skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Magnetic Rayleigh-Taylor instability mitigation and efficient radiation production in gas puff Z-pinch implosions

Abstract

Large radius Z-pinches are inherently susceptible to the magnetic Rayleigh-Taylor (RT) instability because of their relatively long acceleration path. This has been reflected in a significant reduction of the argon K-shell yield as was observed when the diameter of the load was increased from 2.5 to >4 cm. Recently, an approach was demonstrated to overcome the challenge with a structured gas puff load that mitigates the RT instability, enhances the energy coupling, and leads to a high compression, high yield Z-pinch. The novel load consists of a 'pusher', outer region plasma that carries the current and couples energy from the driver, a 'stabilizer', inner region plasma that mitigates the RT growth, and a ''radiator,'' high-density center jet plasma that is heated and compressed to radiate. In 3.5-MA, 200-ns, 12-cm initial diameter implosions, the Ar K-shell yield has increased by a factor of 2, to 21 kJ, matching the yields obtained on the same accelerator with 100-ns, 2.5-cm-diam implosions. Further tests of such structured Ar gas load on {approx}6 MA, 200-ns accelerators have achieved >80 kJ. From laser diagnostics and measurements of the K-shell and extreme ultraviolet emission, initial gas distribution and implosion trajectories were obtained, illustrating the RT suppression andmore » stabilization of the imploding plasma, and identifying the radiation source region in a structured gas puff load. Magnetohydrodynamic simulations, started from actual initial density profiles, reproduce many features of the measurements both qualitatively and quantitatively.« less

Authors:
; ; ; ; ; ; ; ;  [1];  [2];  [2]
  1. L-3 Pulse Sciences, San Leandro, California 94577 (United States)
  2. (United States)
Publication Date:
OSTI Identifier:
20975065
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physics of Plasmas; Journal Volume: 14; Journal Issue: 5; Other Information: DOI: 10.1063/1.2436468; (c) 2007 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; ACCELERATION; ACCELERATORS; ARGON; COMPRESSION; CURRENTS; EXTREME ULTRAVIOLET RADIATION; IMPLOSIONS; K SHELL; MAGNETOHYDRODYNAMICS; PLASMA; PLASMA DENSITY; PLASMA DIAGNOSTICS; PLASMA GUNS; PLASMA JETS; PLASMA SIMULATION; RADIATION SOURCES; RAYLEIGH-TAYLOR INSTABILITY

