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414 results on '"Cohen, B. I."'

2. Multilevel Monte Carlo simulation of Coulomb collisions

Author

Rosin, M. S., Ricketson, L. F., Dimits, A. M., Caflisch, R. E., and Cohen, B. I.

Subjects
Physics - Plasma Physics, Physics - Computational Physics
Abstract

We present a new, for plasma physics, highly efficient multilevel Monte Carlo numerical method for simulating Coulomb collisions. The method separates and optimally minimizes the finite-timestep and finite-sampling errors inherent in the Langevin representation of the Landau-Fokker-Planck equation. It does so by combining multiple solutions to the underlying equations with varying numbers of timesteps. For a desired level of accuracy epsilon, the computational cost of the method is order(epsilon^{-2}) or order(epsilon^{-2} (\ln epsilon)^2), depending on the underlying discretization, Milstein or Euler-Maruyama respectively. This is to be contrasted with a cost of order(epsilon^{-3}) for direct simulation Monte Carlo or binary collision methods. We successfully demonstrate the method with a classic beam diffusion test case in 2D, making use of the Levy area approximation for the correlated Milstein cross terms, and generating a computational saving of a factor of 100 for epsilon = 10^{-5}. We discuss the importance of the method for problems in which collisions constitute the computational rate limiting step, and its limitations., Comment: 32 pages

Published
2013
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3. Kinetic-Ion Simulations Addressing Whether Ion Trapping Inflates Stimulated Brillouin Backscattering Reflectivities

Author

Cohen, B. I., Williams, E. A., and Vu, H. X.

Subjects
Physics - Plasma Physics
Abstract

An investigation of the possible inflation of stimulated Brillouin backscattering (SBS) due to ion kinetic effects is presented using electromagnetic particle simulations and integrations of three-wave coupled-mode equations with linear and nonlinear models of the nonlinear ion physics. Electrostatic simulations of linear ion Landau damping in an ion acoustic wave, nonlinear reduction of damping due to ion trapping, and nonlinear frequency shifts due to ion trapping establish a baseline for modeling the electromagnetic SBS simulations. Systematic scans of the laser intensity have been undertaken with both one-dimensional particle simulations and coupled-mode-equations integrations, and two values of the electron-to-ion temperature ratio (to vary the linear ion Landau damping) are considered. Three of the four intensity scans have evidence of SBS inflation as determined by observing more reflectivity in the particle simulations than in the corresponding three-wave mode-coupling integrations with a linear ion-wave model, and the particle simulations show evidence of ion trapping., Comment: 56 pages, 20 figures

Published
2007
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7. The first target experiments on the National Ignition Facility

