morrell chance | Princeton University (original) (raw)
Related Authors
Centre National de la Recherche Scientifique / French National Centre for Scientific Research
Uploads
Papers by morrell chance
Bulletin of the American Physical Society, 2009
In toroidal plasmas, the toroidal magnetic field is nonuniform over a magnetic surface and causes... more In toroidal plasmas, the toroidal magnetic field is nonuniform over a magnetic surface and causes coupling of different poloidal harmonics. It is shown both analytically and numerically that the toroidicity not only breaks up the shear Alfve´n continuous spectrum, but also creates new, discrete, toroidicity-induced shear Alfve´n eigenmodes with frequencies inside the continuum gaps. Potential applications of the low-n toroidicity-induced
Journal of Geophysical Research, 1973
The VACUUM^1 code is currently being modified to simulate the feedback stabilization of the RWM i... more The VACUUM^1 code is currently being modified to simulate the feedback stabilization of the RWM in the DIII-D device^2. We formulate the problem in terms of the eigenfunctions of the surface Laplacian obtained from the matching of the fields across a thin resistive toroidally symmetric shell. The window pane feedback (C-)coils are modeled accurately in the poloidal angle theta, and approximately by a single harmonic variation in phi. VACUUM relates the perturbations on the various surfaces, i.e., the plasma, both sides of the resistive shell and the C-coil. This results in an operator made up of a set of coupled time dependent equations relating the shell response to the plasma and feedback coil. Various attributes of the system can be calculated, such as the eddy current patterns and the time responses of the eigenmodes of the surface Laplacian operator. As a first appproximation, a PEST or GATO surface eigenmode of an ideal kink is assumed, whose structure remains unchanged during the feedback process, allowing only the magnitude to change. By energizing the C-coils according to the various proposed feedback schemes we propose to correlate with the present experimental results, and also to provide helpful guidance for future runs. rule[1.ex]1.9in.005in This work supported by DoE contract No. DE-AC02-76-CHO-3073 ^1 M.S. Chance, Phys. Plasmas, 4(1997)2161 ^2 A. A. Garofalo et al., Phys. Plasmas 6(1999) 1893
Toroidal plasma rotation in the order of a few percent of the Alfvén velocity can stabilize the r... more Toroidal plasma rotation in the order of a few percent of the Alfvén velocity can stabilize the resistive wall mode and extend the operating regime of tokamaks from the conventional, ideal MHD no-wall limit up to the ideal MHD ideal wall limit. The stabilizing effect has been measured passively by measuring the critical plasma rotation required for stability and actively by probing the plasma with externally applied resonant magnetic fields. These measurements are compared to predictions of rotational stabilization of the sound wave damping and of the kinetic damping model using the MARS code.
External kink modes have been identified as one of the major obstacles to achieving high pressure... more External kink modes have been identified as one of the major obstacles to achieving high pressure plasmas in toroidal devices. From the beginning of fusion research, it has been well known that a conducting shell can improve the stability if the shell is ideal. A shell with finite resistivity can still stabilize the fast growing ideal magnetohydrodynamic (MHD) mode, however, the external kink mode is converted into the resistive wall mode (RWM) branch, which grows with the shell skin time constant.
Under normal circumstances, the resistive wall mode (RWM) limits the performance of discharges in... more Under normal circumstances, the resistive wall mode (RWM) limits the performance of discharges in the DIII-D tokamak when the plasma beta exceeds the no-wall ideal stability limit. These n=1 global kink modes grow on the slow time scale of magnetic diffusion through the surrounding conductive vacuum vessel wall. Active magnetic feedback stabilization experiments on DIII-D during the 2000 campaign succeeded in suppressing the resistive wall mode for periods more than fifty times longer than the resistive penetration time of the wall. Experiments in 2001 have demonstrated dramatic improvements in active control capability, owing largely to an extensive new set of magnetic sensors installed inside the vacuum vessel after the 2000 campaign. The new internal magnetic sensors, together with pre-existing external sensors and a toroidal array of x-ray cameras, have also afforded better characterization of the previously observed mode structure.