Citation Formats

Sze, H., Levine, J. S., Banister, J., Failor, B. H., Qi, N., Steen, P., Velikovich, A. L., Davis, J., Wilson, A., Plasma Physics Division, Naval Research Laboratory, Washington, D.C. 20375, and Avonia Inc., San Diego, California 92130. Magnetic Rayleigh-Taylor instability mitigation and efficient radiation production in gas puff Z-pinch implosions. United States: N. p., 2007. Web. doi:10.1063/1.2436468.
Sze, H., Levine, J. S., Banister, J., Failor, B. H., Qi, N., Steen, P., Velikovich, A. L., Davis, J., Wilson, A., Plasma Physics Division, Naval Research Laboratory, Washington, D.C. 20375, & Avonia Inc., San Diego, California 92130. Magnetic Rayleigh-Taylor instability mitigation and efficient radiation production in gas puff Z-pinch implosions. United States. doi:10.1063/1.2436468.
Sze, H., Levine, J. S., Banister, J., Failor, B. H., Qi, N., Steen, P., Velikovich, A. L., Davis, J., Wilson, A., Plasma Physics Division, Naval Research Laboratory, Washington, D.C. 20375, and Avonia Inc., San Diego, California 92130. Tue . "Magnetic Rayleigh-Taylor instability mitigation and efficient radiation production in gas puff Z-pinch implosions". United States. doi:10.1063/1.2436468.
@article{osti_20975065,
title = {Magnetic Rayleigh-Taylor instability mitigation and efficient radiation production in gas puff Z-pinch implosions},
author = {Sze, H. and Levine, J. S. and Banister, J. and Failor, B. H. and Qi, N. and Steen, P. and Velikovich, A. L. and Davis, J. and Wilson, A. and Plasma Physics Division, Naval Research Laboratory, Washington, D.C. 20375 and Avonia Inc., San Diego, California 92130},
abstractNote = {Large radius Z-pinches are inherently susceptible to the magnetic Rayleigh-Taylor (RT) instability because of their relatively long acceleration path. This has been reflected in a significant reduction of the argon K-shell yield as was observed when the diameter of the load was increased from 2.5 to >4 cm. Recently, an approach was demonstrated to overcome the challenge with a structured gas puff load that mitigates the RT instability, enhances the energy coupling, and leads to a high compression, high yield Z-pinch. The novel load consists of a 'pusher', outer region plasma that carries the current and couples energy from the driver, a 'stabilizer', inner region plasma that mitigates the RT growth, and a ''radiator,'' high-density center jet plasma that is heated and compressed to radiate. In 3.5-MA, 200-ns, 12-cm initial diameter implosions, the Ar K-shell yield has increased by a factor of 2, to 21 kJ, matching the yields obtained on the same accelerator with 100-ns, 2.5-cm-diam implosions. Further tests of such structured Ar gas load on {approx}6 MA, 200-ns accelerators have achieved >80 kJ. From laser diagnostics and measurements of the K-shell and extreme ultraviolet emission, initial gas distribution and implosion trajectories were obtained, illustrating the RT suppression and stabilization of the imploding plasma, and identifying the radiation source region in a structured gas puff load. Magnetohydrodynamic simulations, started from actual initial density profiles, reproduce many features of the measurements both qualitatively and quantitatively.},
doi = {10.1063/1.2436468},
journal = {Physics of Plasmas},
number = 5,
volume = 14,
place = {United States},
year = {Tue May 15 00:00:00 EDT 2007},
month = {Tue May 15 00:00:00 EDT 2007}
}
  • Recently, a new approach for efficiently generating K-shell x-rays in large-diameter, long-implosion time, structured argon gas Z-pinches has been demonstrated based on a 'pusher-stabilizer-radiator' model. In this paper, direct observations of the Rayleigh-Taylor instability mitigation of a 12-cm diameter, 200-ns implosion time argon Z-pinch using a laser shearing interferometer (LSI) and a laser wavefront analyzer (LWA) are presented. Using a zero-dimensional snowplow model, the imploding plasma trajectories are calculated with the driver current waveforms and the initial mass distributions measured using the planar laser induced fluorescence method. From the LSI and LWA images, the plasma density and trajectory during themore » implosion are measured. The measured trajectory agrees with the snowplow calculations. The suppression of hydromagnetic instabilities in the ''pusher-stabilizer-radiator'' structured loads, leading to a high-compression ratio, high-yield Z-pinch, is discussed. For comparison, the LSI and LWA images of an alternative load (without stabilizer) show the evolution of a highly unstable Z-pinch.« less
  • We have proposed and demonstrated successfully a new approach for generating high-yield K-shell radiation with large-diameter gas-puff Z pinches. The novel load design consists of an outer region plasma that carries the current and couples energy from the driver, an inner region plasma that stabilizes the implosion, and a high-density center jet plasma that radiates. It increased the Ar K-shell yield at 3.46 MA in 200 ns implosions from 12 cm initial diameter by a factor of 2, to 21 kJ, matching the yields obtained earlier on the same accelerator with 100 ns implosions. A new ''pusher-stabilizer-radiator'' physical model ismore » advanced to explain this result.« less
  • Numerical simulations have been carried out to investigate the role that magnetic field diffusion and ohmic heating have on the magnetohydrodynamic Rayleigh-Taylor (RT) development in fast z-pinch implosions. Previous work has indicated these terms can strongly influence the evolution of RT growth, leading to a reduction in RT amplitude, and an improvement in pinch performance. Indeed, Roderick et al have suggested that magnetic smoothing is an important mechanism in linear RT growth. To examine this in more detail, simulations are presented for a 1.4 mg, 25.0 mm diameter tungsten wire array imploded in the Saturn long pulse mode. The 130more » ns implosion time of this calculation should enhance any mitigating effects that may be attributed to nonideal MHD. Calculations were performed using the 2D MHD code Mach2. The wire array was approximated by a right cylindrical slab of 1.0 mm width. Both a random density perturbation and single mode density perturbations were incorporated to initiate the instability. In the former case, a 5% cell-to-cell random perturbation was used. This allowed a range of modes to be initially present. In the single mode case, a 1.25 mm wavelength, on the order of the shell thickness, was defined. To isolate the contributions due to field diffusion, joule heating, and equation of state, simulations were run with and without ohmic heating using both constant and material-dependent spitzer resistivities. This analysis was then extended to look at the effect of such parameters on the nested shell load configuration. Detailed analysis of the simulations will be presented.« less
  • The development and use of a single-fluid two-temperature approximated 2-D Magneto-Hydrodynamics code is reported. Z-pinch dynamics and the evolution of Magneto-Rayleigh-Taylor (MRT) instabilities in a gas jet type Extreme Ultraviolet (EUV) source are investigated with this code. The implosion and stagnation processes of the Z-pinch dynamics and the influence of initial perturbations (single mode, multi- mode, and random seeds) on MRT instability are discussed in detail. In the case of single mode seeds, the simulation shows that the growth rates for mm-scale wavelengths up to 4 mm are between 0.05 and 0.065 ns{sup −1}. For multi-mode seeds, the mode couplingmore » effect leads to a series of other harmonics, and complicates MRT instability evolution. For perturbation by random seeds, the modes evolve to longer wavelengths and finally converge to a mm-scale wavelength approximately 1 mm. MRT instabilities can also alter the pinch stagnation state and lead to temperature and density fluctuations along the Z axis, which eventually affects the homogeneity of the EUV radiation output. Finally, the simulation results are related to experimental results to discuss the mitigations of MRT instability.« less
  • Experiments using the Saturn pulsed power generator have produced high-velocity z-pinch plasma implosions with velocities over 100 cm/{mu}s using both annular and uniform-fill gas injection initial conditions. Both types of implosion show evidence of the hydromagnetic Rayleigh{endash}Taylor instability with the uniform-fill plasmas producing a more spatially uniform pinch. Two-dimensional magnetohydrodynamic simulations including unsteady flow of gas from a nozzle into the diode region have been used to investigate these implosions. The instability develops from the nonuniform gas flow field that forms as the gas expands from the injection nozzle. Instability growth is limited to the narrow unstable region of themore » current sheath. For the annular puff the unstable region breaks through the inner edge of the annulus increasing nonlinear growth as mass ejected from the bubble regions is not replenished by accretion. This higher growth leads to bubble thinning and disruption producing greater nonuniformity at pinch for the annular puff. The uniform puff provides gas to replenish bubble mass loss until just before pinch resulting in less bubble thinning and a more uniform pinch. {copyright} {ital 1998 American Institute of Physics.}« less