Author

Landen, O. L., Glenzer, S. H., Froula, D. H., Dewald, E. L., Suter, L. J., Schneider, M. B., Hinkel, D. E., Fernandez, J. C., Kline, J. L., Goldman, S. R., Braun, D. G., Celliers, P. M., Moon, S. J., Robey, H. S., Lanier, N. E., Glendinning, S. G., Blue, B. E., Wilde, B. H., Jones, O. S., Schein, J., Divol, L., Kalantar, D. H., Campbell, K. M., Holder, J. P., McDonald, J. W., Niemann, C., Mackinnon, A. J., Collins, G. W., Bradley, D. K., Eggert, J. H., Hicks, D. G., Gregori, G., Kirkwood, R. K., Young, B. K., Foster, J. M., Hansen, J. F., Perry, T. S., Munro, D. H., Baldis, H. A., Grim, G. P., Heeter, R. F., Hegelich, M. B., Montgomery, D. S., Rochau, G. A., Olson, R. E., Turner, R. E., Workman, J. B., Berger, R. L., Cohen, B. I., Kruer, W. L., Langdon, A. B., Langer, S. H., Meezan, N. B., Rose, H. A., Still, C. H., Williams, E. A., Dodd, E. S., Edwards, M. J., Monteil, M.-C., Stevenson, R. M., Thomas, B. R., Coker, R. F., Magelssen, G. R., Rosen, P. A., Stry, P. E., Woods, D., Weber, S. V., Young, P. E., Alvarez, S., Armstrong, G., Bahr, R., Bourgade, J.-L., Bower, D., Celeste, J., Chrisp, M., Compton, S., Cox, J., Constantin, C., Costa, R., Duncan, J., Ellis, A., Emig, J., Gautier, C., Greenwood, A., Griffith, R., Holdner, F., Holtmeier, G., Hargrove, D., James, T., Kamperschroer, J., Kimbrough, J., Landon, M., Lee, F. D., Malone, R., May, M., Montelongo, S., Moody, J., Ng, E., Nikitin, A., Pellinen, D., Piston, K., Poole, M., Rekow, V., Rhodes, M., Shepherd, R., Shiromizu, S., Voloshin, D., Warrick, A., Watts, P., Weber, F., Young, P., Arnold, P., Atherton, L., Bardsley, G., Bonanno, R., Borger, T., Bowers, M., Bryant, R., Buckman, S., Burkhart, S., Cooper, F., Dixit, S. N., Erbert, G., Eder, D. C., Ehrlich, R. E., Felker, B., Fornes, J., Frieders, G., Gardner, S., Gates, C., Gonzalez, M., Grace, S., Hall, T., Haynam, C. A., Heestand, G., Henesian, M. A., Hermann, M., Hermes, G., Huber, S., Jancaitis, K., Johnson, S., Kauffman, B., Kelleher, T., Kohut, T., Koniges, A. E., Labiak, T., Latray, D., Lee, A., Lund, D., Mahavandi, S., Manes, K. R., Marshall, C., McBride, J., McCarville, T., McGrew, L., Menapace, J., Mertens, E., Murray, J., Neumann, J., Newton, M., Opsahl, P., Padilla, E., Parham, T., Parrish, G., Petty, C., Polk, M., Powell, C., Reinbachs, I., Rinnert, R., Riordan, B., Ross, G., Robert, V., Tobin, M., Sailors, S., Saunders, R., Schmitt, M., Shaw, M., Singh, M., Spaeth, M., Stephens, A., Tietbohl, G., Tuck, J., Van Wonterghem, B. M., Vidal, R., Wegner, P. J., Whitman, P., Williams, K., Winward, K., Work, K., Wallace, R., Nobile, A., Bono, M., Day, B., Elliott, J., Hatch, D., Louis, H., Manzenares, R., O'Brien, D., Papin, P., Pierce, T., Rivera, G., Ruppe, J., Sandoval, D., Schmidt, D., Valdez, L., Zapata, K., MacGowan, B. J., Eckart, M. J., Hsing, W. W., Springer, P. T., Hammel, B. A., Moses, E. I., and Miller, G. H.

Published
2007
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10. Lower hybrid drift instability at the inner edge of the ring current

Author

Roth, I, Cohen, B. I, and Hudson, M. K

Subjects
Geophysics
Abstract

Excitation of electrostatic waves around and above the lower hybrid frequency at the inner edge of the ring current is investigated. The model consists of cold plasmaspheric ions; hot, dilute, inhomogeneous ring current ions; and cold charge neutralizing electrons. It is shown that in the presence of a sufficiently large density gradient the coupling of the lower hybrid with the drift cyclotron harmonic mode destabilizes the plasma. Unstable interactions also occur at higher cyclotron harmonics when the lower hybrid is replaced by an ion Bernstein mode. Additional power at frequencies above the lower hybrid frequency is attributed to the thermal enhancement by the hot ring current ions, which increases with their density gradient. Particle simulations are conducted, and comparison to AMPTE data is discussed.

Published
1990

13. Numerical tokamak turbulence project (OFES grand challenge)

Author

Beer, M, primary, Cohen, B I, additional, Crotinger, J, additional, Dawson, J, additional, Decyk, V, additional, Dimits, A M, additional, Dorland, W D, additional, Hammett, G W, additional, Kerbel, G D, additional, Leboeuf, J N, additional, Lee, W W, additional, Lin, Z, additional, Nevins, W M, additional, Reynders, J, additional, Shumaker, D E, additional, Smith, S, additional, Sydora, R, additional, Waltz, R E, additional, and Williams, T, additional

Published
1999
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23. Controlled and spontaneous magnetic field generation in a gun-driven spheromak

Author

Woodruff, S., Cohen, B. I., Hooper, E. B., Mclean, H. S., Stallard, B. W., Hill, D. N., Holcomb, C. T., Romero-Talamás, C., Wood, R. D., Cone, G., Sovinec, C. R., Woodruff, S., Cohen, B. I., Hooper, E. B., Mclean, H. S., Stallard, B. W., Hill, D. N., Holcomb, C. T., Romero-Talamás, C., Wood, R. D., Cone, G., and Sovinec, C. R.

