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Title: Effect of Current Rise-time on the Formation of Precursor Structures and Mass Ablation Rate in Cylindrical Wire Array Z-Pinches

Abstract

We present the first study to directly compare the mass ablation rates of cylindrical wire arrays as a function of the current rise-rate. Formation of the precursor column is investigated on both the MAPGIE (1 MA, 250 ns) and COBRA (1 MA, 100 ns) generators, and results are used to infer the change in the mass ablation rate induced by the rise-rate of the drive current. Laser shadowography, gated XUV imaging and x-ray diodes are used to compare the dynamical behavior both generators, and x-pinch radiography and XUV spectroscopy and provide density evolution and temperature measurements respectively. Results are compared to predictions from an analytical scaling model based on a fixed ablation rate, and the close correlation achieved suggests that the effective ablation velocity is not a strong function of the current rise rate.

Authors:
; ;  [1]; ;  [2]; ; ; ; ; ; ; ; ; ;  [3]; ; ; ; ;  [4]
  1. Center for Energy Research, University of California San Diego, La Jolla CA 92093 (United States)
  2. Department of Mechanical and Aerospace Engineering, University of California San Diego, La Jolla CA 92093 (United States)
  3. Laboratory of Plasma Studies, Cornell University, NY 14853 (United States)
  4. Blackett Laboratory, Imperial College London, SW7 2BW (United Kingdom) (and others)
Publication Date:
OSTI Identifier:
21255353
Resource Type:
Journal Article
Resource Relation:
Journal Name: AIP Conference Proceedings; Journal Volume: 1088; Journal Issue: 1; Conference: 7. international conference on dense Z-pinches, Alexandria, VA (United States), 12-21 Aug 2008; Other Information: DOI: 10.1063/1.3079743; (c) 2009 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; ABLATION; COMPARATIVE EVALUATIONS; CORRELATIONS; CYLINDRICAL CONFIGURATION; EVOLUTION; EXTREME ULTRAVIOLET RADIATION; FORECASTING; LASERS; LINEAR Z PINCH DEVICES; MASS; PLASMA HEATING; PULSE RISE TIME; SPECTROSCOPY; TEMPERATURE MEASUREMENT; WIRES

