produce a barrier to the electron energy transport. The radius at which the barrier is located increases with the LH wave power. When heated with high power from ion cyclotron resonance heating and neutral beam injection, they can additionally produce transient internal transport barriers (ITBs) seen on the ion temperature, electron density, and toroidal rotation velocity profiles. Due to recent improvements in coupling, q profile control with LH current drive in ITB plasmas with strong combined heating can be explored. These new experiments have led to ITBs sustained for several seconds by the LH wave. Simulations show that the current driven by the LH waves peaks at the ITB location, indicating that it can act in the region of low magnetic shear. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1469026
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  • 5
    Electronic Resource
    Electronic Resource
    Reduction of the electron thermal conductivity produced by ion Bernstein waves on the Frascati Tokamak Upgrade tokamak (2001)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 8 (2001), S. 4721-4724 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Operating with a high frequency and a wave guide antenna, the ion Bernstein wave (IBW) experiment on the Frascati Tokamak Upgrade is not dominated, as expected, by nonlinear plasma edge phenomena. By coupling IBW power, a simultaneous increase of plasma density and central electron temperature (≥2 keV) is produced when the confinement magnetic field is adjusted to set an ion cyclotron resonant layer in the plasma bulk. Transport analysis indicates a reduction of the electron thermal transport inside the internal resonant layer larger than a factor of 2. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1408912
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  • 6
    Electronic Resource
    Electronic Resource
    Investigation of lower hybrid wave damping in the PBX-M tokamak (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 125-133 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Lower hybrid (LH) current drive experiments on the Princeton Beta Experiment-Modified (PBX-M) [Phys. Fluids B 2, 1271 (1990)] have shown that the current profile can be changed by varying the phase velocity of the waves. The radial profile of the current carrying electrons was deduced from two-dimensional hard x-ray tomography. For a certain range of phase velocities, there is a correlation between the peak of the fast electron profile and the launched wave spectrum, despite the presence of a wide spectral gap between the phase velocity and the thermal electron energy distribution. A new model is proposed to explain how first-pass wave damping is possible in such plasmas. The rf power can form a tail of energetic electrons, and subsequently waves with moderate phase velocity can damp on them. For waves with very fast phase velocity, there must be an upshift of the n(parallel) spectrum for any damping to occur. These hypotheses are supported by ray tracing results which are coupled to relativistic Fokker–Planck calculations of the electron distribution function. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872122
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  • 7
    Electronic Resource
    Electronic Resource
    Dynamical self-focusing of high-power free electron laser radiation in a magnetized plasma (1989)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 1 (1989), S. 901-906 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Under the action of very intense free electron laser (FEL) radiation, a homogeneous plasma can manifest nonlinear behavior and dramatically change the spatial distribution of the incident electromagnetic beam. The dominant mechanism is the constriction depletion of the plasma due to an averaged ponderomotive force. The unstable character of the FEL-beam plasma system and the consequent self-focusing are studied in the dynamical "supersonic limit.'' The self-similar structure of the high-frequency field and density distributions is computed and the form of a "trace,'' left by a moving "focus'' in the plasma is determined.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.859014
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  • 8
    Electronic Resource
    Electronic Resource
    Asymptotic analysis of lower hybrid wave propagation in tokamaks (1986)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 29 (1986), S. 810-815 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An asymptotic analysis of the lower hybrid wave propagation in toroidal geometry is presented which relies on the difference in magnitude between the parallel and perpendicular wave vectors when the wave frequency is of the order of the ion plasma frequency. Using the method of matched asymptotic expansions, the equation for the radial position of the ray is solved and the effects of the toroidal corrections are discussed. Moreover, the equation for the parallel wave vector is derived and analytically solved by using a multiple scale analysis. The latter solution is asymptotically matched to a local exact solution near the plasma edge where the multiple scale analysis breaks down. The result of the asymptotic analytical treatment is compared with the findings of a numerical integration of the starting set of equations. Finally, using the previous results, the equation for the variation of the electric field amplitude along the trajectory is analytically solved.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.866017
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  • 9
    Electronic Resource
    Electronic Resource
    Modification of magnetohydrodynamic activity by lower hybrid current drive (1989)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 1 (1989), S. 1659-1662 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effect of magnetic islands on the propagation of lower hybrid waves is investigated analytically for a model slab equilibrium with a single helical perturbation corresponding to an m=1 or m=2 island. From the variation of k(parallel) inside the island, the parallel current is estimated with the same pitch as the original perturbation. The effect of such a current on the nonlinear evolution of an m=2 island corresponds to a destabilization of the mode if the rf driven current is in the same direction as the global parallel current. A comparison with numerical solutions of the problem using a toroidal ray trajectory code is also presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.858944
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  • 10
    Electronic Resource
    Electronic Resource
    Analysis of the effects of elongation and triangularity on the propagation of lower-hybrid waves (1993)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 5 (1993), S. 2922-2932 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Lower-hybrid (LH) wave propagation is studied for a general magnetic-field configuration. The ray-tracing equations in the geometric optics approximation are analytically and numerically solved in flux surface coordinates by using asymptotic techniques. In particular, the effects of elongation, triangularity, and the Shafranov shift on wave penetration are pointed out. Numerical applications devoted to the study of current drive generation for the International Thermonuclear Experimental Reactor (ITER) [Nucl. Fusion 31, 1135 (1991)] plasma parameters will also be presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.860680
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