Abstract

In the Sustained Spheromak Physics Experiment, SSPX [E. B. Hooper, D. Pearlstein, and D. D. Ryutov, Nucl. Fusion 39, 863 (1999)], progress has been made in understanding the mechanisms that generate fields by helicity injection. SSPX injects helicity (linked magnetic flux) from 1 m diameter magnetized coaxial electrodes into a flux-conserving confinement region. Control of magnetic fluctuations (delta B/B similar to 1% on the midplane edge) yields T-e profiles peaked at > 200 eV. Trends indicate a limiting beta (beta(e)similar to 4%-6%), and so we have been motivated to increase T-e by operating with stronger magnetic field. Two new operating modes are observed to increase the magnetic field: (A) Operation with constant current and spontaneous gun voltage fluctuations. In this case, the gun is operated continuously at the threshold for ejection of plasma from the gun: stored magnetic energy of the spheromak increases gradually with delta B/B similar to 2% and large voltage fluctuations (delta V similar to 1 kV), giving a 50% increase in current amplification, I-tor/I-gun. (B) Operation with controlled current pulses. In this case, spheromak magnetic energy increases in a stepwise fashion by pulsing the gun, giving the highest magnetic fields observed for SSPX (similar to 0.7 T along the geometric axis). By increasing the time between pulses, a quasisteady sustainment is produced (with periodic good confinement), comparing well with resistive magnetohydrodynamic simulations. In each case, the processes that transport the helicity into the spheromak are inductive and exhibit a scaling of field with current that exceeds those previously obtained. We use our newly found scaling to suggest how to achieve higher temperatures with a series of pulses.

Published
2005

24. Sustained Spheromak Physics Experiment (SSPX): design and physics results

Author

Hooper, E B, primary, Bulmer, R H, additional, Cohen, B I, additional, Hill, D N, additional, Holcomb, C T, additional, Hudson, B, additional, McLean, H S, additional, Pearlstein, L D, additional, Romero-Talamás, C A, additional, Sovinec, C R, additional, Stallard, B W, additional, Wood, R D, additional, and Woodruff, S, additional

Published
2012
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37. The first target experiments on the National Ignition Facility