Citation Formats

Bott, S. C., Eshaq, Y., Ueda, U., Haas, D. M., Beg, F. N., Hammer, D. A., Kusse, B., Greenly, J., Shelkovenko, T. A., Pikuz, S. A., Blesener, I. C., McBride, R. D., Douglass, J. D., Bell, K., Knapp, P., Chittenden, J. P., Lebedev, S. V., Bland, S. N., Hall, G. N., and Suzuki, F. A.. Effect of Current Rise-time on the Formation of Precursor Structures and Mass Ablation Rate in Cylindrical Wire Array Z-Pinches. United States: N. p., 2009. Web. doi:10.1063/1.3079743.
Bott, S. C., Eshaq, Y., Ueda, U., Haas, D. M., Beg, F. N., Hammer, D. A., Kusse, B., Greenly, J., Shelkovenko, T. A., Pikuz, S. A., Blesener, I. C., McBride, R. D., Douglass, J. D., Bell, K., Knapp, P., Chittenden, J. P., Lebedev, S. V., Bland, S. N., Hall, G. N., & Suzuki, F. A.. Effect of Current Rise-time on the Formation of Precursor Structures and Mass Ablation Rate in Cylindrical Wire Array Z-Pinches. United States. doi:10.1063/1.3079743.
Bott, S. C., Eshaq, Y., Ueda, U., Haas, D. M., Beg, F. N., Hammer, D. A., Kusse, B., Greenly, J., Shelkovenko, T. A., Pikuz, S. A., Blesener, I. C., McBride, R. D., Douglass, J. D., Bell, K., Knapp, P., Chittenden, J. P., Lebedev, S. V., Bland, S. N., Hall, G. N., and Suzuki, F. A.. 2009. "Effect of Current Rise-time on the Formation of Precursor Structures and Mass Ablation Rate in Cylindrical Wire Array Z-Pinches". United States. doi:10.1063/1.3079743.
@article{osti_21255353,
title = {Effect of Current Rise-time on the Formation of Precursor Structures and Mass Ablation Rate in Cylindrical Wire Array Z-Pinches},
author = {Bott, S. C. and Eshaq, Y. and Ueda, U. and Haas, D. M. and Beg, F. N. and Hammer, D. A. and Kusse, B. and Greenly, J. and Shelkovenko, T. A. and Pikuz, S. A. and Blesener, I. C. and McBride, R. D. and Douglass, J. D. and Bell, K. and Knapp, P. and Chittenden, J. P. and Lebedev, S. V. and Bland, S. N. and Hall, G. N. and Suzuki, F. A.},
abstractNote = {We present the first study to directly compare the mass ablation rates of cylindrical wire arrays as a function of the current rise-rate. Formation of the precursor column is investigated on both the MAPGIE (1 MA, 250 ns) and COBRA (1 MA, 100 ns) generators, and results are used to infer the change in the mass ablation rate induced by the rise-rate of the drive current. Laser shadowography, gated XUV imaging and x-ray diodes are used to compare the dynamical behavior both generators, and x-pinch radiography and XUV spectroscopy and provide density evolution and temperature measurements respectively. Results are compared to predictions from an analytical scaling model based on a fixed ablation rate, and the close correlation achieved suggests that the effective ablation velocity is not a strong function of the current rise rate.},
doi = {10.1063/1.3079743},
journal = {AIP Conference Proceedings},
number = 1,
volume = 1088,
place = {United States},
year = 2009,
month = 1
}
  • The limited understanding of the mechanisms driving the mass ablation rate of cylindrical wires arrays is presently one of the major limitations in predicting array performance at the higher current levels required for inertial confinement fusion (ICF) ignition. Continued investigation of this phenomenon is crucial to realize the considerable potential for wire arrays to drive both ICF and inertial fusion energy, by enabling a predictive capability in computational modeling. We present the first study to directly compare the mass ablation rates of wire arrays as a function of the current rise rate. Formation of the precursor column is investigated onmore » both the MAPGIE (1 MA, 250ns [Mitchell et al., Rev. Sci. Instrum. 67, 1533 (1996)]) and COBRA (1 MA, 100ns [Greenly et al., Rev. Sci. Instrum. 79, 073501 (2008)]) generators, and results are used to infer the change in the effective ablation velocity induced by the rise rate of the drive current. Laser shadowography, gated extreme ultraviolet (XUV) imaging, and x-ray diodes are used to compare the dynamical behavior on the two generators, and X-pinch radiography and XUV spectroscopy provide density evolution and temperature measurements respectively. Results are compared to predictions from an analytical scaling model developed previously from MAGPIE data, based on a fixed ablation velocity. For COBRA the column formation time occurs at 116{+-}5 ns and for Al arrays and 146{+-}5 ns for W arrays, with Al column temperature in the range of 70-165 eV. These values lie close to model predictions, inferring only a small change in the ablation velocity is induced by the factor of 2.5 change in current rise time. Estimations suggest the effective ablation velocities for MAGPIE and COBRA experiments vary by a maximum of 30%.« less
  • This paper summarises the present understanding of the processes leading to precursor column formation in cylindrical wire arrays on the 1MA MAGPIE generator at Imperial College London. The presence of precursor plasma affects the interaction of the wire array with on-axis targets, such as in the dynamic hohlraum system, and so good characterisation is essential for such experiments. Column formation parameters are directly determined by the collisionality of the plasma streams ablated from the wires as they arrive at the array axis, which depends on the array material, drive current and velocity. Direct experimental measurements of the diameter variation duringmore » the collapse and formation phase of the precursor column will be presented, along with soft x-ray emission, and quantitative radiography. The correlation of emission to column contraction indicates a non-linear collapse as a result of increasing on-axis density and radiative cooling. Differences in the formation and late-time behaviour for tungsten and aluminium arrays are observed, and characteristic values for several common materials are seen to vary according to atomic mass. Data is in good agreement with hydrodynamic code, and a recently published kinetic description of the precursor column, which predict many of the observed features.« less
  • Abstract not provided.
  • X-ray production by imploding wire-array Z pinches is studied using radiation magnetohydrodynamics simulation. It is found that the density distribution created by ablating wire material influences both x-ray power production, and how the peak power scales with applied current. For a given array there is an optimum ablation rate that maximizes the peak x-ray power, and produces the strongest scaling of peak power with peak current. This work is consistent with trends in wire-array Z pinch x-ray power scaling experiments on the Z accelerator.