Two-dimensional modeling of the x-radiation output from perturbed Z pinches

Matuska, W.; Bowers, R.L.; Brownell, J. H.; Lee, H.; Lund, C.M.; Peterson, Darrell L.; Roderick, N. F.

doi:10.1063/1.871731

Cited by 20 publications

(10 citation statements)

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“…In contrast, here we show that the measured rise time of the total radiation pulse and the ''effective'' pulse width ͑de-fined as the total radiated energy divided by the peak power͒ scale as the gap over the entire gap range explored, and show no discontinuity near gϭ2 mm. Importantly, this data, together with RMHC 18,19 simulations in the r-z plane 7,20 suggest that the shape of the primary power pulse and the general change in peak power may be related to the evolution of the plasma thickness, due to r-z dynamics in the presence of Rayleigh-Taylor ͑RT͒ instabilities. These data and calculations thus suggest a direct relation between the initial interwire gap and the thickness of the imploding annulus at stagnation.…”

Section: Introductionmentioning

confidence: 87%

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Systematic trends in x-ray emission characteristics of variable-wire-number, fixed-mass, aluminum-array, Z-pinch implosions

et al. 1999

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Increasing the number of wires an order of magnitude from 10 to almost 200 while simultaneously fixing the total wire mass in annular aluminum-wire-array Z-pinch implosions on the 20 TW Saturn generator [Proceedings of the 6th International IEEE Pulsed Power Conference (Institute of Electrical and Electronics Engineers, Piscataway, NJ, 1987), p. 310] demonstrates two separate power-law trends in the measured x-ray characteristics as a function of the initial interwire gap (g). These trends are approximately independent of the array radius. When g decreases from ∼6 to 0.4 mm, the peak total radiated power increases by a factor of 20 and the total energy by a factor of 2. There is a more rapid increase in peak power and energy radiated as g decreases for gaps greater than ∼2 mm. This increase is related to a measured decrease in precursor plasma and to a calculated decreased sensitivity of the implosion to azimuthal asymmetries that occurs when individual wire plasmas begin to merge following their vaporization. The substantial increase in power arises from an inferred increase in plasma compression and can be correlated with an almost linear reduction in the calculated effective thickness of the plasma annulus near stagnation as g decreases.

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Section: Introductionmentioning

confidence: 87%

“…The error bars show the uncertainties of inferring pinch sizes from irregular pinhole pictures and ion densities from plasmas with density gradients ͑see Tables I and II͒. FIG. 19. The temperatures inferred from the K-series spectra and shown in Fig.…”

Section: (A) Is Primarily Due To Increased Plasma Density [Figs 4(a)mentioning

confidence: 99%

Systematic trends in x-ray emission characteristics of variable-wire-number, fixed-mass, aluminum-array, Z-pinch implosions

et al. 1999

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“…Additionally, two-dimensional ͑2-D͒ Eulerian radiationmagnetohydrodynamic code ͑E-RMHC͒ 11,12 simulations are compared with the data to gain insight into the fundamental implosion processes that are now free of the large asymmetries and resulting instabilities that have limited previous detailed comparisons. The main result from the measurements and comparisons is that, contrary to the low-wire-number loads, the quality of the implosion, as measured by the radial convergence, radiated energy, and radiated power, remains remarkably constant with increasing array radius.…”

Section: Introductionmentioning

confidence: 99%

Symmetric aluminum-wire arrays generate high-quality Z pinches at large array radii

et al. 1998

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A Saturn-accelerator study of annular, aluminum-wire array, Z-pinch implosions, in the calculated high-wire-number plasma-shell regime ͓Phys. Rev. Lett. 77, 5063 ͑1996͔͒, shows that the radiated x-ray pulse width increases from about 4 nsec to about 7 nsec, when the radius of the array is increased from 8.75 to 20 mm at a fixed array mass of 0.6 mg. Eulerian radiationmagnetohydrodynamic code ͑E-RMHC͒ simulations in the r-z plane suggest that this pulse-width increase with radius is due to the faster growth of the shell thickness ͑that arises from a two-stage development in the magnetic Rayleigh-Taylor instability͒ relative to the increase in the shell implosion velocity. Over the array radii explored, the measured peak total x-ray power of ϳ40 TW and energy of ϳ325 kJ show little change outside of a Ϯ15% shot-to-shot fluctuation and are consistent with the E-RMHC simulations. Similarly, the measured peak K-shell ͑lines plus continuum͒ power of ϳ8 TW and energy of ϳ70 kJ show little change with radius. The minimal change in K-shell yield is in agreement with simple K-shell radiation scaling models that assume a fixed radial compression for all initial array radii. These results suggest that the improved uniformity provided by the large number of wires in the initial array reduces the disruptive effects of the Rayleigh-Taylor instability observed in small-wire-number imploding loads.

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“…[30][31][32] Such calculations sometimes include the radiation output that is generated when the plasma stagnates on axis. 33 The magnetized Rayleigh-Taylor instability that develops during the implosion has a significant impact on how much energy can be converted into radiation from the pinch. To study expanding plasmas that involve shorter wavelength phenomena, plasma models that extend beyond fluid modes are typically used.…”

Section: Introductionmentioning

confidence: 99%

Regimes of the magnetized Rayleigh–Taylor instability

Winske

1996

Physics of Plasmas

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Hybrid simulations with kinetic ions and massless fluid electrons are used to investigate the linear and nonlinear behavior of the magnetized Rayleigh-Taylor instability in slab geometry with the plasma subject to a constant gravity. Three regimes are found, which are determined by the magnitude of the complex frequency ϭ r ϩi␥. For ͉͉Ӷ⍀ i (⍀ i ϭ ion gyrofrequency͒, one finds the typical behavior of the usual fluid regime, namely the development of ''mushroom-head'' spikes and bubbles in the density and a strongly convoluted boundary between the plasma and magnetic field, where the initial gradient is not relaxed much. A second regime, where ͉͉ϳ0.1⍀ i , is characterized by the importance of the Hall term. Linearly, the developing flute modes are more finger-like and tilted along the interface; nonlinearly, clump-like structures form, leading to a significant broadening of the interface. The third regime is characterized by unmagnetized ion behavior, with ͉͉ϳ⍀ i . Density clumps, rather than flutes, form in the linear stage, while nonlinearly, longer-wavelength modes that resemble those in fluid regime dominate. Finite Larmor radius stabilization of short-wavelength modes is observed in each regime.

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Two-dimensional modeling of the x-radiation output from perturbed Z pinches

Cited by 20 publications

References 1 publication

Systematic trends in x-ray emission characteristics of variable-wire-number, fixed-mass, aluminum-array, Z-pinch implosions

Systematic trends in x-ray emission characteristics of variable-wire-number, fixed-mass, aluminum-array, Z-pinch implosions

Symmetric aluminum-wire arrays generate high-quality Z pinches at large array radii

Regimes of the magnetized Rayleigh–Taylor instability

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