Bulletin of the American Physical Society, 2009
In toroidal plasmas, the toroidal magnetic field is nonuniform over a magnetic surface and causes... more In toroidal plasmas, the toroidal magnetic field is nonuniform over a magnetic surface and causes coupling of different poloidal harmonics. It is shown both analytically and numerically that the toroidicity not only breaks up the shear Alfve´n continuous spectrum, but also creates new, discrete, toroidicity-induced shear Alfve´n eigenmodes with frequencies inside the continuum gaps. Potential applications of the low-n toroidicity-induced
Journal of Geophysical Research, 1973
The VACUUM^1 code is currently being modified to simulate the feedback stabilization of the RWM i... more The VACUUM^1 code is currently being modified to simulate the feedback stabilization of the RWM in the DIII-D device^2. We formulate the problem in terms of the eigenfunctions of the surface Laplacian obtained from the matching of the fields across a thin resistive toroidally symmetric shell. The window pane feedback (C-)coils are modeled accurately in the poloidal angle theta, and approximately by a single harmonic variation in phi. VACUUM relates the perturbations on the various surfaces, i.e., the plasma, both sides of the resistive shell and the C-coil. This results in an operator made up of a set of coupled time dependent equations relating the shell response to the plasma and feedback coil. Various attributes of the system can be calculated, such as the eddy current patterns and the time responses of the eigenmodes of the surface Laplacian operator. As a first appproximation, a PEST or GATO surface eigenmode of an ideal kink is assumed, whose structure remains unchanged during the feedback process, allowing only the magnitude to change. By energizing the C-coils according to the various proposed feedback schemes we propose to correlate with the present experimental results, and also to provide helpful guidance for future runs. rule[1.ex]1.9in.005in This work supported by DoE contract No. DE-AC02-76-CHO-3073 ^1 M.S. Chance, Phys. Plasmas, 4(1997)2161 ^2 A. A. Garofalo et al., Phys. Plasmas 6(1999) 1893
Toroidal plasma rotation in the order of a few percent of the Alfvén velocity can stabilize the r... more Toroidal plasma rotation in the order of a few percent of the Alfvén velocity can stabilize the resistive wall mode and extend the operating regime of tokamaks from the conventional, ideal MHD no-wall limit up to the ideal MHD ideal wall limit. The stabilizing effect has been measured passively by measuring the critical plasma rotation required for stability and actively by probing the plasma with externally applied resonant magnetic fields. These measurements are compared to predictions of rotational stabilization of the sound wave damping and of the kinetic damping model using the MARS code.
External kink modes have been identified as one of the major obstacles to achieving high pressure... more External kink modes have been identified as one of the major obstacles to achieving high pressure plasmas in toroidal devices. From the beginning of fusion research, it has been well known that a conducting shell can improve the stability if the shell is ideal. A shell with finite resistivity can still stabilize the fast growing ideal magnetohydrodynamic (MHD) mode, however, the external kink mode is converted into the resistive wall mode (RWM) branch, which grows with the shell skin time constant.
Under normal circumstances, the resistive wall mode (RWM) limits the performance of discharges in... more Under normal circumstances, the resistive wall mode (RWM) limits the performance of discharges in the DIII-D tokamak when the plasma beta exceeds the no-wall ideal stability limit. These n=1 global kink modes grow on the slow time scale of magnetic diffusion through the surrounding conductive vacuum vessel wall. Active magnetic feedback stabilization experiments on DIII-D during the 2000 campaign succeeded in suppressing the resistive wall mode for periods more than fifty times longer than the resistive penetration time of the wall. Experiments in 2001 have demonstrated dramatic improvements in active control capability, owing largely to an extensive new set of magnetic sensors installed inside the vacuum vessel after the 2000 campaign. The new internal magnetic sensors, together with pre-existing external sensors and a toroidal array of x-ray cameras, have also afforded better characterization of the previously observed mode structure.