Author

Landen, O. L., primary, Glenzer, S. H., additional, Froula, D. H., additional, Dewald, E. L., additional, Suter, L. J., additional, Schneider, M. B., additional, Hinkel, D. E., additional, Fernandez, J. C., additional, Kline, J. L., additional, Goldman, S. R., additional, Braun, D. G., additional, Celliers, P. M., additional, Moon, S. J., additional, Robey, H. S., additional, Lanier, N. E., additional, Glendinning, S. G., additional, Blue, B. E., additional, Wilde, B. H., additional, Jones, O. S., additional, Schein, J., additional, Divol, L., additional, Kalantar, D. H., additional, Campbell, K. M., additional, Holder, J. P., additional, McDonald, J. W., additional, Niemann, C., additional, Mackinnon, A. J., additional, Collins, G. W., additional, Bradley, D. K., additional, Eggert, J. H., additional, Hicks, D. G., additional, Gregori, G., additional, Kirkwood, R. K., additional, Young, B. K., additional, Foster, J. M., additional, Hansen, J. F., additional, Perry, T. S., additional, Munro, D. H., additional, Baldis, H. A., additional, Grim, G. P., additional, Heeter, R. F., additional, Hegelich, M. B., additional, Montgomery, D. S., additional, Rochau, G. A., additional, Olson, R. E., additional, Turner, R. E., additional, Workman, J. B., additional, Berger, R. L., additional, Cohen, B. I., additional, Kruer, W. L., additional, Langdon, A. B., additional, Langer, S. H., additional, Meezan, N. B., additional, Rose, H. A., additional, Still, C. H., additional, Williams, E. A., additional, Dodd, E. S., additional, Edwards, M. J., additional, Monteil, M.-C., additional, Stevenson, R. M., additional, Thomas, B. R., additional, Coker, R. F., additional, Magelssen, G. R., additional, Rosen, P. A., additional, Stry, P. E., additional, Woods, D., additional, Weber, S. V., additional, Young, P. E., additional, Alvarez, S., additional, Armstrong, G., additional, Bahr, R., additional, Bourgade, J.-L., additional, Bower, D., additional, Celeste, J., additional, Chrisp, M., additional, Compton, S., additional, Cox, J., additional, Constantin, C., additional, Costa, R., additional, Duncan, J., additional, Ellis, A., additional, Emig, J., additional, Gautier, C., additional, Greenwood, A., additional, Griffith, R., additional, Holdner, F., additional, Holtmeier, G., additional, Hargrove, D., additional, James, T., additional, Kamperschroer, J., additional, Kimbrough, J., additional, Landon, M., additional, Lee, F. D., additional, Malone, R., additional, May, M., additional, Montelongo, S., additional, Moody, J., additional, Ng, E., additional, Nikitin, A., additional, Pellinen, D., additional, Piston, K., additional, Poole, M., additional, Rekow, V., additional, Rhodes, M., additional, Shepherd, R., additional, Shiromizu, S., additional, Voloshin, D., additional, Warrick, A., additional, Watts, P., additional, Weber, F., additional, Young, P., additional, Arnold, P., additional, Atherton, L., additional, Bardsley, G., additional, Bonanno, R., additional, Borger, T., additional, Bowers, M., additional, Bryant, R., additional, Buckman, S., additional, Burkhart, S., additional, Cooper, F., additional, Dixit, S. N., additional, Erbert, G., additional, Eder, D. C., additional, Ehrlich, R. E., additional, Felker, B., additional, Fornes, J., additional, Frieders, G., additional, Gardner, S., additional, Gates, C., additional, Gonzalez, M., additional, Grace, S., additional, Hall, T., additional, Haynam, C. A., additional, Heestand, G., additional, Henesian, M. A., additional, Hermann, M., additional, Hermes, G., additional, Huber, S., additional, Jancaitis, K., additional, Johnson, S., additional, Kauffman, B., additional, Kelleher, T., additional, Kohut, T., additional, Koniges, A. E., additional, Labiak, T., additional, Latray, D., additional, Lee, A., additional, Lund, D., additional, Mahavandi, S., additional, Manes, K. R., additional, Marshall, C., additional, McBride, J., additional, McCarville, T., additional, McGrew, L., additional, Menapace, J., additional, Mertens, E., additional, Murray, J., additional, Neumann, J., additional, Newton, M., additional, Opsahl, P., additional, Padilla, E., additional, Parham, T., additional, Parrish, G., additional, Petty, C., additional, Polk, M., additional, Powell, C., additional, Reinbachs, I., additional, Rinnert, R., additional, Riordan, B., additional, Ross, G., additional, Robert, V., additional, Tobin, M., additional, Sailors, S., additional, Saunders, R., additional, Schmitt, M., additional, Shaw, M., additional, Singh, M., additional, Spaeth, M., additional, Stephens, A., additional, Tietbohl, G., additional, Tuck, J., additional, Van Wonterghem, B. M., additional, Vidal, R., additional, Wegner, P. J., additional, Whitman, P., additional, Williams, K., additional, Winward, K., additional, Work, K., additional, Wallace, R., additional, Nobile, A., additional, Bono, M., additional, Day, B., additional, Elliott, J., additional, Hatch, D., additional, Louis, H., additional, Manzenares, R., additional, O'Brien, D., additional, Papin, P., additional, Pierce, T., additional, Rivera, G., additional, Ruppe, J., additional, Sandoval, D., additional, Schmidt, D., additional, Valdez, L., additional, Zapata, K., additional, MacGowan, B. J., additional, Eckart, M. J., additional, Hsing, W. W., additional, Springer, P. T., additional, Hammel, B. A., additional, Moses, E. I., additional, and Miller, G. H., additional

Published
2006
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